Internet Magazine 2003 May/INTERNET103.ISO/pc/software/windows/building/mysql/data1.cab/Documentation/Docs/manual.txt

Text File | 2003-01-22 | 2.2 MB | 56,388 lines

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* mysql: (mysql).               MySQL documentation.
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Table of Contents
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General Information
  About This Manual
    Conventions Used in This Manual
  What Is MySQL?
    History of MySQL
    The Main Features of MySQL
    How Stable Is MySQL?
    How Big Can MySQL Tables Be?
    Year 2000 Compliance
  What Is MySQL AB?
    The Business Model and Services of MySQL AB
      Support
      Training and Certification
      Consulting
      Commercial Licenses
      Partnering
      Advertising
    Contact Information
  MySQL Support and Licensing
    Support Offered by MySQL AB
    Copyrights and Licenses Used by MySQL
    MySQL Licenses
      Using the MySQL Software Under a Commercial License
      Using the MySQL Software for Free Under GPL
    MySQL AB Logos and Trademarks
      The Original MySQL Logo
      MySQL Logos that may be Used Without Written Permission
      When do you need a Written Permission to use MySQL Logos?
      MySQL AB Partnership Logos
      Using the word `MySQL' in Printed Text or Presentations
      Using the word `MySQL' in Company and Product Names
  MySQL 4.x In A Nutshell
    Stepwise Rollout
    Ready for Immediate Use
    Embedded MySQL
    Other Features Available From MySQL 4.0
    Future MySQL 4.x Features
    MySQL 4.1, The Following Development Release
  MySQL Information Sources
    MySQL Mailing Lists
      The MySQL Mailing Lists
      Asking Questions or Reporting Bugs
      How to Report Bugs or Problems
      Guidelines for Answering Questions on the Mailing List
    MySQL Community Support on IRC (Internet Relay Chat)
  How Standards-compatible Is MySQL?
    What Standards Does MySQL Follow?
    Running MySQL in ANSI Mode
    MySQL Extensions to ANSI SQL92
    MySQL Differences Compared to ANSI SQL92
      Sub`SELECT's
      `SELECT INTO TABLE'
      Transactions and Atomic Operations
      Stored Procedures and Triggers
      Foreign Keys
      Views
      `--' as the Start of a Comment
    Known Errors and Design Deficiencies in MySQL
  MySQL and The Future (The TODO)
    Things That Should be in 4.0
    Things That Should be in 4.1
    Things That Must be Done in the Near Future
    Things That Have to be Done Sometime
    Things We Don't Plan To Do
  How MySQL Compares to Other Databases
    How MySQL Compares to `mSQL'
      How to Convert `mSQL' Tools for MySQL
      How `mSQL' and MySQL Client/Server Communications Protocols Differ
      How `mSQL' 2.0 SQL Syntax Differs from MySQL
    How MySQL Compares to `PostgreSQL'
      MySQL and PostgreSQL development strategies
      Featurewise Comparison of MySQL and PostgreSQL
      Benchmarking MySQL and PostgreSQL

MySQL Installation
  Quick Standard Installation of MySQL
    Installing MySQL on Linux
    Installing MySQL on Windows
      Installing the Binaries
      Preparing the Windows MySQL Environment
      Starting the Server for the First Time
  General Installation Issues
    How to Get MySQL
    Operating Systems Supported by MySQL
    Which MySQL Version to Use
    Installation Layouts
    How and When Updates Are Released
    MySQL Binaries Compiled by MySQL AB
    Installing a MySQL Binary Distribution
  Installing a MySQL Source Distribution
    Quick Installation Overview
    Applying Patches
    Typical `configure' Options
    Installing from the Development Source Tree
    Problems Compiling?
    MIT-pthreads Notes
    Windows Source Distribution
  Post-installation Setup and Testing
    Problems Running `mysql_install_db'
    Problems Starting the MySQL Server
    Starting and Stopping MySQL Automatically
  Upgrading/Downgrading MySQL
    Upgrading From Version 4.0 to Version 4.1
    Upgrading From Version 3.23 to Version 4.0
    Upgrading From Version 3.22 to Version 3.23
    Upgrading from Version 3.21 to Version 3.22
    Upgrading from Version 3.20 to Version 3.21
    Upgrading to Another Architecture
  Operating System Specific Notes
    Linux Notes (All Linux Versions)
      Linux Notes for Binary Distributions
      Linux x86 Notes
      Linux SPARC Notes
      Linux Alpha Notes
      Linux PowerPC Notes
      Linux MIPS Notes
      Linux IA64 Notes
    Windows Notes
      Starting MySQL on Windows 95, 98 or Me
      Starting MySQL on Windows NT, 2000 or XP
      Running MySQL on Windows
      Connecting to a Remote MySQL from Windows with SSH
      Splitting Data Across Different Disks on Windows
      Compiling MySQL Clients on Windows
      MySQL-Windows Compared to Unix MySQL
    Solaris Notes
      Solaris 2.7/2.8 Notes
      Solaris x86 Notes
    BSD Notes
      FreeBSD Notes
      NetBSD notes
      OpenBSD 2.5 Notes
      OpenBSD 2.8 Notes
      BSD/OS Version 2.x Notes
      BSD/OS Version 3.x Notes
      BSD/OS Version 4.x Notes
    Mac OS X Notes
      Mac OS X Public Beta
      Mac OS X Server
    Other Unix Notes
      HP-UX Notes for Binary Distributions
      HP-UX Version 10.20 Notes
      HP-UX Version 11.x Notes
      IBM-AIX notes
      SunOS 4 Notes
      Alpha-DEC-UNIX Notes (Tru64)
      Alpha-DEC-OSF/1 Notes
      SGI Irix Notes
      Caldera (SCO) Notes
      Caldera (SCO) Unixware Version 7.0 Notes
    OS/2 Notes
    BeOS Notes
    Novell NetWare Notes
  Perl Installation Comments
    Installing Perl on Unix
    Installing ActiveState Perl on Windows
    Installing the MySQL Perl Distribution on Windows
    Problems Using the Perl `DBI'/`DBD' Interface

Tutorial Introduction
  Connecting to and Disconnecting from the Server
  Entering Queries
  Creating and Using a Database
    Creating and Selecting a Database
    Creating a Table
    Loading Data into a Table
    Retrieving Information from a Table
      Selecting All Data
      Selecting Particular Rows
      Selecting Particular Columns
      Sorting Rows
      Date Calculations
      Working with `NULL' Values
      Pattern Matching
      Counting Rows
      Using More Than one Table
  Getting Information About Databases and Tables
  Examples of Common Queries
    The Maximum Value for a Column
    The Row Holding the Maximum of a Certain Column
    Maximum of Column per Group
    The Rows Holding the Group-wise Maximum of a Certain Field
    Using user variables
    Using Foreign Keys
    Searching on Two Keys
    Calculating Visits Per Day
    Using `AUTO_INCREMENT'
  Using `mysql' in Batch Mode
  Queries from Twin Project
    Find all Non-distributed Twins
    Show a Table on Twin Pair Status
  Using MySQL with Apache

Database Administration
  Configuring MySQL
    `mysqld' Command-line Options
    `my.cnf' Option Files
    Installing Many Servers on the Same Machine
    Running Multiple MySQL Servers on the Same Machine
  General Security Issues and the MySQL Access Privilege System
    General Security Guidelines
    How to Make MySQL Secure Against Crackers
    Startup Options for `mysqld' Concerning Security
    Security issues with LOAD DATA LOCAL
    What the Privilege System Does
    How the Privilege System Works
    Privileges Provided by MySQL
    Connecting to the MySQL Server
    Access Control, Stage 1: Connection Verification
    Access Control, Stage 2: Request Verification
    Causes of `Access denied' Errors
  MySQL User Account Management
    `GRANT' and `REVOKE' Syntax
    MySQL User Names and Passwords
    When Privilege Changes Take Effect
    Setting Up the Initial MySQL Privileges
    Adding New Users to MySQL
    Limiting user resources
    Setting Up Passwords
    Keeping Your Password Secure
    Using Secure Connections
      Basics
      Requirements
      `GRANT' Options
  Disaster Prevention and Recovery
    Database Backups
    `BACKUP TABLE' Syntax
    `RESTORE TABLE' Syntax
    `CHECK TABLE' Syntax
    `REPAIR TABLE' Syntax
    Using `myisamchk' for Table Maintenance and Crash Recovery
      `myisamchk' Invocation Syntax
      General Options for `myisamchk'
      Check Options for `myisamchk'
      Repair Options for myisamchk
      Other Options for `myisamchk'
      `myisamchk' Memory Usage
      Using `myisamchk' for Crash Recovery
      How to Check Tables for Errors
      How to Repair Tables
      Table Optimisation
    Setting Up a Table Maintenance Regimen
    Getting Information About a Table
  Database Administration Language Reference
    `OPTIMIZE TABLE' Syntax
    `ANALYZE TABLE' Syntax
    `FLUSH' Syntax
    `RESET' Syntax
    `KILL' Syntax
    `SHOW' Syntax
      Retrieving information about Database, Tables, Columns, and Indexes
      `SHOW TABLE STATUS'
      `SHOW STATUS'
      `SHOW VARIABLES'
      `SHOW LOGS'
      `SHOW PROCESSLIST'
      `SHOW GRANTS'
      `SHOW CREATE TABLE'
      `SHOW WARNINGS | ERRORS'
  MySQL Localisation and International Usage
    The Character Set Used for Data and Sorting
      German character set
    Non-English Error Messages
    Adding a New Character Set
    The Character Definition Arrays
    String Collating Support
    Multi-byte Character Support
    Problems With Character Sets
  MySQL Server-Side Scripts and Utilities
    Overview of the Server-Side Scripts and Utilities
    `safe_mysqld', The Wrapper Around `mysqld'
    `mysqld_multi', A Program for Managing Multiple MySQL Servers
    `myisampack', The MySQL Compressed Read-only Table Generator
    `mysqld-max', An Extended `mysqld' Server
  MySQL Client-Side Scripts and Utilities
    Overview of the Client-Side Scripts and Utilities
    `mysql', The Command-line Tool
    `mysqladmin', Administrating a MySQL Server
    Using `mysqlcheck' for Table Maintenance and Crash Recovery
    `mysqldump', Dumping Table Structure and Data
    `mysqlhotcopy', Copying MySQL Databases and Tables
    `mysqlimport', Importing Data from Text Files
    Showing Databases, Tables, and Columns
    perror, Explaining Error Codes
    How to Run SQL Commands from a Text File
  The MySQL Log Files
    The Error Log
    The General Query Log
    The Update Log
    The Binary Update Log
    The Slow Query Log
    Log File Maintenance
  Replication in MySQL
    Introduction
    Replication Implementation Overview
    How To Set Up Replication
    Replication Features and Known Problems
    Replication Options in `my.cnf'
    SQL Commands Related to Replication
    Replication FAQ
    Troubleshooting Replication

MySQL Optimisation
  Optimisation Overview
    MySQL Design Limitations/Tradeoffs
    Portability
    What Have We Used MySQL For?
    The MySQL Benchmark Suite
    Using Your Own Benchmarks
  Optimising `SELECT's and Other Queries
    `EXPLAIN' Syntax (Get Information About a `SELECT')
    Estimating Query Performance
    Speed of `SELECT' Queries
    How MySQL Optimises `WHERE' Clauses
    How MySQL Optimises `DISTINCT'
    How MySQL Optimises `LEFT JOIN' and `RIGHT JOIN'
    How MySQL Optimises `ORDER BY'
    How MySQL Optimises `LIMIT'
    Speed of `INSERT' Queries
    Speed of `UPDATE' Queries
    Speed of `DELETE' Queries
    Other Optimisation Tips
  Locking Issues
    How MySQL Locks Tables
    Table Locking Issues
  Optimising Database Structure
    Design Choices
    Get Your Data as Small as Possible
    How MySQL Uses Indexes
    Column Indexes
    Multiple-Column Indexes
    Why So Many Open tables?
    How MySQL Opens and Closes Tables
    Drawbacks to Creating Large Numbers of Tables in the Same Database
  Optimising the MySQL Server
    System/Compile Time and Startup Parameter Tuning
    Tuning Server Parameters
    How Compiling and Linking Affects the Speed of MySQL
    How MySQL Uses Memory
    How MySQL uses DNS
    `SET' Syntax
  Disk Issues
    Using Symbolic Links
      Using Symbolic Links for Databases
      Using Symbolic Links for Tables

MySQL Language Reference
  Language Structure
    Literals: How to Write Strings and Numbers
      Strings
      Numbers
      Hexadecimal Values
      `NULL' Values
    Database, Table, Index, Column, and Alias Names
    Case Sensitivity in Names
    User Variables
    System Variables
    Comment Syntax
    Is MySQL Picky About Reserved Words?
  Column Types
    Numeric Types
    Date and Time Types
      Y2K Issues and Date Types
      The `DATETIME', `DATE', and `TIMESTAMP' Types
      The `TIME' Type
      The `YEAR' Type
    String Types
      The `CHAR' and `VARCHAR' Types
      The `BLOB' and `TEXT' Types
      The `ENUM' Type
      The `SET' Type
    Choosing the Right Type for a Column
    Using Column Types from Other Database Engines
    Column Type Storage Requirements
  Functions for Use in `SELECT' and `WHERE' Clauses
    Non-Type-Specific Operators and Functions
      Parentheses
      Comparison Operators
      Logical Operators
      Control Flow Functions
    String Functions
      String Comparison Functions
      Case-Sensitivity
    Numeric Functions
      Arithmetic Operations
      Mathematical Functions
    Date and Time Functions
    Cast Functions
    Other Functions
      Bit Functions
      Miscellaneous Functions
    Functions for Use with `GROUP BY' Clauses
  Data Manipulation: `SELECT', `INSERT', `UPDATE', `DELETE'
    `SELECT' Syntax
      `JOIN' Syntax
      `UNION' Syntax
    `HANDLER' Syntax
    `INSERT' Syntax
      `INSERT ... SELECT' Syntax
    `INSERT DELAYED' Syntax
    `UPDATE' Syntax
    `DELETE' Syntax
    `TRUNCATE' Syntax
    `REPLACE' Syntax
    `LOAD DATA INFILE' Syntax
    `DO' Syntax
  Data Definition: `CREATE', `DROP', `ALTER'
    `CREATE DATABASE' Syntax
    `DROP DATABASE' Syntax
    `CREATE TABLE' Syntax
      Silent Column Specification Changes
    `ALTER TABLE' Syntax
    `RENAME TABLE' Syntax
    `DROP TABLE' Syntax
    `CREATE INDEX' Syntax
    `DROP INDEX' Syntax
  Basic MySQL User Utility Commands
    `USE' Syntax
    `DESCRIBE' Syntax (Get Information About Columns)
  MySQL Transactional and Locking Commands
    `BEGIN/COMMIT/ROLLBACK' Syntax
    `LOCK TABLES/UNLOCK TABLES' Syntax
    `SET TRANSACTION' Syntax
  MySQL Full-text Search
    Full-text Restrictions
    Fine-tuning MySQL Full-text Search
    Full-text Search TODO
  MySQL Query Cache
    How The Query Cache Operates
    Query Cache Configuration
    Query Cache Options in `SELECT'
    Query Cache Status and Maintenance

MySQL Table Types
  `MyISAM' Tables
    Space Needed for Keys
    `MyISAM' Table Formats
      Static (Fixed-length) Table Characteristics
      Dynamic Table Characteristics
      Compressed Table Characteristics
    `MyISAM' Table Problems
      Corrupted `MyISAM' Tables
      Clients is using or hasn't closed the table properly
  `MERGE' Tables
    `MERGE' Table Problems
  `ISAM' Tables
  `HEAP' Tables
  `InnoDB' Tables
    InnoDB Tables Overview
    InnoDB Startup Options
    Creating InnoDB Tablespace
      If Something Goes Wrong in Database Creation
    Creating InnoDB Tables
      Converting MyISAM Tables to InnoDB
      Foreign Key Constraints
    Adding and Removing InnoDB Data and Log Files
    Backing up and Recovering an InnoDB Database
      Checkpoints
    Moving an InnoDB Database to Another Machine
    InnoDB Transaction Model
      Consistent Read
      Locking Reads
      Next-key Locking: Avoiding the Phantom Problem
      Locks Set by Different SQL Statements in InnoDB
      Deadlock Detection and Rollback
      An Example of How the Consistent Read Works in InnoDB
      How to cope with deadlocks?
      Performance Tuning Tips
      The InnoDB Monitor
    Implementation of Multi-versioning
    Table and Index Structures
      Physical Structure of an Index
      Insert Buffering
      Adaptive Hash Indexes
      Physical Record Structure
      How an Auto-increment Column Works in InnoDB
    File Space Management and Disk I/O
      Disk I/O
      File Space Management
      Defragmenting a Table
    Error Handling
    Restrictions on InnoDB Tables
    InnoDB Change History
      MySQL/InnoDB-4.1, January xx, 2003
      MySQL/InnoDB-4.0.8, January 7, 2003
      MySQL/InnoDB-4.0.7, December 26, 2002
      MySQL/InnoDB-4.0.6, December 19, 2002
      MySQL/InnoDB-3.23.54, December 12, 2002
      MySQL/InnoDB-4.0.5, November 18, 2002
      MySQL/InnoDB-3.23.53, October 9, 2002
      MySQL/InnoDB-4.0.4, October 2, 2002
      MySQL/InnoDB-4.0.3, August 28, 2002
      MySQL/InnoDB-3.23.52, August 16, 2002
      MySQL/InnoDB-4.0.2, July 10, 2002
      MySQL/InnoDB-3.23.51, June 12, 2002
      MySQL/InnoDB-3.23.50, April 23, 2002
      MySQL/InnoDB-3.23.49, February 17, 2002
      MySQL/InnoDB-3.23.48, February 9, 2002
      MySQL/InnoDB-3.23.47, December 28, 2001
      MySQL/InnoDB-4.0.1, December 23, 2001
      MySQL/InnoDB-3.23.46, November 30, 2001
      MySQL/InnoDB-3.23.45, November 23, 2001
      MySQL/InnoDB-3.23.44, November 2, 2001
      MySQL/InnoDB-3.23.43, October 4, 2001
      MySQL/InnoDB-3.23.42, September 9, 2001
      MySQL/InnoDB-3.23.41, August 13, 2001
      MySQL/InnoDB-3.23.40, July 16, 2001
      MySQL/InnoDB-3.23.39, June 13, 2001
      MySQL/InnoDB-3.23.38, May 12, 2001
    InnoDB Contact Information
  `BDB' or `BerkeleyDB' Tables
    Overview of `BDB' Tables
    Installing `BDB'
    `BDB' startup options
    Characteristics of `BDB' tables:
    Things we need to fix for `BDB' in the near future:
    Operating systems supported by `BDB'
    Restrictions on `BDB' Tables
    Errors That May Occur When Using `BDB' Tables

MySQL APIs
  MySQL PHP API
    Common Problems with MySQL and PHP
  MySQL Perl API
    `DBI' with `DBD::mysql'
    The `DBI' Interface
    More `DBI'/`DBD' Information
  MySQL ODBC Support
    How To Install MyODBC
    How to Fill in the Various Fields in the ODBC Administrator Program
    Connect parameters for MyODBC
    How to Report Problems with MyODBC
    Programs Known to Work with MyODBC
    How to Get the Value of an `AUTO_INCREMENT' Column in ODBC
    Reporting Problems with MyODBC
  MySQL C API
    C API Datatypes
    C API Function Overview
    C API Function Descriptions
      `mysql_affected_rows()'
      `mysql_change_user()'
      `mysql_character_set_name()'
      `mysql_close()'
      `mysql_connect()'
      `mysql_create_db()'
      `mysql_data_seek()'
      `mysql_debug()'
      `mysql_drop_db()'
      `mysql_dump_debug_info()'
      `mysql_eof()'
      `mysql_errno()'
      `mysql_error()'
      `mysql_escape_string()'
      `mysql_fetch_field()'
      `mysql_fetch_fields()'
      `mysql_fetch_field_direct()'
      `mysql_fetch_lengths()'
      `mysql_fetch_row()'
      `mysql_field_count()'
      `mysql_field_seek()'
      `mysql_field_tell()'
      `mysql_free_result()'
      `mysql_get_client_info()'
      `mysql_get_host_info()'
      `mysql_get_proto_info()'
      `mysql_get_server_info()'
      `mysql_info()'
      `mysql_init()'
      `mysql_insert_id()'
      `mysql_kill()'
      `mysql_list_dbs()'
      `mysql_list_fields()'
      `mysql_list_processes()'
      `mysql_list_tables()'
      `mysql_num_fields()'
      `mysql_num_rows()'
      `mysql_options()'
      `mysql_ping()'
      `mysql_query()'
      `mysql_real_connect()'
      `mysql_real_escape_string()'
      `mysql_real_query()'
      `mysql_reload()'
      `mysql_row_seek()'
      `mysql_row_tell()'
      `mysql_select_db()'
      `mysql_shutdown()'
      `mysql_stat()'
      `mysql_store_result()'
      `mysql_thread_id()'
      `mysql_use_result()'
    C Threaded Function Descriptions
      `my_init()'
      `mysql_thread_init()'
      `mysql_thread_end()'
      `mysql_thread_safe()'
    C Embedded Server Function Descriptions
      `mysql_server_init()'
      `mysql_server_end()'
    Common questions and problems when using the C API
      Why Is It that After `mysql_query()' Returns Success, `mysql_store_result()' Sometimes Returns `NULL'?
      What Results Can I Get From a Query?
      How Can I Get the Unique ID for the Last Inserted Row?
      Problems Linking with the C API
    Building Client Programs
    How to Make a Threaded Client
    libmysqld, the Embedded MySQL Server Library
      Overview of the Embedded MySQL Server Library
      Compiling Programs with `libmysqld'
      Restrictions when using the Embedded MySQL Server
      Using Option Files with the Embedded Server
      Things left to do in Embedded Server (TODO)
      A Simple Embedded Server Example
      Licensing the Embedded Server
  MySQL C++ APIs
    Borland C++
  MySQL Java Connectivity (JDBC)
  MySQL Python APIs
  MySQL Tcl APIs
  MySQL Eiffel wrapper

Extending MySQL
  MySQL Internals
    MySQL Threads
    MySQL Test Suite
      Running the MySQL Test Suite
      Extending the MySQL Test Suite
      Reporting Bugs in the MySQL Test Suite
  Adding New Functions to MySQL
    `CREATE FUNCTION/DROP FUNCTION' Syntax
    Adding a New User-definable Function
      UDF Calling Sequences for simple functions
      UDF Calling Sequences for aggregate functions
      Argument Processing
      Return Values and Error Handling
      Compiling and Installing User-definable Functions
    Adding a New Native Function
  Adding New Procedures to MySQL
    Procedure Analyse
    Writing a Procedure

Problems and Common Errors
  How to Determine What Is Causing Problems
  Common Errors When Using MySQL
    `Access denied' Error
    `MySQL server has gone away' Error
    `Can't connect to [local] MySQL server' Error
    `Host '...' is blocked' Error
    `Too many connections' Error
    `Some non-transactional changed tables couldn't be rolled back' Error
    `Out of memory' Error
    `Packet too large' Error
    Communication Errors / Aborted Connection
    `The table is full' Error
    `Can't create/write to file' Error
    `Commands out of sync' Error in Client
    `Ignoring user' Error
    `Table 'xxx' doesn't exist' Error
    `Can't initialize character set xxx' error
    File Not Found
  Installation Related Issues
    Problems When Linking with the MySQL Client Library
    How to Run MySQL As a Normal User
    Problems with File Permissions
  Administration Related Issues
    What To Do If MySQL Keeps Crashing
    How to Reset a Forgotten Root Password
    How MySQL Handles a Full Disk
    Where MySQL Stores Temporary Files
    How to Protect or Change the MySQL Socket File `/tmp/mysql.sock'
    Time Zone Problems
  Query Related Issues
    Case-Sensitivity in Searches
    Problems Using `DATE' Columns
    Problems with `NULL' Values
    Problems with `alias'
    Deleting Rows from Related Tables
    Solving Problems with No Matching Rows
    Problems with Floating-Point Comparison
  Table Definition Related Issues
    Problems with `ALTER TABLE'.
    How To Change the Order of Columns in a Table
    TEMPORARY TABLE problems

Contributed Programs
  APIs
  Converters
  Utilities

Credits
  Developers at MySQL AB
  Contributors to MySQL
  Supporters to MySQL

MySQL Change History
  Changes in release 4.1.x (Alpha)
    Changes in release 4.1.0
  Changes in release 4.0.x (Gamma)
    Changes in release 4.0.10 (not released yet)
    Changes in release 4.0.9 (10 Jan 2003)
    Changes in release 4.0.8 (07 Jan 2003)
    Changes in release 4.0.7 (20 Dec 2002)
    Changes in release 4.0.6 (14 Dec 2002: Gamma)
    Changes in release 4.0.5 (13 Nov 2002)
    Changes in release 4.0.4 (29 Sep 2002)
    Changes in release 4.0.3 (26 Aug 2002: Beta)
    Changes in release 4.0.2 (01 Jul 2002)
    Changes in release 4.0.1 (23 Dec 2001)
    Changes in release 4.0.0 (Oct 2001: Alpha)
  Changes in release 3.23.x (Stable)
    Changes in release 3.23.56 (not released yet)
    Changes in release 3.23.55 (to be released shortly)
    Changes in release 3.23.54 (05 Dec 2002)
    Changes in release 3.23.53 (09 Oct 2002)
    Changes in release 3.23.52 (14 Aug 2002)
    Changes in release 3.23.51 (31 May 2002)
    Changes in release 3.23.50 (21 Apr 2002)
    Changes in release 3.23.49
    Changes in release 3.23.48 (07 Feb 2002)
    Changes in release 3.23.47 (27 Dec 2001)
    Changes in release 3.23.46 (29 Nov 2001)
    Changes in release 3.23.45 (22 Nov 2001)
    Changes in release 3.23.44 (31 Oct 2001)
    Changes in release 3.23.43 (04 Oct 2001)
    Changes in release 3.23.42 (08 Sep 2001)
    Changes in release 3.23.41 (11 Aug 2001)
    Changes in release 3.23.40
    Changes in release 3.23.39 (12 Jun 2001)
    Changes in release 3.23.38 (09 May 2001)
    Changes in release 3.23.37 (17 Apr 2001)
    Changes in release 3.23.36 (27 Mar 2001)
    Changes in release 3.23.35 (15 Mar 2001)
    Changes in release 3.23.34a
    Changes in release 3.23.34 (10 Mar 2001)
    Changes in release 3.23.33 (09 Feb 2001)
    Changes in release 3.23.32 (22 Jan 2001: Stable)
    Changes in release 3.23.31 (17 Jan 2001)
    Changes in release 3.23.30 (04 Jan 2001)
    Changes in release 3.23.29 (16 Dec 2000)
    Changes in release 3.23.28 (22 Nov 2000: Gamma)
    Changes in release 3.23.27 (24 Oct 2000)
    Changes in release 3.23.26 (18 Oct 2000)
    Changes in release 3.23.25 (29 Sep 2000)
    Changes in release 3.23.24 (08 Sep 2000)
    Changes in release 3.23.23 (01 Sep 2000)
    Changes in release 3.23.22 (31 Jul 2000)
    Changes in release 3.23.21
    Changes in release 3.23.20
    Changes in release 3.23.19
    Changes in release 3.23.18
    Changes in release 3.23.17
    Changes in release 3.23.16
    Changes in release 3.23.15 (May 2000: Beta)
    Changes in release 3.23.14
    Changes in release 3.23.13
    Changes in release 3.23.12 (07 Mar 2000)
    Changes in release 3.23.11
    Changes in release 3.23.10
    Changes in release 3.23.9
    Changes in release 3.23.8 (02 Jan 2000)
    Changes in release 3.23.7 (10 Dec 1999)
    Changes in release 3.23.6
    Changes in release 3.23.5 (20 Oct 1999)
    Changes in release 3.23.4 (28 Sep 1999)
    Changes in release 3.23.3
    Changes in release 3.23.2 (09 Aug 1999)
    Changes in release 3.23.1
    Changes in release 3.23.0 (05 Aug 1999: Alpha)
  Changes in release 3.22.x (Older; still supported)
    Changes in release 3.22.35
    Changes in release 3.22.34
    Changes in release 3.22.33
    Changes in release 3.22.32 (14 Feb 2000)
    Changes in release 3.22.31
    Changes in release 3.22.30
    Changes in release 3.22.29 (02 Jan 2000)
    Changes in release 3.22.28 (20 Oct 1999)
    Changes in release 3.22.27
    Changes in release 3.22.26 (16 Sep 1999)
    Changes in release 3.22.25
    Changes in release 3.22.24 (05 Jul 1999)
    Changes in release 3.22.23 (08 Jun 1999)
    Changes in release 3.22.22 (30 Apr 1999)
    Changes in release 3.22.21
    Changes in release 3.22.20 (18 Mar 1999)
    Changes in release 3.22.19 (Mar 1999: Stable)
    Changes in release 3.22.18
    Changes in release 3.22.17
    Changes in release 3.22.16 (Feb 1999: Gamma)
    Changes in release 3.22.15
    Changes in release 3.22.14
    Changes in release 3.22.13
    Changes in release 3.22.12
    Changes in release 3.22.11
    Changes in release 3.22.10
    Changes in release 3.22.9
    Changes in release 3.22.8
    Changes in release 3.22.7 (Sep 1998: Beta)
    Changes in release 3.22.6
    Changes in release 3.22.5
    Changes in release 3.22.4
    Changes in release 3.22.3
    Changes in release 3.22.2
    Changes in release 3.22.1 (Jun 1998: Alpha)
    Changes in release 3.22.0
  Changes in release 3.21.x
    Changes in release 3.21.33
    Changes in release 3.21.32
    Changes in release 3.21.31
    Changes in release 3.21.30
    Changes in release 3.21.29
    Changes in release 3.21.28
    Changes in release 3.21.27
    Changes in release 3.21.26
    Changes in release 3.21.25
    Changes in release 3.21.24
    Changes in release 3.21.23
    Changes in release 3.21.22
    Changes in release 3.21.21a
    Changes in release 3.21.21
    Changes in release 3.21.20
    Changes in release 3.21.19
    Changes in release 3.21.18
    Changes in release 3.21.17
    Changes in release 3.21.16
    Changes in release 3.21.15
    Changes in release 3.21.14b
    Changes in release 3.21.14a
    Changes in release 3.21.13
    Changes in release 3.21.12
    Changes in release 3.21.11
    Changes in release 3.21.10
    Changes in release 3.21.9
    Changes in release 3.21.8
    Changes in release 3.21.7
    Changes in release 3.21.6
    Changes in release 3.21.5
    Changes in release 3.21.4
    Changes in release 3.21.3
    Changes in release 3.21.2
    Changes in release 3.21.0
  Changes in release 3.20.x
    Changes in release 3.20.18
    Changes in release 3.20.17
    Changes in release 3.20.16
    Changes in release 3.20.15
    Changes in release 3.20.14
    Changes in release 3.20.13
    Changes in release 3.20.11
    Changes in release 3.20.10
    Changes in release 3.20.9
    Changes in release 3.20.8
    Changes in release 3.20.7
    Changes in release 3.20.6
    Changes in release 3.20.3
    Changes in release 3.20.0
  Changes in release 3.19.x
    Changes in release 3.19.5
    Changes in release 3.19.4
    Changes in release 3.19.3

Porting to Other Systems
  Debugging a MySQL server
    Compiling MYSQL for Debugging
    Creating Trace Files
    Debugging mysqld under gdb
    Using a Stack Trace
    Using Log Files to Find Cause of Errors in mysqld
    Making a Test Case When You Experience Table Corruption
  Debugging a MySQL client
  The DBUG Package
  Locking methods
  Comments about RTS threads
  Differences between different thread packages

Environment Variables

MySQL Regular Expressions

GNU General Public License
  Preamble
  How to Apply These Terms to Your New Programs

GNU Lesser General Public License
  Preamble
  How to Apply These Terms to Your New Libraries

SQL command, type and function index

Concept Index


This is the Reference Manual for the `MySQL Database System'.  This
version refers to the 3.23.55 version of `MySQL Server' but it is also
applicable for any older version as changes are always indicated.

General Information
*******************

The `MySQL (TM)' software delivers a very fast, multi-threaded,
multi-user, and robust `SQL' (`Structured Query Language') database
server.  `MySQL Server' is intended for mission-critical, heavy-load
production systems as well as for embedding into mass-deployed software.
`MySQL' is a trademark of `MySQL AB'.

The `MySQL' software is `Dual Licensed'. Users can choose to use the
`MySQL' software as an `Open Source'/`Free Software' product under the
terms of the `GNU General Public License'
(`http://www.gnu.org/licenses/') or can purchase a standard commercial
license from `MySQL AB'.  *Note Licensing and Support::.

The `MySQL' web site (`http://www.mysql.com/') provides the latest
information about the `MySQL' software.

The following list describes some sections of particular interest in
this manual:

   * For information about the company behind the `MySQL Database
     Server', see *Note What is MySQL AB::.

   * For a discussion about the capabilities of the `MySQL Database
     Server', see *Note Features::.

   * For installation instructions, see *Note Installing::.

   * For tips on porting the `MySQL Database Software' to new
     architectures or operating systems, see *Note Porting::.

   * For information about upgrading from a Version 3.23 release, see
     *Note Upgrading-from-3.23::.

   * For information about upgrading from a Version 3.22 release, see
     *Note Upgrading-from-3.22::.

   * For a tutorial introduction to the `MySQL Database Server', see
     *Note Tutorial::.

   * For examples of `SQL' and benchmarking information, see the
     benchmarking directory (`sql-bench' in the distribution).

   * For a history of new features and bug fixes, see *Note News::.

   * For a list of currently known bugs and misfeatures, see *Note
     Bugs::.

   * For future plans, see *Note TODO::.

   * For a list of all the contributors to this project, see *Note
     Credits::.

*Important*:

Reports of errors (often called bugs), as well as questions and
comments, should be sent to the mailing list at <[e-mail]>.
*Note Bug reports::.

The `mysqlbug' script should be used to generate bug reports.  For
source distributions, the `mysqlbug' script can be found in the
`scripts' directory.  For binary distributions, `mysqlbug' can be found
in the `bin' directory. If you have found a sensitive security bug in
`MySQL Server', you should send an e-mail to <[e-mail]>.

About This Manual
=================

This is the `MySQL' reference manual; it documents `MySQL' upto Version
3.23.55. Functional changes are always indicated with reference to the
version, so this manual is also suitable if you are using an older
version of the `MySQL' software.  Being a reference manual, it does not
provide general instruction on `SQL' or relational database concepts.

As the `MySQL Database Software' is under constant development, the
manual is also updated frequently.  The most recent version of this
manual is available at `http://www.mysql.com/documentation/' in many
different formats, including HTML, PDF, and Windows HLP versions.

The primary document is the Texinfo file.  The HTML version is produced
automatically using a modified version of `texi2html'.  The plain text
and Info versions are produced with `makeinfo'.  The PostScript version
is produced using `texi2dvi' and `dvips'.  The PDF version is produced
with `pdftex'.

If you have a hard time finding information in the manual, you can try
our searchable version at `http://www.mysql.com/doc/'.

If you have any suggestions concerning additions or corrections to this
manual, please send them to the documentation team at <[e-mail]>.

This manual was initially written by David Axmark and Michael (Monty)
Widenius. It is currently maintained by Michael (Monty) Widenius, Arjen
Lentz, and Paul DuBois. For other contributors, see *Note Credits::.

The copyright (2002) to this manual is owned by the Swedish company
`MySQL AB'. *Note Copyright::.

Conventions Used in This Manual
-------------------------------

This manual uses certain typographical conventions:

`constant'
     Constant-width font is used for command names and options; SQL
     statements; database, table, and column names; C and Perl code;
     and environment variables.  Example: "To see how `mysqladmin'
     works, invoke it with the `--help' option."

`filename'
     Constant-width font with surrounding quotes is used for filenames
     and pathnames.  Example: "The distribution is installed under the
     `/usr/local/' directory."

`c'
     Constant-width font with surrounding quotes is also used to
     indicate character sequences.  Example: "To specify a wildcard,
     use the `%' character."

_italic_
     Italic font is used for emphasis, _like this_.

*boldface*
     Boldface font is used in table headings and to convey *especially
     strong emphasis*.

When commands are shown that are meant to be executed by a particular
program, the program is indicated by a prompt shown before the command.
For example, `shell>' indicates a command that you execute from your
login shell, and `mysql>' indicates a command that you execute from the
`mysql' client program:

     shell> type a shell command here
     mysql> type a mysql command here

Shell commands are shown using Bourne shell syntax.  If you are using a
`csh'-style shell, you may need to issue commands slightly differently.
For example, the sequence to set an environment variable and run a
command looks like this in Bourne shell syntax:

     shell> VARNAME=value some_command

For `csh', you would execute the sequence like this:

     shell> setenv VARNAME value
     shell> some_command

Often database, table, and column names must be substituted into
commands.  To indicate that such substitution is necessary, this manual
uses `db_name', `tbl_name' and `col_name'.  For example, you might see
a statement like this:

     mysql> SELECT col_name FROM db_name.tbl_name;

This means that if you were to enter a similar statement, you would
supply your own database, table, and column names, perhaps like this:

     mysql> SELECT author_name FROM biblio_db.author_list;

SQL keywords are not case-sensitive and may be written in uppercase or
lowercase.  This manual uses uppercase.

In syntax descriptions, square brackets (`[' and `]') are used to
indicate optional words or clauses.  For example, in the following
statement, `IF EXISTS' is optional:

     DROP TABLE [IF EXISTS] tbl_name

When a syntax element consists of a number of alternatives, the
alternatives are separated by vertical bars (`|').  When one member
from a set of choices *may* be chosen, the alternatives are listed
within square brackets (`[' and `]'):

     TRIM([[BOTH | LEADING | TRAILING] [remstr] FROM] str)

When one member from a set of choices *must* be chosen, the
alternatives are listed within braces (`{' and `}'):

     {DESCRIBE | DESC} tbl_name {col_name | wild}

What Is MySQL?
==============

`MySQL', the most popular `Open Source' SQL database, is developed,
distributed and supported by `MySQL AB'.  `MySQL AB' is a commercial
company founded by the MySQL developers that builds its business
providing services around the `MySQL' database.  *Note What is MySQL
AB::.

The `MySQL' web site (`http://www.mysql.com/') provides the latest
information about `MySQL' software and `MySQL AB'.

`MySQL' is a database management system.
     A database is a structured collection of data.  It may be anything
     from a simple shopping list to a picture gallery or the vast
     amounts of information in a corporate network.  To add, access,
     and process data stored in a computer database, you need a
     database management system such as `MySQL' Server.  Since
     computers are very good at handling large amounts of data,
     database management plays a central role in computing, as
     stand-alone utilities, or as parts of other applications.

MySQL is a relational database management system.
     A relational database stores data in separate tables rather than
     putting all the data in one big storeroom.  This adds speed and
     flexibility.  The tables are linked by defined relations making it
     possible to combine data from several tables on request. The `SQL'
     part of "`MySQL'" stands for "`Structured Query Language'"the most
     common standardised language used to access databases.

MySQL software is `Open Source'.
     `Open Source' means that it is possible for anyone to use and
     modify.  Anybody can download the `MySQL' software from the
     Internet and use it without paying anything.  Anybody so inclined
     can study the source code and change it to fit their needs.  The
     `MySQL' software uses the `GPL' (`GNU General Public License'),
     `http://www.gnu.org/licenses/', to define what you may and may not
     do with the software in different situations.  If you feel
     uncomfortable with the `GPL' or need to embed `MySQL' code into a
     commercial application you can buy a commercially licensed version
     from us.  *Note MySQL licenses::.

Why use the MySQL Database Server?
     The `MySQL Database Server' is very fast, reliable, and easy to
     use.  If that is what you are looking for, you should give it a
     try.  `MySQL Server' also has a practical set of features
     developed in close cooperation with our users.  You can find a
     performance comparison of `MySQL Server' to some other database
     managers on our benchmark page.  *Note MySQL Benchmarks::.

     `MySQL Server' was originally developed to handle large databases
     much faster than existing solutions and has been successfully used
     in highly demanding production environments for several years.
     Though under constant development, `MySQL Server' today offers a
     rich and useful set of functions.  Its connectivity, speed, and
     security make `MySQL Server' highly suited for accessing databases
     on the Internet.

The technical features of MySQL Server
     For advanced technical information, see *Note Reference::.  The
     `MySQL Database Software' is a client/server system that consists
     of a multi-threaded `SQL' server that supports different backends,
     several different client programs and libraries, administrative
     tools, and a wide range of programming interfaces (`API's).

     We also provide `MySQL Server' as a multi-threaded library which
     you can link into your application to get a smaller, faster,
     easier-to-manage product.

There is a large amount of contributed MySQL software available.
     It is very likely that you will find that your favorite
     application or language already supports the `MySQL Database
     Server'.

The official way to pronounce `MySQL' is "My Ess Que Ell" (not "my
sequel"), but we don't mind if you pronounce it as "my sequel" or in
some other localised way.

History of MySQL
----------------

We once started out with the intention of using `mSQL' to connect to our
tables using our own fast low-level (ISAM) routines. However, after some
testing we came to the conclusion that `mSQL' was not fast enough nor
flexible enough for our needs.  This resulted in a new SQL interface to
our database but with almost the same API interface as `mSQL'.  This
API was chosen to ease porting of third-party code.

The derivation of the name `MySQL' is not perfectly clear.  Our base
directory and a large number of our libraries and tools have had the
prefix "my" for well over 10 years.  However, Monty's daughter (some
years younger) is also named My.  Which of the two gave its name to
`MySQL' is still a mystery, even for us.

The Main Features of MySQL
--------------------------

The following list describes some of the important characteristics of
the `MySQL Database Software'. *Note MySQL 4.0 In A Nutshell::.

Internals and Portability
        * Written in C and C++.  Tested with a broad range of different
          compilers.

        * Works on many different platforms.  *Note Which OS::.

        * Uses GNU Automake, Autoconf, and Libtool for portability.

        * APIs for C, C++, Eiffel, Java, Perl, PHP, Python, Ruby, and
          Tcl.  *Note Clients::.

        * Fully multi-threaded using kernel threads.  This means it can
          easily use multiple CPUs if available.

        * Very fast B-tree disk tables with index compression.

        * A very fast thread-based memory allocation system.

        * Very fast joins using an optimised one-sweep multi-join.

        * In-memory hash tables which are used as temporary tables.

        * SQL functions are implemented through a highly optimised
          class library and should be as fast as possible!  Usually
          there isn't any memory allocation at all after query
          initialisation.

        * The `MySQL' code gets tested with Purify (a commercial memory
          leakage detector) as well as with Valgrind, a GPL tool
          (`http://developer.kde.org/~sewardj/').

Column Types
        * Many column types: signed/unsigned integers 1, 2, 3, 4, and 8
          bytes long, `FLOAT', `DOUBLE', `CHAR', `VARCHAR', `TEXT',
          `BLOB', `DATE', `TIME', `DATETIME', `TIMESTAMP', `YEAR',
          `SET', and `ENUM' types.  *Note Column types::.

        * Fixed-length and variable-length records.

        * All columns have default values.  You can use `INSERT' to
          insert a subset of a table's columns; those columns that are
          not explicitly given values are set to their default values.

Commands and Functions
        * Full operator and function support in the `SELECT' and `WHERE'
          parts of queries.  For example:

               mysql> SELECT CONCAT(first_name, " ", last_name)
                   -> FROM tbl_name
                   -> WHERE income/dependents > 10000 AND age > 30;

        * Full support for SQL `GROUP BY' and `ORDER BY' clauses.
          Support for group functions (`COUNT()', `COUNT(DISTINCT ...)',
          `AVG()', `STD()', `SUM()', `MAX()', and `MIN()').

        * Support for `LEFT OUTER JOIN' and `RIGHT OUTER JOIN' with ANSI
          SQL and ODBC syntax.

        * Aliases on tables and columns are allowed as in the SQL92
          standard.

        * `DELETE', `INSERT', `REPLACE', and `UPDATE' return the number
          of rows that were changed (affected).  It is possible to
          return the number of rows matched instead by setting a flag
          when connecting to the server.

        * The `MySQL'-specific `SHOW' command can be used to retrieve
          information about databases, tables, and indexes.  The
          `EXPLAIN' command can be used to determine how the optimiser
          resolves a query.

        * Function names do not clash with table or column names.  For
          example, `ABS' is a valid column name.  The only restriction
          is that for a function call, no spaces are allowed between
          the function name and the `(' that follows it.  *Note
          Reserved words::.

        * You can mix tables from different databases in the same query
          (as of Version 3.22).

Security
        * A privilege and password system that is very flexible and
          secure, and allows host-based verification.  Passwords are
          secure because all password traffic is encrypted when you
          connect to a server.

Scalability and Limits
        * Handles large databases.  We are using `MySQL Server' with
          some databases that contain 50 million records and we know of
          users that use `MySQL Server' with 60,000 tables and about
          5,000,000,000 rows.

        * Up to 32 indexes per table are allowed.  Each index may
          consist of 1 to 16 columns or parts of columns.  The maximum
          index width is 500 bytes (this may be changed when compiling
          `MySQL Server').  An index may use a prefix of a `CHAR' or
          `VARCHAR' field.

Connectivity
        * Clients may connect to the `MySQL' server using TCP/IP
          Sockets, Unix Sockets (Unix), or Named Pipes (NT).

        * `ODBC' (Open-DataBase-Connectivity) support for Win32 (with
          source).  All ODBC 2.5 functions and many others.  For
          example, you can use MS Access to connect to your `MySQL'
          server.  *Note ODBC::.

Localisation
        * The server can provide error messages to clients in many
          languages.  *Note Languages::.

        * Full support for several different character sets, including
          ISO-8859-1 (Latin1), german, big5, ujis, and more.  For
          example, the Scandinavian characters 'σ', 'Σ' and '÷' are
          allowed in table and column names.

        * All data is saved in the chosen character set.  All
          comparisons for normal string columns are case-insensitive.

        * Sorting is done according to the chosen character set (the
          Swedish way by default).  It is possible to change this when
          the `MySQL' server is started.  To see an example of very
          advanced sorting, look at the Czech sorting code.  `MySQL
          Server' supports many different character sets that can be
          specified at compile and runtime.

Clients and Tools
        * Includes `myisamchk', a very fast utility for table checking,
          optimisation, and repair.  All of the functionality of
          `myisamchk' is also available through the SQL interface as
          well.  *Note MySQL Database Administration::.

        * All `MySQL' programs can be invoked with the `--help' or `-?'
          options to obtain online assistance.

How Stable Is MySQL?
--------------------

This section addresses the questions "_How stable is MySQL Server?_"
and "_Can I depend on MySQL Server in this project?_" We will try to
clarify these issues and answer some important questions that concern
many potential users. The information in this section is based on data
gathered from the mailing list, which is very active in identifying
problems as well as reporting types of use.

Original code stems back from the early '80s, providing a stable code
base, and the ISAM table format remains backward-compatible.  At TcX,
the predecessor of `MySQL AB', `MySQL' code has worked in projects
since mid-1996, without any problems.  When the `MySQL Database
Software' was released to a wider public, we noticed that there were
some pieces of "untested code" that were quickly found by the new users
who made different types of queries from us. Each new release has had
fewer portability problems (even though each new release has had many
new features).

Each release of the `MySQL Server' has been usable. There have only
been problems when users try code from the "gray zones."  Naturally,
new users don't know what the gray zones are; this section attempts to
indicate those that are currently known.  The descriptions mostly deal
with Version 3.23 of `MySQL Server'.  All known and reported bugs are
fixed in the latest version, with the exception of those listed in the
bugs section, which are things that are design-related.  *Note Bugs::.

The `MySQL Server' design is multi-layered with independent modules.
Some of the newer modules are listed here with an indication of how
well-tested each of them is:

*Replication - Gamma*
     Large server clusters using replication are in production use, with
     good results. Work on enhanced replication features is continuing
     in `MySQL' 4.x.

*`InnoDB' tables - Stable (in 3.23 from 3.23.49)*
     The `InnoDB' transactional storage engine has now been declared
     stable in the `MySQL' 3.23 tree, starting from version 3.23.49.
     `InnoDB' is being used in large, heavy-load production systems.

*`BDB' tables - Gamma*
     The `Berkeley DB' code is very stable, but we are still improving
     the `BDB' transactional storage engine interface in `MySQL
     Server', so it will take some time before this is as well tested
     as the other table types.

*`FULLTEXT' - Beta*
     Full-text search works but is not yet widely used.  Important
     enhancements are being implemented for `MySQL' 4.0.

*`MyODBC 2.50' (uses ODBC SDK 2.5) - Gamma*
     Increasingly in wide use. Some issues brought up appear to be
     application-related and independent of the ODBC driver or
     underlying database server.

*Automatic recovery of `MyISAM' tables - Gamma*
     This status only regards the new code in the `MyISAM' storage
     engine that checks if the table was closed properly on open and
     executes an automatic check/repair of the table if it wasn't.

*Bulk-insert - Alpha*
     New feature in `MyISAM' tables in `MySQL' 4.0 for faster insert of
     many rows.

*Locking - Gamma*
     This is very system-dependent.  On some systems there are big
     problems using standard OS locking (`fcntl()').  In these cases,
     you should run `mysqld' with the `--skip-external-locking' flag.
     Problems are known to occur on some Linux systems, and on SunOS
     when using NFS-mounted filesystems.

`MySQL AB' provides high-quality support for paying customers, but the
`MySQL' mailing list usually provides answers to common questions. Bugs
are usually fixed right away with a patch; for serious bugs, there is
almost always a new release.

How Big Can MySQL Tables Be?
----------------------------

`MySQL' Version 3.22 has a 4G limit on table size. With the new
`MyISAM' table type in `MySQL' Version 3.23, the maximum table size is
pushed up to 8 million terabytes (2 ^ 63 bytes).

Note, however, that operating systems have their own file-size limits.
Here are some examples:

*Operating System*     *File-Size Limit*
Linux-Intel 32 bit     2G, 4G or more, depends on Linux
                       version
Linux-Alpha            8T (?)
Solaris 2.5.1          2G (possible 4G with patch)
Solaris 2.6            4G (can be changed with flag)
Solaris 2.7 Intel      4G
Solaris 2.7            512G
UltraSPARC

On Linux 2.2 you can get bigger tables than 2G by using the LFS patch
for the ext2 filesystem.  On Linux 2.4 patches also exist for ReiserFS
to get support for big files.

This means that the table size for `MySQL' databases is normally
limited by the operating system.

By default, `MySQL' tables have a maximum size of about 4G.  You can
check the maximum table size for a table with the `SHOW TABLE STATUS'
command or with the `myisamchk -dv table_name'.  *Note SHOW::.

If you need bigger tables than 4G (and your operating system supports
this), you should set the `AVG_ROW_LENGTH' and `MAX_ROWS' parameter
when you create your table.  *Note CREATE TABLE::.  You can also set
these later with `ALTER TABLE'. *Note ALTER TABLE::.

If your big table is going to be read-only, you could use `myisampack'
to merge and compress many tables to one.  `myisampack' usually
compresses a table by at least 50%, so you can have, in effect, much
bigger tables.  *Note `myisampack': myisampack.

You can go around the operating system file limit for `MyISAM' data
files by using the `RAID' option. *Note CREATE TABLE::.

Another solution can be the included `MERGE' library, which allows you
to handle a collection of identical tables as one.  *Note `MERGE'
tables: MERGE.

Year 2000 Compliance
--------------------

The `MySQL Server' itself has no problems with Year 2000 (Y2K)
compliance:

   * `MySQL Server' uses Unix time functions and has no problems with
     dates until `2069'; all 2-digit years are regarded to be in the
     range `1970' to `2069', which means that if you store `01' in a
     `year' column, `MySQL Server' treats it as `2001'.

   * All `MySQL' date functions are stored in one file, `sql/time.cc',
     and are coded very carefully to be year 2000-safe.

   * In `MySQL' Version 3.22 and later, the new `YEAR' column type can
     store years `0' and `1901' to `2155' in 1 byte and display them
     using 2 or 4 digits.

You may run into problems with applications that use `MySQL Server' in
a way that is not Y2K-safe.  For example, many old applications store
or manipulate years using 2-digit values (which are ambiguous) rather
than 4-digit values.  This problem may be compounded by applications
that use values such as `00' or `99' as "missing" value indicators.

Unfortunately, these problems may be difficult to fix because different
applications may be written by different programmers, each of whom may
use a different set of conventions and date-handling functions.

Here is a simple demonstration illustrating that `MySQL Server' doesn't
have any problems with dates until the year 2030:

     mysql> DROP TABLE IF EXISTS y2k;
     Query OK, 0 rows affected (0.01 sec)

     mysql> CREATE TABLE y2k (date DATE,
         ->                   date_time DATETIME,
         ->                   time_stamp TIMESTAMP);
     Query OK, 0 rows affected (0.00 sec)

     mysql> INSERT INTO y2k VALUES
         -> ("1998-12-31","1998-12-31 23:59:59",19981231235959),
         -> ("1999-01-01","1999-01-01 00:00:00",19990101000000),
         -> ("1999-09-09","1999-09-09 23:59:59",19990909235959),
         -> ("2000-01-01","2000-01-01 00:00:00",20000101000000),
         -> ("2000-02-28","2000-02-28 00:00:00",20000228000000),
         -> ("2000-02-29","2000-02-29 00:00:00",20000229000000),
         -> ("2000-03-01","2000-03-01 00:00:00",20000301000000),
         -> ("2000-12-31","2000-12-31 23:59:59",20001231235959),
         -> ("2001-01-01","2001-01-01 00:00:00",20010101000000),
         -> ("2004-12-31","2004-12-31 23:59:59",20041231235959),
         -> ("2005-01-01","2005-01-01 00:00:00",20050101000000),
         -> ("2030-01-01","2030-01-01 00:00:00",20300101000000),
         -> ("2050-01-01","2050-01-01 00:00:00",20500101000000);
     Query OK, 13 rows affected (0.01 sec)
     Records: 13  Duplicates: 0  Warnings: 0

     mysql> SELECT * FROM y2k;
     +------------+---------------------+----------------+
     | date       | date_time           | time_stamp     |
     +------------+---------------------+----------------+
     | 1998-12-31 | 1998-12-31 23:59:59 | 19981231235959 |
     | 1999-01-01 | 1999-01-01 00:00:00 | 19990101000000 |
     | 1999-09-09 | 1999-09-09 23:59:59 | 19990909235959 |
     | 2000-01-01 | 2000-01-01 00:00:00 | 20000101000000 |
     | 2000-02-28 | 2000-02-28 00:00:00 | 20000228000000 |
     | 2000-02-29 | 2000-02-29 00:00:00 | 20000229000000 |
     | 2000-03-01 | 2000-03-01 00:00:00 | 20000301000000 |
     | 2000-12-31 | 2000-12-31 23:59:59 | 20001231235959 |
     | 2001-01-01 | 2001-01-01 00:00:00 | 20010101000000 |
     | 2004-12-31 | 2004-12-31 23:59:59 | 20041231235959 |
     | 2005-01-01 | 2005-01-01 00:00:00 | 20050101000000 |
     | 2030-01-01 | 2030-01-01 00:00:00 | 20300101000000 |
     | 2050-01-01 | 2050-01-01 00:00:00 | 00000000000000 |
     +------------+---------------------+----------------+
     13 rows in set (0.00 sec)

This shows that the `DATE' and `DATETIME' types will not give any
problems with future dates (they handle dates until the year 9999).

The `TIMESTAMP' type, which is used to store the current time, has a
range up to only `2030-01-01'.  `TIMESTAMP' has a range of `1970' to
`2030' on 32-bit machines (signed value).  On 64-bit machines it
handles times up to `2106' (unsigned value).

Even though `MySQL Server' is Y2K-compliant, it is your responsibility
to provide unambiguous input.  See *Note Y2K issues:: for `MySQL
Server''s rules for dealing with ambiguous date input data (data
containing 2-digit year values).

What Is MySQL AB?
=================

`MySQL AB' is the company of the `MySQL' founders and main developers.
`MySQL AB' was originally established in Sweden by David Axmark, Allan
Larsson, and Michael `Monty' Widenius.

All the developers of the `MySQL' server are employed by the company.
We are a virtual organisation with people in a dozen countries around
the world. We communicate extensively over the Net every day with each
other and with our users, supporters and partners.

We are dedicated to developing the `MySQL' software and spreading our
database to new users. `MySQL AB' owns the copyright to the `MySQL'
source code, the `MySQL' logo and trademark, and this manual. *Note
What-is::.

The `MySQL' core values show our dedication to `MySQL' and `Open
Source'.

We want the `MySQL Database Software' to be:
   * The best and the most widely used database in the world.

   * Available and affordable for all.

   * Easy to use.

   * Continuously improving while remaining fast and safe.

   * Fun to use and improve.

   * Free from bugs.

`MySQL AB' and the people at `MySQL AB':
   * Promote `Open Source' philosophy and support the `Open Source'
     community.

   * Aim to be good citizens.

   * Prefer partners that share our values and mind-set.

   * Answer e-mail and provide support.

   * Are a virtual company, networking with others.

   * Work against software patents.

The `MySQL' web site (`http://www.mysql.com/') provides the latest
information about `MySQL' and `MySQL AB'.

The Business Model and Services of MySQL AB
-------------------------------------------

One of the most common questions we encounter is: "_How can you make a
living from something you give away for free?_" This is how.

`MySQL AB' makes money on support, services, commercial licenses, and
royalties, and we use these revenues to fund product development and to
expand the `MySQL' business.

The company has been profitable since its inception. In October 2001,
we accepted venture financing from leading Scandinavian investors and a
handful of business angels. This investment is used to solidify our
business model and build a basis for sustainable growth.

Support
.......

`MySQL AB' is run and owned by the founders and main developers of the
`MySQL' database. The developers are committed to giving support to
customers and other users in order to stay in touch with their needs
and problems. All our support is given by qualified developers. Really
tricky questions are answered by Michael `Monty' Widenius, principal
author of the `MySQL Server'.  *Note Support::.

For more information and ordering support at various levels, see
`http://www.mysql.com/support/' or contact our sales staff at
<[e-mail]>.

Training and Certification
..........................

`MySQL AB' delivers `MySQL' and related training worldwide.  We offer
both open courses and in-house courses tailored to the specific needs
of your company. `MySQL Training' is also available through our
partners, the `Authorised MySQL Training Centers'.

Our training material uses the same example databases as our
documentation and our sample applications, and it is always updated to
reflect the latest `MySQL' version. Our trainers are backed by the
development team to guarantee the quality of the training and the
continuous development of the course material. This also ensures that
no questions raised during the courses remain unanswered.

Attending our training courses will enable you to achieve your goals
related to your `MySQL' applications. You will also:
   * Save time.

   * Improve the performance of your application(s).

   * Reduce or eliminate the need for additional hardware, decreasing
     cost.

   * Enhance security.

   * Increase customers' and co-workers' satisfaction.

   * Prepare yourself for `MySQL Certification'.

If you are interested in our training as a potential participant or as
a training partner, please visit the training section at
`http://www.mysql.com/training/' or contact us at: <[e-mail]>.

The `MySQL Certification Program' is being released in the second half
of 2002. For details please see `http://www.mysql.com/certification/'.

Consulting
..........

`MySQL AB' and its `Authorised Partners' offer consulting services to
users of `MySQL Server' and to those who embed `MySQL Server' in their
own software, all over the world.

Our consultants can help you design and tune your databases, construct
efficient queries, tune your platform for optimal performance, resolve
migration issues, set up replication, build robust transactional
applications, and more.  We also help customers embed `MySQL Server' in
their products and applications for large-scale deployment.

Our consultants work in close collaboration with our development team,
which ensures the technical quality of our professional services.
Consulting assignments range from 2-day power-start sessions to
projects that span weeks and months. Our expertise not only covers
`MySQL Server', but also extends into programming and scripting
languages such as PHP, Perl, and more.

If you are interested in our consulting services or want to become a
consulting partner, please visit the consulting section of our web site
at `http://www.mysql.com/consulting/' or contact our consulting staff
at <[e-mail]>.

Commercial Licenses
...................

The `MySQL' database is released under the `GNU General Public License'
(`GPL').  This means that the `MySQL' software can be used free of
charge under the `GPL'. If you do not want to be bound by the `GPL'
terms (like the requirement that your own application becomes `GPL' as
well), you may purchase a commercial license for the same product from
`MySQL AB'.  See `http://www.mysql.com/products/pricing.html'.  Since
`MySQL AB' owns the copyright to the `MySQL' source code, we are able
to employ `Dual Licensing' which means that the same product is
available under `GPL' and under a commercial license. This does not in
any way affect the `Open Source' commitment of `MySQL AB'. For details
about when a commercial license is required, please see *Note MySQL
licenses::.

We also sell commercial licenses of third-party `Open Source GPL'
software that adds value to `MySQL Server'. A good example is the
`InnoDB' transactional storage engine that offers `ACID' support,
row-level locking, crash recovery, multi-versioning, foreign key
support, and more. *Note InnoDB::.

Partnering
..........

`MySQL AB' has a worldwide partner programme that covers training
courses, consulting & support, publications plus reselling and
distributing `MySQL' and related products. `MySQL AB Partners' get
visibility on the `http://www.mysql.com/' web site and the right to use
special versions of the `MySQL' trademarks to identify their products
and promote their business.

If you are interested in becoming a `MySQL AB Partner', please e-mail
<[e-mail]>.

The word `MySQL' and the `MySQL' dolphin logo are trademarks of `MySQL
AB'. *Note MySQL AB Logos and Trademarks::.  These trademarks represent
a significant value that the `MySQL' founders have built over the years.

Advertising
...........

The `MySQL' web site (`http://www.mysql.com/') is popular among
developers and users. In October 2001, we served 10 million page views.
Our visitors represent a group that makes purchase decisions and
recommendations for both software and hardware. Twelve percent of our
visitors authorise purchase decisions, and only nine percent are not
involved in purchase decisions at all. More than 65% have made one or
more online business purchase within the last half-year, and 70% plan
to make one in the next months.

Contact Information
-------------------

The `MySQL' web site (`http://www.mysql.com/') provides the latest
information about `MySQL' and `MySQL AB'.

For press service and inquiries not covered in our News releases
(`http://www.mysql.com/news/'), please send e-mail to <[e-mail]>.

If you have a valid support contract with `MySQL AB', you will get
timely, precise answers to your technical questions about the `MySQL'
software. For more information, see *Note Support::.  On our website,
see `http://www.mysql.com/support/', or send an e-mail message to
<[e-mail]>.

For information about `MySQL' training, please visit the training
section at `http://www.mysql.com/training/'. If you have restricted
access to the Internet, please contact the `MySQL AB' training staff at
<[e-mail]>.  *Note Business Services Training::.

For information on the `MySQL Certification Program', please see
`http://www.mysql.com/certification/'.  *Note Business Services
Training::.

If you're interested in consulting, please visit the consulting section
at `http://www.mysql.com/consulting/'. If you have restricted access to
the Internet, please contact the `MySQL AB' consulting staff at
<[e-mail]>.  *Note Business Services Consulting::.

Commercial licenses may be purchased online at
`https://order.mysql.com/'. There you will also find information on how
to fax your purchase order to `MySQL AB'. More information about
licensing can be found at `http://www.mysql.com/products/pricing.html'.
If you have questions regarding licensing or you want a quote for a
high-volume license deal, please fill in the contact form on our web
site (`http://www.mysql.com/') or send an e-mail message to
<[e-mail]> (for licensing questions) or to <[e-mail]>
(for sales inquiries).  *Note MySQL licenses::.

If you represent a business that is interested in partnering with
`MySQL AB', please send e-mail to <[e-mail]>.  *Note Business
Services Partnering::.

For more information on the `MySQL' trademark policy, refer to
`http://www.mysql.com/company/trademark.html' or send e-mail to
<[e-mail]>.  *Note MySQL AB Logos and Trademarks::.

If you are interested in any of the `MySQL AB' jobs listed in our jobs
section (`http://www.mysql.com/company/jobs/'), please send an e-mail
message to <[e-mail]>.  Please do not send your CV as an
attachment, but rather as plain text at the end of your e-mail message.

For general discussion among our many users, please direct your
attention to the appropriate mailing list.  *Note Questions::.

Reports of errors (often called bugs), as well as questions and
comments, should be sent to the mailing list at
<[e-mail]>. If you have found a sensitive security bug in
the `MySQL Server', please send an e-mail to <[e-mail]>.
*Note Bug reports::.

If you have benchmark results that we can publish, please contact us at
<[e-mail]>.

If you have any suggestions concerning additions or corrections to this
manual, please send them to the manual team at <[e-mail]>.

For questions or comments about the workings or content of the `MySQL'
web site (`http://www.mysql.com/'), please send e-mail to
<[e-mail]>.

`MySQL AB' has a privacy policy, which can be read at
`http://www.mysql.com/company/privacy.html'.  For any queries regarding
this policy, please e-mail <[e-mail]>.

For all other inquires, please send e-mail to <[e-mail]>.

MySQL Support and Licensing
===========================

This section describes `MySQL' support and licensing arrangements.

Support Offered by MySQL AB
---------------------------

Technical support from `MySQL AB' means individualised answers to your
unique problems direct from the software engineers who code the `MySQL'
database engine.

We try to take a broad and inclusive view of technical support. Almost
any problem involving `MySQL' software is important to us if it's
important to you.  Typically customers seek help on how to get
different commands and utilities to work, remove performance
bottlenecks, restore crashed systems, understand operating system or
networking impacts on `MySQL', set up best practices for backup and
recovery, utilise `API's, etc.  Our support covers only the `MySQL'
server and our own utilities, not third-party products that access the
`MySQL' server, though we try to help with these where we can.

Detailed information about our various support options is given at
`http://www.mysql.com/support/', where support contracts can also be
ordered online. If you have restricted access to the Internet, contact
our sales staff at <[e-mail]>.

Technical support is like life insurance. You can live happily without
it for years, but when your hour arrives it becomes critically
important, yet it's too late to buy it!  If you use `MySQL' Server for
important applications and encounter sudden troubles,  it might take
too long to figure out all the answers yourself. You may need immediate
access to the most experienced `MySQL' troubleshooters available, those
employed by `MySQL AB'.

Copyrights and Licenses Used by MySQL
-------------------------------------

`MySQL AB' owns the copyright to the `MySQL' source code, the `MySQL'
logos and trademarks and this manual.  *Note What is MySQL AB::.
Several different licenses are relevant to the `MySQL' distribution:

  1. All the `MySQL'-specific source in the server, the `mysqlclient'
     library and the client, as well as the `GNU' `readline' library is
     covered by the `GNU General Public License'.  *Note GPL license::.
     The text of this license can also be found as the file `COPYING'
     in the distributions.

  2. The `GNU' `getopt' library is covered by the `GNU Lesser General
     Public License'.  *Note LGPL license::.

  3. Some parts of the source (the `regexp' library) are covered by a
     Berkeley-style copyright.

  4. Older versions of `MySQL' (3.22 and earlier) are subject to a more
     strict license (`http://www.mysql.com/products/mypl.html').  See
     the documentation of the specific version for information.

  5. The manual is currently *not* distributed under a `GPL'-style
     license.  Use of the manual is subject to the following terms:
        * Conversion to other formats is allowed, but the actual content
          may not be altered or edited in any way.

        * You may create a printed copy for your own personal use.

        * For all other uses, such as selling printed copies or using
          (parts of) the manual in another publication, prior written
          agreement from `MySQL AB' is required.
     Please e-mail <[e-mail]> for more information or if you are
     interested in doing a translation.

For information about how the `MySQL' licenses work in practice, please
refer to *Note MySQL licenses::.  Also see *Note MySQL AB Logos and
Trademarks::.

MySQL Licenses
--------------

The `MySQL' software is released under the `GNU General Public License'
(`GPL'), which probably is the best known `Open Source' license.  The
formal terms of the `GPL' license can be found at
`http://www.gnu.org/licenses/'.  See also
`http://www.gnu.org/licenses/gpl-faq.html' and
`http://www.gnu.org/philosophy/enforcing-gpl.html'.

Since the `MySQL' software is released under the `GPL', it may often be
used for free, but for certain uses you may want or need to buy
commercial licenses from `MySQL AB' at `https://order.mysql.com/'.  See
`http://www.mysql.com/products/licensing.html' for more information.

Older versions of `MySQL' (3.22 and earlier) are subject to a more
strict license (`http://www.mysql.com/products/mypl.html').  See the
documentation of the specific version for information.

Please note that the use of the `MySQL' software under commercial
license, `GPL', or the old `MySQL' license does not automatically give
you the right to use `MySQL AB' trademarks.  *Note MySQL AB Logos and
Trademarks::.

Using the MySQL Software Under a Commercial License
...................................................

The `GPL' license is contagious in the sense that when a program is
linked to a `GPL' program all the source code for all the parts of the
resulting product must also be released under the `GPL'.  Otherwise you
break the license terms and forfeit your right to use the `GPL' program
altogether and also risk damages.

You need a commercial license:

   * When you link a program with any `GPL' code from the `MySQL'
     software and don't want the resulting product to be `GPL', maybe
     because you want to build a commercial product or keep the added
     non-`GPL' code closed source for other reasons. When purchasing
     commercial licenses, you are not using the `MySQL' software under
     `GPL' even though it's the same code.

   * When you distribute a non-`GPL' application that *only* works with
     the `MySQL' software and ship it with the `MySQL' software. This
     type of solution is actually considered to be linking even if it's
     done over a network.

   * When you distribute copies of the `MySQL' software without
     providing the source code as required under the `GPL' license.

   * When you want to support the further development of the `MySQL'
     database even if you don't formally need a commercial license.
     Purchasing support directly from `MySQL AB' is another good way of
     contributing to the development of the `MySQL' software, with
     immediate advantages for you.  *Note Support::.

If you require a license, you will need one for each installation of the
`MySQL' software. This covers any number of CPUs on a machine, and there
is no artificial limit on the number of clients that connect to the
server in any way.

For commercial licenses, please visit our website at
`http://www.mysql.com/products/licensing.html'.  For support contracts,
see `http://www.mysql.com/support/'.  If you have special needs or you
have restricted access to the Internet, please contact our sales staff
at <[e-mail]>.

Using the MySQL Software for Free Under GPL
...........................................

You can use the `MySQL' software for free under the `GPL' if you adhere
to the conditions of the `GPL'.  For more complete coverage of the
common questions about the `GPL' see the generic FAQ from the Free
Software Foundation at `http://www.gnu.org/licenses/gpl-faq.html'.
Some common cases:

   * When you distribute both your own application as well as the
     `MySQL' source code under the `GPL' with your product.

   * When you distribute the `MySQL' source code bundled with other
     programs that are not linked to or dependent on the `MySQL' system
     for their functionality even if you sell the distribution
     commercially.  This is called mere aggregation in the `GPL'
     license.

   * If you are not distributing *any* part of the `MySQL' system, you
     can use it for free.

   * When you are an Internet Service Provider (ISP), offering web
     hosting with `MySQL' servers for your customers.  However, we do
     encourage people to use ISPs that have MySQL support, as this will
     give them the confidence that if they have some problem with the
     `MySQL' installation, their ISP will in fact have the resources to
     solve the problem for them.  Note that even if an ISP does not
     have a commercial license for `MySQL Server', they should at least
     give their customers read access to the source of the `MySQL'
     installation so that the customers can verify that it is patched
     correctly.

   * When you use the `MySQL' Database Software in conjunction with a
     web server, you do not need a commercial license (so long as it is
     not a product you distribute). This is true even if you run a
     commercial web server that uses `MySQL Server', because you are not
     distributing any part of the `MySQL' system. However, in this case
     we would like you to purchase `MySQL' support because the `MySQL'
     software is helping your enterprise.

If your use of `MySQL' database software does not require a commercial
license, we encourage you to purchase support from `MySQL AB' anyway.
This way you contribute toward `MySQL' development and also gain
immediate advantages for yourself. *Note Support::.

If you use the `MySQL' database software in a commercial context such
that you profit by its use, we ask that you further the development of
the `MySQL' software by purchasing some level of support.  We feel that
if the `MySQL' database helps your business, it is reasonable to ask
that you help `MySQL AB'.  (Otherwise, if you ask us support questions,
you are not only using for free something into which we've put a lot a
work, you're asking us to provide free support, too.)

MySQL AB Logos and Trademarks
-----------------------------

Many users of the `MySQL' database want to display the `MySQL AB'
dolphin logo on their web sites, books, or boxed products. We welcome
and encourage this, although it should be noted that the word `MySQL'
and the `MySQL' dolphin logo are trademarks of `MySQL AB' and may only
be used as stated in our trademark policy at
`http://www.mysql.com/company/trademark.html'.

The Original MySQL Logo
.......................

The `MySQL' dolphin logo was designed by the Finnish advertising agency
Priority in 2001.  The dolphin was chosen as a suitable symbol for the
`MySQL' database since it is a smart, fast, and lean animal,
effortlessly navigating oceans of data. We also happen to like dolphins.

The original `MySQL' logo may only be used by representatives of `MySQL
AB' and by those having a written agreement allowing them to do so.

MySQL Logos that may be Used Without Written Permission
.......................................................

We have designed a set of special _Conditional Use_ logos that may be
downloaded from our web site at `http://www.mysql.com/press/logos.html'
and used on third-party web sites without written permission from
`MySQL AB'.  The use of these logos is not entirely unrestricted but,
as the name implies, subject to our trademark policy that is also
available on our web site. You should read through the trademark policy
if you plan to use them. The requirements are basically:

   * Use the logo you need as displayed on the `http://www.mysql.com/'
     site. You may scale it to fit your needs, but not change colours
     or design, or alter the graphics in any way.

   * Make it evident that you, and not `MySQL AB', are the creator and
     owner of the site that displays the `MySQL' trademark.

   * Don't use the trademark in a way that is detrimental to `MySQL AB'
     or to the value of `MySQL AB' trademarks. We reserve the right to
     revoke the right to use the `MySQL AB' trademark.

   * If you use the trademark on a web site, make it clickable, leading
     directly to `http://www.mysql.com/'.

   * If you are using the `MySQL' database under `GPL' in an
     application, your application must be `Open Source' and be able to
     connect to a `MySQL' server.

Contact us at <[e-mail]> to inquire about special
arrangements to fit your needs.

When do you need a Written Permission to use MySQL Logos?
.........................................................

In the following cases you need a written permission from `MySQL AB'
before using `MySQL' logos:

   * When displaying any `MySQL AB' logo anywhere except on your web
     site.

   * When displaying any `MySQL AB' logo except the _Conditional Use_
     logos mentioned previously on web sites or elsewhere.

Out of legal and commercial reasons we have to monitor the use of MySQL
trademarks on products, books, etc. We will usually require a fee for
displaying `MySQL AB' logos on commercial products, since we think it
is reasonable that some of the revenue is returned to fund further
development of the `MySQL' database.

MySQL AB Partnership Logos
..........................

`MySQL' partnership logos may only be used by companies and persons
having a written partnership agreement with `MySQL AB'. Partnerships
include certification as a `MySQL' trainer or consultant.  Please see
*Note Partnering: Business Services Partnering.

Using the word `MySQL' in Printed Text or Presentations
.......................................................

`MySQL AB' welcomes references to the `MySQL' database, but note that
the word `MySQL' is a trademark of `MySQL AB'.  Because of this, you
should append the trademark symbol (`TM') to the first or most
prominent use of the word `MySQL' in a text and where appropriate,
state that `MySQL' is a trademark of `MySQL AB'. Please refer to our
trademark policy at `http://www.mysql.com/company/trademark.html' for
details.

Using the word `MySQL' in Company and Product Names
...................................................

Use of the word `MySQL' in product or company names or in Internet
domain names is not allowed without written permission from `MySQL AB'.

MySQL 4.x In A Nutshell
=======================

Long promised by `MySQL AB' and long awaited by our users, MySQL Server
4.0 is now available in beta version for download from
`http://www.mysql.com/' and our mirrors.

Main new features of MySQL Server 4.0 are geared toward our existing
business and community users, enhancing the MySQL database software as
the solution for mission-critical, heavy-load database systems.  Other
new features target the users of embedded databases.

Stepwise Rollout
----------------

MySQL is starting from 4.0.6 been labelled gamma, which means that 4.0.x
has been available more than 2 months (first in alpha and then in beta)
without any found serious hard to fix bugs and should now be ready for
production use.

We will drop the gamma prefix when MySQL 4.0 has been out for more than
a month without any serious bugs.

Further new features are being added in MySQL 4.1, which is now
available from our bk source tree, and is targeted for alpha release in
first quarter of 2003. *Note Installing source tree::.

Ready for Immediate Use
-----------------------

All binary releases pass our extensive test suite without any errors on
any of the platforms we test on.  MySQL 4.0 has been tested on by a
large number of users and is in production used by several big sites.

Embedded MySQL
--------------

`libmysqld' makes MySQL Server suitable for a vastly expanded realm of
applications. Using the embedded MySQL server library, one can embed
MySQL Server into various applications and electronics devices, where
the end user has no knowledge of there actually being an underlying
database. Embedded MySQL Server is ideal for use behind the scenes in
Internet appliances, public kiosks, turnkey hardware/software
combination units, high performance Internet servers, self-contained
databases distributed on CD-ROM, etc.

Many users of `libmysqld' will benefit from the MySQL _Dual Licensing_.
For those not wishing to be bound by the GPL, the software is also made
available under a commercial license.  The embedded MySQL library uses
the same interface as the normal client library, so it is convenient
and easy to use. *Note libmysqld::.

Other Features Available From MySQL 4.0
---------------------------------------

   * Version 4.0 further increases _the speed of MySQL Server_ in a
     number of areas, such as bulk `INSERT's, searching on packed
     indexes, creation of `FULLTEXT' indexes, as well as
     `COUNT(DISTINCT)'.

   * The `InnoDB' storage engine is now offered as a feature of the
     standard MySQL server, including full support for `transactions'
     and `row-level locking'.

   * Our German, Austrian, and Swiss users will note that we have a new
     character set, `latin1_de', which corrects the _German sorting
     order_, placing German umlauts in the same order as German
     telephone books.

   * Features to simplify migration from other database systems to MySQL
     Server include `TRUNCATE TABLE' (like in Oracle) and `IDENTITY' as
     a synonym for automatically incremented keys (like in Sybase).
     Many users will also be happy to learn that MySQL Server now
     supports the `UNION' statement, a long-awaited standard SQL
     feature.

   * In the process of building features for new users, we have not
     forgotten requests by the community of loyal users.  We have
     multi-table `DELETE' and `UPDATE' statements.  By adding support
     for `symbolic linking' to `MyISAM' on the table level (and not
     just the database level as before), as well as by enabling symlink
     handling by default on Windows, we hope to show that we take
     enhancement requests seriously.  Functions like
     `SQL_CALC_FOUND_ROWS' and `FOUND_ROWS()' make it possible to know
     how many rows a query would have returned without a `LIMIT' clause.

Future MySQL 4.x Features
-------------------------

For the upcoming MySQL Server 4.x releases, expect the following
features now still under development:

   * Mission-critical, heavy-load users of MySQL Server will appreciate
     the additions to our replication system and our online hot backup.
     Later versions of 4.x will include `fail-safe replication';
     already existing in 4.0, the `LOAD DATA FROM MASTER' command will
     soon automate slave setup. The `online backup' will make it easy
     to add a new replication slave without taking down the master, and
     have a very low performance penalty on update-heavy systems.

   * A convenience feature for Database Administrators is that `mysqld'
     parameters (startup options) can soon be set without taking down
     the servers.

   * The new `FULLTEXT' search properties of MySQL Server 4.0 enable the
     use of `FULLTEXT' indexing of large text masses with both binary
     and natural-language searching logic. Users can customise minimal
     word length and define their own stop word lists in any human
     language, enabling a new set of applications to be built on MySQL
     Server.

   * Many read-heavy applications will benefit from further increased
     speed through the rewritten `key cache'.

   * Many developers will also be happy to see the `MySQL command help'
     in the client.

MySQL 4.1, The Following Development Release
--------------------------------------------

MySQL Server 4.0 lays the foundation for the new features of MySQL
Server 4.1 and onward, such as `nested subqueries' (4.1), `stored
procedures' (5.0), and `foreign key integrity rules' for `MyISAM'
tables (5.0), which form the top of the wish list for many of our
customers.

After those additions, critics of the MySQL Database Server have to be
more imaginative than ever in pointing out deficiencies in the MySQL
Database Management System. For long already known for its stability,
speed, and ease of use, MySQL Server will then match the requirement
checklist of very demanding buyers.

MySQL Information Sources
=========================

MySQL Mailing Lists
-------------------

This section introduces you to the MySQL mailing lists, and gives some
guidelines as to how to use them. By subscribing to a mailing list, you
will receive as e-mail messages all other postings on the list, and you
will be able to send in your own questions and answers.

The MySQL Mailing Lists
.......................

To subscribe to the main MySQL mailing list, send a message to the
electronic mail address <[e-mail]>.

To unsubscribe from the main MySQL mailing list, send a message to the
electronic mail address <[e-mail]>.

Only the address to which you send your messages is significant.  The
subject line and the body of the message are ignored.

If your reply address is not valid, you can specify your address
explicitly, by adding a hyphen to the subscribe or unsubscribe command
word, followed by your address with the `@' character in your address
replaced by a `='.  For example, to subscribe `[e-mail]',
send a message to
`mysql-subscribe-your_name=[e-mail]'.

Mail to <[e-mail]> or
<[e-mail]> is handled automatically by the
ezmlm mailing list processor.  Information about ezmlm is available at
the ezmlm web site (`http://www.ezmlm.org/').

To post a message to the list itself, send your message to
`[e-mail]'.  However, please *do not* send mail about
subscribing or unsubscribing to <[e-mail]> because any
mail sent to that address is distributed automatically to thousands of
other users.

Your local site may have many subscribers to <[e-mail]>.
If so, it may have a local mailing list, so messages sent from
`lists.mysql.com' to your site are propagated to the local list.  In
such cases, please contact your system administrator to be added to or
dropped from the local MySQL list.

If you wish to have traffic for a mailing list go to a separate mailbox
in your mail program, set up a filter based on the message headers.
You can use either the `List-ID:' or `Delivered-To:' headers to identify
list messages.

The following MySQL mailing lists exist:

`<[e-mail]> announce'
     This is for announcement of new versions of MySQL and related
     programs.  This is a low-volume list all MySQL users should
     subscribe to.

`<[e-mail]> mysql'
     The main list for general MySQL discussion.  Please note that some
     topics are better discussed on the more-specialised lists.  If you
     post to the wrong list, you may not get an answer!

`<[e-mail]> mysql-digest'
     The `mysql' list in digest form.  That means you get all individual
     messages, sent as one large mail message once a day.

`<[e-mail]> bugs'
     On this list you should only post a full, repeatable bug report
     using the `mysqlbug' script (if you are running on Windows, you
     should include a description of the operating system and the MySQL
     version).  Preferably, you should test the problem using the
     latest stable or development version of MySQL Server before
     posting!  Anyone should be able to repeat the bug by just using
     `mysql test < script' on the included test case.  All bugs posted
     on this list will be corrected or documented in the next MySQL
     release!  If only small code changes are needed, we will also post
     a patch that fixes the problem.

`<[e-mail]> bugs-digest'
     The `bugs' list in digest form.

`<[e-mail]> internals'
     A list for people who work on the MySQL code.  On this list one
     can also discuss MySQL development and post patches.

`<[e-mail]> internals-digest'
     A digest version of the `internals' list.

`<[e-mail]> java'
     Discussion about the MySQL server and Java.  Mostly about the JDBC
     drivers including MySQL Connector/J.

`<[e-mail]> java-digest'
     A digest version of the `java' list.

`<[e-mail]> win32'
     All things concerning the MySQL software on Microsoft operating
     systems such as Windows 9x/Me/NT/2000/XP.

`<[e-mail]> win32-digest'
     A digest version of the `win32' list.

`<[e-mail]> myodbc'
     All things about connecting to the MySQL server with ODBC.

`<[e-mail]> myodbc-digest'
     A digest version of the `myodbc' list.

`<[e-mail]> mysqlcc'
     All things about the `MySQL Control Center' graphical client.

`<[e-mail]> mysqlcc-digest'
     A digest version of the `mysqlcc' list.

`<[e-mail]> plusplus'
     All things concerning programming with the C++ API to MySQL.

`<[e-mail]> plusplus-digest'
     A digest version of the `plusplus' list.

`<[e-mail]> msql-mysql-modules'
     A list about the Perl support for MySQL with msql-mysql-modules.

`<[e-mail]> msql-mysql-modules-digest'
     A digest version of the `msql-mysql-modules' list.

You subscribe or unsubscribe to all lists in the same way as described
previously.  In your subscribe or unsubscribe message, just put the
appropriate mailing list name rather than `mysql'.  For example, to
subscribe to or unsubscribe from the `myodbc' list, send a message to
<[e-mail]> or
<[e-mail]>.

If you can't get an answer for your questions from the mailing list, one
option is to pay for support from MySQL AB, which will put you in
direct contact with MySQL developers. *Note Support::.

The following table shows some MySQL mailing in languages other than
English.  Note that these are not operated by MySQL AB, so we can't
guarantee the quality on these.

`<[e-mail]> A French mailing list'

`<[e-mail]> A Korean mailing list'
     E-mail `subscribe mysql [e-mail]' to this list.

`<[e-mail]> A German mailing list'
     E-mail `subscribe mysql-de [e-mail]' to this list.  You
     can find information about this mailing list at
     `http://www.4t2.com/mysql/'.

`<[e-mail]> A Portugese mailing list'
     E-mail `subscribe mysql-br [e-mail]' to this list.

`<[e-mail]> A Spanish mailing list'
     E-mail `subscribe mysql [e-mail]' to this list.

Asking Questions or Reporting Bugs
..................................

Before posting a bug report or question, please do the following:

   * Start by searching the MySQL online manual at:
     `http://www.mysql.com/doc/'
     We try to keep the manual up to date by updating it frequently with
     solutions to newly found problems! The change history appendix
     (`http://www.mysql.com/doc/en/News.html') can be particularly
     useful since it is quite possible that a newer version already
     contains a solution to your problem.

   * Search the MySQL mailing list archives:
     `http://lists.mysql.com/'
   * You can also use `http://www.mysql.com/search/' to search all the
     web pages (including the manual) that are located at
     `http://www.mysql.com/'.

If you can't find an answer in the manual or the archives, check with
your local MySQL expert.  If you still can't find an answer to your
question, go ahead and read the next section about how to send mail to
<[e-mail]>.

How to Report Bugs or Problems
..............................

Writing a good bug report takes patience, but doing it right the first
time saves time for us and for you.  A good bug report containing a full
test case for the bug will make it very likely that we will fix it in
the next release.  This section will help you write your report
correctly so that you don't waste your time doing things that may not
help us much or at all.

We encourage everyone to use the `mysqlbug' script to generate a bug
report (or a report about any problem), if possible.  `mysqlbug' can be
found in the `scripts' directory in the source distribution, or for a
binary distribution, in the `bin' directory under your MySQL
installation directory.  If you are unable to use `mysqlbug', you should
still include all the necessary information listed in this section.

The `mysqlbug' script helps you generate a report by determining much
of the following information automatically, but if something important
is missing, please include it with your message!  Please read this
section carefully and make sure that all the information described here
is included in your report.

The normal place to report bugs and problems is
<[e-mail]>.  If you can make a test case that clearly
demonstrates the bug, you should post it to the <[e-mail]>
list.  Note that on this list you should only post a full, repeatable
bug report using the `mysqlbug' script.  If you are running on Windows,
you should include a description of the operating system and the MySQL
version.  Preferably, you should test the problem using the latest
stable or development version of MySQL Server before posting!  Anyone
should be able to repeat the bug by just using "`mysql test < script'"
on the included test case or run the shell or Perl script that is
included in the bug report.  All bugs posted on the `bugs' list will be
corrected or documented in the next MySQL release!  If only small code
changes are needed to correct this problem, we will also post a patch
that fixes the problem.

If you have found a sensitive security bug in MySQL, you should send an
e-mail to <[e-mail]>.

Remember that it is possible to respond to a message containing too much
information, but not to one containing too little.  Often people omit
facts because they think they know the cause of a problem and assume
that some details don't matter.  A good principle is: if you are in
doubt about stating something, state it!  It is a thousand times faster
and less troublesome to write a couple of lines more in your report
than to be forced to ask again and wait for the answer because you
didn't include enough information the first time.

The most common errors are that people don't indicate the version
number of the MySQL distribution they are using, or don't indicate what
platform they have the MySQL server installed on (including the platform
version number).  This is highly relevant information, and in 99 cases
out of 100 the bug report is useless without it!  Very often we get
questions like, "Why doesn't this work for me?" Then we find that the
feature requested wasn't implemented in that MySQL version, or that a
bug described in a report has been fixed already in newer MySQL
versions.  Sometimes the error is platform-dependent; in such cases, it
is next to impossible to fix anything without knowing the operating
system and the version number of the platform.

Remember also to provide information about your compiler, if it is
related to the problem.  Often people find bugs in compilers and think
the problem is MySQL-related.  Most compilers are under development all
the time and become better version by version.  To determine whether
your problem depends on your compiler, we need to know what compiler is
used.  Note that every compiling problem should be regarded as a bug
report and reported accordingly.

It is most helpful when a good description of the problem is included
in the bug report.  That is, a good example of all the things you did
that led to the problem and the problem itself exactly described.  The
best reports are those that include a full example showing how to
reproduce the bug or problem.  *Note Reproduceable test case::.

If a program produces an error message, it is very important to include
the message in your report!  If we try to search for something from the
archives using programs, it is better that the error message reported
exactly matches the one that the program produces.  (Even the case
should be observed!)  You should never try to remember what the error
message was; instead, copy and paste the entire message into your
report!

If you have a problem with MyODBC, you should try to generate a MyODBC
trace file.  *Note MyODBC bug report::.

Please remember that many of the people who will read your report will
do so using an 80-column display.  When generating reports or examples
using the `mysql' command-line tool, you should therefore use the
`--vertical' option (or the `\G' statement terminator) for output that
would exceed the available width for such a display (for example, with
the `EXPLAIN SELECT' statement; see the example later in this section).

Please include the following information in your report:

   * The version number of the MySQL distribution you are using (for
     example, MySQL Version 3.22.22). You can find out which version you
     are running by executing `mysqladmin version'.  `mysqladmin' can be
     found in the `bin' directory under your MySQL installation
     directory.

   * The manufacturer and model of the machine you are working on.

   * The operating system name and version.  For most operating
     systems, you can get this information by executing the Unix
     command `uname -a'.

   * Sometimes the amount of memory (real and virtual) is relevant. If
     in doubt, include these values.

   * If you are using a source distribution of the MySQL software, the
     name and version number of the compiler used is needed.  If you
     have a binary distribution, the distribution name is needed.

   * If the problem occurs during compilation, include the exact error
     message(s) and also a few lines of context around the offending
     code in the file where the error occurred.

   * If `mysqld' died, you should also report the query that crashed
     `mysqld'.  You can usually find this out by running `mysqld' with
     logging enabled.  *Note Using log files::.

   * If any database table is related to the problem, include the
     output from `mysqldump --no-data db_name tbl_name1 tbl_name2 ...'.
     This is very easy to do and is a powerful way to get information
     about any table in a database that will help us create a situation
     matching the one you have.

   * For speed-related bugs or problems with `SELECT' statements, you
     should always include the output of `EXPLAIN SELECT ...', and at
     least the number of rows that the `SELECT' statement produces.  You
     should also include the output from `SHOW CREATE TABLE table_name'
     for each involved table. The more information you give about your
     situation, the more likely it is that someone can help you!  For
     example, the following is an example of a very good bug report (it
     should of course be posted with the `mysqlbug' script):

     Example run using the `mysql' command-line tool (note the use of
     the `\G' statement terminator for statements whose output width
     would otherwise exceed that of an 80-column display device):

          mysql> SHOW VARIABLES;
          mysql> SHOW COLUMNS FROM ...\G
                 <output from SHOW COLUMNS>
          mysql> EXPLAIN SELECT ...\G
                 <output from EXPLAIN>
          mysql> FLUSH STATUS;
          mysql> SELECT ...;
                 <A short version of the output from SELECT,
                 including the time taken to run the query>
          mysql> SHOW STATUS;
                 <output from SHOW STATUS>

   * If a bug or problem occurs while running `mysqld', try to provide
     an input script that will reproduce the anomaly.  This script
     should include any necessary source files.  The more closely the
     script can reproduce your situation, the better.  If you can make
     a reproduceable test case, you should post this to
     <[e-mail]> for a high-priority treatment!

     If you can't provide a script, you should at least include the
     output from `mysqladmin variables extended-status processlist' in
     your mail to provide some information of how your system is
     performing!

   * If you can't produce a test case in a few rows, or if the test
     table is too big to be mailed to the mailing list (more than 10
     rows), you should dump your tables using `mysqldump' and create a
     `README' file that describes your problem.

     Create a compressed archive of your files using `tar' and `gzip'
     or `zip', and use `ftp' to transfer the archive to
     `ftp://support.mysql.com/pub/mysql/secret/'.  Then send a short
     description of the problem to <[e-mail]>.

   * If you think that the MySQL server produces a strange result from
     a query, include not only the result, but also your opinion of
     what the result should be, and an account describing the basis for
     your opinion.

   * When giving an example of the problem, it's better to use the
     variable names, table names, etc., that exist in your actual
     situation than to come up with new names.  The problem could be
     related to the name of a variable or table!  These cases are rare,
     perhaps, but it is better to be safe than sorry.  After all, it
     should be easier for you to provide an example that uses your
     actual situation, and it is by all means better for us.  In case
     you have data you don't want to show to others, you can use `ftp'
     to transfer it to `ftp://support.mysql.com/pub/mysql/secret/'.  If
     the data is really top secret and you don't want to show it even
     to us, then go ahead and provide an example using other names, but
     please regard this as the last choice.

   * Include all the options given to the relevant programs, if
     possible.  For example, indicate the options that you use when you
     start the `mysqld' daemon and that you use to run any MySQL client
     programs.  The options to programs like `mysqld' and `mysql', and
     to the `configure' script, are often keys to answers and are very
     relevant!  It is never a bad idea to include them anyway!  If you
     use any modules, such as Perl or PHP, please include the version
     number(s) of those as well.

   * If your question is related to the privilege system, please
     include the output of `mysqlaccess', the output of `mysqladmin
     reload', and all the error messages you get when trying to
     connect!  When you test your privileges, you should first run
     `mysqlaccess'.  After this, execute `mysqladmin reload version'
     and try to connect with the program that gives you trouble.
     `mysqlaccess' can be found in the `bin' directory under your MySQL
     installation directory.

   * If you have a patch for a bug, that is good. But don't assume the
     patch is all we need, or that we will use it, if you don't provide
     some necessary information such as test cases showing the bug that
     your patch fixes.  We might find problems with your patch or we
     might not understand it at all; if so, we can't use it.

     If we can't verify exactly what the patch is meant for, we won't
     use it.  Test cases will help us here.  Show that the patch will
     handle all the situations that may occur.  If we find a borderline
     case (even a rare one) where the patch won't work, it may be
     useless.

   * Guesses about what the bug is, why it occurs, or what it depends on
     are usually wrong.  Even the MySQL team can't guess such things
     without first using a debugger to determine the real cause of a
     bug.

   * Indicate in your mail message that you have checked the reference
     manual and mail archive so that others know you have tried to
     solve the problem yourself.

   * If you get a `parse error', please check your syntax closely!  If
     you can't find something wrong with it, it's extremely likely that
     your current version of MySQL Server doesn't support the query you
     are using.  If you are using the current version and the manual at
     `http://www.mysql.com/doc/' doesn't cover the syntax you are
     using, MySQL Server doesn't support your query.  In this case,
     your only options are to implement the syntax yourself or e-mail
     <[e-mail]> and ask for an offer to implement it!

     If the manual covers the syntax you are using, but you have an
     older version of MySQL Server, you should check the MySQL change
     history to see when the syntax was implemented.  In this case, you
     have the option of upgrading to a newer version of MySQL Server.
     *Note News::.

   * If you have a problem such that your data appears corrupt or you
     get errors when you access some particular table, you should first
     check and then try repairing your tables with `myisamchk' or
     `CHECK TABLE' and `REPAIR TABLE'.  *Note MySQL Database
     Administration::.

   * If you often get corrupted tables you should try to find out when
     and why this happens.  In this case, the
     `mysql-data-directory/'hostname'.err' file may contain some
     information about what happened.  *Note Error log::.  Please
     include any relevant information from this file in your bug
     report.  Normally `mysqld' should *never* crash a table if nothing
     killed it in the middle of an update!  If you can find the cause
     of `mysqld' dying, it's much easier for us to provide you with a
     fix for the problem.  *Note What is crashing::.

   * If possible, download and install the most recent version of MySQL
     Server and check whether it solves your problem.  All versions of
     the MySQL software are thoroughly tested and should work without
     problems.  We believe in making everything as backward-compatible
     as possible, and you  should be able to switch MySQL versions
     without any hassle.  *Note Which version::.

If you are a support customer, please cross-post the bug report to
<[e-mail]> for higher-priority treatment, as well as to
the appropriate mailing list to see if someone else has experienced (and
perhaps solved) the problem.

For information on reporting bugs in `MyODBC', see *Note ODBC
Problems::.

For solutions to some common problems, see *Note Problems::.

When answers are sent to you individually and not to the mailing list,
it is considered good etiquette to summarise the answers and send the
summary to the mailing list so that others may have the benefit of
responses you received that helped you solve your problem!

Guidelines for Answering Questions on the Mailing List
......................................................

If you consider your answer to have broad interest, you may want to
post it to the mailing list instead of replying directly to the
individual who asked.  Try to make your answer general enough that
people other than the original poster may benefit from it.  When you
post to the list, please make sure that your answer is not a
duplication of a previous answer.

Try to summarise the essential part of the question in your reply;
don't feel obliged to quote the entire original message.

Please don't post mail messages from your browser with HTML mode turned
on!  Many users don't read mail with a browser!

MySQL Community Support on IRC (Internet Relay Chat)
----------------------------------------------------

In addition to the various MySQL mailing lists, you can find experienced
community people on `IRC' (`Internet Relay Chat').  These are the best
networks/channels currently known to us:

   * *freenode* (see `http://www.freenode.net/' for servers)
        * `#mysql' Primarily MySQL questions but other database and SQL
          questions welcome.

        * `#mysqlphp' Questions about MySQL+PHP, a popular combo.

   * *EFnet* (see `http://www.efnet.org/' for servers)
        * `#mysql' MySQL questions.

If you are looking for IRC client software to connect to an IRC network,
take a peek at `X-Chat' (`http://www.xchat.org/').  X-Chat is available
for Unix as well as for Windows platforms.

How Standards-compatible Is MySQL?
==================================

This section describes how MySQL relates to the ANSI SQL standards.
MySQL Server has many extensions to the ANSI SQL standards, and here you
will find out what they are and how to use them.  You will also find
information about functionality missing from MySQL Server, and how to
work around some differences.

Our goal is to not, without a very good reason, restrict MySQL Server
usability for any usage.  Even if we don't have the resources to do
development for every possible use, we are always willing to help and
offer suggestions to people who are trying to use MySQL Server in new
territories.

One of our main goals with the product is to continue to work toward
ANSI 99 compliancy, but without sacrificing speed or reliability.  We
are not afraid to add extensions to SQL or support for non-SQL features
if this greatly increases the usability of MySQL Server for a big part
of our users.  (The new `HANDLER' interface in MySQL Server 4.0 is an
example of this strategy. *Note `HANDLER': HANDLER.)

We will continue to support transactional and non-transactional
databases to satisfy both heavy web/logging usage and mission-critical
24/7 usage.

MySQL Server was designed from the start to work with medium size
databases (10-100 million rows, or about 100 MB per table) on small
computer systems.  We will continue to extend MySQL Server to work even
better with terabyte-size databases, as well as to make it possible to
compile a reduced MySQL version that is more suitable for hand-held
devices and embedded usage.  The compact design of the MySQL server
makes both of these directions possible without any conflicts in the
source tree.

We are currently not targeting realtime support or clustered databases
(even if you can already do a lot of things with our replication
services).

We don't believe that one should have native XML support in the
database, but will instead add the XML support our users request from
us on the client side.  We think it's better to keep the main server
code as "lean and clean" as possible and instead develop libraries to
deal with the complexity on the client side.  This is part of the
strategy mentioned previously of not sacrificing speed or reliability
in the server.

What Standards Does MySQL Follow?
---------------------------------

Entry-level SQL92. ODBC levels 0-3.51.

We are aiming toward supporting the full ANSI SQL99 standard, but
without concessions to speed and quality of the code.

Running MySQL in ANSI Mode
--------------------------

If you start `mysqld' with the `--ansi' option, the following behaviour
of MySQL Server changes:

   * `||' is string concatenation instead of `OR'.

   * You can have any number of spaces between a function name and the
     `('.  This forces all function names to be treated as reserved
     words.

   * `"' will be an identifier quote character (like the MySQL Server
     ``' quote character) and not a string quote character.

   * `REAL' will be a synonym for `FLOAT' instead of a synonym for
     `DOUBLE'.

   * The default transaction isolation level is `SERIALIZABLE'.  *Note
     SET TRANSACTION::.

This is the same as using
`--sql-mode=REAL_AS_FLOAT,PIPES_AS_CONCAT,ANSI_QUOTES,
IGNORE_SPACE,SERIALIZE,ONLY_FULL_GROUP_BY'.

MySQL Extensions to ANSI SQL92
------------------------------

MySQL Server includes some extensions that you probably will not find in
other SQL databases.  Be warned that if you use them, your code will
not be portable to other SQL servers.  In some cases, you can write
code that includes MySQL extensions, but is still portable, by using
comments of the form `/*! ... */'.  In this case, MySQL Server will
parse and execute the code within the comment as it would any other
MySQL statement, but other SQL servers will ignore the extensions.  For
example:

     SELECT /*! STRAIGHT_JOIN */ col_name FROM table1,table2 WHERE ...

If you add a version number after the `'!'', the syntax will be
executed only if the MySQL version is equal to or newer than the used
version number:

     CREATE /*!32302 TEMPORARY */ TABLE t (a int);

This means that if you have Version 3.23.02 or newer, MySQL Server will
use the `TEMPORARY' keyword.

The following is a list of MySQL extensions:

   * The field types `MEDIUMINT', `SET', `ENUM', and the different
     `BLOB' and `TEXT' types.

   * The field attributes `AUTO_INCREMENT', `BINARY', `NULL',
     `UNSIGNED', and `ZEROFILL'.

   * All string comparisons are case-insensitive by default, with sort
     ordering determined by the current character set (ISO-8859-1
     Latin1 by default).  If you don't like this, you should declare
     your columns with the `BINARY' attribute or use the `BINARY' cast,
     which causes comparisons to be done according to the ASCII order
     used on the MySQL server host.

   * MySQL Server maps each database to a directory under the MySQL
     data directory, and tables within a database to filenames in the
     database directory.

     This has a few implications:

        - Database names and table names are case-sensitive in MySQL
          Server on operating systems that have case-sensitive
          filenames (like most Unix systems). *Note Name case
          sensitivity::.

        - Database, table, index, column, or alias names may begin with
          a digit (but may not consist solely of digits).

        - You can use standard system commands to back up, rename,
          move, delete, and copy tables.  For example, to rename a
          table, rename the `.MYD', `.MYI', and `.frm' files to which
          the table corresponds.

   * In SQL statements, you can access tables from different databases
     with the `db_name.tbl_name' syntax.  Some SQL servers provide the
     same functionality but call this `User space'.  MySQL Server
     doesn't support tablespaces as in: `create table
     ralph.my_table...IN my_tablespace'.

   * `LIKE' is allowed on numeric columns.

   * Use of `INTO OUTFILE' and `STRAIGHT_JOIN' in a `SELECT' statement.
     *Note `SELECT': SELECT.

   * The `SQL_SMALL_RESULT' option in a `SELECT' statement.

   * `EXPLAIN SELECT' to get a description on how tables are joined.

   * Use of index names, indexes on a prefix of a field, and use of
     `INDEX' or `KEY' in a `CREATE TABLE' statement. *Note `CREATE
     TABLE': CREATE TABLE.

   * Use of `TEMPORARY' or `IF NOT EXISTS' with `CREATE TABLE'.

   * Use of `COUNT(DISTINCT list)' where `list' is more than one
     element.

   * Use of `CHANGE col_name', `DROP col_name', or `DROP INDEX',
     `IGNORE' or `RENAME' in an `ALTER TABLE' statement. *Note `ALTER
     TABLE': ALTER TABLE.

   * Use of `RENAME TABLE'. *Note `RENAME TABLE': RENAME TABLE.

   * Use of multiple `ADD', `ALTER', `DROP', or `CHANGE' clauses in an
     `ALTER TABLE' statement.

   * Use of `DROP TABLE' with the keywords `IF EXISTS'.

   * You can drop multiple tables with a single `DROP TABLE' statement.

   * The `LIMIT' clause of the `DELETE' statement.

   * The `DELAYED' clause of the `INSERT' and `REPLACE' statements.

   * The `LOW_PRIORITY' clause of the `INSERT', `REPLACE', `DELETE',
     and `UPDATE' statements.

   * Use of `LOAD DATA INFILE'. In many cases, this syntax is
     compatible with Oracle's `LOAD DATA INFILE'. *Note `LOAD DATA':
     LOAD DATA.

   * The `ANALYZE TABLE', `CHECK TABLE', `OPTIMIZE TABLE', and `REPAIR
     TABLE' statements.

   * The `SHOW' statement.  *Note `SHOW': SHOW.

   * Strings may be enclosed by either `"' or `'', not just by `''.

   * Use of the escape `\' character.

   * The `SET' statement. *Note `SET': SET OPTION.

   * You don't need to name all selected columns in the `GROUP BY' part.
     This gives better performance for some very specific, but quite
     normal queries.  *Note Group by functions::.

   * One can specify `ASC' and `DESC' with `GROUP BY'.

   * To make it easier for users who come from other SQL environments,
     MySQL Server supports aliases for many functions. For example, all
     string functions support both ANSI SQL syntax and ODBC syntax.

   * MySQL Server understands the `||' and `&&' operators to mean
     logical OR and AND, as in the C programming language.  In MySQL
     Server, `||' and `OR' are synonyms, as are `&&' and `AND'.
     Because of this nice syntax, MySQL Server doesn't support the ANSI
     SQL `||' operator for string concatenation; use `CONCAT()'
     instead. Because `CONCAT()' takes any number of arguments, it's
     easy to convert use of the `||' operator to MySQL Server.

   * `CREATE DATABASE' or `DROP DATABASE'.  *Note `CREATE DATABASE':
     CREATE DATABASE.

   * The `%' operator is a synonym for `MOD()'.  That is, `N % M' is
     equivalent to `MOD(N,M)'.  `%' is supported for C programmers and
     for compatibility with PostgreSQL.

   * The `=', `<>', `<=' ,`<', `>=',`>', `<<', `>>', `<=>', `AND',
     `OR', or `LIKE' operators may be used in column comparisons to the
     left of the `FROM' in `SELECT' statements.  For example:

          mysql> SELECT col1=1 AND col2=2 FROM tbl_name;

   * The `LAST_INSERT_ID()' function.  *Note `mysql_insert_id()':
     mysql_insert_id.

   * The `REGEXP' and `NOT REGEXP' extended regular expression
     operators.

   * `CONCAT()' or `CHAR()' with one argument or more than two
     arguments.  (In MySQL Server, these functions can take any number
     of arguments.)

   * The `BIT_COUNT()', `CASE', `ELT()', `FROM_DAYS()', `FORMAT()',
     `IF()', `PASSWORD()', `ENCRYPT()', `MD5()', `ENCODE()', `DECODE()',
     `PERIOD_ADD()', `PERIOD_DIFF()', `TO_DAYS()', or `WEEKDAY()'
     functions.

   * Use of `TRIM()' to trim substrings. ANSI SQL only supports removal
     of single characters.

   * The `GROUP BY' functions `STD()', `BIT_OR()', and `BIT_AND()'.

   * Use of `REPLACE' instead of `DELETE' + `INSERT'.  *Note `REPLACE':
     REPLACE.

   * The `FLUSH', `RESET' and `DO' statements.

   * The ability to set variables in a statement with `:=':
          SELECT @a:=SUM(total),@b=COUNT(*),@a/@b AS avg FROM test_table;
          SELECT @t1:=(@t2:=1)+@t3:=4,@t1,@t2,@t3;


MySQL Differences Compared to ANSI SQL92
----------------------------------------

We try to make MySQL Server follow the ANSI SQL standard and the ODBC
SQL standard, but in some cases MySQL Server does things differently:

   * For `VARCHAR' columns, trailing spaces are removed when the value
     is stored. *Note Bugs::.

   * In some cases, `CHAR' columns are silently changed to `VARCHAR'
     columns. *Note Silent column changes::.

   * Privileges for a table are not automatically revoked when you
     delete a table. You must explicitly issue a `REVOKE' to revoke
     privileges for a table. *Note `GRANT': GRANT.

   * `NULL AND FALSE' will evaluate to `NULL' and not to `FALSE'.  This
     is because we don't think it's good to have to evaluate a lot of
     extra conditions in this case.

For a prioritised list indicating when new extensions will be added to
MySQL Server, you should consult the online MySQL TODO list at
`http://www.mysql.com/doc/en/TODO.html'.  That is the latest version of
the TODO list in this manual. *Note TODO::.

Sub`SELECT's
............

MySQL Server until version 4.0 only supports nested queries of the form
`INSERT ... SELECT ...' and `REPLACE ... SELECT ...'.  You can,
however, use the function `IN()' in other contexts.  Subselects are
being implemented in the 4.1 development tree.

Meanwhile, you can often rewrite the query without a subselect:

     SELECT * FROM table1 WHERE id IN (SELECT id FROM table2);

This can be rewritten as:

     SELECT table1.* FROM table1,table2 WHERE table1.id=table2.id;

The queries:
     SELECT * FROM table1 WHERE id NOT IN (SELECT id FROM table2);
     SELECT * FROM table1 WHERE NOT EXISTS (SELECT id FROM table2
                                            WHERE table1.id=table2.id);

Can be rewritten as:

     SELECT table1.* FROM table1 LEFT JOIN table2 ON table1.id=table2.id
                                            WHERE table2.id IS NULL;

For more complicated subqueries you can often create temporary tables
to hold the subquery.  In some cases, however, this option will not
work. The most frequently encountered of these cases arises with
`DELETE' statements, for which standard SQL does not support joins
(except in subselects).  For this situation there are two options
available until subqueries are supported by MySQL Server.

The first option is to use a procedural programming language (such as
Perl or PHP) to submit a `SELECT' query to obtain the primary keys for
the records to be deleted, and then use these values to construct the
`DELETE' statement (`DELETE FROM ... WHERE ... IN (key1, key2, ...)').

The second option is to use interactive SQL to construct a set of
`DELETE' statements automatically, using the MySQL extension `CONCAT()'
(in lieu of the standard `||' operator).  For example:

     SELECT CONCAT('DELETE FROM tab1 WHERE pkid = ', "'", tab1.pkid, "'", ';')
       FROM tab1, tab2
      WHERE tab1.col1 = tab2.col2;

You can place this query in a script file and redirect input from it to
the `mysql' command-line interpreter, piping its output back to a
second instance of the interpreter:

     shell> mysql --skip-column-names mydb < myscript.sql | mysql mydb

MySQL Server 4.0 supports multi-table deletes that can be used to
efficiently delete rows based on information from one table or even
from many tables at the same time.

`SELECT INTO TABLE'
...................

MySQL Server doesn't yet support the Oracle SQL extension: `SELECT ...
INTO TABLE ...'.  MySQL Server supports instead the ANSI SQL syntax
`INSERT INTO ... SELECT ...', which is basically the same thing. *Note
INSERT SELECT::.

     INSERT INTO tblTemp2 (fldID) SELECT tblTemp1.fldOrder_ID
            FROM tblTemp1 WHERE tblTemp1.fldOrder_ID > 100;

Alternatively, you can use `SELECT INTO OUTFILE...' or `CREATE TABLE
... SELECT'.

Transactions and Atomic Operations
..................................

MySQL Server supports transactions with the `InnoDB' and `BDB'
`Transactional table handlers'. *Note Table types::.  `InnoDB' provides
`ACID' compliancy.

However, the non-transactional table types in MySQL Server such as
`MyISAM' follow another paradigm for data integrity called "`Atomic
Operations'." Atomic operations often offer equal or even better
integrity with much better performance.  With MySQL Server supporting
both paradigms, the user is able to decide if he needs the speed of
atomic operations or if he need to use transactional features in his
applications. This choice can be made on a per-table basis.

How does one use the features of MySQL Server to maintain rigorous
integrity and how do these features compare with the transactional
paradigm?

  1. In the transactional paradigm, if your applications are written in
     a way that is dependent on the calling of `ROLLBACK' instead of
     `COMMIT' in critical situations, transactions are more convenient.
     Transactions also ensure that unfinished updates or corrupting
     activities are not committed to the database; the server is given
     the opportunity to do an automatic rollback and your database is
     saved.

     MySQL Server, in almost all cases, allows you to resolve potential
     problems by including simple checks before updates and by running
     simple scripts that check the databases for inconsistencies and
     automatically repair or warn if such an inconsistency occurs. Note
     that just by using the MySQL log or even adding one extra log, one
     can normally fix tables perfectly with no data integrity loss.

  2. More often than not, fatal transactional updates can be rewritten
     to be atomic. Generally speaking, all integrity problems that
     transactions solve can be done with `LOCK TABLES' or atomic
     updates, ensuring that you never will get an automatic abort from
     the database, which is a common problem with transactional
     databases.

  3. Even a transactional system can lose data if the server goes down.
     The difference between different systems lies in just how small the
     time-lap is where they could lose data. No system is 100% secure,
     only "secure enough." Even Oracle, reputed to be the safest of
     transactional databases, is reported to sometimes lose data in such
     situations.

     To be safe with MySQL Server, whether using transactional tables
     or not, you only need to have backups and have the update logging
     turned on. With this you can recover from any situation that you
     could with any other transactional database.  It is, of course,
     always good to have backups, independent of which database you use.

The transactional paradigm has its benefits and its drawbacks. Many
users and application developers depend on the ease with which they can
code around problems where an abort appears to be, or is necessary.
However, even if you are new to the atomic operations paradigm, or more
familiar with transactions, do consider the speed benefit that
non-transactional tables can offer on the order of three to five times
the speed of the fastest and most optimally tuned transactional tables.

In situations where integrity is of highest importance, MySQL Server
offers transaction-level or better reliability and integrity even for
non-transactional tables.  If you lock tables with `LOCK TABLES', all
updates will stall until any integrity checks are made. If you only
obtain a read lock (as opposed to a write lock), reads and inserts are
still allowed to happen. The new inserted records will not be seen by
any of the clients that have a read lock until they release their read
locks. With `INSERT DELAYED' you can queue inserts into a local queue,
until the locks are released, without having the client wait for the
insert to complete. *Note INSERT DELAYED::.

"Atomic," in the sense that we mean it, is nothing magical. It only
means that you can be sure that while each specific update is running,
no other user can interfere with it, and there will never be an
automatic rollback (which can happen with transactional tables if you
are not very careful).  MySQL Server also guarantees that there will
not be any dirty reads.

Following are some techniques for working with non-transactional tables:

   * Loops that need transactions normally can be coded with the help of
     `LOCK TABLES', and you don't need cursors when you can update
     records on the fly.

   * To avoid using `ROLLBACK', you can use the following strategy:

       1. Use `LOCK TABLES ...' to lock all the tables you want to
          access.

       2. Test conditions.

       3. Update if everything is okay.

       4. Use `UNLOCK TABLES' to release your locks.

     This is usually a much faster method than using transactions with
     possible `ROLLBACK's, although not always. The only situation this
     solution doesn't handle is when someone kills the threads in the
     middle of an update. In this case, all locks will be released but
     some of the updates may not have been executed.

   * You can also use functions to update records in a single operation.
     You can get a very efficient application by using the following
     techniques:

        * Modify fields relative to their current value.

        * Update only those fields that actually have changed.

     For example, when we are doing updates to some customer
     information, we update only the customer data that has changed and
     test only that none of the changed data, or data that depends on
     the changed data, has changed compared to the original row. The
     test for changed data is done with the `WHERE' clause in the
     `UPDATE' statement. If the record wasn't updated, we give the
     client a message: "Some of the data you have changed has been
     changed by another user." Then we show the old row versus the new
     row in a window, so the user can decide which version of the
     customer record he should use.

     This gives us something that is similar to column locking but is
     actually even better because we only update some of the columns,
     using values that are relative to their current values.  This
     means that typical `UPDATE' statements look something like these:

          UPDATE tablename SET pay_back=pay_back+'relative change';

          UPDATE customer
            SET
              customer_date='current_date',
              address='new address',
              phone='new phone',
              money_he_owes_us=money_he_owes_us+'new_money'
            WHERE
              customer_id=id AND address='old address' AND phone='old phone';

     As you can see, this is very efficient and works even if another
     client has changed the values in the `pay_back' or
     `money_he_owes_us' columns.

   * In many cases, users have wanted `ROLLBACK' and/or `LOCK TABLES'
     for the purpose of managing unique identifiers for some tables.
     This can be handled much more efficiently by using an
     `AUTO_INCREMENT' column and either the SQL function
     `LAST_INSERT_ID()' or the C API function `mysql_insert_id()'.
     *Note `mysql_insert_id()': mysql_insert_id.

     You can generally code around row-level locking. Some situations
     really need it, but they are very few. `InnoDB' tables support
     row-level locking. With MyISAM, you can use a flag column in the
     table and do something like the following:

          UPDATE tbl_name SET row_flag=1 WHERE id=ID;

     MySQL returns 1 for the number of affected rows if the row was
     found and `row_flag' wasn't already 1 in the original row.

     You can think of it as though MySQL Server changed the preceding
     query to:

          UPDATE tbl_name SET row_flag=1 WHERE id=ID AND row_flag <> 1;

Stored Procedures and Triggers
..............................

A stored procedure is a set of SQL commands that can be compiled and
stored in the server. Once this has been done, clients don't need to
keep re-issuing the entire query but can refer to the stored procedure.
This provides better performance because the query has to be parsed
only once, and less information needs to be sent between the server and
the client. You can also raise the conceptual level by having libraries
of functions in the server.

A trigger is a stored procedure that is invoked when a particular event
occurs.  For example, you can install a stored procedure that is
triggered each time a record is deleted from a transaction table and
that automatically deletes the corresponding customer from a customer
table when all his transactions are deleted.

The planned update language will be able to handle stored procedures.
Our aim is to have stored procedures implemented in MySQL Server around
version 5.0. We are also looking at triggers.

Foreign Keys
............

Note that foreign keys in SQL are not used to join tables, but are used
mostly for checking referential integrity (foreign key constraints).  If
you want to get results from multiple tables from a `SELECT' statement,
you do this by joining tables:

     SELECT * FROM table1,table2 WHERE table1.id = table2.id;

*Note `JOIN': JOIN. *Note example-Foreign keys::.

In MySQL Server 3.23.44 and up, `InnoDB' tables support checking of
foreign key constraints. *Note InnoDB::. For other table types, MySQL
Server does parse the `FOREIGN KEY' syntax in `CREATE TABLE' commands,
but without further action being taken.

The `FOREIGN KEY' syntax without `ON DELETE ...' is mostly used for
documentation purposes. Some ODBC applications may use this to produce
automatic `WHERE' clauses, but this is usually easy to override.
`FOREIGN KEY' is sometimes used as a constraint check, but this check
is unnecessary in practice if rows are inserted into the tables in the
right order.

In MySQL Server, you can work around the problem of `ON DELETE ...' not
being implemented by adding the appropriate `DELETE' statement to an
application when you delete records from a table that has a foreign
key. In practice this is as quick (in some cases quicker) and much more
portable than using foreign keys.

In MySQL Server 4.0 you can use multi-table delete to delete rows from
many tables with one command. *Note DELETE::.

In the near future we will extend the `FOREIGN KEY' implementation so
that the information will be saved in the table specification file and
may be retrieved by `mysqldump' and ODBC. At a later stage we will
implement the foreign key constraints for applications that can't
easily be coded to avoid them.

Do keep in mind that foreign keys are often misused, which can cause
severe problems. Even when used properly, it is not a magic solution for
the referential integrity problem, although it does make things easier
in some cases.

Some advantages of foreign key enforcement:

   * Assuming proper design of the relations, foreign key constraints
     will make it more difficult for a programmer to introduce an
     inconsistency into the database.

   * Using cascading updates and deletes can simplify the client code.

   * Properly designed foreign key rules aid in documenting relations
     between tables.

Disadvantages:

   * Mistakes, which are easy to make in designing key relations, can
     cause severe problemsfor example, circular rules, or the wrong
     combination of cascading deletes.

   * A properly written application will make sure internally that it is
     not violating referential integrity constraints before proceding
     with a query. Thus, additional checks on the database level will
     only slow down performance for such an application.

   * It is not uncommon for a DBA to make such a complex topology of
     relations that it becomes very difficult, and in some cases
     impossible, to back up or restore individual tables.

Views
.....

It is planned to implement views in MySQL Server around version 5.0.

Views are mostly useful for letting users access a set of relations as
one table (in read-only mode).  Many SQL databases don't allow one to
update any rows in a view, but you have to do the updates in the
separate tables.

As MySQL Server is mostly used in applications and on web systems where
the application writer has full control on the database usage, most of
our users haven't regarded views to be very important.  (At least no
one has been interested enough in this to be prepared to finance the
implementation of views.)

One doesn't need views in MySQL Server to restrict access to columns,
as MySQL Server has a very sophisticated privilege system.  *Note
Privilege system::.

`--' as the Start of a Comment
..............................

Some other SQL databases use `--' to start comments.  MySQL Server has
`#' as the start comment character. You can also use the C comment
style `/* this is a comment */' with MySQL Server.  *Note Comments::.

MySQL Server Version 3.23.3 and above support the `--' comment style,
provided the comment is followed by a space.  This is because this
comment style has caused many problems with automatically generated SQL
queries that have used something like the following code, where we
automatically insert the value of the payment for `!payment!':

     UPDATE tbl_name SET credit=credit-!payment!

Think about what happens if the value of `payment' is negative.
Because `1--1' is legal in SQL, the consequences of allowing comments
to start with `--' are terrible.

Using our implementation of this method of commenting in MySQL Server
Version 3.23.3 and up, `1-- This is a comment' is actually safe.

Another safe feature is that the `mysql' command-line client removes
all lines that start with `--'.

The following information is relevant only if you are running a MySQL
version earlier than 3.23.3:

If you have a SQL program in a text file that contains `--' comments
you should use:

     shell> replace " --" " #" < text-file-with-funny-comments.sql \
              | mysql database

instead of the usual:

     shell> mysql database < text-file-with-funny-comments.sql

You can also edit the command file "in place" to change the `--'
comments to `#' comments:

     shell> replace " --" " #" -- text-file-with-funny-comments.sql

Change them back with this command:

     shell> replace " #" " --" -- text-file-with-funny-comments.sql

Known Errors and Design Deficiencies in MySQL
---------------------------------------------

The following problems are known and have a very high priority to get
fixed:

   * `ANALYZE TABLE' on a BDB table may in some case make the table
     unusable until one has restarted `mysqld'.  When this happens you
     will see errors like the following in the MySQL error file:

          001207 22:07:56  bdb:  log_flush: LSN past current end-of-log

   * Don't execute `ALTER TABLE' on a `BDB' table on which you are
     running multi-statement transactions until all those transactions
     complete.  (The transaction will probably be ignored.)

   * `ANALYZE TABLE', `OPTIMIZE TABLE', and `REPAIR TABLE' may cause
     problems on tables for which you are using `INSERT DELAYED'.

   * Doing a `LOCK TABLE ...' and `FLUSH TABLES ...' doesn't guarantee
     that there isn't a half-finished transaction in progress on the
     table.

   * BDB tables are a bit slow to open. If you have many BDB tables in a
     database, it will take a long time to use the `mysql' client on the
     database if you are not using the `-A' option or if you are using
     `rehash'. This is especially notable when you have a big table
     cache.


The following problems are known and will be fixed in due time:

   * When using `RPAD' function, or any other string function that ends
     up adding blanks to the right, in a query that has to use temporary
     table to be resolved, then all resulting strings will be RTRIM'ed.
     This is an example of the query:

     `SELECT    RPAD(t1.field1, 50, ' ') AS f2,    RPAD(t2.field2, 50, '
     ') AS f1  FROM    table1 as t1     LEFT JOIN table2 AS t2 ON
     t1.record=t2.joinID ORDER BY t2.record;'

     Final result of this bug is that use will not be able to get
     blanks on the right side of the resulting field.

     The above behaviour exists in all versions of MySQL.

     The reason for this is due to the fact that HEAP tables, which are
     used first for temporary tables, are not capable of handling
     VARCHAR columns.

     This behaviour will be fixed in one of 4.1 releases.

   * When using `SET CHARACTER SET', one can't use translated
     characters in database, table, and column names.

   * One can't use `_' or `%' with `ESCAPE' in `LIKE ... ESCAPE'.

   * If you have a `DECIMAL' column with a  number stored in different
     formats (+01.00, 1.00, 01.00), `GROUP BY' may regard each value as
     a different value.

   * `DELETE FROM merge_table' used without a `WHERE' will only clear
     the mapping for the table, not delete everything in the mapped
     tables.

   * You cannot build the server in another directory when using
     MIT-pthreads. Because this requires changes to MIT-pthreads, we
     are not likely to fix this. *Note MIT-pthreads::.

   * `BLOB' values can't "reliably" be used in `GROUP BY' or `ORDER BY'
     or `DISTINCT'. Only the first `max_sort_length' bytes (default
     1024) are used when comparing `BLOB's in these cases.  This can be
     changed with the `-O max_sort_length' option to `mysqld'. A
     workaround for most cases is to use a substring: `SELECT DISTINCT
     LEFT(blob,2048) FROM tbl_name'.

   * Calculation is done with `BIGINT' or `DOUBLE' (both are normally
     64 bits long). It depends on the function which precision one
     gets. The general rule is that bit functions are done with `BIGINT'
     precision, `IF', and `ELT()' with `BIGINT' or `DOUBLE' precision
     and the rest with `DOUBLE' precision.  One should try to avoid
     using unsigned long long values if they resolve to be bigger than
     63 bits (9223372036854775807) for anything else than bit fields!
     MySQL Server 4.0 has better `BIGINT' handling than 3.23.

   * All string columns, except `BLOB' and `TEXT' columns, automatically
     have all trailing spaces removed when retrieved. For `CHAR' types
     this is okay, and may be regarded as a feature according to ANSI
     SQL92. The bug is that in MySQL Server, `VARCHAR' columns are
     treated the same way.

   * You can only have up to 255 `ENUM' and `SET' columns in one table.

   * In `MIN()', `MAX()' and other aggregate functions, MySQL currently
     compares `ENUM' and `SET' columns by their string value rather
     than by the string's relative position in the set.

   * `safe_mysqld' redirects all messages from `mysqld' to the `mysqld'
     log.  One problem with this is that if you execute `mysqladmin
     refresh' to close and reopen the log, `stdout' and `stderr' are
     still redirected to the old log.  If you use `--log' extensively,
     you should edit `safe_mysqld' to log to `'hostname'.err' instead
     of `'hostname'.log' so you can easily reclaim the space for the
     old log by deleting the old one and executing `mysqladmin refresh'.

   * In the `UPDATE' statement, columns are updated from left to right.
     If you refer to an updated column, you will get the updated value
     instead of the original value. For example:

          mysql> UPDATE tbl_name SET KEY=KEY+1,KEY=KEY+1;

     This will update `KEY' with `2' instead of with `1'.

   * You can't use temporary tables more than once in the same query.
     For example, the following doesn't work:

          mysql> SELECT * FROM temporary_table, temporary_table AS t2;

   * `RENAME' doesn't work with `TEMPORARY' tables or tables used in a
     `MERGE' table.

   * The optimiser may handle `DISTINCT' differently if you are using
     'hidden' columns in a join or not.  In a join, hidden columns are
     counted as part of the result (even if they are not shown) while in
     normal queries hidden columns don't participate in the `DISTINCT'
     comparison.  We will probably change this in the future to never
     compare the hidden columns when executing `DISTINCT'.

     An example of this is:

          SELECT DISTINCT mp3id FROM band_downloads
                 WHERE userid = 9 ORDER BY id DESC;

     and

          SELECT DISTINCT band_downloads.mp3id
                 FROM band_downloads,band_mp3
                 WHERE band_downloads.userid = 9
                 AND band_mp3.id = band_downloads.mp3id
                 ORDER BY band_downloads.id DESC;

     In the second case you may in MySQL Server 3.23.x get two
     identical rows in the result set (because the hidden `id' column
     may differ).

     Note that this happens only for queries where you don't have the
     ORDER BY columns in the result, something that you are not allowed
     to do in ANSI SQL.

   * Because MySQL Server allows you to work with table types that don't
     support transactions, and thus can't `rollback' data, some things
     behave a little differently in MySQL Server than in other SQL
     servers.  This is just to ensure that MySQL Server never needs to
     do a rollback for a SQL command.  This may be a little awkward at
     times as column values must be checked in the application, but
     this will actually give you a nice speed increase as it allows
     MySQL Server to do some optimisations that otherwise would be very
     hard to do.

     If you set a column to an incorrect value, MySQL Server will,
     instead of doing a rollback, store the `best possible value' in
     the column:

        - If you try to store a value outside the range in a numerical
          column, MySQL Server will instead store the smallest or
          biggest possible value in the column.

        - If you try to store a string that doesn't start with a number
          into a numerical column, MySQL Server will store 0 into it.

        - If you try to store `NULL' into a column that doesn't take
          `NULL' values, MySQL Server will store 0 or `''' (empty
          string) in it instead. (This behaviour can, however, be
          changed with the -DDONT_USE_DEFAULT_FIELDS compile option.)

        - MySQL allows you to store some wrong date values into `DATE'
          and `DATETIME' columns (like 2000-02-31 or 2000-02-00).  The
          idea is that it's not the SQL server job to validate date.
          If MySQL can store a date and retrieve exactly the same date,
          then MySQL will store the date. If the date is totally wrong
          (outside the server's ability to store it), then the special
          date value 0000-00-00 will be stored in the column.

        - If you set an `ENUM' column to an unsupported value, it will
          be set to the error value `empty string', with numeric value
          0.

        - If you set a `SET' column to an unsupported value, the value
          will be ignored.


   * If you execute a `PROCEDURE' on a query that returns an empty set,
     in some cases the `PROCEDURE' will not transform the columns.

   * Creation of a table of type `MERGE' doesn't check if the underlying
     tables are of compatible types.

   * MySQL Server can't yet handle `NaN', `-Inf', and `Inf' values in
     double. Using these will cause problems when trying to export and
     import data. We should as an intermediate solution change `NaN' to
     `NULL' (if possible) and `-Inf' and `Inf' to the minimum
     respective maximum possible `double' value.

   * `LIMIT' on negative numbers are treated as big positive numbers.

   * If you use `ALTER TABLE' to first add a `UNIQUE' index to a table
     used in a `MERGE' table and then use `ALTER TABLE' to add a normal
     index on the `MERGE' table, the key order will be different for
     the tables if there was an old key that was not unique in the
     table. This is because `ALTER TABLE' puts `UNIQUE' keys before
     normal keys to be able to detect duplicate keys as early as
     possible.

The following are known bugs in earlier versions of MySQL:

   * You can get a hung thread if you do a `DROP TABLE' on a table that
     is one among many tables that is locked with `LOCK TABLES'.

   * In the following case you can get a core dump:

        - Delayed insert handler has pending inserts to a table.

        - `LOCK table' with `WRITE'.

        - `FLUSH TABLES'.

   * Before MySQL Server Version 3.23.2 an `UPDATE' that updated a key
     with a `WHERE' on the same key may have failed because the key was
     used to search for records and the same row may have been found
     multiple times:

          UPDATE tbl_name SET KEY=KEY+1 WHERE KEY > 100;

     A workaround is to use:

          mysql> UPDATE tbl_name SET KEY=KEY+1 WHERE KEY+0 > 100;

     This will work because MySQL Server will not use an index on
     expressions in the `WHERE' clause.

   * Before MySQL Server Version 3.23, all numeric types where treated
     as fixed-point fields. That means you had to specify how many
     decimals a floating-point field shall have. All results were
     returned with the correct number of decimals.

For platform-specific bugs, see the sections about compiling and
porting.

MySQL and The Future (The TODO)
===============================

This section lists the features that we plan to implement in MySQL
Server.

Everything in this list is approximately in the order it will be done.
If you want to affect the priority order, please register a license or
support us and tell us what you want to have done more quickly. *Note
Licensing and Support::.

The plan is that we in the future will support the full ANSI SQL99
standard, but with a lot of useful extensions. The challenge is to do
this without sacrificing the speed or compromising the code.

Things That Should be in 4.0
----------------------------

All done. We now only do bug fixes for MySQL 4.0. *Note News-4.0.x::.
Development has shifted to 4.1

Things That Should be in 4.1
----------------------------

The following features are planned for inclusion into MySQL 4.1.  Note
that because we have many developers that are working on different
projects, there will also be many additional features. There is also a
small chance that some of these features will be added to MySQL 4.0.
Some of the work on MySQL 4.1 is already in progress.

   * Subqueries.
          SELECT id FROM t WHERE grp IN (SELECT grp FROM g WHERE u > 100);

   * New table definition file format (`.frm' files). This will enable
     us to not run out of bits when adding more table options.  One
     will still be able to use the old `.frm' file format with 4.0.
     All newly created tables will, however, use the new format.

     The new file format will enable us to add new column types, more
     options for keys, and possibly to store and retrieve `FOREIGN KEY'
     definitions.

   * `SHOW COLUMNS FROM table_name' (used by `mysql' client to allow
     expansions of column names) should not open the table, only the
     definition file. This will require less memory and be much faster.

   * Foreign keys for `MyISAM' tables, including cascading delete.

   * Fail-safe replication.

   * Replication should work with `RAND()' and user variables `@var'.

   * Online backup with very low performance penalty.  The online
     backup will make it easy to add a new replication slave without
     taking down the master.

   * Derived tables:
          SELECT a.col1, b.col2
                 FROM (SELECT MAX(col1) AS col1 FROM root_table) a,
                 other_table b
                 WHERE a.col1=b.col1;

     This could be done by automatically creating temporary tables for
     the derived tables for the duration of the query.

     Please, do note, that as per SQL-99, all derived tables have to be
     aliased. This is enforced in MySQL too ...

   * `ROLLUP' and `CUBE' OLAP (Online Analytical Processing) grouping
     options for data warehousing applications.

   * Allow `DELETE' on `MyISAM' tables to use the record cache.  To do
     this, we need to update the threads record cache when we update
     the `.MYD' file.

   * When using `SET CHARACTER SET' we should translate the whole query
     at once and not only strings. This will enable users to use the
     translated characters in database, table, and column names.

   * Add `record_in_range()' method to `MERGE' tables to be able to
     choose the right index when there are many to choose from. We
     should also extend the info interface to get the key distribution
     for each index, if `analyze' is run on all subtables.

   * Resolving the issue of `RENAME TABLE' on a table used in an active
     `MERGE' table possibly corrupting the table.

   * A faster, smaller embedded MySQL library (compatible with the old
     one).

   * Stable OpenSSL support (MySQL 4.0 supports rudimentary, not 100%
     tested, support for OpenSSL).

   * Add support for sorting on `UNICODE'.

   * Character set casts and syntax for handling multiple character
     sets.

   * Help for all commands from the client.

   * New faster client/server protocol which will support prepared
     statements, bound parameters, and bound result columns, binary
     transfer of data, warnings...

   * Add database and real table name (in case of alias) to the
     MYSQL_FIELD structure.

   * Add options to the client/server protocol to get progress notes
     for long running commands.

   * Implement `RENAME DATABASE'. To make this safe for all storage
     engines, it should work as follows:
        * Create the new database.

        * For every table do a rename of the table to another database,
          as we do with the `RENAME' command.

        * Drop the old database.

   * Add true `VARCHAR' support (there is already support for this in
     `MyISAM').

   * Optimise `BIT' type to take 1 bit (now `BIT' takes 1 char).

   * New internal file interface change.  This will make all file
     handling much more general and make it easier to add extensions
     like RAID.  (the current implementation is a hack.)

   * Better in-memory (`HEAP') tables:
        * Support for B-tree indexes

        * Dynamic size rows

        * Faster row handling (less copying)

Things That Must be Done in the Near Future
-------------------------------------------

   * Don't allow more than a defined number of threads to run MyISAM
     recover at the same time.

   * Change `INSERT ... SELECT' to optionally use concurrent inserts.

   * Return the original field types() when doing `SELECT MIN(column)
     ... GROUP BY'.

   * Multiple result sets.

   * Make it possible to specify `long_query_time' with a granularity
     in microseconds.

   * Link the `myisampack' code into the server.

   * Port of the MySQL code to QNX.

   * Port of the MySQL code to BeOS.

   * Port of the MySQL clients to LynxOS.

   * Add a temporary key buffer cache during `INSERT/DELETE/UPDATE' so
     that we can gracefully recover if the index file gets full.

   * If you perform an `ALTER TABLE' on a table that is symlinked to
     another disk, create temporary tables on this disk.

   * Implement a `DATE/DATETIME' type that handles time zone information
     properly so that dealing with dates in different time zones is
     easier.

   * FreeBSD and MIT-pthreads; do sleeping threads take CPU time?

   * Check if locked threads take any CPU time.

   * Fix configure so that one can compile all libraries (like `MyISAM')
     without threads.

   * Add an option to periodically flush key pages for tables with
     delayed keys if they haven't been used in a while.

   * Allow join on key parts (optimisation issue).

   * `INSERT SQL_CONCURRENT' and `mysqld --concurrent-insert' to do a
     concurrent insert at the end of the file if the file is
     read-locked.

   * Server-side cursors.

   * Check if `lockd' works with modern Linux kernels; if not, we have
     to fix `lockd'!  To test this, start `mysqld' with
     `--enable-locking' and run the different fork* test suits. They
     shouldn't give any errors if `lockd' works.

   * Allow SQL variables in `LIMIT', like in `LIMIT @a,@b'.

   * Allow update of variables in `UPDATE' statements. For example:
     `UPDATE TABLE foo SET @a=a+b,a=@a, b=@a+c'.

   * Change when user variables are updated so that one can use them
     with `GROUP BY', as in the following example: `SELECT id,
     @a:=COUNT(*), SUM(sum_col)/@a FROM table_name GROUP BY id'.

   * Don't add automatic `DEFAULT' values to columns.  Give an error
     when using an `INSERT' that doesn't contain a column that doesn't
     have a `DEFAULT'.

   * Fix `libmysql.c' to allow two `mysql_query()' commands in a row
     without reading results or give a nice error message when one does
     this.

   * Check why MIT-pthreads `ctime()' doesn't work on some FreeBSD
     systems.

   * Add an `IMAGE' option to `LOAD DATA INFILE' to not update
     `TIMESTAMP' and `AUTO_INCREMENT' fields.

   * Added `LOAD DATE INFILE ... UPDATE' syntax.
        * For tables with primary keys, if the data contains the
          primary key, entries matching that primary key are updated
          from the remainder of the columns. However, columns *missing*
          from the incoming data feed are not touched.

        * For tables with primary keys that are missing some part of
          the key in the incoming data stream, or that have no primary
          key, the feed is treated as a `LOAD DATA INFILE ... REPLACE
          INTO' now.

   * Make `LOAD DATA INFILE' understand syntax like:
          LOAD DATA INFILE 'file_name.txt' INTO TABLE tbl_name
               TEXT_FIELDS (text_field1, text_field2, text_field3)
               SET table_field1=CONCAT(text_field1, text_field2),
                   table_field3=23
               IGNORE text_field3
     This can be used to skip over extra columns in the text file, or
     update columns based on expressions of the read data.

   * `LOAD DATA INFILE 'file_name' INTO TABLE 'table_name' ERRORS TO
     err_table_name'.  This would cause any errors and warnings to be
     logged into the `err_table_name' table. That table would have a
     structure like:

          line_number    - line number in datafile
          error_message  - the error/warning message
          and maybe
          data_line      - the line from the datafile

   * Automatic output from `mysql' to Netscape.

   * `LOCK DATABASES' (with various options.)

   * Functions: ADD_TO_SET(value,set) and REMOVE_FROM_SET(value,set).

   * Add use of `t1 JOIN t2 ON ...' and `t1 JOIN t2 USING ...'
     Currently, you can only use this syntax with `LEFT JOIN'.

   * Many more variables for `show status'.  Records reads and updates.
     Selects on 1 table and selects with joins.  Mean number of tables
     in select. Number of `ORDER BY' and `GROUP BY' queries.

   * If you abort `mysql' in the middle of a query, you should open
     another connection and kill the old running query.  Alternatively,
     an attempt should be made to detect this in the server.

   * Add a storage engine interface for table information so that you
     can use it as a system table. This would be a bit slow if you
     requested information about all tables, but very flexible.  `SHOW
     INFO FROM tbl_name' for basic table information should be
     implemented.

   * `NATURAL JOIN'.

   * Allow `SELECT a FROM crash_me LEFT JOIN crash_me2 USING (a)'; in
     this case `a' is assumed to come from the `crash_me' table.

   * Fix so that `ON' and `USING' works with the `JOIN' join type.

   * Oracle-like `CONNECT BY PRIOR ...' to search hierarchy structures.

   * `mysqladmin copy database new-database'; requires `COPY' command
     to be added to `mysqld'.

   * Processlist should show number of queries/threads.

   * `SHOW HOSTS' for printing information about the hostname cache.

   * `DELETE' and `REPLACE' options to the `UPDATE' statement (this
     will delete rows when one gets a duplicate key error while
     updating).

   * Change the format of `DATETIME' to store fractions of seconds.

   * Add all missing ANSI92 and ODBC 3.0 types.

   * Change table names from empty strings to `NULL' for calculated
     columns.

   * Don't use `Item_copy_string' on numerical values to avoid
     number->string->number conversion in case of: `SELECT
     COUNT(*)*(id+0) FROM table_name GROUP BY id'

   * Make it possible to use the new GNU regexp library instead of the
     current one (the GNU library should be much faster than the old
     one).

   * Change so that `ALTER TABLE' doesn't abort clients that execute
     `INSERT DELAYED'.

   * Fix so that when columns are referenced in an `UPDATE' clause,
     they contain the old values from before the update started.

   * Add simulation of `pread()'/`pwrite()' on Windows to enable
     concurrent inserts.

   * A logfile analyser that could parse out information about which
     tables are hit most often, how often multi-table joins are
     executed, etc.  It should help users identify areas or table
     design that could be optimised to execute much more efficient
     queries.

   * Add `SUM(DISTINCT)'.

   * Add `ANY()', `EVERY()', and `SOME()' group functions. In ANSI SQL
     these work only on boolean columns, but we can extend these to
     work on any columns/expressions by applying: value == 0 -> FALSE
     and value <> 0 -> TRUE.

   * Fix that the type for `MAX(column)' is the same as the column type:
          mysql> CREATE TABLE t1 (a DATE);
          mysql> INSERT INTO t1 VALUES (NOW());
          mysql> CREATE TABLE t2 SELECT MAX(a) FROM t1;
          mysql> SHOW COLUMNS FROM t2;

   * Come up with a nice syntax for a statement that will `UPDATE' the
     row if it exists and `INSERT' a new row if the row didn't exist
     (like `REPLACE' works with `INSERT' / `DELETE').

Things That Have to be Done Sometime
------------------------------------

   * Implement function:
     `get_changed_tables(timeout,table1,table2,...)'.

   * Change reading through tables to use memmap when possible. Now only
     compressed tables use memmap.

   * Make the automatic timestamp code nicer.  Add timestamps to the
     update log with `SET TIMESTAMP=#;'.

   * Use read/write mutex in some places to get more speed.

   * Full foreign key support in for `MyISAM' tables, probably after
     the implementation of stored procedures with triggers.

   * Simple views (first on one table, later on any expression).

   * Automatically close some tables if a table, temporary table, or
     temporary files gets error 23 (not enough open files).

   * When one finds a field=#, change all occurrences of field to #.
     Now this is only done for some simple cases.

   * Change all const expressions with calculated expressions if
     possible.

   * Optimise key = expression. At the moment only key = field or key =
     constant are optimised.

   * Join some of the copy functions for nicer code.

   * Change `sql_yacc.yy' to an inline parser to reduce its size and get
     better error messages (5 days).

   * Change the parser to use only one rule per different number of
     arguments in function.

   * Use of full calculation names in the order part (for ACCESS97).

   * `MINUS', `INTERSECT', and `FULL OUTER JOIN'.  (Currently `UNION'
     [in 4.0] and `LEFT OUTER JOIN' are supported.)

   * `SQL_OPTION MAX_SELECT_TIME=#' to put a time limit on a query.

   * Make the update log write to a database.

   * Add to `LIMIT' to allow retrieval of data from the end of a result
     set.

   * Alarm around client connect/read/write functions.

   * Please note the changes to `safe_mysqld': according to FSSTND
     (which Debian tries to follow) PID files should go into
     `/var/run/<progname>.pid' and log files into `/var/log'. It would
     be nice if you could put the "DATADIR" in the first declaration of
     "pidfile" and "log", so the placement of these files can be
     changed with a single statement.

   * Allow a client to request logging.

   * Add use of `zlib()' for `gzip'-ed files to `LOAD DATA INFILE'.

   * Fix sorting and grouping of `BLOB' columns (partly solved now).

   * Stored procedures. Triggers are also being looked at.

   * A simple (atomic) update language that can be used to write loops
     and such in the MySQL server.

   * Change to use semaphores when counting threads.  One should first
     implement a semaphore library to MIT-pthreads.

   * Don't assign a new `AUTO_INCREMENT' value when one sets a column
     to 0.  Use `NULL' instead.

   * Add full support for `JOIN' with parentheses.

   * As an alternative for one thread/connection manage a pool of
     threads to handle the queries.

   * Allow one to get more than one lock with `GET_LOCK'.  When doing
     this, one must also handle the possible deadlocks this change will
     introduce.

Time is given according to amount of work, not real time.

Things We Don't Plan To Do
--------------------------

   * Nothing; we aim toward full ANSI 92/ANSI 99 compliancy.

How MySQL Compares to Other Databases
=====================================

Our users have successfully run their own benchmarks against a number
of `Open Source' and traditional database servers.  We are aware of
tests against `Oracle' server, `DB/2' server, `Microsoft SQL Server',
and other commercial products.  Due to legal reasons we are restricted
from publishing some of those benchmarks in our reference manual.

This section includes a comparison with `mSQL' for historical reasons
and with `PostgreSQL' as it is also an `Open Source' database. If you
have benchmark results that we can publish, please contact us at
<[e-mail]>.

For comparative lists of all supported functions and types as well as
measured operational limits of many different database systems, see the
`crash-me' web page at `http://www.mysql.com/information/crash-me.php'.

How MySQL Compares to `mSQL'
----------------------------

*Performance*
     For a true comparison of speed, consult the growing MySQL benchmark
     suite. *Note MySQL Benchmarks::.

     Because there is no thread creation overhead, a small parser, few
     features, and simple security, `mSQL' should be quicker at:

        * Tests that perform repeated connects and disconnects, running
          a very simple query during each connection.

        * `INSERT' operations into very simple tables with few columns
          and keys.

        * `CREATE TABLE' and `DROP TABLE'.

        * `SELECT' on something that isn't an index. (A table scan is
          very easy.)

     Because these operations are so simple, it is hard to be better at
     them when you have a higher startup overhead. After the connection
     is established, MySQL Server should perform much better.

     On the other hand, MySQL Server is much faster than `mSQL' (and
     most other SQL implementations) on the following:

        * Complex `SELECT' operations.

        * Retrieving large results (MySQL Server has a better, faster,
          and safer protocol).

        * Tables with variable-length strings because MySQL Server has
          more efficient handling and can have indexes on `VARCHAR'
          columns.

        * Handling tables with many columns.

        * Handling tables with large record lengths.

        * `SELECT' with many expressions.

        * `SELECT' on large tables.

        * Handling many connections at the same time. MySQL Server is
          fully multi-threaded. Each connection has its own thread,
          which means that no thread has to wait for another (unless a
          thread is modifying a table another thread wants to access).
          In `mSQL', once one connection is established, all others
          must wait until the first has finished, regardless of whether
          the connection is running a query that is short or long. When
          the first connection terminates, the next can be served,
          while all the others wait again, etc.

        * Joins.  `mSQL' can become pathologically slow if you change
          the order of tables in a `SELECT'. In the benchmark suite, a
          time more than 15,000 times slower than MySQL Server was
          seen.  This is due to `mSQL''s lack of a join optimiser to
          order tables in the optimal order.  However, if you put the
          tables in exactly the right order in `mSQL'2 and the `WHERE'
          is simple and uses index columns, the join will be relatively
          fast!  *Note MySQL Benchmarks::.

        * `ORDER BY' and `GROUP BY'.

        * `DISTINCT'.

        * Using `TEXT' or `BLOB' columns.

*SQL Features*
        * `GROUP BY' and `HAVING'.  `mSQL' does not support `GROUP BY'
          at all.  MySQL Server supports a full `GROUP BY' with both
          `HAVING' and the following functions: `COUNT()', `AVG()',
          `MIN()', `MAX()', `SUM()', and `STD()'.  `COUNT(*)' is
          optimised to return very quickly if the `SELECT' retrieves
          from one table, no other columns are retrieved, and there is
          no `WHERE' clause.  `MIN()' and `MAX()' may take string
          arguments.

        * `INSERT' and `UPDATE' with calculations.  MySQL Server can do
          calculations in an `INSERT' or `UPDATE'.  For example:

               mysql> UPDATE SET x=x*10+y WHERE x<20;

        * Aliasing.  MySQL Server has column aliasing.

        * Qualifying column names.  In MySQL Server, if a column name
          is unique among the tables used in a query, you do not have
          to use the full qualifier.

        * `SELECT' with functions.  MySQL Server has many functions
          (too many to list here; see *Note Functions::).


*Disk Space Efficiency*
     That is, how small can you make your tables?

     MySQL Server has very precise types, so you can create tables that
     take very little space. An example of a useful MySQL datatype is
     the `MEDIUMINT' that is 3 bytes long. If you have 100 million
     records, saving even 1 byte per record is very important.

     `mSQL2' has a more limited set of column types, so it is more
     difficult to get small tables.

*Stability*
     This is harder to judge objectively. For a discussion of MySQL
     Server stability, see *Note Stability::.

     We have no experience with `mSQL' stability, so we cannot say
     anything about that.

*Price*
     Another important issue is the license. MySQL Server has a more
     flexible license than `mSQL', and is also less expensive than
     `mSQL'.  Whichever product you choose to use, remember to at least
     consider paying for a license or e-mail support.

*Perl Interfaces*
     MySQL Server has basically the same interfaces to Perl as `mSQL'
     with some added features.

*JDBC (Java)*
     MySQL Server currently has a lot of different JDBC drivers:

        * MySQL Connector/J is a native Java driver.  Version 3.x is
          released under dual licensing (GPL and commercial).

        * The Resin driver: this is a commercial JDBC driver released
          under open source.
          `http://www.caucho.com/projects/jdbc-mysql/index.xtp'

        * The gwe driver: a Java interface by GWE technologies (not
          supported anymore).

        * The jms driver: an improved gwe driver by Xiaokun Kelvin ZHU
          <[e-mail]> (not supported anymore).

        * The twz driver: a type 4 JDBC driver by Terrence W. Zellers
          <[e-mail]>.  This is commercial but is free for
          private and educational use (not supported anymore).

     The recommended driver is the mm driver. The Resin driver may also
     be good (at least the benchmarks look good), but we haven't
     received that much information about this yet.

     We know that `mSQL' has a JDBC driver, but we have too little
     experience with it to compare.

*Rate of Development*
     MySQL Server has a small core team of developers, but we are quite
     used to coding C and C++ very rapidly. Because threads, functions,
     `GROUP BY', and so on are still not implemented in `mSQL', it has
     a lot of catching up to do. To get some perspective on this, you
     can view the `mSQL' `HISTORY' file for the last year and compare
     it with the News section of the MySQL Reference Manual (*note
     News::). It should be pretty obvious which one has developed most
     rapidly.

*Utility Programs*
     Both `mSQL' and MySQL Server have many interesting third-party
     tools. Because it is very easy to port upward (from `mSQL' to
     MySQL Server), almost all the interesting applications that are
     available for `mSQL' are also available for MySQL Server.

     MySQL Server comes with a simple `msql2mysql' program that fixes
     differences in spelling between `mSQL' and MySQL Server for the
     most-used C API functions.  For example, it changes instances of
     `msqlConnect()' to `mysql_connect()'. Converting a client program
     from `mSQL' to MySQL Server usually requires only minor effort.

How to Convert `mSQL' Tools for MySQL
.....................................

According to our experience, it doesn't take long to convert tools such
as `msql-tcl' and `msqljava' that use the `mSQL' C API so that they
work with the MySQL C API.

The conversion procedure is:

  1. Run the shell script `msql2mysql' on the source. This requires the
     `replace' program, which is distributed with MySQL Server.

  2. Compile.

  3. Fix all compiler errors.

Differences between the `mSQL' C API and the MySQL C API are:

   * MySQL Server uses a `MYSQL' structure as a connection type (`mSQL'
     uses an `int').

   * `mysql_connect()' takes a pointer to a `MYSQL' structure as a
     parameter.  It is easy to define one globally or to use `malloc()'
     to get one.  `mysql_connect()' also takes two parameters for
     specifying the user and password.  You may set these to `NULL,
     NULL' for default use.

   * `mysql_error()' takes the `MYSQL' structure as a parameter.  Just
     add the parameter to your old `msql_error()' code if you are
     porting old code.

   * MySQL Server returns an error number and a text error message for
     all errors. `mSQL' returns only a text error message.

   * Some incompatibilities exist as a result of MySQL Server supporting
     multiple connections to the server from the same process.

How `mSQL' and MySQL Client/Server Communications Protocols Differ
..................................................................

There are enough differences that it is impossible (or at least not
easy) to support both.

The most significant ways in which the MySQL protocol differs from the
`mSQL' protocol are listed here:

   * A message buffer may contain many result rows.

   * The message buffers are dynamically enlarged if the query or the
     result is bigger than the current buffer, up to a configurable
     server and client limit.

   * All packets are numbered to catch duplicated or missing packets.

   * All column values are sent in ASCII. The lengths of columns and
     rows are sent in packed binary coding (1, 2, or 3 bytes).

   * MySQL can read in the result unbuffered (without having to store
     the full set in the client).

   * If a single read/write takes more than 30 seconds, the server
     closes the connection.

   * If a connection is idle for 8 hours, the server closes the
     connection.

How `mSQL' 2.0 SQL Syntax Differs from MySQL
............................................

*Column types*

`MySQL Server'
     Has the following additional types (among others; *note `CREATE
     TABLE': CREATE TABLE.):
        * `ENUM' type for one of a set of strings.

        * `SET' type for many of a set of strings.

        * `BIGINT' type for 64-bit integers.

`'
     MySQL Server also supports the following additional type
     attributes:
        * `UNSIGNED' option for integer and floating-point columns.

        * `ZEROFILL' option for integer columns.

        * `AUTO_INCREMENT' option for integer columns that are a
          `PRIMARY KEY'.  *Note `mysql_insert_id()': mysql_insert_id.

        * `DEFAULT' value for all columns.

`mSQL2'
     `mSQL' column types correspond to the MySQL types shown in the
     following table:
     `mSQL'     *Corresponding MySQL type*
     *type*
     `CHAR(len)'`CHAR(len)'
     `TEXT(len)'`TEXT(len)'. `len' is the maximal length.  And
                `LIKE' works.
     `INT'      `INT'. With many more options!
     `REAL'     `REAL'. Or `FLOAT'. Both 4- and 8-byte
                versions are available.
     `UINT'     `INT UNSIGNED'
     `DATE'     `DATE'. Uses ANSI SQL format rather than
                `mSQL''s own format.
     `TIME'     `TIME'
     `MONEY'    `DECIMAL(12,2)'. A fixed-point value with two
                decimals.

*Index Creation*

`MySQL Server'
     Indexes may be specified at table creation time with the `CREATE
     TABLE' statement.

`mSQL'
     Indexes must be created after the table has been created, with
     separate `CREATE INDEX' statements.

*To Insert a Unique Identifier into a Table*

`MySQL Server'
     Use `AUTO_INCREMENT' as a column type specifier.  *Note
     `mysql_insert_id()': mysql_insert_id.

`mSQL'
     Create a `SEQUENCE' on a table and select the `_seq' column.

*To Obtain a Unique Identifier for a Row*

`MySQL Server'
     Add a `PRIMARY KEY' or `UNIQUE' key to the table and use this.
     New in Version 3.23.11: If the `PRIMARY' or `UNIQUE' key consists
     of only one column and this is of type integer, one can also refer
     to it as `_rowid'.

`mSQL'
     Use the `_rowid' column. Observe that `_rowid' may change over time
     depending on many factors.

*To Get the Time a Column Was Last Modified*

`MySQL Server'
     Add a `TIMESTAMP' column to the table. This column is
     automatically set to the current date and time for `INSERT' or
     `UPDATE' statements if you don't give the column a value or if you
     give it a `NULL' value.

`mSQL'
     Use the `_timestamp' column.

*`NULL' Value Comparisons*

`MySQL Server'
     MySQL Server follows ANSI SQL, and a comparison with `NULL' is
     always `NULL'.

`mSQL'
     In `mSQL', `NULL = NULL' is TRUE.  You must change `=NULL' to `IS
     NULL' and `<>NULL' to `IS NOT NULL' when porting old code from
     `mSQL' to MySQL Server.

*String Comparisons*

`MySQL Server'
     Normally, string comparisons are performed in case-independent
     fashion with the sort order determined by the current character
     set (ISO-8859-1 Latin1 by default).  If you don't like this,
     declare your columns with the `BINARY' attribute, which causes
     comparisons to be done according to the ASCII order used on the
     MySQL server host.

`mSQL'
     All string comparisons are performed in case-sensitive fashion with
     sorting in ASCII order.

*Case-insensitive Searching*

`MySQL Server'
     `LIKE' is a case-insensitive or case-sensitive operator, depending
     on the columns involved. If possible, MySQL uses indexes if the
     `LIKE' argument doesn't start with a wildcard character.

`mSQL'
     Use `CLIKE'.

*Handling of Trailing Spaces*

`MySQL Server'
     Strips all spaces at the end of `CHAR' and `VARCHAR' columns. Use
     a `TEXT' column if this behaviour is not desired.

`mSQL'
     Retains trailing space.

*`WHERE' Clauses*

`MySQL Server'
     MySQL correctly prioritises everything (`AND' is evaluated before
     `OR'). To get `mSQL' behaviour in MySQL Server, use parentheses
     (as shown in an example later in this section).

`mSQL'
     Evaluates everything from left to right. This means that some
     logical calculations with more than three arguments cannot be
     expressed in any way. It also means you must change some queries
     when you upgrade to MySQL Server. You do this easily by adding
     parentheses.  Suppose you have the following `mSQL' query:
          mysql> SELECT * FROM table WHERE a=1 AND b=2 OR a=3 AND b=4;
     To make MySQL Server evaluate this the way that `mSQL' would, you
     must add parentheses:
          mysql> SELECT * FROM table WHERE (a=1 AND (b=2 OR (a=3 AND (b=4))));

*Access Control*

`MySQL Server'
     Has tables to store grant (permission) options per user, host, and
     database. *Note Privileges::.

`mSQL'
     Has a file `mSQL.acl' in which you can grant read/write privileges
     for users.

How MySQL Compares to `PostgreSQL'
----------------------------------

When reading the following, please note that both products are
continually evolving.  We at MySQL AB and the PostgreSQL developers are
both working on making our respective databases as good as possible, so
we are both a serious alternative to any commercial database.

The following comparison is made by us at MySQL AB.  We have tried to be
as accurate and fair as possible, but although we know MySQL Server
thoroughly, we don't have a full knowledge of all PostgreSQL features,
so we may have got some things wrong.  We will, however, correct these
when they come to our attention.

We would first like to note that PostgreSQL and MySQL Server are both
widely used products, but with different design goals, even if we are
both striving toward ANSI SQL compliancy.  This means that for some
applications MySQL Server is more suited, while for others PostgreSQL
is more suited.  When choosing which database to use, you should first
check if the database's feature set satisfies your application.  If you
need raw speed, MySQL Server is probably your best choice.  If you need
some of the extra features that only PostgreSQL can offer, you should
use `PostgreSQL'.

MySQL and PostgreSQL development strategies
...........................................

When adding things to MySQL Server we take pride to do an optimal,
definite solution.  The code should be so good that we shouldn't have
any need to change it in the foreseeable future.  We also do not like
to sacrifice speed for features but instead will do our utmost to find
a solution that will give maximal throughput.  This means that
development will take a little longer, but the end result will be well
worth this.  This kind of development is only possible because all
server code are checked by one of a few (currently two) persons before
it's included in the MySQL server.

We at MySQL AB believe in frequent releases to be able to push out new
features quickly to our users.  Because of this we do a new small
release about every three weeks, and a major branch every year.  All
releases are thoroughly tested with our testing tools on a lot of
different platforms.

PostgreSQL is based on a kernel with lots of contributors. In this setup
it makes sense to prioritise adding a lot of new features, instead of
implementing them optimally, because one can always optimise things
later if there arises a need for this.

Another big difference between MySQL Server and PostgreSQL is that
nearly all of the code in the MySQL server is coded by developers that
are employed by MySQL AB and are still working on the server code. The
exceptions are the transaction engines and the regexp library.

This is in sharp contrast to the PostgreSQL code, the majority of which
is coded by a big group of people with different backgrounds.  It was
only recently that the PostgreSQL developers announced that their
current developer group had finally had time to take a look at all the
code in the current PostgreSQL release.

Both of the aforementioned development methods have their own merits
and drawbacks.  We here at MySQL AB think, of course, that our model is
better because our model gives better code consistency, more optimal
and reusable code, and in our opinion, fewer bugs.  Because we are the
authors of the MySQL server code, we are better able to coordinate new
features and releases.

Featurewise Comparison of MySQL and PostgreSQL
..............................................

On the `crash-me' page (`http://www.mysql.com/information/crash-me.php')
you can find a list of those database constructs and limits that one
can detect automatically with a program.  Note, however, that a lot of
the numerical limits may be changed with startup options for their
respective databases.  This web page is, however, extremely useful when
you want to ensure that your applications work with many different
databases or when you want to convert your application from one
database to another.

MySQL Server offers the following advantages over PostgreSQL:

   * `MySQL' Server is generally much faster than PostgreSQL.  MySQL
     4.0.1 also has a query cache that can boost up the query speed for
     mostly-read-only sites many times.

   * MySQL has a much larger user base than PostgreSQL. Therefore, the
     code is tested more and has historically proven more stable than
     PostgreSQL.  MySQL Server is used more in production environments
     than PostgreSQL, mostly thanks to the fact that MySQL AB, formerly
     TCX DataKonsult AB, has provided top-quality commercial support
     for MySQL Server from the day it was released, whereas until
     recently PostgreSQL was unsupported.

   * MySQL Server works better on Windows than PostgreSQL does.  MySQL
     Server runs as a native Windows application (a service on
     NT/2000/XP), while PostgreSQL is run under the `Cygwin' emulation.
     We have heard that PostgreSQL is not yet that stable on Windows
     but we haven't been able to verify this ourselves.

   * MySQL has more APIs to other languages and is supported by more
     existing programs than PostgreSQL.  *Note Contrib::.

   * MySQL Server works on 24/7 heavy-duty systems.  In most
     circumstances you never have to run any cleanups on MySQL Server.
     PostgreSQL doesn't yet support 24/7 systems because you have to
     run `VACUUM' once in a while to reclaim space from `UPDATE' and
     `DELETE' commands and to perform statistics analyses that are
     critical to get good performance with PostgreSQL.  `VACUUM' is
     also needed after adding a lot of new rows to a table.  On a busy
     system with lots of changes, `VACUUM' must be run very frequently,
     in the worst cases even many times a day.  During the `VACUUM'
     run, which may take hours if the database is big, the database is,
     from a production standpoint, practically dead. Please note: in
     PostgreSQL version 7.2, basic vacuuming no longer locks tables,
     thus allowing normal user access during the vacuum.  A new `VACUUM
     FULL' command does old-style vacuum by locking the table and
     shrinking the on-disk copy of the table.

   * MySQL replication has been thoroughly tested, and is used by sites
     like:
        - Yahoo Finance (`http://finance.yahoo.com/')

        - Mobile.de (`http://www.mobile.de/')

        - Slashdot (`http://www.slashdot.org/')

   * Included in the MySQL distribution are two different testing
     suites, `mysql-test-run' and `crash-me'
     (`http://www.mysql.com/information/crash-me.php'), as well as a
     benchmark suite.  The test system is actively updated with code to
     test each new feature and almost all reproduceable bugs that have
     come to our attention.  We test MySQL Server with these on a lot
     of platforms before every release.  These tests are more
     sophisticated than anything we have seen from PostgreSQL, and they
     ensure that the MySQL Server is kept to a high standard.

   * There are far more books in print about MySQL Server than about
     PostgreSQL.  O'Reilly, SAMS, Que, and New Riders are all major
     publishers with books about MySQL.  All MySQL features are also
     documented in the MySQL online manual because when a new feature
     is implemented, the MySQL developers are required to document it
     before it's included in the source.

   * MySQL Server supports more of the standard ODBC functions than
     `PostgreSQL'.

   * MySQL Server has a much more sophisticated `ALTER TABLE'.

   * MySQL Server has support for tables without transactions for
     applications that need all the speed they can get. The tables may
     be memory-based, `HEAP' tables or disk based `MyISAM'.  *Note
     Table types::.

   * MySQL Server has support for two different storage engines that
     support transactions, `InnoDB', and `BerkeleyDB'.  Because every
     transaction engine performs differently under different
     conditions, this gives the application writer more options to find
     an optimal solution for his or her setup, if need be per
     individual table.  *Note Table types::.

   * `MERGE' tables gives you a unique way to instantly make a view over
     a set of identical tables and use these as one.  This is perfect
     for systems where you have log files that you order, for example,
     by month.  *Note MERGE::.

   * The option to compress read-only tables, but still have direct
     access to the rows in the table, gives you better performance by
     minimising disk reads.  This is very useful when you are archiving
     things.  *Note `myisampack': myisampack.

   * MySQL Server has internal support for full-text search. *Note
     Fulltext Search::.

   * You can access many databases from the same connection (depending,
     of course, on your privileges).

   * MySQL Server is coded from the start to be multi-threaded, while
     PostgreSQL uses processes.  Context switching and access to common
     storage areas is much faster between threads than between separate
     processes. This gives MySQL Server a big speed advantage in
     multi-user applications and also makes it easier for MySQL Server
     to take full advantage of symmetric multiprocessor (SMP) systems.

   * MySQL Server has a much more sophisticated privilege system than
     PostgreSQL.  While PostgreSQL only supports `INSERT', `SELECT',
     and `UPDATE/DELETE' grants per user on a database or a table,
     MySQL Server allows you to define a full set of different
     privileges on the database, table, and column level.  MySQL Server
     also allows you to specify the privilege on host and user
     combinations.  *Note GRANT::.

   * MySQL Server supports a compressed client/server protocol which
     improves performance over slow links.

   * MySQL Server employs a "storage engine" concept, and is the only
     relational database we know of built around this concept.  This
     allows different low-level table types to be called from the SQL
     engine, and each table type can be optimised for different
     performance characteristics.

   * All MySQL table types (except `InnoDB') are implemented as files
     (one table per file), which makes it really easy to back up, move,
     delete, and even symlink databases and tables, even when the
     server is down.

   * Tools to repair and optimise `MyISAM' tables (the most common
     MySQL table type).  A repair tool is only needed when a physical
     corruption of a datafile happens, usually from a hardware failure.
     It allows a majority of the data to be recovered.

   * Upgrading MySQL Server is painless.  When you are upgrading MySQL
     Server, you don't need to dump/restore your data, as you have to
     do with most PostgreSQL upgrades.

Drawbacks with MySQL Server compared to PostgreSQL:

   * The transaction support in MySQL Server is not yet as well tested
     as PostgreSQL's system.

   * Because MySQL Server uses threads, which are not yet flawless on
     many OSes, one must either use binaries from
     `http://www.mysql.com/downloads/', or carefully follow our
     instructions in *Note Installing source:: to get an optimal binary
     that works in all cases.

   * Table locking, as used by the non-transactional `MyISAM' tables, is
     in many cases faster than page locks, row locks, or versioning.
     The drawback, however, is that if one doesn't take into account
     how table locks work, a single long-running query can block a
     table for updates for a long time. This can usually be avoided
     when designing the application.  If not, one can always switch the
     trouble table to use one of the transactional table types. *Note
     Table locking::.

   * With UDF (user-defined functions) one can extend MySQL Server with
     both normal SQL functions and aggregates, but this is not yet as
     easy or as flexible as in PostgreSQL.  *Note Adding functions::.

   * Updates that run over multiple tables used to be harder to do in
     MySQL Server. However, this has been fixed in MySQL Server 4.0.2
     with multi-table `UPDATE' and in MySQL Server 4.1 with subselects.
     In MySQL Server 4.0 one can use multi-table deletes to delete from
     many tables at the same time. *Note DELETE::.

PostgreSQL currently offers the following advantages over MySQL Server:

Note that because we know the MySQL road map, we have included in the
following table the version when MySQL Server should support this
feature.  Unfortunately we couldn't do this for previous comparisons,
because we don't know the PostgreSQL roadmap.

*Feature*              *MySQL version*
Subselects             4.1
Foreign keys           5.0 (3.23 with InnoDB)
Views                  5.0
Stored procedures      5.0
Triggers               5.0
Unions                 4.0
Full join              4.1
Constraints            4.1 or 5.0
Cursors                4.1 or 5.0
R-trees                4.1 (for MyISAM
                       tables)
Inherited tables       Not planned
Extensible type        Not planned
system

Other reasons someone may consider using PostgreSQL:

   * Standard usage in PostgreSQL is closer to ANSI SQL in some cases.

   * One can speed up PostgreSQL by coding things as stored procedures.

   * For geographical data, R-trees make PostgreSQL better than MySQL
     Server.  (note: MySQL version 4.1 has R-trees for MyISAM tables).

   * The PostgreSQL optimiser can do some optimisation that the current
     MySQL optimiser can't do.  Most notable is doing joins when you
     don't have the proper keys in place and doing a join where you are
     using different keys combined with OR.  The MySQL benchmark suite
     at `http://www.mysql.com/information/benchmarks.html' shows you
     what kind of constructs you should watch out for when using
     different databases.

   * PostgreSQL has a bigger team of developers that contribute to the
     server.

Drawbacks with PostgreSQL compared to MySQL Server:

   * `VACUUM' makes PostgreSQL hard to use in a 24/7 environment.

   * Only transactional tables.

   * Much slower `INSERT', `DELETE', and `UPDATE'.

For a complete list of drawbacks, you should also examine the first
table in this section.

Benchmarking MySQL and PostgreSQL
.................................

The only `Open Source' benchmark that we know of that can be used to
benchmark MySQL Server and PostgreSQL (and other databases) is our own.
It can be found at `http://www.mysql.com/information/benchmarks.html'.

We have many times asked the PostgreSQL developers and some PostgreSQL
users to help us extend this benchmark to make it the definitive
benchmark for databases, but unfortunately we haven't gotten any
feedback for this.

We, the MySQL developers, have, because of this, spent a lot of hours
to get maximum performance from PostgreSQL for the benchmarks, but
because we don't know PostgreSQL intimately, we are sure that there are
things that we have missed.  We have on the benchmark page documented
exactly how we did run the benchmark so that it should be easy for
anyone to repeat and verify our results.

The benchmarks are usually run with and without the `--fast' option.
When run with `--fast' we are trying to use every trick the server can
do to get the code to execute as fast as possible.  The idea is that the
normal run should show how the server would work in a default setup and
the `--fast' run shows how the server would do if the application
developer would use extensions in the server to make his application run
faster.

When running with PostgreSQL and `--fast' we do a `VACUUM' after every
major table `UPDATE' and `DROP TABLE' to make the database in perfect
shape for the following `SELECT's.  The time for `VACUUM' is measured
separately.

When running with PostgreSQL 7.1.1 we could, however, not run with
`--fast' because during the `INSERT' test, the postmaster (the
PostgreSQL deamon) died and the database was so corrupted that it was
impossible to restart postmaster.   After this happened twice, we
decided to postpone the `--fast' test until the next PostgreSQL
release.  The details about the machine we run the benchmark on can be
found on the benchmark page.

Before going to the other benchmarks we know of, we would like to give
some background on benchmarks.

It's very easy to write a test that shows *any* database to be the best
database in the world, by just restricting the test to something the
database is very good at and not testing anything that the database is
not good at.  If one, after doing this, summarises the result as a
single figure, things are even easier.

This would be like us measuring the speed of MySQL Server compared to
PostgreSQL by looking at the summary time of the MySQL benchmarks on
our web page.  Based on this MySQL Server would be more than 40 times
faster than PostgreSQL, something that is, of course, not true.  We
could make things even worse by just taking the test where PostgreSQL
performs worst and claim that MySQL Server is more than 2000 times
faster than PostgreSQL.

The case is that MySQL does a lot of optimisations that PostgreSQL
doesn't do. This is, of course, also true the other way around.  An SQL
optimiser is a very complex thing, and a company could spend years just
making the optimiser faster and faster.

When looking at the benchmark results you should look for things that
you do in your application and just use these results to decide which
database would be best suited for your application.  The benchmark
results also show things a particular database is not good at and should
give you a notion about things to avoid and what you may have to do in
other ways.

We know of two benchmark tests that claim that PostgreSQL performs
better than MySQL Server.  These both where multi-user tests, a test
that we here at MySQL AB haven't had time to write and include in the
benchmark suite, mainly because it's a big task to do this in a manner
that is fair to all databases.

One is the benchmark paid for by Great Bridge, the company that for 16
months attempted to build a business based on PostgreSQL but now has
ceased operations. This is probably the worst benchmark we have ever
seen anyone conduct.  This was not only tuned to only test what
PostgreSQL is absolutely best at, but it was also totally unfair to
every other database involved in the test.

*Note*:  We know that even some of the main PostgreSQL developers did
not like the way Great Bridge conducted the benchmark, so we don't
blame the PostgreSQL team for the way the benchmark was done.

This benchmark has been condemned in a lot of postings and newsgroups,
so here we will just briefly repeat some things that were wrong with it.

   * The tests were run with an expensive commercial tool that makes it
     impossible for an `Open Source' company like us to verify the
     benchmarks, or even check how the benchmarks were really done.
     The tool is not even a true benchmark tool, but an
     application/setup testing tool.  To refer to this as a "standard"
     benchmark tool is to stretch the truth a long way.

   * Great Bridge admitted that they had optimised the PostgreSQL
     database (with `VACUUM' before the test) and tuned the startup for
     the tests, something they hadn't done for any of the other
     databases involved.  They say "This process optimises indexes and
     frees up disk space a bit.  The optimised indexes boost
     performance by some margin."  Our benchmarks clearly indicate that
     the difference in running a lot of selects on a database with and
     without `VACUUM' can easily differ by a factor of 10.

   * The test results were also strange.  The AS3AP test documentation
     mentions that the test does "selections, simple joins, projections,
     aggregates, one-tuple updates, and bulk updates."

     PostgreSQL is good at doing `SELECT's and `JOIN's (especially
     after a `VACUUM'), but doesn't perform as well on `INSERT's or
     `UPDATE's.  The benchmarks seem to indicate that only `SELECT's
     were done (or very few updates).  This could easily explain the
     good results for PostgreSQL in this test.  The bad results for
     MySQL will be obvious a bit down in this document.

   * They did run the so-called benchmark from a Windows machine
     against a Linux machine over ODBC, a setup that no normal database
     user would ever do when running a heavy multi-user application.
     This tested more the ODBC driver and the Windows protocol used
     between the clients than the database itself.

   * When running the database against Oracle and MS-SQL (Great Bridge
     has indirectly indicated the databases they used in the test), they
     didn't use the native protocol but instead ODBC.  Anyone that has
     ever used Oracle knows that all real applications use the native
     interface instead of ODBC.  Doing a test through ODBC and claiming
     that the results had anything to do with using the database in a
     real-world situation can't be regarded as fair.  They should have
     done two tests with and without ODBC to provide the right facts
     (after having gotten experts to tune all involved databases, of
     course).

   * They refer to the TPC-C tests, but they don't mention anywhere
     that the test they did was not a true TPC-C test and they were not
     even allowed to call it a TPC-C test.  A TPC-C test can only be
     conducted by the rules approved by the TPC Council
     (`http://www.tpc.org/'). Great Bridge didn't do that.  By doing
     this they have both violated the TPC trademark and miscredited
     their own benchmarks.  The rules set by the TPC Council are very
     strict to ensure that no one can produce false results or make
     unprovable statements.  Apparently Great Bridge wasn't interested
     in doing this.

   * After the first test, we contacted Great Bridge and mentioned to
     them some of the obvious mistakes they had done with MySQL Server:

        - Running with a debug version of our ODBC driver

        - Running on a Linux system that wasn't optimised for threads

        - Using an old MySQL version when there was a recommended newer
          one available

        - Not starting MySQL Server with the right options for heavy
          multi-user use (the default installation of MySQL Server is
          tuned for minimal resource use)

     Great Bridge did run a new test, with our optimised ODBC driver
     and with better startup options for MySQL Server, but refused to
     either use our updated glibc library or our standard binary (used
     by 80% of our users), which was statically linked with a fixed
     glibc library.

     According to what we know, Great Bridge did nothing to ensure that
     the other databases were set up correctly to run well in their test
     environment.  We are sure, however, that they didn't contact
     Oracle or Microsoft to ask for their advice in this matter. ;)

   * The benchmark was paid for by Great Bridge, and they decided to
     publish only partial, chosen results (instead of publishing it
     all).

Tim Perdue, a long-time PostgreSQL fan and a reluctant MySQL user,
published a comparison on PHPbuilder
(`http://www.phpbuilder.com/columns/tim20001112.php3').

When we became aware of the comparison, we phoned Tim Perdue about this
because there were a lot of strange things in his results.  For example,
he claimed that MySQL Server had a problem with five users in his
tests, when we know that there are users with similar machines as his
that are using MySQL Server with 2000 simultaneous connections doing
400 queries per second.  (In this case the limit was the web bandwidth,
not the database.)

It sounded like he was using a Linux kernel that either had some
problems with many threads, such as kernels before 2.4, which had a
problem with many threads on multi-CPU machines. We have documented in
this manual how to fix this and Tim should be aware of this problem.

The other possible problem could have been an old glibc library and
that Tim didn't use a MySQL binary from our site, which is linked with
a corrected glibc library, but had compiled a version of his own.  In
any of these cases, the symptom would have been exactly what Tim had
measured.

We asked Tim if we could get access to his data so that we could repeat
the benchmark and if he could check the MySQL version on the machine to
find out what was wrong and he promised to come back to us about this.
He has not done that yet.

Because of this we can't put any trust in this benchmark either. :(

Over time things also change and the preceding benchmarks are not that
relevant anymore.  MySQL Server now has a couple of different storage
engines with different speed/concurrency tradeoffs.  *Note Table
types::. It would be interesting to see how the above tests would run
with the different transactional table types in MySQL Server.
PostgreSQL has, of course, also got new features since the test was
made.  As these tests are not publicly available there is no way for us
to know how the database would perform in the same tests today.

Conclusion:

The only benchmarks that exist today that anyone can download and run
against MySQL Server and PostgreSQL are the MySQL benchmarks.  We here
at MySQL AB believe that `Open Source' databases should be tested with
`Open Source' tools!  This is the only way to ensure that no one does
tests that nobody can reproduce and use this to claim that one database
is better than another.  Without knowing all the facts it's impossible
to answer the claims of the tester.

The thing we find strange is that every test we have seen about
PostgreSQL, that is impossible to reproduce, claims that PostgreSQL is
better in most cases while our tests, which anyone can reproduce,
clearly show otherwise.  With this we don't want to say that PostgreSQL
isn't good at many things (it is!) or that it isn't faster than MySQL
Server under certain conditions.  We would just like to see a fair test
where PostgreSQL performs very well, so that we could get some friendly
competition going!

For more information about our benchmark suite, see *Note MySQL
Benchmarks::.

We are working on an even better benchmark suite, including multi-user
tests, and a better documentation of what the individual tests really
do and how to add more tests to the suite.

MySQL Installation
******************

This chapter describes how to obtain and install MySQL:

   * For a list of sites from which you can obtain MySQL, see *Note
     Getting MySQL: Getting MySQL.

   * To see which platforms are supported, see *Note Which OS::. Please
     note that not all supported systems are equally good for running
     MySQL on them.  On some it is much more robust and efficient than
     otherssee *Note Which OS:: for details.

   * Several versions of MySQL are available in both binary and source
     distributions.  We also provide public access to our current
     source tree for those who want to see our most recent developments
     and help us test new code.  To determine which version and type of
     distribution you should use, see *Note Which version::. When in
     doubt, use the binary distribution.

   * Installation instructions for binary and source distributions are
     described in *Note Installing binary::, and *Note Installing
     source::.  Each set of instructions includes a section on
     system-specific problems you may run into.

   * For post-installation procedures, see *Note Post-installation::.
     These procedures apply whether you install MySQL using a binary or
     source distribution.

Quick Standard Installation of MySQL
====================================

Installing MySQL on Linux
-------------------------

The recommended way to install MySQL on Linux is by using an RPM file.
The MySQL RPMs are currently being built on a SuSE Linux 7.3 system but
should work on most versions of Linux that support `rpm' and use
`glibc'.

If you have problems with an RPM file, for example, if you receive the
error "`Sorry, the host 'xxxx' could not be looked up'"see *Note Binary
notes-Linux::.

The RPM files you may want to use are:

   * `MySQL-VERSION.i386.rpm'

     The MySQL server.  You will need this unless you only want to
     connect to a MySQL server running on another machine.

   * `MySQL-client-VERSION.i386.rpm'

     The standard MySQL client programs. You probably always want to
     install this package.

   * `MySQL-bench-VERSION.i386.rpm'

     Tests and benchmarks. Requires Perl and msql-mysql-modules RPMs.

   * `MySQL-devel-VERSION.i386.rpm'

     Libraries and include files needed if you want to compile other
     MySQL clients, such as the Perl modules.

   * `MySQL-embedded-VERSION.i386.rpm'

     The embedded MySQL server library. (MySQL 4.x only)

   * `MySQL-VERSION.src.rpm'

     This contains the source code for all of the previous packages. It
     can also be used to rebuild the RPMs on other architectures (for
     example, Alpha or SPARC).

To see all files in an RPM package, run:
     shell> rpm -qpl MySQL-VERSION.i386.rpm

To perform a standard minimal installation, run:

     shell> rpm -i MySQL-VERSION.i386.rpm MySQL-client-VERSION.i386.rpm

To install just the client package, run:

     shell> rpm -i MySQL-client-VERSION.i386.rpm

The RPM places data in `/var/lib/mysql'. The RPM also creates the
appropriate entries in `/etc/init.d/' to start the server automatically
at boot time. (This means that if you have performed a previous
installation, you may want to make a copy of your previously installed
MySQL startup file if you made any changes to it, so you don't lose
your changes.)

If you want to install the MySQL RPM on older Linux distributions that
do not support init scripts in `/etc/init.d' (directly or via a
symlink), you should create a symbolic link pointing to the old
location before installing the RPM:

     shell> cd /etc ; ln -s rc.d/init.d .

However, all current major Linux distributions should already support
this new directory layout as it is required for LSB (Linux Standard
Base) compliance.

After installing the RPM file(s), the `mysqld' daemon should be up and
running and you should now be able to start using MySQL.  *Note
Post-installation::.

If something goes wrong, you can find more information in the binary
installation chapter. *Note Installing binary::.

Installing MySQL on Windows
---------------------------

The MySQL server for Windows is available in two distribution types:
  1. The binary distribution contains a setup program which installs
     everything you need so that you can start the server immediately.

  2. The source distribution contains all the code and support files
     for building the executables using the VC++ 6.0 compiler.  *Note
     Windows source build::.

Generally speaking, you should use the binary distribution.

You will need the following:
   * A 32-bit Windows Operating System such as 9x, Me, NT, 2000, or XP.
     The NT family (NT, Windows 2000 and XP) permits running the MySQL
     server as a service. *Note NT start::.

     If you want to use tables bigger than 4G, you should install MySQL
     on an NTFS or newer filesystem. Don't forget to use `MAX_ROWS' and
     `AVG_ROW_LENGTH' when you create the table. *Note CREATE TABLE::.

   * TCP/IP protocol support.

   * A copy of the MySQL binary or distribution for Windows, which can
     be downloaded from `http://www.mysql.com/downloads/'.

     Note: The distribution files are supplied with a zipped format and
     we recommend the use of an adequate FTP client with resume feature
     to avoid corruption of files during the download process.

   * A `ZIP' program to unpack the distribution file.

   * Enough space on the hard drive to unpack, install, and create the
     databases in accorandance with your requirements.

   * If you plan to connect to the MySQL server via `ODBC', you will
     also need the `MyODBC' driver. *Note ODBC::.

Installing the Binaries
.......................

  1. If you are working on an NT/2000/XP server, logon as a user with
     administrator privileges.

  2. If you are doing an upgrade of an earlier MySQL installation, it
     is necessary to stop the server. If you are running the server as
     a service, use:

          C:\> NET STOP MySQL

     Otherwise, use:

          C:\mysql\bin> mysqladmin -u root shutdown

  3. On NT/2000/XP machines, if you want to change the server executable
     (e.g., -max or -nt), it is also necessary to remove the service:

          C:\mysql\bin> mysqld-max-nt --remove

  4. Unzip the distribution file to a temporary directory.

  5. Run the `setup.exe' file to begin the installation process.  If
     you want to install into another directory than the default
     `c:\mysql', use the `Browse' button to specify your preferred
     directory.

  6. Finish the install process.

Preparing the Windows MySQL Environment
.......................................

Starting with MySQL 3.23.38, the Windows distribution includes both the
normal and the MySQL-Max server binaries.  Here is a list of the
different MySQL servers you can use:

*Binary*       *Description*
`mysqld'        Compiled with full debugging and automatic memory
               allocation checking, symbolic links, InnoDB, and BDB
               tables.
`mysqld-opt'    Optimised binary with no support for transactional
               tables.
`mysqld-nt'     Optimised binary for NT/2000/XP with support for named
               pipes.  You can run this version on Windows 9x/Me, but in
               this case no named pipes are created and you must have
               TCP/IP installed.
`mysqld-max'    Optimised binary with support for symbolic links, InnoDB
               and BDB tables.
`mysqld-max-nt' Like `mysqld-max', but compiled with support for named
               pipes.

Starting from 3.23.50, named pipes are only enabled if one starts
mysqld with `--enable-named-pipe'.

All of the preceding binaries are optimised for the Pentium Pro
processor but should work on any Intel processor >= i386.

You will need to use an option file to specify your MySQL configuration
under the following circumstances:
   * The installation or data directories are different from the default
     locations (`c:\mysql' and `c:\mysql\data').

   * You want to use one of these servers:
        * mysqld.exe

        * mysqld-max.exe

        * mysqld-max-nt.exe

   * You need to tune the server settings.

Normally you can use the `WinMySQLAdmin' tool to edit the option file
`my.ini'.  In this case you don't have to worry about the following
section.

There are two option files with the same function: `my.cnf' and
`my.ini'.  However, to avoid confusion, it's best if you use only of
one them. Both files are plain text.  The `my.cnf' file, if used,
should be created in the root directory of the C drive.  The `my.ini'
file, if used, should be created in the Windows system directory.  (This
directory is typically something like `C:\WINDOWS' or `C:\WINNT'.  You
can determine its exact location from the value of the `windir'
environment variable.)  MySQL looks first for the `my.ini' file, then
for the `my.cnf' file.

If your PC uses a boot loader where the C drive isn't the boot drive,
your only option is to use the `my.ini' file.  Also note that if you
use the `WinMySQLAdmin' tool, it uses only the `my.ini' file.  The
`\mysql\bin' directory contains a help file with instructions for using
this tool.

Using `notepad.exe', create the option file and edit the `[mysqld]'
section to specify values for the `basedir' and `datadir' parameters:

     [mysqld]
     # set basedir to installation path, e.g., c:/mysql
     basedir=the_install_path
     # set datadir to location of data directory,
     # e.g., c:/mysql/data or d:/mydata/data
     datadir=the_data_path

Note that Windows pathnames should be specified in option files using
forward slashes rather than backslashes.  If you do use backslashes, you
must double them.

If you would like to use a data directory different from the default of
`c:\mysql\data', you must copy the entire contents of the
`c:\mysql\data' directory to the new location.

If you want to use the `InnoDB' transactional tables, you need to
manually create two new directories to hold the InnoDB data and log
filese.g., `c:\ibdata' and `c:\iblogs'.  You will also need to add some
extra lines to the option file. *Note InnoDB start::.

If you don't want to use `InnoDB' tables, add the `skip-innodb' option
to the option file.

Now you are ready to test starting the server.

Starting the Server for the First Time
......................................

Testing from a DOS command prompt is the best thing to do because the
server displays status messages that appear in the DOS window.  If
something is wrong with your configuration, these messages will make it
easier for you to identify and fix any problems.

Make sure you are in the directory where the server is located, then
enter this command:

     C:\mysql\bin> mysqld-max --standalone

You should see the following messages as the server starts up:

     InnoDB: The first specified datafile c:\ibdata\ibdata1 did not exist:
     InnoDB: a new database to be created!
     InnoDB: Setting file c:\ibdata\ibdata1 size to 209715200
     InnoDB: Database physically writes the file full: wait...
     InnoDB: Log file c:\iblogs\ib_logfile0 did not exist: new to be created
     InnoDB: Setting log file c:\iblogs\ib_logfile0 size to 31457280
     InnoDB: Log file c:\iblogs\ib_logfile1 did not exist: new to be created
     InnoDB: Setting log file c:\iblogs\ib_logfile1 size to 31457280
     InnoDB: Log file c:\iblogs\ib_logfile2 did not exist: new to be created
     InnoDB: Setting log file c:\iblogs\ib_logfile2 size to 31457280
     InnoDB: Doublewrite buffer not found: creating new
     InnoDB: Doublewrite buffer created
     InnoDB: creating foreign key constraint system tables
     InnoDB: foreign key constraint system tables created
     011024 10:58:25  InnoDB: Started

For further information about running MySQL on Windows, see *Note
Windows::.

General Installation Issues
===========================

How to Get MySQL
----------------

Check the MySQL homepage (`http://www.mysql.com/') for information
about the current version and for downloading instructions.

Our main mirror is located at `http://mirrors.sunsite.dk/mysql/'.

For a complete upto-date list of MySQL web/download mirrors, see
`http://www.mysql.com/downloads/mirrors.html'.  There you will also
find information about becoming a MySQL mirror site and how to report a
bad or out-of-date mirror.

Operating Systems Supported by MySQL
------------------------------------

We use GNU Autoconf, so it is possible to port MySQL to all modern
systems with working Posix threads and a C++ compiler.  (To compile
only the client code, a C++ compiler is required but not threads.)  We
use and develop the software ourselves primarily on Sun Solaris
(Versions 2.5 - 2.7) and SuSE Linux Version 7.x.

Note that for many operating systems, the native thread support works
only in the latest versions. MySQL has been reported to compile
successfully on the following operating system/thread package
combinations:

   * AIX 4.x, 5.x with native threads.  *Note IBM-AIX::.

   * Amiga.

   * BSDI 2.x with the MIT-pthreads package.  *Note BSDI::.

   * BSDI 3.0, 3.1 and 4.x with native threads.  *Note BSDI::.

   * DEC Unix 4.x with native threads.  *Note Alpha-DEC-UNIX::.

   * FreeBSD 2.x with the MIT-pthreads package.  *Note FreeBSD::.

   * FreeBSD 3.x and 4.x with native threads.  *Note FreeBSD::.

   * HP-UX 10.20 with the DCE threads or the MIT-pthreads package.
     *Note HP-UX 10.20::.

   * HP-UX 11.x with the native threads.  *Note HP-UX 11.x::.

   * Linux 2.0+ with LinuxThreads 0.7.1+ or `glibc' 2.0.7+.  *Note
     Linux::.

   * Mac OS X.  *Note Mac OS X::.

   * NetBSD 1.3/1.4 Intel and NetBSD 1.3 Alpha (Requires GNU make).
     *Note NetBSD::.

   * OpenBSD > 2.5 with native threads. OpenBSD < 2.5 with the
     MIT-pthreads package.  *Note OpenBSD::.

   * OS/2 Warp 3, FixPack 29 and OS/2 Warp 4, FixPack 4.  *Note OS/2::.

   * SGI Irix 6.x with native threads.  *Note SGI-Irix::.

   * Solaris 2.5 and above with native threads on SPARC and x86.  *Note
     Solaris::.

   * SunOS 4.x with the MIT-pthreads package.  *Note Solaris::.

   * Caldera (SCO) OpenServer with a recent port of the FSU Pthreads
     package.  *Note Caldera::.

   * Caldera (SCO) UnixWare 7.0.1.  *Note Caldera Unixware::.

   * Tru64 Unix

   * Windows 9x, Me, NT, 2000 and XP.  *Note Windows::.

Note that not all platforms are suited equally well for running MySQL.
How well a certain platform is suited for a high-load mission-critical
MySQL server is determined by the following factors:

   * General stability of the thread library. A platform may have
     excellent reputation otherwise, but if the thread library is
     unstable in the code that is called by MySQL, even if everything
     else is perfect, MySQL will be only as stable as the thread
     library.

   * The ability of the kernel and/or thread library to take advantage
     of *SMP* on multi-processor systems. In other words, when a process
     creates a thread, it should be possible for that thread to run on
     a different CPU than the original process.

   * The ability of the kernel and/or the thread library to run many
     threads which acquire/release a mutex over a short critical region
     frequently without excessive context switches. In other words, if
     the implementation of `pthread_mutex_lock()' is too anxious to
     yield CPU time, this will hurt MySQL tremendously. If this issue
     is not taken care of, adding extra CPUs will actually make MySQL
     slower.

   * General filesystem stability/performance.

   * Ability of the filesystem to deal with large files at all and deal
     with them efficiently, if your tables are big.

   * Our level of expertise here at MySQL AB with the platform. If we
     know a platform well, we introduce platform-specific
     optimisations/fixes enabled at compile time. We can also provide
     advice on configuring your system optimally for MySQL.

   * The amount of testing of similar configurations we have done
     internally.

   * The number of users that have successfully run MySQL on that
     platform in similar configurations. If this number is high, the
     chances of hitting some platform-specific surprises are much
     smaller.

Based on the preceding criteria, the best platforms for running MySQL
at this point are x86 with SuSE Linux 7.1, 2.4 kernel, and ReiserFS (or
any similar Linux distribution) and SPARC with Solaris 2.7 or 2.8.
FreeBSD comes third, but we really hope it will join the top club once
the thread library is improved. We also hope that at some point we will
be able to include all other platforms on which MySQL compiles, runs
okay, but not quite with the same level of stability and performance,
into the top category. This will require some effort on our part in
cooperation with the developers of the OS/library components MySQL
depends upon. If you are interested in making one of those components
better, are in a position to influence their development, and need more
detailed instructions on what MySQL needs to run better, send an e-mail
to <[e-mail]>.

Please note that the preceding comparison is not to say that one OS is
better or worse than the other in general. We are talking about
choosing a particular OS for a dedicated purposerunning MySQL, and
compare platforms in that regard only. With this in mind, the result of
this comparison would be different if we included more issues into it.
And in some cases, the reason one OS is better than the other could
simply be that we have put forth more effort into testing on and
optimising for that particular platform.  We are just stating our
observations to help you decide on which platform to use MySQL on in
your setup.

Which MySQL Version to Use
--------------------------

The first decision to make is whether you want to use the latest
development release or the last stable release:

   * Normally, if you are beginning to use MySQL for the first time or
     trying to port it to some system for which there is no binary
     distribution, we recommend going with the stable release
     (currently version 3.23).  Note that all MySQL releases are
     checked with the MySQL benchmarks and an extensive test suite
     before each release (even the development releases).

   * Otherwise, if you are running an old system and want to upgrade,
     but don't want to take chances with a non-seamless upgrade, you
     should upgrade to the latest in the same branch you are using
     (where only the last version number is newer than yours).  We have
     tried to fix only fatal bugs and make small, relatively safe
     changes to that version.

The second decision to make is whether you want to use a source
distribution or a binary distribution.  In most cases you should
probably use a binary distribution, if one exists for your platform, as
this generally will be easier to install than a source distribution.

In the following cases you probably will be better off with a source
installation:

   * If you want to install MySQL at some explicit location.  (The
     standard binary distributions are "ready to run" at any place, but
     you may want to get even more flexibility).

   * To be able to satisfy different user requirements, we are
     providing two different binary versions: one compiled with the
     non-transactional storage engines (a small, fast binary), and one
     configured with the most important extended options like
     transaction-safe tables.  Both versions are compiled from the same
     source distribution.  All native `MySQL' clients can connect to
     both MySQL versions.

     The extended MySQL binary distribution is marked with the `-max'
     suffix and is configured with the same options as `mysqld-max'.
     *Note `mysqld-max': mysqld-max.

     If you want to use the MySQL-Max RPM, you must first install the
     standard MySQL RPM.

   * If you want to configure `mysqld' with some extra features that are
     not in the standard binary distributions.  Here is a list of the
     most common extra options that you may want to use:

        * `--with-innodb'

        * `--with-berkeley-db'

        * `--with-raid'

        * `--with-libwrap'

        * `--with-named-z-lib  (This is done for some of the binaries)'

        * `--with-debug[=full]'

   * The default binary distribution is normally compiled with support
     for all character sets and should work on a variety of processors
     from the same processor family.

     If you want a faster MySQL server you may want to recompile it
     with support for only the character sets you need, use a better
     compiler (like `pgcc'), or use compiler options that are better
     optimised for your processor.

   * If you have found a bug and reported it to the MySQL development
     team you will probably receive a patch that you need to apply to
     the source distribution to get the bug fixed.

   * If you want to read (and/or modify) the C and C++ code that makes
     up MySQL, you should get a source distribution.  The source code is
     always the ultimate manual.  Source distributions also contain more
     tests and examples than binary distributions.

The MySQL naming scheme uses release numbers that consist of three
numbers and a suffix.  For example, a release name like
`mysql-3.21.17-beta' is interpreted like this:

   * The first number (`3') describes the file format.  All Version 3
     releases have the same file format.

   * The second number (`21') is the release level.  Normally there are
     two to choose from. One is the release/stable branch (currently
     `23') and the other is the development branch (currently `4.0').
     Normally both are stable, but the development version may have
     quirks, may be missing documentation on new features, or may fail
     to compile on some systems.

   * The third number (`17') is the version number within the release
     level.  This is incremented for each new distribution.  Usually you
     want the latest version for the release level you have chosen.

   * The suffix (`beta') indicates the stability level of the release.
     The possible suffixes are:

        - `alpha' indicates that the release contains some large
          section of new code that hasn't been 100% tested.  Known bugs
          (usually there are none) should be documented in the News
          section.  *Note News::.  There are also new commands and
          extensions in most alpha releases.  Active development that
          may involve major code changes can occur on an alpha release,
          but everything will be tested before doing a release.  There
          should be no known bugs in any MySQL release.

        - `beta' means that all new code has been tested.  No major new
          features that could cause corruption on old code are added.
          There should be no known bugs.  A version changes from alpha
          to beta when there haven't been any reported fatal bugs
          within an alpha version for at least a month and we don't
          plan to add any features that could make any old command more
          unreliable.

        - `gamma' is a beta that has been around a while and seems to
          work fine.  Only minor fixes are added.  This is what many
          other companies call a release.

        - If there is no suffix, it means that the version has been run
          for a while at many different sites with no reports of bugs
          other than platform-specific bugs.  Only critical bug fixes
          are applied to the release. This is what we call a stable
          release.

All versions of MySQL are run through our standard tests and benchmarks
to ensure that they are relatively safe to use.  Because the standard
tests are extended over time to check for all previously found bugs,
the test suite keeps getting better.

Note that all releases have been tested at least with:

An internal test suite
     This is part of a production system for a customer.  It has many
     tables with hundreds of megabytes of data.

The MySQL benchmark suite
     This runs a range of common queries.  It is also a test to see
     whether the latest batch of optimisations actually made the code
     faster.  *Note MySQL Benchmarks::.

The `crash-me' test
     This tries to determine what features the database supports and
     what its capabilities and limitations are.  *Note MySQL
     Benchmarks::.

Another test is that we use the newest MySQL version in our internal
production environment, on at least one machine.  We have more than 100
gigabytes of data to work with.

Installation Layouts
--------------------

This section describes the default layout of the directories created by
installing binary and source distributions.

A binary distribution is installed by unpacking it at the installation
location you choose (typically `/usr/local/mysql') and creates the
following directories in that location:

*Directory* *Contents of directory*
`bin'       Client programs and the
            `mysqld' server
`data'      Log files, databases
`include'   Include (header) files
`lib'       Libraries
`scripts'   `mysql_install_db'
`share/mysql'Error message files
`sql-bench' Benchmarks

A source distribution is installed after you configure and compile it.
By default, the installation step installs files under `/usr/local', in
the following subdirectories:

*Directory* *Contents of directory*
`bin'       Client programs and scripts
`include/mysql'Include (header) files
`info'      Documentation in Info format
`lib/mysql' Libraries
`libexec'   The `mysqld' server
`share/mysql'Error message files
`sql-bench' Benchmarks and `crash-me' test
`var'       Databases and log files

Within an installation directory, the layout of a source installation
differs from that of a binary installation in the following ways:

   * The `mysqld' server is installed in the `libexec' directory rather
     than in the `bin' directory.

   * The data directory is `var' rather than `data'.

   * `mysql_install_db' is installed in the `/usr/local/bin' directory
     rather than in `/usr/local/mysql/scripts'.

   * The header file and library directories are `include/mysql' and
     `lib/mysql' rather than `include' and `lib'.

You can create your own binary installation from a compiled source
distribution by executing the script `scripts/make_binary_distribution'.

How and When Updates Are Released
---------------------------------

MySQL is evolving quite rapidly here at MySQL AB and we want to share
this with other MySQL users.  We try to make a release when we have
very useful features that others seem to have a need for.

We also try to help out users who request features that are easy to
implement.  We take note of what our licensed users want to have, and
we especially take note of what our extended e-mail supported customers
want and try to help them out.

No one has to download a new release.  The News section will tell you if
the new release has something you really want.  *Note News::.

We use the following policy when updating MySQL:

   * For each minor update, the last number in the version string is
     incremented.  When there are major new features or minor
     incompatibilities with previous versions, the second number in the
     version string is incremented.  When the file format changes, the
     first number is increased.

   * Stable-tested releases are meant to appear about 1-2 times a year,
     but if small bugs are found, a release with only bug fixes will be
     released.

   * Working releases/bug fixes to old releases are meant to appear
     about every 1-8 weeks.

   * Binary distributions for some platforms will be made by us for
     major releases.  Other people may make binary distributions for
     other systems but probably less frequently.

   * We usually make patches available as soon as we have located and
     fixed small bugs. They are posted to <[e-mail]> and
     will be added to the next release.

   * For non-critical but annoying bugs, we will add them the MySQL
     source repository and they will be fixed in the next release.

   * If there is, by any chance, a fatal bug in a release we will make
     a new release as soon as possible.  We would like other companies
     to do this, too.

The current stable release is Version 3.23; we have already moved active
development to Version 4.0.  Bugs will still be fixed in the stable
version.  We don't believe in a complete freeze, as this also leaves
out bug fixes and things that "must be done."  "Somewhat frozen" means
that we may add small things that "almost surely will not affect
anything that's already working."

MySQL uses a slightly different naming scheme from most other products.
In general it's relatively safe to use any version that has been out for
a couple of weeks without being replaced with a new version.  *Note
Which version::.

MySQL Binaries Compiled by MySQL AB
-----------------------------------

As a service, we at MySQL AB provide a set of binary distributions of
MySQL that are compiled at our site or at sites where customers kindly
have given us access to their machines.

These distributions are generated using the script
`Build-tools/Do-compile' which compiles the source code and creates the
binary `tar.gz' archive using `scripts/make_binary_distribution' These
binaries are configured and built with the following compilers and
options.

Binaries built on MySQL AB development systems:

Linux 2.4.xx i386 with `gcc' 2.95.3
     `CFLAGS="-O2 -mcpu=pentiumpro" CXX=gcc CXXFLAGS="-O2
     -mcpu=pentiumpro -felide-constructors" ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile
     --enable-assembler --disable-shared
     --with-client-ldflags=-all-static
     --with-mysqld-ldflags=-all-static'

Linux 2.4.xx ia64 with `ecc' (Intel C++ Itanium Compiler 7.0)
     `CC=ecc CFLAGS=-tpp1 CXX=ecc CXXFLAGS=-tpp1 ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile'

Linux 2.4.xx alpha with `ccc' (Compaq C V6.2-505 / Compaq C++ V6.3-006)
     `CC=ccc CFLAGS="-fast -arch generic" CXX=cxx CXXFLAGS="-fast -arch
     generic -noexceptions -nortti" ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile
     --with-mysqld-ldflags=-non_shared
     --with-client-ldflags=-non_shared --disable-shared'

Linux 2.2.xx sparc with `egcs' 1.1.2
     `CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3
     -fno-omit-frame-pointer -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --enable-assembler --disable-shared'

Linux 2.4.xx s390 with `gcc' 2.95.3
     `CFLAGS="-O2" CXX=gcc CXXFLAGS="-O2 -felide-constructors"
     ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --disable-shared
     --with-client-ldflags=-all-static
     --with-mysqld-ldflags=-all-static'

Sun Solaris 2.8 sparc with `gcc' 3.2
     `CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3
     -fno-omit-frame-pointer -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --enable-assembler --with-named-z-libs=no
     --with-named-curses-libs=-lcurses --disable-shared'

Sun Solaris 2.9 sparc with `gcc' 2.95.3
     `CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3
     -fno-omit-frame-pointer -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --enable-assembler
     --with-named-curses-libs=-lcurses --disable-shared'

Sun Solaris 2.9 sparc with `cc-5.0' (Sun Forte 5.0)
     `CC=cc-5.0 CXX=CC ASFLAGS="-xarch=v9" CFLAGS="-Xa -xstrconst -mt
     -D_FORTEC_ -xarch=v9" CXXFLAGS="-noex -mt -D_FORTEC_ -xarch=v9"
     ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --enable-assembler --with-named-z-libs=no
     --enable-thread-safe-client --disable-shared'

IBM AIX 4.3.2 ppc with `gcc' 3.2.1
     `CFLAGS="-O2 -mcpu=powerpc -Wa,-many " CXX=gcc CXXFLAGS="-O2
     -mcpu=powerpc -Wa,-many  -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --with-named-z-libs=no --disable-shared'

IBM AIX 5.1.0 ppc with `gcc' 3.2.1
     `CFLAGS="-O2 -mcpu=powerpc -Wa,-many" CXX=gcc CXXFLAGS="-O2
     -mcpu=powerpc -Wa,-many  -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --with-server-suffix="-pro"
     --enable-thread-safe-client --enable-local-infile
     --with-named-z-libs=no --disable-shared --with-innodb'

HP-UX 10.20 pa-risc1.1 with `gcc' 3.1
     `CFLAGS="-DHPUX -I/opt/dce/include -O3 -fPIC" CXX=gcc
     CXXFLAGS="-DHPUX -I/opt/dce /include -felide-constructors
     -fno-exceptions -fno-rtti -O3 -fPIC" ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile  --with-pthread
     --with-named-thread-libs=-ldce --with-lib-ccflags=-fPIC
     --disable-shared'

HP-UX 11.11 pa-risc2.0 with `aCC' (HP ANSI C++ B3910B A.03.33)
     `CC=cc CXX=aCC CFLAGS=+DD64 CXXFLAGS=+DD64 ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile --disable-shared'

Apple MacOS X 10.2 powerpc with `gcc' 3.1
     `CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc CXXFLAGS="-O3
     -fno-omit-frame-pointer -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile  --disable-shared'

FreeBSD 4.7 i386 with `gcc' 2.95.4
     `CFLAGS=-DHAVE_BROKEN_REALPATH ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile
     --enable-assembler --with-named-z-libs=not-used --disable-shared'

The following binaries are built on third-party systems kindly provided
to MySQL AB by other users. Please note that these are only provided as
a courtesy. Since MySQL AB does not have full control over these
systems, we can only provide limited support for the binaries built on
these systems.

SCO Unix 3.2v5.0.6 i386 with `gcc' 2.95.3
     `CFLAGS="-O3 -mpentium" LDFLAGS=-static CXX=gcc CXXFLAGS="-O3
     -mpentium -felide-constructors" ./configure
     --prefix=/usr/local/mysql --with-extra-charsets=complex
     --enable-thread-safe-client --enable-local-infile
     --with-named-z-libs=no --enable-thread-safe-client
     --disable-shared'

Caldera Open Unix 8.0.0 i386 with `CC' 3.2
     `CC=cc CFLAGS="-O" CXX=CC ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --with-named-z-libs=no
     --enable-thread-safe-client --disable-shared'

Compaq Tru64 OSF/1 V5.1 732 alpha with `cc/cxx' (Compaq C V6.3-029i / DIGITAL C++ V6.1-027)
     `CC="cc -pthread" CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline
     speed -speculate all" CXX="cxx -pthread" CXXFLAGS="-O4 -ansi_alias
     -fast -inline speed -speculate all -noexceptions -nortti"
     ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile --with-prefix=/usr/local/mysql
     --with-named-thread-libs="-lpthread -lmach -lexc -lc"
     --disable-shared --with-mysqld-ldflags=-all-static'

SGI Irix 6.5 IP32 with `gcc' 3.0.1
     `CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXXFLAGS="-O3
     -fno-omit-frame-pointer -felide-constructors -fno-exceptions
     -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex --enable-thread-safe-client
     --enable-local-infile  --disable-shared'

The following compile options have been used for binary packages MySQL
AB used to provide in the past. These binaries are currently not being
updated anymore, but the compile options are kept in here for reference
purposes.

Linux 2.2.x with x686 with `gcc' 2.95.2
     `CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro
     -felide-constructors -fno-exceptions -fno-rtti" ./configure
     --prefix=/usr/local/mysql --enable-assembler
     --with-mysqld-ldflags=-all-static --disable-shared
     --with-extra-charsets=complex'

SunOS 4.1.4 2 sun4c with `gcc' 2.7.2.1
     `CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors" ./configure
     --prefix=/usr/local/mysql --disable-shared
     --with-extra-charsets=complex --enable-assembler'

SunOS 5.5.1 (and above) sun4u with `egcs' 1.0.3a or 2.90.27 or gcc 2.95.2 and newer
     `CC=gcc CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors
     -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql
     --with-low-memory --with-extra-charsets=complex --enable-assembler'

SunOS 5.6 i86pc with `gcc' 2.8.1
     `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
     --with-low-memory --with-extra-charsets=complex'

BSDI BSD/OS 3.1 i386 with `gcc' 2.7.2.1
     `CC=gcc CXX=gcc CXXFLAGS=-O ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex'

BSDI BSD/OS 2.1 i386 with `gcc' 2.7.2
     `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex'

AIX 2 4 with `gcc' 2.7.2.2
     `CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql
     --with-extra-charsets=complex'

Anyone who has more optimal options for any of the preceding
configurations listed can always mail them to the developer's mailing
list at <[e-mail]>.

RPM distributions prior to MySQL Version 3.22 are user-contributed.
Beginning with Version 3.22, the RPMs are generated by us at MySQL AB.

If you want to compile a debug version of MySQL, you should add
`--with-debug' or `--with-debug=full' to the preceding configure lines
and remove any `-fomit-frame-pointer' options.

For the Windows distribution, please see *Note Windows installation::.

Installing a MySQL Binary Distribution
--------------------------------------

See also *Note Windows binary installation::, *Note Linux-RPM::, and
*Note Building clients::.

You need the following tools to install a MySQL binary distribution:

   * GNU `gunzip' to uncompress the distribution.

   * A reasonable `tar' to unpack the distribution. GNU `tar' is known
     to work.  Sun `tar' is known to have problems.

An alternative installation method under Linux is to use RPM-based (RPM
Package Manager) distributions.  *Note Linux-RPM::.

If you run into problems, *please always use `mysqlbug'* when posting
questions to <[e-mail]>.  Even if the problem isn't a bug,
`mysqlbug' gathers system information that will help others solve your
problem.  By not using `mysqlbug', you lessen the likelihood of getting
a solution to your problem!  You will find `mysqlbug' in the `bin'
directory after you unpack the distribution.  *Note Bug reports::.

The basic commands you must execute to install and use a MySQL binary
distribution are:

     shell> groupadd mysql
     shell> useradd -g mysql mysql
     shell> cd /usr/local
     shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf -
     shell> ln -s full-path-to-mysql-VERSION-OS mysql
     shell> cd mysql
     shell> scripts/mysql_install_db
     shell> chown -R root  .
     shell> chown -R mysql data
     shell> chgrp -R mysql .
     shell> bin/safe_mysqld --user=mysql &
     or
     shell> bin/mysqld_safe --user=mysql &
     if you are running MySQL 4.x

You can add new users using the `bin/mysql_setpermission' script if you
install the `DBI' and `Msql-Mysql-modules' Perl modules.

A more detailed description follows.

To install a binary distribution, follow these steps, then proceed to
*Note Post-installation::, for post-installation setup and testing:

  1. Pick the directory under which you want to unpack the
     distribution, and move into it.  In the following example, we
     unpack the distribution under `/usr/local' and create a directory
     `/usr/local/mysql' into which MySQL is installed.  (The following
     instructions, therefore, assume you have permission to create
     files in `/usr/local'.  If that directory is protected, you will
     need to perform the installation as `root'.)

  2. Obtain a distribution file from one of the sites listed in *Note
     Getting MySQL: Getting MySQL.

     MySQL binary distributions are provided as compressed `tar'
     archives and have names like `mysql-VERSION-OS.tar.gz', where
     `VERSION' is a number (for example, `3.21.15'), and `OS' indicates
     the type of operating system for which the distribution is intended
     (for example, `pc-linux-gnu-i586').

  3. If you see a binary distribution marked with the `-max' suffix,
     this means that the binary has support for transaction-safe tables
     and other features. *Note `mysqld-max': mysqld-max.  Note that all
     binaries are built from the same MySQL source distribution.

  4. Add a user and group for `mysqld' to run as:

          shell> groupadd mysql
          shell> useradd -g mysql mysql

     These commands add the `mysql' group and the `mysql' user.  The
     syntax for `useradd' and `groupadd' may differ slightly on
     different versions of Unix.  They may also be called `adduser' and
     `addgroup'.  You may wish to call the user and group something
     else instead of `mysql'.

  5. Change into the intended installation directory:

          shell> cd /usr/local

  6. Unpack the distribution and create the installation directory:

          shell> gunzip < /path/to/mysql-VERSION-OS.tar.gz | tar xvf -
          shell> ln -s full-path-to-mysql-VERSION-OS mysql

     The first command creates a directory named `mysql-VERSION-OS'.
     The second command makes a symbolic link to that directory.  This
     lets you refer more easily to the installation directory as
     `/usr/local/mysql'.

  7. Change into the installation directory:

          shell> cd mysql

     You will find several files and subdirectories in the `mysql'
     directory.  The most important for installation purposes are the
     `bin' and `scripts' subdirectories.

    `bin'
          This directory contains client programs and the server You
          should add the full pathname of this directory to your `PATH'
          environment variable so that your shell finds the MySQL
          programs properly. *Note Environment variables::.

    `scripts'
          This directory contains the `mysql_install_db' script used to
          initialise the `mysql' database containing the grant tables
          that store the server access permissions.

  8. If you would like to use `mysqlaccess' and have the MySQL
     distribution in some non-standard place, you must change the
     location where `mysqlaccess' expects to find the `mysql' client.
     Edit the `bin/mysqlaccess' script at approximately line 18.
     Search for a line that looks like this:

          $MYSQL     = '/usr/local/bin/mysql';    # path to mysql executable

     Change the path to reflect the location where `mysql' actually is
     stored on your system.  If you do not do this, you will get a
     `Broken pipe' error when you run `mysqlaccess'.

  9. Create the MySQL grant tables (necessary only if you haven't
     installed MySQL before):
          shell> scripts/mysql_install_db

     Note that MySQL versions older than Version 3.22.10 started the
     MySQL server when you run `mysql_install_db'.  This is no longer
     true!

 10. Change ownership of binaries to `root' and ownership of the data
     directory to the user that you will run `mysqld' as:

          shell> chown -R root  /usr/local/mysql/.
          shell> chown -R mysql /usr/local/mysql/data
          shell> chgrp -R mysql /usr/local/mysql/.

     The first command changes the `owner' attribute of the files to the
     `root' user, the second one changes the `owner' attribute of the
     data directory to the `mysql' user, and the third one changes the
     `group' attribute to the `mysql' group.

 11. If you want to install support for the Perl `DBI'/`DBD' interface,
     see *Note Perl support::.

 12. If you would like MySQL to start automatically when you boot your
     machine, you can copy `support-files/mysql.server' to the location
     where your system has its startup files.  More information can be
     found in the `support-files/mysql.server' script itself and in
     *Note Automatic start::.


After everything has been unpacked and installed, you should initialise
and test your distribution.

You can start the MySQL server with the following command:

     shell> bin/safe_mysqld --user=mysql &

Now proceed to *Note `safe_mysqld': safe_mysqld, and *Note
Post-installation::.

Installing a MySQL Source Distribution
======================================

Before you proceed with the source installation, check first to see if
our binary is available for your platform and if it will work for you.
We put a lot of effort into making sure that our binaries are built
with the best possible options.

You need the following tools to build and install MySQL from source:

   * GNU `gunzip' to uncompress the distribution.

   * A reasonable `tar' to unpack the distribution.  GNU `tar' is known
     to work.  Sun `tar' is known to have problems.

   * A working ANSI C++ compiler.  `gcc' >= 2.95.2, `egcs' >= 1.0.2 or
     `egcs 2.91.66', SGI C++, and SunPro C++ are some of the compilers
     that are known to work.  `libg++' is not needed when using `gcc'.
     `gcc' 2.7.x has a bug that makes it impossible to compile some
     perfectly legal C++ files, such as `sql/sql_base.cc'.  If you only
     have `gcc' 2.7.x, you must upgrade your `gcc' to be able to
     compile MySQL. `gcc' 2.8.1 is also known to have problems on some
     platforms, so it should be avoided if a new compiler exists for
     the platform.

     `gcc' >= 2.95.2 is recommended when compiling MySQL Version 3.23.x.

   * A good `make' program.  GNU `make' is always recommended and is
     sometimes required.  If you have problems, we recommend trying GNU
     `make' 3.75 or newer.

If you are using a recent version of `gcc', recent enough to understand
the `-fno-exceptions' option, it is *very important* that you use it.
Otherwise, you may compile a binary that crashes randomly. We also
recommend that you use `-felide-constructors' and `-fno-rtti' along
with `-fno-exceptions'. When in doubt, do the following:


     CFLAGS="-O3" CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions \
            -fno-rtti" ./configure --prefix=/usr/local/mysql --enable-assembler \
            --with-mysqld-ldflags=-all-static

On most systems this will give you a fast and stable binary.

If you run into problems, *please always use `mysqlbug'* when posting
questions to <[e-mail]>.  Even if the problem isn't a bug,
`mysqlbug' gathers system information that will help others solve your
problem.  By not using `mysqlbug', you lessen the likelihood of getting
a solution to your problem!  You will find `mysqlbug' in the `scripts'
directory after you unpack the distribution.  *Note Bug reports::.

Quick Installation Overview
---------------------------

The basic commands you must execute to install a MySQL source
distribution are:

     shell> groupadd mysql
     shell> useradd -g mysql mysql
     shell> gunzip < mysql-VERSION.tar.gz | tar -xvf -
     shell> cd mysql-VERSION
     shell> ./configure --prefix=/usr/local/mysql
     shell> make
     shell> make install
     shell> scripts/mysql_install_db
     shell> chown -R root  /usr/local/mysql
     shell> chown -R mysql /usr/local/mysql/var
     shell> chgrp -R mysql /usr/local/mysql
     shell> cp support-files/my-medium.cnf /etc/my.cnf
     shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &
     or
     shell> /usr/local/mysql/bin/mysqld_safe --user=mysql &
     if you are running MySQL 4.x.

If you want to have support for InnoDB tables, you should edit the
`/etc/my.cnf' file and remove the `#' character before the parameter
that starts with `innodb_...'.  *Note Option files::, and *Note InnoDB
start::.

If you start from a source RPM, do the following:

     shell> rpm --rebuild MySQL-VERSION.src.rpm

This will make a binary RPM that you can install.

You can add new users using the `bin/mysql_setpermission' script if you
install the `DBI' and `Msql-Mysql-modules' Perl modules.

A more detailed description follows.

To install a source distribution, follow these steps, then proceed to
*Note Post-installation::, for post-installation initialisation and
testing:

  1. Pick the directory under which you want to unpack the
     distribution, and move into it.

  2. Obtain a distribution file from one of the sites listed in *Note
     Getting MySQL: Getting MySQL.

  3. If you are interested in using Berkeley DB tables with MySQL, you
     will need to obtain a patched version of the Berkeley DB source
     code.  Please read the chapter on Berkeley DB tables before
     proceeding.  *Note BDB::.

     MySQL source distributions are provided as compressed `tar'
     archives and have names like `mysql-VERSION.tar.gz', where
     `VERSION' is a number like 3.23.55.

  4. Add a user and group for `mysqld' to run as:

          shell> groupadd mysql
          shell> useradd -g mysql mysql

     These commands add the `mysql' group and the `mysql' user.  The
     syntax for `useradd' and `groupadd' may differ slightly on
     different versions of Unix.  They may also be called `adduser' and
     `addgroup'.  You may wish to call the user and group something
     else instead of `mysql'.

  5. Unpack the distribution into the current directory:
          shell> gunzip < /path/to/mysql-VERSION.tar.gz | tar xvf -

     This command creates a directory named `mysql-VERSION'.

  6. Change into the top-level directory of the unpacked distribution:

          shell> cd mysql-VERSION

     Note that currently you must configure and build MySQL from this
     top-level directory.  You cannot build it in a different directory.

  7. Configure the release and compile everything:

          shell> ./configure --prefix=/usr/local/mysql
          shell> make

     When you run `configure', you might want to specify some options.
     Run `./configure --help' for a list of options.  *Note `configure'
     options: configure options, discusses some of the more useful
     options.

     If `configure' fails, and you are going to send mail to
     <[e-mail]> to ask for assistance, please include any
     lines from `config.log' that you think can help solve the problem.
     Also include the last couple of lines of output from `configure'
     if `configure' aborts.  Post the bug report using the `mysqlbug'
     script.  *Note Bug reports::.

     If the compile fails, see *Note Compilation problems::, for help
     with a number of common problems.

  8. Install everything:

          shell> make install

     You might need to run this command as `root'.

  9. Create the MySQL grant tables (necessary only if you haven't
     installed MySQL before):

          shell> scripts/mysql_install_db

     Note that MySQL versions older than Version 3.22.10 started the
     MySQL server when you run `mysql_install_db'.  This is no longer
     true!

 10. Change ownership of binaries to `root' and ownership of the data
     directory to the user that you will run `mysqld' as:

          shell> chown -R root  /usr/local/mysql
          shell> chown -R mysql /usr/local/mysql/var
          shell> chgrp -R mysql /usr/local/mysql

     The first command changes the `owner' attribute of the files to the
     `root' user, the second one changes the `owner' attribute of the
     data directory to the `mysql' user, and the third one changes the
     `group' attribute to the `mysql' group.

 11. If you want to install support for the Perl `DBI'/`DBD' interface,
     see *Note Perl support::.

 12. If you would like MySQL to start automatically when you boot your
     machine, you can copy `support-files/mysql.server' to the location
     where your system has its startup files.  More information can be
     found in the `support-files/mysql.server' script itself and in
     *Note Automatic start::.

After everything has been installed, you should initialise and test your
distribution:

     shell> /usr/local/mysql/bin/safe_mysqld --user=mysql &

If that command fails immediately with `mysqld daemon ended', you can
find some information in the file `mysql-data-directory/'hostname'.err'.
The likely reason is that you already have another `mysqld' server
running.  *Note Multiple servers::.

Now proceed to *Note Post-installation::.

Applying Patches
----------------

Sometimes patches appear on the mailing list or are placed in the
patches area of the MySQL web site
(`http://www.mysql.com/downloads/patches.html').

To apply a patch from the mailing list, save the message in which the
patch appears in a file, change into the top-level directory of your
MySQL source tree, and run these commands:

     shell> patch -p1 < patch-file-name
     shell> rm config.cache
     shell> make clean

Patches from the FTP site are distributed as plain text files or as
files compressed with `gzip'.  Apply a plain patch as shown previously
for mailing list patches.  To apply a compressed patch, change into the
top-level directory of your MySQL source tree and run these commands:

     shell> gunzip < patch-file-name.gz | patch -p1
     shell> rm config.cache
     shell> make clean

After applying a patch, follow the instructions for a normal source
install, beginning with the `./configure' step.  After running the `make
install' step, restart your MySQL server.

You may need to bring down any currently running server before you run
`make install'.  (Use `mysqladmin shutdown' to do this.)  Some systems
do not allow you to install a new version of a program if it replaces
the version that is currently executing.

Typical `configure' Options
---------------------------

The `configure' script gives you a great deal of control over how you
configure your MySQL distribution.  Typically you do this using options
on the `configure' command-line.  You can also affect `configure' using
certain environment variables.  *Note Environment variables::.  For a
list of options supported by `configure', run this command:

     shell> ./configure --help

Some of the more commonly-used `configure' options are described here:

   * To compile just the MySQL client libraries and client programs and
     not the server, use the `--without-server' option:

          shell> ./configure --without-server

     If you don't have a C++ compiler, `mysql' will not compile (it is
     the one client program that requires C++).  In this case, you can
     remove the code in `configure' that tests for the C++ compiler and
     then run `./configure' with the `--without-server' option. The
     compile step will still try to build `mysql', but you can ignore
     any warnings about `mysql.cc'.  (If `make' stops, try `make -k' to
     tell it to continue with the rest of the build even if errors
     occur.)

   * If you want to get an embedded MySQL library (`libmysqld.a') you
     should use the `--with-embedded-server' option.

   * If you don't want your log files and database directories located
     under `/usr/local/var', use a `configure' command, something like
     one of these:

          shell> ./configure --prefix=/usr/local/mysql
          shell> ./configure --prefix=/usr/local \
                     --localstatedir=/usr/local/mysql/data

     The first command changes the installation prefix so that
     everything is installed under `/usr/local/mysql' rather than the
     default of `/usr/local'.  The second command preserves the default
     installation prefix, but overrides the default location for
     database directories (normally `/usr/local/var') and changes it to
     `/usr/local/mysql/data'.  After you have compiled MySQL, you can
     change these options with option files. *Note Option files::.

   * If you are using Unix and you want the MySQL socket located
     somewhere other than the default location (normally in the
     directory `/tmp' or `/var/run') use a `configure' command like
     this:

          shell> ./configure --with-unix-socket-path=/usr/local/mysql/tmp/mysql.sock

     Note that the given file must be an absolute pathname!  You can
     also later change the location `mysql.sock' by using the MySQL
     option files. *Note Problems with mysql.sock::.

   * If you want to compile statically linked programs (for example, to
     make a binary distribution, to get more speed, or to work around
     problems with some RedHat Linux distributions), run `configure'
     like this:

          shell> ./configure --with-client-ldflags=-all-static \
                     --with-mysqld-ldflags=-all-static

   * If you are using `gcc' and don't have `libg++' or `libstdc++'
     installed, you can tell `configure' to use `gcc' as your C++
     compiler:

          shell> CC=gcc CXX=gcc ./configure

     When you use `gcc' as your C++ compiler, it will not attempt to
     link in `libg++' or `libstdc++'.  This may be a good idea to do
     even if you have the above libraries installed, as some versions
     of these libraries have caused strange problems for MySQL users in
     the past.

     Here are some common environment variables to set depending on the
     compiler you are using:

     *Compiler*    *Recommended options*
     gcc 2.7.2.1    CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors"
     egcs 1.0.3a    CC=gcc CXX=gcc CXXFLAGS="-O3 -felide-constructors
                   -fno-exceptions -fno-rtti"
     gcc 2.95.2     CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3
                   -mpentiumpro \ -felide-constructors -fno-exceptions
                   -fno-rtti"
     pgcc 2.90.29   CFLAGS="-O3 -mpentiumpro -mstack-align-double"
     or newer      CXX=gcc \ CXXFLAGS="-O3 -mpentiumpro
                   -mstack-align-double -felide-constructors \
                   -fno-exceptions -fno-rtti"

     In most cases you can get a reasonably optimal MySQL binary by
     using the options from the preceding table and adding the
     following options to the configure line:

          --prefix=/usr/local/mysql --enable-assembler \
          --with-mysqld-ldflags=-all-static

     The full configure line would, in other words, be something like
     the following for all recent gcc versions:

          CFLAGS="-O3 -mpentiumpro" CXX=gcc CXXFLAGS="-O3 -mpentiumpro \
          -felide-constructors -fno-exceptions -fno-rtti" ./configure \
          --prefix=/usr/local/mysql --enable-assembler \
          --with-mysqld-ldflags=-all-static

     The binaries we provide on the MySQL web site at
     `http://www.mysql.com/' are all compiled with full optimisation and
     should be perfect for most users.  *Note MySQL binaries::.  There
     are some things you can tweak to make an even faster binary, but
     this is only for advanced users.  *Note Compile and link options::.

     If the build fails and produces errors about your compiler or
     linker not being able to create the shared library
     `libmysqlclient.so.#' (`#' is a version number), you can work
     around this problem by giving the `--disable-shared' option to
     `configure'.  In this case, `configure' will not build a shared
     `libmysqlclient.so.#' library.

   * You can configure MySQL not to use `DEFAULT' column values for
     non-`NULL' columns (that is, columns that are not allowed to be
     `NULL').  This causes `INSERT' statements to generate an error
     unless you explicitly specify values for all columns that require a
     non-`NULL' value.  To suppress use of default values, run
     `configure' like this:

          shell> CXXFLAGS=-DDONT_USE_DEFAULT_FIELDS ./configure

   * By default, MySQL uses the ISO-8859-1 (Latin1) character set. To
     change the default set, use the `--with-charset' option:
          shell> ./configure --with-charset=CHARSET
     `CHARSET' may be one of `big5', `cp1251', `cp1257', `czech',
     `danish', `dec8', `dos', `euc_kr', `gb2312', `gbk', `german1',
     `hebrew', `hp8', `hungarian', `koi8_ru', `koi8_ukr', `latin1',
     `latin2', `sjis', `swe7', `tis620', `ujis', `usa7', or
     `win1251ukr'.  *Note Character sets::.

     If you want to convert characters between the server and the
     client, you should take a look at the `SET CHARACTER SET' command.
     *Note `SET': SET OPTION.

     *Warning*: If you change character sets after having created any
     tables, you will have to run `myisamchk -r -q
     --set-character-set=charset' on every table. Your indexes may be
     sorted incorrectly otherwise.  (This can happen if you install
     MySQL, create some tables, then reconfigure MySQL to use a
     different character set and reinstall it.)

     With the option `--with-extra-charsets=LIST' you can define which
     additional character sets should be compiled into the server.

     Here `LIST' is either a list of character sets separated with
     spaces, `complex' to include all characters that can't be
     dynamically loaded, or `all' to include all character sets into
     the binaries.

   * To configure MySQL with debugging code, use the `--with-debug'
     option:
          shell> ./configure --with-debug
     This causes a safe memory allocator to be included that can find
     some errors and that provides output about what is happening.
     *Note Debugging server::.

   * If your client programs are using threads, you need to also
     compile a thread-safe version of the MySQL client library with the
     `--enable-thread-safe-client' configure options. This will create a
     `libmysqlclient_r' library with which you should link your threaded
     applications.  *Note Threaded clients::.

   * Options that pertain to particular systems can be found in the
     system-specific section of this manual.  *Note Operating System
     Specific Notes::.

Installing from the Development Source Tree
-------------------------------------------

*Caution*: You should read this section only if you are interested in
helping us test our new code. If you just want to get MySQL up and
running on your system, you should use a standard release distribution
(either a source or binary distribution will do).

To obtain our most recent development source tree, use these
instructions:

  1. Download `BitKeeper' from
     `http://www.bitmover.com/cgi-bin/download.cgi'.  You will need
     `Bitkeeper' 3.0 or newer to access our repository.

  2. Follow the instructions to install it.

  3. After `BitKeeper' is installed, first go to the directory you want
     to work from, and then use one of the following commands to clone
     the MySQL version branch of your choice:

     To clone the 3.23 branch, use this command:

          shell> bk clone bk://mysql.bkbits.net/mysql-3.23 mysql-3.23

     To clone the 4.0 branch, use this command:

          shell> bk clone bk://mysql.bkbits.net/mysql-4.0 mysql-4.0

     To clone the 4.1 branch, use this command:

          shell> bk clone bk://mysql.bkbits.net/mysql-4.1 mysql-4.1

     In the preceding examples the source tree will be set up in the
     `mysql-3.23/', `mysql-4.0/', or `mysql-4.1/' subdirectory of your
     current directory.

     The initial download of the source tree may take a while,
     depending on the speed of your connection; be patient.

  4. You will need GNU `make', `autoconf 2.53 (or newer)', `automake
     1.5', `libtool 1.4', and `m4' to run the next set of commands.
     Note that `automake 1.7 or newer' doesn't yet work.

     If you are using trying to configure MySQL 4.1 you will also need
     `bison 1.75'.  Older versions of `bison' may report this error:
     `sql_yacc.yy:#####: fatal error: maximum table size (32767)
     exceeded'. Note: the maximum table size is not actually exceeded,
     the error is caused by bugs in these earlier `bison' versions.

     The typical command to do in a shell is:

          cd mysql-4.0
          bk -r get -Sq
          aclocal; autoheader; autoconf; automake
          (cd innobase ; aclocal; autoheader; autoconf; automake) # for InnoDB
          (cd bdb/dist ; sh s_all ) # for Berkeley DB
          ./configure  # Add your favorite options here
          make

     If you get some strange error during this stage, check that you
     really have `libtool' installed!

     A collection of our standard configure scripts is located in the
     `BUILD/' subdirectory.  If you are lazy, you can use
     `BUILD/compile-pentium-debug'. To compile on a different
     architecture, modify the script by removing flags that are
     Pentium-specific.

  5. When the build is done, run `make install'.  Be careful with this
     on a production machine; the command may overwrite your live
     release installation.  If you have another installation of MySQL,
     we recommand that you run `./configure' with different values for
     the `prefix', `with-tcp-port', and `unix-socket-path' options than
     those used for your production server.

  6. Play hard with your new installation and try to make the new
     features crash.  Start by running `make test'.  *Note MySQL test
     suite::.

  7. If you have gotten to the `make' stage and the distribution does
     not compile, please report it to <[e-mail]>.  If you
     have installed the latest versions of the required GNU tools, and
     they crash trying to process our configuration files, please
     report that also.  However, if you execute `aclocal' and get a
     `command not found' error or a similar problem, do not report it.
     Instead, make sure all the necessary tools are installed and that
     your `PATH' variable is set correctly so that your shell can find
     them.

  8. After the initial `bk clone' operation to get the source tree, you
     should run `bk pull' periodically to get the updates.

  9. You can examine the change history for the tree with all the diffs
     by using `bk sccstool'.  If you see some funny diffs or code that
     you have a question about, do not hesitate to send e-mail to
     <[e-mail]>. Also, if you think you have a better
     idea on how to do something, send an e-mail to the same address
     with a patch.  `bk diffs' will produce a patch for you after you
     have made changes to the source. If you do not have the time to
     code your idea, just send a description.

 10. `BitKeeper' has a nice help utility that you can access via `bk
     helptool'.

 11. Please note that any commits (`bk ci' or `bk citool') will trigger
     the posting of a message with the changeset to our internals
     mailing list, as well as the usual openlogging.org submission with
     just the changeset comments.  Generally, you wouldn't need to use
     commit (since the public tree will not allow `bk push'), but
     rather use the `bk diffs' method described previously.


You can also browse changesets, comments and sourcecode online by
browsing to e.g. `http://mysql.bkbits.net/mysql-4.1' For MySQL 4.1.

The manual is in a separate tree which can be cloned with:

     shell> bk clone bk://mysql.bkbits.net/mysqldoc mysqldoc

Problems Compiling?
-------------------

All MySQL programs compile cleanly for us with no warnings on Solaris
or Linux using `gcc'.  On other systems, warnings may occur due to
differences in system include files.  See *Note MIT-pthreads:: for
warnings that may occur when using MIT-pthreads.  For other problems,
check the following list.

The solution to many problems involves reconfiguring.  If you do need to
reconfigure, take note of the following:

   * If `configure' is run after it already has been run, it may use
     information that was gathered during its previous invocation.  This
     information is stored in `config.cache'.  When `configure' starts
     up, it looks for that file and reads its contents if it exists, on
     the assumption that the information is still correct.  That
     assumption is invalid when you reconfigure.

   * Each time you run `configure', you must run `make' again to
     recompile.  However, you may want to remove old object files from
     previous builds first because they were compiled using different
     configuration options.

To prevent old configuration information or object files from being
used, run these commands before rerunning `configure':

     shell> rm config.cache
     shell> make clean

Alternatively, you can run `make distclean'.

The following list describes some of the problems when compiling MySQL
that have been found to occur most often:

   * If you get errors when compiling `sql_yacc.cc', such as the ones
     shown here, you have probably run out of memory or swap space:

          Internal compiler error: program cc1plus got fatal signal 11
            or
          Out of virtual memory
            or
          Virtual memory exhausted

     The problem is that `gcc' requires huge amounts of memory to
     compile `sql_yacc.cc' with inline functions.  Try running
     `configure' with the `--with-low-memory' option:

          shell> ./configure --with-low-memory

     This option causes `-fno-inline' to be added to the compile line
     if you are using `gcc' and `-O0' if you are using something else.
     You should try the `--with-low-memory' option even if you have so
     much memory and swap space that you think you can't possibly have
     run out.  This problem has been observed to occur even on systems
     with generous hardware configurations, and the `--with-low-memory'
     option usually fixes it.

   * By default, `configure' picks `c++' as the compiler name and GNU
     `c++' links with `-lg++'.  If you are using `gcc', that behaviour
     can cause problems during configuration such as this:

          configure: error: installation or configuration problem:
          C++ compiler cannot create executables.

     You might also observe problems during compilation related to
     `g++', `libg++', or `libstdc++'.

     One cause of these problems is that you may not have `g++', or you
     may have `g++' but not `libg++', or `libstdc++'.  Take a look at
     the `config.log' file.  It should contain the exact reason why
     your c++ compiler didn't work!  To work around these problems, you
     can use `gcc' as your C++ compiler.  Try setting the environment
     variable `CXX' to `"gcc -O3"'.  For example:

          shell> CXX="gcc -O3" ./configure

     This works because `gcc' compiles C++ sources as well as `g++'
     does, but does not link in `libg++' or `libstdc++' by default.

     Another way to fix these problems, of course, is to install `g++',
     `libg++', and `libstdc++'.  We would however like to recommend you
     to not use `libg++' or `libstdc++' with MySQL as this will only
     increase the binary size of mysqld without giving you any benefits.
     Some versions of these libraries have also caused strange problems
     for MySQL users in the past.

   * If your compile fails with errors, such as any of the following,
     you must upgrade your version of `make' to GNU `make':

          making all in mit-pthreads
          make: Fatal error in reader: Makefile, line 18:
          Badly formed macro assignment
            or
          make: file `Makefile' line 18: Must be a separator (:
            or
          pthread.h: No such file or directory

     Solaris and FreeBSD are known to have troublesome `make' programs.

     GNU `make' Version 3.75 is known to work.

   * If you want to define flags to be used by your C or C++ compilers,
     do so by adding the flags to the `CFLAGS' and `CXXFLAGS'
     environment variables.  You can also specify the compiler names
     this way using `CC' and `CXX'.  For example:

          shell> CC=gcc
          shell> CFLAGS=-O3
          shell> CXX=gcc
          shell> CXXFLAGS=-O3
          shell> export CC CFLAGS CXX CXXFLAGS

     See *Note MySQL binaries::, for a list of flag definitions that
     have been found to be useful on various systems.

   * If you get an error message like this, you need to upgrade your
     `gcc' compiler:

          client/libmysql.c:273: parse error before `__attribute__'

     `gcc' 2.8.1 is known to work, but we recommend using `gcc' 2.95.2
     or `egcs' 1.0.3a instead.

   * If you get errors such as those shown here when compiling `mysqld',
     `configure' didn't correctly detect the type of the last argument
     to `accept()', `getsockname()', or `getpeername()':

          cxx: Error: mysqld.cc, line 645: In this statement, the referenced
               type of the pointer value "&length" is "unsigned long", which
               is not compatible with "int".
          new_sock = accept(sock, (struct sockaddr *)&cAddr, &length);

     To fix this, edit the `config.h' file (which is generated by
     `configure').  Look for these lines:

          /* Define as the base type of the last arg to accept */
          #define SOCKET_SIZE_TYPE XXX

     Change `XXX' to `size_t' or `int', depending on your operating
     system.  (Note that you will have to do this each time you run
     `configure' because `configure' regenerates `config.h'.)

   * The `sql_yacc.cc' file is generated from `sql_yacc.yy'.  Normally
     the build process doesn't need to create `sql_yacc.cc', because
     MySQL comes with an already generated copy.  However, if you do
     need to re-create it, you might encounter this error:

          "sql_yacc.yy", line xxx fatal: default action causes potential...

     This is a sign that your version of `yacc' is deficient.  You
     probably need to install `bison' (the GNU version of `yacc') and
     use that instead.

   * If you need to debug `mysqld' or a MySQL client, run `configure'
     with the `--with-debug' option, then recompile and link your
     clients with the new client library.  *Note Debugging client::.

MIT-pthreads Notes
------------------

This section describes some of the issues involved in using
MIT-pthreads.

Note that on Linux you should *not* use MIT-pthreads but install
LinuxThreads!  *Note Linux::.

If your system does not provide native thread support, you will need to
build MySQL using the MIT-pthreads package.  This includes older
FreeBSD systems, SunOS 4.x, Solaris 2.4 and earlier, and some others.
*Note Which OS::.

Note, that beginning with MySQL 4.0.2 MIT-pthreads are no longer part of
the source distribution! If you require this package, you need to
download it separately from
<http://www.mysql.com/Downloads/Contrib/pthreads-1_60_beta6-mysql.tar.gz>

After downloading, extract this source archive into the top level of the
MySQL source directory. It will create a new subdirectory
`mit-pthreads'.

   * On most systems, you can force MIT-pthreads to be used by running
     `configure' with the `--with-mit-threads' option:

          shell> ./configure --with-mit-threads

     Building in a non-source directory is not supported when using
     MIT-pthreads because we want to minimise our changes to this code.

   * The checks that determine whether to use MIT-pthreads occur only
     during the part of the configuration process that deals with the
     server code.  If you have configured the distribution using
     `--without-server' to build only the client code, clients will not
     know whether MIT-pthreads is being used and will use Unix socket
     connections by default.  Because Unix sockets do not work under
     MIT-pthreads on some platforms, this means you will need to use
     `-h' or `--host' when you run client programs.

   * When MySQL is compiled using MIT-pthreads, system locking is
     disabled by default for performance reasons.  You can tell the
     server to use system locking with the `--external-locking' option.
     This is only needed if you want to be able to run two MySQL
     servers against the same data files (not recommended).

   * Sometimes the pthread `bind()' command fails to bind to a socket
     without any error message (at least on Solaris).  The result is
     that all connections to the server fail.  For example:

          shell> mysqladmin version
          mysqladmin: connect to server at '' failed;
          error: 'Can't connect to mysql server on localhost (146)'

     The solution to this is to kill the `mysqld' server and restart it.
     This has only happened to us when we have forced the server down
     and done a restart immediately.

   * With MIT-pthreads, the `sleep()' system call isn't interruptible
     with `SIGINT' (break).  This is only noticeable when you run
     `mysqladmin --sleep'.  You must wait for the `sleep()' call to
     terminate before the interrupt is served and the process stops.

   * When linking, you may receive warning messages like these (at
     least on Solaris); they can be ignored:

          ld: warning: symbol `_iob' has differing sizes:
              (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
          file /usr/lib/libc.so value=0x140);
              /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken
          ld: warning: symbol `__iob' has differing sizes:
              (file /my/local/pthreads/lib/libpthread.a(findfp.o) value=0x4;
          file /usr/lib/libc.so value=0x140);
              /my/local/pthreads/lib/libpthread.a(findfp.o) definition taken

   * Some other warnings also can be ignored:

          implicit declaration of function `int strtoll(...)'
          implicit declaration of function `int strtoul(...)'

   * We haven't gotten `readline' to work with MIT-pthreads.  (This
     isn't needed, but may be interesting for someone.)

Windows Source Distribution
---------------------------

You will need the following:

   * VC++ 6.0 compiler (updated with 4 or 5 SP and Pre-processor
     package) The Pre-processor package is necessary for the macro
     assembler.  More details at:
     `http://msdn.microsoft.com/vstudio/sp/vs6sp5/faq.asp'.

   * The MySQL source distribution for Windows, which can be downloaded
     from `http://www.mysql.com/downloads/'.

Building MySQL

  1. Create a work directory (e.g., workdir).

  2. Unpack the source distribution in the aforementioned directory.

  3. Start the VC++ 6.0 compiler.

  4. In the `File' menu, select `Open Workspace'.

  5. Open the `mysql.dsw' workspace you find on the work directory.

  6. From the `Build' menu, select the `Set Active Configuration' menu.

  7. Click over the screen selecting `mysqld - Win32 Debug' and click
     OK.

  8. Press `F7' to begin the build of the debug server, libs, and some
     client applications.

  9. When the compilation finishes, copy the libs and the executables
     to a separate directory.

 10. Compile the release versions that you want, in the same way.

 11. Create the directory for the MySQL stuff: e.g., `c:\mysql'

 12. From the workdir directory copy for the c:\mysql directory the
     following directories:

        * Data

        * Docs

        * Share

 13. Create the directory `c:\mysql\bin' and copy all the servers and
     clients that you compiled previously.

 14. If you want, also create the `lib' directory and copy the libs
     that you compiled previously.

 15. Do a clean using Visual Studio.

Set up and start the server in the same way as for the binary Windows
distribution. *Note Windows prepare environment::.

Post-installation Setup and Testing
===================================

Once you've installed MySQL (from either a binary or source
distribution), you need to initialise the grant tables, start the
server, and make sure that the server works okay.  You may also wish to
arrange for the server to be started and stopped automatically when
your system starts up and shuts down.

Normally you install the grant tables and start the server like this
for installation from a source distribution:

     shell> ./scripts/mysql_install_db
     shell> cd mysql_installation_directory
     shell> ./bin/safe_mysqld --user=mysql &

For a binary distribution (not RPM or pkg packages), do this:

     shell> cd mysql_installation_directory
     shell> ./scripts/mysql_install_db
     shell> ./bin/safe_mysqld --user=mysql &
     or
     shell> ./bin/mysqld_safe --user=mysql &
     if you are running MySQL 4.x.

This creates the `mysql' database which will hold all database
privileges, the `test' database which you can use to test MySQL, and
also privilege entries for the user that run `mysql_install_db' and a
`root' user (without any passwords).  This also starts the `mysqld'
server.

`mysql_install_db' will not overwrite any old privilege tables, so it
should be safe to run in any circumstances.  If you don't want to have
the `test' database you can remove it with `mysqladmin -u root drop
test'.

Testing is most easily done from the top-level directory of the MySQL
distribution.  For a binary distribution, this is your installation
directory (typically something like `/usr/local/mysql').  For a source
distribution, this is the main directory of your MySQL source tree.

In the commands shown in this section and in the following subsections,
`BINDIR' is the path to the location in which programs like
`mysqladmin' and `safe_mysqld' are installed.  For a binary
distribution, this is the `bin' directory within the distribution.  For
a source distribution, `BINDIR' is probably `/usr/local/bin', unless
you specified an installation directory other than `/usr/local' when
you ran `configure'.  `EXECDIR' is the location in which the `mysqld'
server is installed.  For a binary distribution, this is the same as
`BINDIR'.  For a source distribution, `EXECDIR' is probably
`/usr/local/libexec'.

Testing is described in detail:

  1. If necessary, start the `mysqld' server and set up the initial
     MySQL grant tables containing the privileges that determine how
     users are allowed to connect to the server.  This is normally done
     with the `mysql_install_db' script:

          shell> scripts/mysql_install_db

     Typically, `mysql_install_db' needs to be run only the first time
     you install MySQL.  Therefore, if you are upgrading an existing
     installation, you can skip this step.  (However,
     `mysql_install_db' is quite safe to use and will not update any
     tables that already exist, so if you are unsure of what to do, you
     can always run `mysql_install_db'.)

     `mysql_install_db' creates six tables (`user', `db', `host',
     `tables_priv', `columns_priv', and `func') in the `mysql'
     database.  A description of the initial privileges is given in
     *Note Default privileges::.  Briefly, these privileges allow the
     MySQL `root' user to do anything, and allow anybody to create or
     use databases with a name of `test' or starting with `test_'.

     If you don't set up the grant tables, the following error will
     appear in the log file when you start the server:

          mysqld: Can't find file: 'host.frm'

     This may also happen with a binary MySQL distribution if you don't
     start MySQL by executing exactly `./bin/safe_mysqld'!  *Note
     `safe_mysqld': safe_mysqld.

     You might need to run `mysql_install_db' as `root'.  However, if
     you prefer, you can run the MySQL server as an unprivileged
     (non-`root') user, provided that the user can read and write files
     in the database directory.  Instructions for running MySQL as an
     unprivileged user are given in *Note Changing MySQL user: Changing
     MySQL user.

     If you have problems with `mysql_install_db', see *Note
     `mysql_install_db': mysql_install_db.

     There are some alternatives to running the `mysql_install_db'
     script as it is provided in the MySQL distribution:

        * You may want to edit `mysql_install_db' before running it, to
          change the initial privileges that are installed into the
          grant tables.  This is useful if you want to install MySQL on
          a lot of machines with the same privileges.  In this case you
          probably should need only to add a few extra `INSERT'
          statements to the `mysql.user' and `mysql.db' tables!

        * If you want to change things in the grant tables after
          installing them, you can run `mysql_install_db', then use
          `mysql -u root mysql' to connect to the grant tables as the
          MySQL `root' user and issue SQL statements to modify the
          grant tables directly.

        * It is possible to re-create the grant tables completely after
          they have already been created.  You might want to do this if
          you've already installed the tables but then want to
          re-create them after editing `mysql_install_db'.

     For more information about these alternatives, see *Note Default
     privileges::.

  2. Start the MySQL server like this:

          shell> cd mysql_installation_directory
          shell> bin/safe_mysqld &

     If you have problems starting the server, see *Note Starting
     server::.

  3. Use `mysqladmin' to verify that the server is running.  The
     following commands provide a simple test to check that the server
     is up and responding to connections:

          shell> BINDIR/mysqladmin version
          shell> BINDIR/mysqladmin variables

     The output from `mysqladmin version' varies slightly depending on
     your platform and version of MySQL, but should be similar to that
     shown here:

          shell> BINDIR/mysqladmin version
          mysqladmin  Ver 8.14 Distrib 3.23.32, for linux on i586
          Copyright (C) 2000 MySQL AB & MySQL Finland AB & TCX DataKonsult AB
          This software comes with ABSOLUTELY NO WARRANTY. This is free software,
          and you are welcome to modify and redistribute it under the GPL license.

          Server version          3.23.32-debug
          Protocol version        10
          Connection              Localhost via Unix socket
          TCP port                3306
          UNIX socket             /tmp/mysql.sock
          Uptime:                 16 sec

          Threads: 1  Questions: 9  Slow queries: 0
          Opens: 7  Flush tables: 2  Open tables: 0
          Queries per second avg: 0.000
          Memory in use: 132K  Max memory used: 16773K

     To get a feeling for what else you can do with `BINDIR/mysqladmin',
     invoke it with the `--help' option.

  4. Verify that you can shut down the server:

          shell> BINDIR/mysqladmin -u root shutdown

  5. Verify that you can restart the server.  Do this using
     `safe_mysqld' or by invoking `mysqld' directly.  For example:

          shell> BINDIR/safe_mysqld --log &

     If `safe_mysqld' fails, try running it from the MySQL installation
     directory (if you are not already there).  If that doesn't work,
     see *Note Starting server::.

  6. Run some simple tests to verify that the server is working.  The
     output should be similar to what is shown here:

          shell> BINDIR/mysqlshow
          +-----------+
          | Databases |
          +-----------+
          | mysql     |
          +-----------+

          shell> BINDIR/mysqlshow mysql
          Database: mysql
          +--------------+
          |    Tables    |
          +--------------+
          | columns_priv |
          | db           |
          | func         |
          | host         |
          | tables_priv  |
          | user         |
          +--------------+

          shell> BINDIR/mysql -e "SELECT host,db,user FROM db" mysql
          +------+--------+------+
          | host | db     | user |
          +------+--------+------+
          | %    | test   |      |
          | %    | test_% |      |
          +------+--------+------+

     There is also a benchmark suite in the `sql-bench' directory
     (under the MySQL installation directory) that you can use to
     compare how MySQL performs on different platforms.  The
     `sql-bench/Results' directory contains the results from many runs
     against different databases and platforms.  To run all tests,
     execute these commands:

          shell> cd sql-bench
          shell> run-all-tests

     If you don't have the `sql-bench' directory, you are probably
     using an RPM for a binary distribution.  (Source distribution RPMs
     include the benchmark directory.)  In this case, you must first
     install the benchmark suite before you can use it.  Beginning with
     MySQL Version 3.22, there are benchmark RPM files named
     `mysql-bench-VERSION-i386.rpm' that contain benchmark code and
     data.

     If you have a source distribution, you can also run the tests in
     the `tests' subdirectory. For example, to run
     `auto_increment.tst', do this:

          shell> BINDIR/mysql -vvf test < ./tests/auto_increment.tst

     The expected results are shown in the `./tests/auto_increment.res'
     file.

Problems Running `mysql_install_db'
-----------------------------------

The purpose of the `mysql_install_db' script is to generate new MySQL
privilege tables.  It will not affect any other data!  It will also not
do anything if you already have MySQL privilege tables installed!

If you want to re-create your privilege tables, you should take down
the `mysqld' server, if it's running, and then do something like:

     mv mysql-data-directory/mysql mysql-data-directory/mysql-old
     mysql_install_db

This section lists problems you might encounter when you run
`mysql_install_db':

*`mysql_install_db' doesn't install the grant tables*
     You may find that `mysql_install_db' fails to install the grant
     tables and terminates after displaying the following messages:

          starting mysqld daemon with databases from XXXXXX
          mysql daemon ended

     In this case, you should examine the log file very carefully!  The
     log should be located in the directory `XXXXXX' named by the error
     message, and should indicate why `mysqld' didn't start.  If you
     don't understand what happened, include the log when you post a
     bug report using `mysqlbug'!  *Note Bug reports::.

*There is already a `mysqld' daemon running*
     In this case, you probably don't have to run `mysql_install_db' at
     all.  You have to run `mysql_install_db' only once, when you
     install MySQL the first time.

*Installing a second `mysqld' daemon doesn't work when one daemon is running*
     This can happen when you already have an existing MySQL
     installation, but want to put a new installation in a different
     place (for example, for testing, or perhaps you simply want to run
     two installations at the same time).  Generally the problem that
     occurs when you try to run the second server is that it tries to
     use the same socket and port as the old one.  In this case you
     will get the error message: `Can't start server: Bind on TCP/IP
     port: Address already in use' or `Can't start server: Bind on unix
     socket...'. *Note Installing many servers::.

*You don't have write access to `/tmp'*
     If you don't have write access to create a socket file at the
     default place (in `/tmp') or permission to create temporary files
     in `/tmp,' you will get an error when running `mysql_install_db'
     or when starting or using `mysqld'.

     You can specify a different socket and temporary directory as
     follows:

          shell> TMPDIR=/some_tmp_dir/
          shell> MYSQL_UNIX_PORT=/some_tmp_dir/mysqld.sock
          shell> export TMPDIR MYSQL_UNIX_PORT

     See *Note Problems with mysql.sock::.

     `some_tmp_dir' should be the path to some directory for which you
     have write permission. *Note Environment variables::.

     After this you should be able to run `mysql_install_db' and start
     the server with these commands:

          shell> scripts/mysql_install_db
          shell> BINDIR/safe_mysqld &

*`mysqld' crashes immediately*
     If you are running RedHat Version 5.0 with a version of `glibc'
     older than 2.0.7-5, you should make sure you have installed all
     `glibc' patches!  There is a lot of information about this in the
     MySQL mail archives.  Links to the mail archives are available
     online at `http://lists.mysql.com/'.  Also, see *Note Linux::.

     You can also start `mysqld' manually using the
     `--skip-grant-tables' option and add the privilege information
     yourself using `mysql':

          shell> BINDIR/safe_mysqld --skip-grant-tables &
          shell> BINDIR/mysql -u root mysql

     From `mysql', manually execute the SQL commands in
     `mysql_install_db'.  Make sure you run `mysqladmin
     flush-privileges' or `mysqladmin reload' afterward to tell the
     server to reload the grant tables.

Problems Starting the MySQL Server
----------------------------------

If you are going to use tables that support transactions (InnoDB, BDB),
you should first create a `my.cnf' file and set startup options for the
table types you plan to use. *Note Table types::.

Generally, you start the `mysqld' server in one of these ways:

   * By invoking `mysql.server'.  This script is used primarily at
     system startup and shutdown, and is described more fully in *Note
     Automatic start::.

   * By invoking `safe_mysqld', which tries to determine the proper
     options for `mysqld' and then runs it with those options. *Note
     `safe_mysqld': safe_mysqld.

   * For Windows NT/2000/XP, please see *Note NT start::.

   * By invoking `mysqld' directly.

When the `mysqld' daemon starts up, it changes the directory to the
data directory.  This is where it expects to write log files and the pid
(process ID) file, and where it expects to find databases.

The data directory location is hardwired in when the distribution is
compiled.  However, if `mysqld' expects to find the data directory
somewhere other than where it really is on your system, it will not work
properly.  If you have problems with incorrect paths, you can find out
what options `mysqld' allows and what the default path settings are by
invoking `mysqld' with the `--help' option.  You can override the
defaults by specifying the correct pathnames as command-line arguments
to `mysqld'.  (These options can be used with `safe_mysqld' as well.)

Normally you should need to tell `mysqld' only the base directory under
which MySQL is installed.  You can do this with the `--basedir' option.
You can also use `--help' to check the effect of changing path options
(note that `--help' *must* be the final option of the `mysqld'
command).  For example:

     shell> EXECDIR/mysqld --basedir=/usr/local --help

Once you determine the path settings you want, start the server without
the `--help' option.

Whichever method you use to start the server, if it fails to start up
correctly, check the log file to see if you can find out why.  Log files
are located in the data directory (typically `/usr/local/mysql/data'
for a binary distribution, `/usr/local/var' for a source distribution,
and `\mysql\data\mysql.err' on Windows).  Look in the data directory for
files with names of the form `host_name.err' and `host_name.log' where
`host_name' is the name of your server host.  Then check the last few
lines of these files:

     shell> tail host_name.err
     shell> tail host_name.log

Look for something like the following in the log file:
     000729 14:50:10  bdb:  Recovery function for LSN 1 27595 failed
     000729 14:50:10  bdb:  warning: ./test/t1.db: No such file or directory
     000729 14:50:10  Can't init databases

This means that you didn't start `mysqld' with `--bdb-no-recover' and
Berkeley DB found something wrong with its log files when it tried to
recover your databases.  To be able to continue, you should move away
the old Berkeley DB log file from the database directory to some other
place, where you can later examine it.  The log files are named
`log.0000000001', where the number will increase over time.

If you are running `mysqld' with BDB table support and `mysqld' core
dumps at start this could be because of some problems with the BDB
recover log.  In this case you can try starting `mysqld' with
`--bdb-no-recover'.  If this helps, then you should remove all `log.*'
files from the data directory and try starting `mysqld' again.

If you get the following error, it means that some other program (or
another `mysqld' server) is already using the TCP/IP port or socket
`mysqld' is trying to use:

     Can't start server: Bind on TCP/IP port: Address already in use
       or
     Can't start server : Bind on unix socket...

Use `ps' to make sure that you don't have another `mysqld' server
running.  If you can't find another server running, you can try to
execute the command `telnet your-host-name tcp-ip-port-number' and press
Enter a couple of times.  If you don't get an error message like
`telnet: Unable to connect to remote host: Connection refused',
something is using the TCP/IP port `mysqld' is trying to use.  See
*Note mysql_install_db:: and *Note Multiple servers::.

If `mysqld' is currently running, you can find out what path settings
it is using by executing this command:

     shell> mysqladmin variables

or

     shell> mysqladmin -h 'your-host-name' variables

If you get `Errcode 13', which means `Permission denied', when starting
`mysqld' this means that you didn't have the right to read/create files
in the MySQL database or log directory. In this case you should either
start `mysqld' as the root user or change the permissions for the
involved files and directories so that you have the right to use them.

If `safe_mysqld' starts the server but you can't connect to it, you
should make sure you have an entry in `/etc/hosts' that looks like this:

     127.0.0.1       localhost

This problem occurs only on systems that don't have a working thread
library and for which MySQL must be configured to use MIT-pthreads.

If you can't get `mysqld' to start you can try to make a trace file to
find the problem. *Note Making trace files::.

If you are using InnoDB tables, refer to the InnoDB-specific startup
options.  *Note InnoDB start::.

If you are using BDB (Berkeley DB) tables, you should familiarise
yourself with the different BDB-specific startup options.  *Note BDB
start::.

Starting and Stopping MySQL Automatically
-----------------------------------------

The `mysql.server' and `safe_mysqld' scripts can be used to start the
server automatically at system startup time. `mysql.server' can also be
used to stop the server.

The `mysql.server' script can be used to start or stop the server by
invoking it with `start' or `stop' arguments:

     shell> mysql.server start
     shell> mysql.server stop

`mysql.server' can be found in the `share/mysql' directory under the
MySQL installation directory or in the `support-files' directory of the
MySQL source tree.

Before `mysql.server' starts the server, it changes the directory to
the MySQL installation directory, then invokes `safe_mysqld'.  You
might need to edit `mysql.server' if you have a binary distribution
that you've installed in a non-standard location.  Modify it to `cd'
into the proper directory before it runs `safe_mysqld'. If you want the
server to run as some specific user, add an appropriate `user' line to
the `/etc/my.cnf' file, as shown later in this section.

`mysql.server stop' brings down the server by sending a signal to it.
You can also take down the server manually by executing `mysqladmin
shutdown'.

You need to add these start and stop commands to the appropriate places
in your `/etc/rc*' files when you want to start up MySQL automatically
on your server.

On most current Linux distributions, it is sufficient to copy the file
`mysql.server' into the `/etc/init.d' directory (or `/etc/rc.d/init.d'
on older Red Hat systems). Afterwards, run the following command to
enable the startup of MySQL on system bootup:

     shell> chkconfig --add mysql.server

As an alternative to the above, some operating systems also use
`/etc/rc.local' or `/etc/init.d/boot.local' to start additional
services on bootup. To start up MySQL using this method, you could
append something like the following to it:

     /bin/sh -c 'cd /usr/local/mysql ; ./bin/safe_mysqld --user=mysql &'

You can also add options for `mysql.server' in a global `/etc/my.cnf'
file.  A typical `/etc/my.cnf' file might look like this:

     [mysqld]
     datadir=/usr/local/mysql/var
     socket=/var/tmp/mysql.sock
     port=3306
     user=mysql

     [mysql_server]
     basedir=/usr/local/mysql

The `mysql.server' script understands the following options: `datadir',
`basedir', and `pid-file'.

The following table shows which option groups each of the startup
scripts read from option files:

*Script*    *Option groups*
`mysqld'    `mysqld' and `server'
`mysql.server'`mysql.server',
            `mysqld', and `server'
`safe_mysqld'`mysql.server',
            `mysqld', and `server'

*Note Option files::.

Upgrading/Downgrading MySQL
===========================

You can always move the MySQL form and datafiles between different
versions on the same architecture as long as you have the same base
version of MySQL. The current base version is 3. If you change the
character set when running MySQL (which may also change the sort
order), you must run `myisamchk -r -q --set-character-set=charset' on
all tables.  Otherwise, your indexes may not be ordered correctly.

If you are afraid of new versions, you can always rename your old
`mysqld' to something like `mysqld-old-version-number'.  If your new
`mysqld' then does something unexpected, you can simply shut it down
and restart with your old `mysqld'!

When you do an upgrade you should also back up your old databases, of
course.

If after an upgrade, you experience problems with recompiled client
programs, like `Commands out of sync' or unexpected core dumps, you
probably have used an old header or library file when compiling your
programs.  In this case you should check the date for your `mysql.h'
file and `libmysqlclient.a' library to verify that they are from the new
MySQL distribution.  If not, please recompile your programs!

If you get some problems that the new `mysqld' server doesn't want to
start or that you can't connect without a password, check that you don't
have some old `my.cnf' file from your old installation!  You can check
this with: `program-name --print-defaults'.  If this outputs anything
other than the program name, you have an active `my.cnf' file that will
affect things!

It is a good idea to rebuild and reinstall the `Msql-Mysql-modules'
distribution whenever you install a new release of MySQL, particularly
if you notice symptoms such as all your `DBI' scripts dumping core
after you upgrade MySQL.

Upgrading From Version 4.0 to Version 4.1
-----------------------------------------

In general what you have to do when upgrading to 4.1 from an earlier
MySQL version:

   * Run the `mysql_fix_privilege_tables' to get the new password field
     that is needed for secure handling of passwords.

The following is a more complete lists tell what you have to watch out
for when upgrading to version 4.1;

   * Functions that return a DATE, DATETIME or TIME result is now fixed
     up when returned to the client.

          mysql> SELECT cast("2001-1-1" as DATE)
              -> '2001-01-01'

   * All column and tables now have a character set, which shows up in
     `SHOW CREATE TABLE' and `mysqldump'.  (MySQL 4.0.6 and above can
     read the new dump files, but not previous MySQL versions).

   * Timestamp is now returned as string of type `'YYYY-MM-DD
     HH:MM:DD''.  If you want to have this as a number you should add
     +0 to the timestamp column.  Different timestamp lengths are not
     supported.

Upgrading From Version 3.23 to Version 4.0
------------------------------------------

In general what you have to do when upgrading to 4.0 from an earlier
MySQL version:

   * Run the `mysql_fix_privilege_tables' to add new privileges and
     features to the MySQL privilege tables.

   * Edit any MySQL startup scripts or configure files to not use any
     of the deprecated options listed below.

   * Convert your old ISAM files to MyISAM files with the command:
     `mysql_convert_table_format database'.  Note that this should only
     be run if all tables in the given database is ISAM or MyISAM
     tables. If this is not the case you should run `ALTER TABLE
     table_name TYPE=MyISAM' on all ISAM tables.

   * Ensure that you don't have any MySQL clients that uses shared
     libraries (like the perl Msql-Mysql-modules). If you have, you
     should recompile them as structures used in `libmysqlclient.so'
     have changed.

MySQL 4.0 will work even if you don't do the above, but you will not be
able to use the new security privileges that MySQL 4.0 and you may run
into problems when upgrading later to MySQL 4.1 or newer.  The ISAM file
format still works in MySQL 4.0 but it's deprecated and will be disabled
in MySQL 5.0.

Old clients should work with a Version 4.0 server without any problems.

Even if you do the above, you can still downgrade to MySQL 3.23.52 or
newer if you run into problems with the MySQL 4.0 series.  In this case
you have to do a `mysqldump' of any tables using a full-text index and
restore these in 3.23 (because 4.0 uses a new format for full-text
index).

The following is a more complete lists tell what you have to watch out
for when upgrading to version 4.0;

   * MySQL 4.0 has a lot of new privileges in the `mysql.user' table.
     *Note GRANT::.

     To get these new privileges to work, one must run the
     `mysql_fix_privilege_tables' script.  Until this script is run all
     users have the `SHOW DATABASES', `CREATE TEMPORARY TABLES', and
     `LOCK TABLES' privileges. `SUPER' and `EXECUTE' privileges take
     their value from `PROCESS'.  `REPLICATION SLAVE' and `REPLICATION
     CLIENT' take their values from `FILE'.

     If you have any scripts that creates new users, you may want to
     change them to use the new privileges.  If you are not using
     `GRANT' commands in the scripts, this is a good time to change
     your scripts.

     In version 4.0.2 the option `--safe-show-database' is deprecated
     (and no longer does anything). *Note Privileges options::.

     If you get access denied errors for new users in version 4.0.2, you
     should check if you need some of the new grants that you didn't
     need before.  In particular, you will need `REPLICATION SLAVE'
     (instead of `FILE') for new slaves.

   * The startup parameters `myisam_max_extra_sort_file_size' and
     `myisam_max_extra_sort_file_size' are now given in bytes (was
     megabytes before 4.0.3).  External system locking of MyISAM/ISAM
     files is now turned off by default.  One can turn this on by doing
     `--external-locking'. (For most users this is never needed).

   * The following startup variables/options have been renamed:
     *From*                             *to*.
     `myisam_bulk_insert_tree_size'     `bulk_insert_buffer_size'
     `query_cache_startup_type'         `query_cache_type'
     `record_buffer'                    `read_buffer_size'
     `record_rnd_buffer'                `read_rnd_buffer_size'
     `sort_buffer'                      `sort_buffer_size'
     `warnings'                         `log-warnings'

     The startup options `record_buffer', `sort_buffer' and `warnings'
     will still work in MySQL 4.0 but are deprecated.

   * The following SQL variables have changed name.
     *From*                             *To*.
     `SQL_BIG_TABLES'                   `BIG_TABLES'
     `SQL_LOW_PRIORITY_UPDATES'         `LOW_PRIORITY_UPDATES'
     `SQL_MAX_JOIN_SIZE'                `MAX_JOIN_SIZE'
     `SQL_QUERY_CACHE_TYPE'             `QUERY_CACHE_TYPE'
     The old names still work in MySQL 4.0 but are deprecated.

   * You have to use `SET GLOBAL SQL_SLAVE_SKIP_COUNTER=#' instead of
     `SET SQL_SLAVE_SKIP_COUNTER=#'.

   * Renamed mysqld startup options `--skip-locking' to
     `--skip-external-locking' and `--enable-locking' to
     `--external-locking'.

   * `SHOW MASTER STATUS' now returns an empty set if binary log is not
     enabled.

   * `SHOW SLAVE STATUS' now returns an empty set if slave is not
     initialised.

   * mysqld now has the option `--temp-pool' enabled by default as this
     gives better performance with some OS (Most notable Linux).

   * `DOUBLE' and `FLOAT' columns now honour the `UNSIGNED' flag on
     storage (before, `UNSIGNED' was ignored for these columns).

   * `ORDER BY column DESC' now always sorts `NULL' values first; in
     3.23 this was not always consistent.

   * `SHOW INDEX' has 2 columns more (`Null' and `Index_type') than it
     had in 3.23.

   * `CHECK', `SIGNED', `LOCALTIME' and `LOCALTIMESTAMP' are now
     reserved words.

   * The result of all bitwise operators `|', `&', `<<', `>>', and `~'
     is now unsigned.  This may cause problems if you are using them in
     a context where you want a signed result.  *Note Cast Functions::.

   * *Note*: when you use subtraction between integer values where one
     is of type `UNSIGNED', the result will be unsigned!  In other
     words, before upgrading to MySQL 4.0, you should check your
     application for cases where you are subtracting a value from an
     unsigned entity and want a negative answer or subtracting an
     unsigned value from an integer column. You can disable this
     behaviour by using the `--sql-mode=NO_UNSIGNED_SUBTRACTION' option
     when starting `mysqld'.  *Note Cast Functions::.

   * To use `MATCH ... AGAINST (... IN BOOLEAN MODE)' with your tables,
     you need to rebuild them with `REPAIR TABLE table_name USE_FRM'.

   * `LOCATE()' and `INSTR()' are case-sensitive if one of the
     arguments is a binary string. Otherwise they are case-insensitive.

   * `STRCMP()' now uses the current character set when doing
     comparisons, which means that the default comparison behaviour now
     is case-insensitive.

   * `HEX(string)' now returns the characters in string converted to
     hexadecimal.  If you want to convert a number to hexadecimal, you
     should ensure that you call `HEX()' with a numeric argument.

   * In 3.23, `INSERT INTO ... SELECT' always had `IGNORE' enabled.  In
     4.0.1, MySQL will stop (and possibly roll back) in case of an
     error if you don't specify `IGNORE'.

   * `safe_mysqld' is renamed to `mysqld_safe'.  For some time we will
     in our binary distributions include `safe_mysqld' as a symlink to
     `mysqld_safe'.

   * The old C API functions `mysql_drop_db', `mysql_create_db', and
     `mysql_connect' are not supported anymore, unless you compile
     MySQL with `CFLAGS=-DUSE_OLD_FUNCTIONS'.  Instead of doing this,
     it is preferable to change the client to use the new 4.0 API.

   * In the `MYSQL_FIELD' structure, `length' and `max_length' have
     changed from `unsigned int' to `unsigned long'. This should not
     cause any problems, except that they may generate warning messages
     when used as arguments in the `printf()' class of functions.

   * You should use `TRUNCATE TABLE' when you want to delete all rows
     from a table and you don't care how many rows were deleted.
     (Because `TRUNCATE TABLE' is faster than `DELETE FROM table_name').

   * You will get an error if you have an active `LOCK TABLES' or
     transaction when trying to execute `TRUNCATE TABLE' or `DROP
     DATABASE'.

   * You should use integers to store values in BIGINT columns (instead
     of using strings, as you did in MySQL 3.23).  Using strings will
     still work, but using integers is more efficient.

   * Format of `SHOW OPEN TABLE' has changed.

   * Multi-threaded clients should use `mysql_thread_init()' and
     `mysql_thread_end()'. *Note Threaded clients::.

   * If you want to recompile the Perl DBD::mysql module, you must get
     Msql-Mysql-modules version 1.2218 or newer because the older DBD
     modules used the deprecated `drop_db()' call.

   * `RAND(seed)' returns a different random number series in 4.0 than
     in 3.23; this was done to further differentiate `RAND(seed)' and
     `RAND(seed+1)'.

   * The default type returned by `IFNULL(A,B)' is now set to be the
     more 'general' of the types of `A' and `B'. (The order is
     `STRING', `REAL' or `INTEGER').

Upgrading From Version 3.22 to Version 3.23
-------------------------------------------

MySQL Version 3.23 supports tables of the new `MyISAM' type and the old
`ISAM' type.  You don't have to convert your old tables to use these
with Version 3.23.  By default, all new tables will be created with
type `MyISAM' (unless you start `mysqld' with the
`--default-table-type=isam' option). You can change an `ISAM' table to
a `MyISAM' table with `ALTER TABLE table_name TYPE=MyISAM' or the Perl
script `mysql_convert_table_format'.

Version 3.22 and 3.21 clients will work without any problems with a
Version 3.23 server.

The following list tells what you have to watch out for when upgrading
to Version 3.23:

   * All tables that use the `tis620' character set must be fixed with
     `myisamchk -r' or `REPAIR TABLE'.

   * If you do a `DROP DATABASE' on a symbolic linked database, both the
     link and the original database are deleted.  (This didn't happen
     in 3.22 because configure didn't detect the `readlink' system
     call.)

   * `OPTIMIZE TABLE' now works only for `MyISAM' tables.  For other
     table types, you can use `ALTER TABLE' to optimise the table.
     During `OPTIMIZE TABLE' the table is now locked from other threads.

   * The MySQL client `mysql' is now by default started with the option
     `--no-named-commands (-g)'. This option can be disabled with
     `--enable-named-commands (-G)'. This may cause incompatibility
     problems in some casesfor example, in SQL scripts that use named
     commands without a semicolon!  Long format commands still work
     from the first line.

   * Date functions that work on parts of dates (like `MONTH()') will
     now return 0 for `0000-00-00' dates. (MySQL 3.22 returned `NULL'.)

   * If you are using the `german' character sort order, you must repair
     all your tables with `isamchk -r', as we have made some changes in
     the sort order!

   * The default return type of `IF' will now depend on both arguments
     and not only the first argument.

   * `AUTO_INCREMENT' will not work with negative numbers. The reason
     for this is that negative numbers caused problems when wrapping
     from -1 to 0.  `AUTO_INCREMENT' for MyISAM tables is now handled
     at a lower level and is much faster than before. For MyISAM tables
     old numbers are also not reused anymore, even if you delete some
     rows from the table.

   * `CASE', `DELAYED', `ELSE', `END', `FULLTEXT', `INNER', `RIGHT',
     `THEN', and `WHEN' are now reserved words.

   * `FLOAT(X)' is now a true floating-point type and not a value with a
     fixed number of decimals.

   * When declaring `DECIMAL(length,dec)' the length argument no longer
     includes a place for the sign or the decimal point.

   * A `TIME' string must now be of one of the following formats:
     `[[[DAYS] [H]H:]MM:]SS[.fraction]' or
     `[[[[[H]H]H]H]MM]SS[.fraction]'.

   * `LIKE' now compares strings using the same character comparison
     rules as `='.  If you require the old behaviour, you can compile
     MySQL with the `CXXFLAGS=-DLIKE_CMP_TOUPPER' flag.

   * `REGEXP' is now case-insensitive for normal (not binary) strings.

   * When you check/repair tables you should use `CHECK TABLE' or
     `myisamchk' for `MyISAM' tables (`.MYI') and `isamchk' for ISAM
     (`.ISM') tables.

   * If you want your `mysqldump' files to be compatible between MySQL
     Version 3.22 and Version 3.23, you should not use the `--opt' or
     `--all' option to `mysqldump'.

   * Check all your calls to `DATE_FORMAT()' to make sure there is a
     `%' before each format character.  (MySQL Version 3.22 and later
     already allowed this syntax.)

   * `mysql_fetch_fields_direct' is now a function (it was a macro) and
     it returns a pointer to a `MYSQL_FIELD' instead of a `MYSQL_FIELD'.

   * `mysql_num_fields()' can no longer be used on a `MYSQL*' object
     (it's now a function that takes `MYSQL_RES*' as an argument, so
     you should use `mysql_field_count()' instead).

   * In MySQL Version 3.22, the output of `SELECT DISTINCT ...' was
     almost always sorted.  In Version 3.23, you must use `GROUP BY' or
     `ORDER BY' to obtain sorted output.

   * `SUM()' now returns `NULL', instead of 0, if there are no matching
     rows. This is according to ANSI SQL.

   * An `AND' or `OR' with `NULL' values will now return `NULL' instead
     of 0. This mostly affects queries that use `NOT' on an `AND/OR'
     expression as `NOT NULL' = `NULL'.  `LPAD()' and `RPAD()' will
     shorten the result string if it's longer than the length argument.

Upgrading from Version 3.21 to Version 3.22
-------------------------------------------

Nothing that affects compatibility has changed between versions 3.21
and 3.22.  The only pitfall is that new tables that are created with
`DATE' type columns will use the new way to store the date. You can't
access these new fields from an old version of `mysqld'.

After installing MySQL Version 3.22, you should start the new server
and then run the `mysql_fix_privilege_tables' script. This will add the
new privileges that you need to use the `GRANT' command.  If you forget
this, you will get `Access denied' when you try to use `ALTER TABLE',
`CREATE INDEX', or `DROP INDEX'. If your MySQL root user requires a
password, you should give this as an argument to
`mysql_fix_privilege_tables'.

The C API interface to `mysql_real_connect()' has changed.  If you have
an old client program that calls this function, you must place a `0' for
the new `db' argument (or recode the client to send the `db' element
for faster connections).  You must also call `mysql_init()' before
calling `mysql_real_connect()'!  This change was done to allow the new
`mysql_options()' function to save options in the `MYSQL' handler
structure.

The `mysqld' variable `key_buffer' has changed names to
`key_buffer_size', but you can still use the old name in your startup
files.

Upgrading from Version 3.20 to Version 3.21
-------------------------------------------

If you are running a version older than Version 3.20.28 and want to
switch to Version 3.21, you need to do the following:

You can start the `mysqld' Version 3.21 server with `safe_mysqld
--old-protocol' to use it with clients from a Version 3.20 distribution.
In this case, the new client function `mysql_errno()' will not return
any server error, only `CR_UNKNOWN_ERROR' (but it works for client
errors), and the server uses the old `password()' checking rather than
the new one.

If you are *not* using the `--old-protocol' option to `mysqld', you
will need to make the following changes:

   * All client code must be recompiled. If you are using ODBC, you
     must get the new `MyODBC' 2.x driver.

   * The script `scripts/add_long_password' must be run to convert the
     `Password' field in the `mysql.user' table to `CHAR(16)'.

   * All passwords must be reassigned in the `mysql.user' table (to get
     62-bit rather than 31-bit passwords).

   * The table format hasn't changed, so you don't have to convert any
     tables.

MySQL Version 3.20.28 and above can handle the new `user' table format
without affecting clients. If you have a MySQL version earlier than
Version 3.20.28, passwords will no longer work with it if you convert
the `user' table. So to be safe, you should first upgrade to at least
Version 3.20.28 and then upgrade to Version 3.21.

The new client code works with a 3.20.x `mysqld' server, so if you
experience problems with 3.21.x, you can use the old 3.20.x server
without having to recompile the clients again.

If you are not using the `--old-protocol' option to `mysqld', old
clients will issue the error message:

     ERROR: Protocol mismatch. Server Version = 10 Client Version = 9

The new Perl `DBI'/`DBD' interface also supports the old `mysqlperl'
interface.  The only change you have to make if you use `mysqlperl' is
to change the arguments to the `connect()' function.  The new arguments
are: `host', `database', `user', and `password' (the `user' and
`password' arguments have changed places).  *Note Perl `DBI' Class:
Perl DBI Class.

The following changes may affect queries in old applications:

   * `HAVING' must now be specified before any `ORDER BY' clause.

   * The parameters to `LOCATE()' have been swapped.

   * There are some new reserved words. The most notable are `DATE',
     `TIME', and `TIMESTAMP'.

Upgrading to Another Architecture
---------------------------------

If you are using MySQL Version 3.23, you can copy the `.frm', `.MYI',
and `.MYD' files between different architectures that support the same
floating-point format.  (MySQL takes care of any byte-swapping issues.)

The MySQL `ISAM' data and index files (`.ISD' and `*.ISM',
respectively) are architecture-dependent and in some cases
OS-dependent.  If you want to move your applications to another machine
that has a different architecture or OS than your current machine, you
should not try to move a database by simply copying the files to the
other machine. Use `mysqldump' instead.

By default, `mysqldump' will create a file full of SQL statements.  You
can then transfer the file to the other machine and feed it as input to
the `mysql' client.

Try `mysqldump --help' to see what options are available.  If you are
moving the data to a newer version of MySQL, you should use `mysqldump
--opt' with the newer version to get a fast, compact dump.

The easiest (although not the fastest) way to move a database between
two machines is to run the following commands on the machine on which
the database is located:

     shell> mysqladmin -h 'other hostname' create db_name
     shell> mysqldump --opt db_name \
             | mysql -h 'other hostname' db_name

If you want to copy a database from a remote machine over a slow
network, you can use:

     shell> mysqladmin create db_name
     shell> mysqldump -h 'other hostname' --opt --compress db_name \
             | mysql db_name

You can also store the result in a file, then transfer the file to the
target machine and load the file into the database there.  For example,
you can dump a database to a file on the source machine like this:

     shell> mysqldump --quick db_name | gzip > db_name.contents.gz

(The file created in this example is compressed.) Transfer the file
containing the database contents to the target machine and run these
commands there:

     shell> mysqladmin create db_name
     shell> gunzip < db_name.contents.gz | mysql db_name

You can also use `mysqldump' and `mysqlimport' to accomplish the
database transfer.  For big tables, this is much faster than simply
using `mysqldump'.  In the following commands, `DUMPDIR' represents the
full pathname of the directory you use to store the output from
`mysqldump'.

First, create the directory for the output files and dump the database:

     shell> mkdir DUMPDIR
     shell> mysqldump --tab=DUMPDIR db_name

Then transfer the files in the `DUMPDIR' directory to some corresponding
directory on the target machine and load the files into MySQL there:

     shell> mysqladmin create db_name           # create database
     shell> cat DUMPDIR/*.sql | mysql db_name   # create tables in database
     shell> mysqlimport db_name DUMPDIR/*.txt   # load data into tables

Also, don't forget to copy the `mysql' database because that's where the
grant tables (`user', `db', `host') are stored.  You may have to run
commands as the MySQL `root' user on the new machine until you have the
`mysql' database in place.

After you import the `mysql' database on the new machine, execute
`mysqladmin flush-privileges' so that the server reloads the grant table
information.

Operating System Specific Notes
===============================

Linux Notes (All Linux Versions)
--------------------------------

The following notes regarding `glibc' apply only to the situation when
you build MySQL yourself. If you are running Linux on an x86 machine,
in most cases it is much better for you to just use our binary. We link
our binaries against the best patched version of `glibc' we can come up
with and with the best compiler options, in an attempt to make it
suitable for a high-load server. So if you read the following text, and
are in doubt about what you should do, try our binary first to see if
it meets your needs, and worry about your own build only after you have
discovered that our binary is not good enough. In that case, we would
appreciate a note about it, so we can build a better binary next time.
For a typical user, even for setups with a lot of concurrent
connections and/or tables exceeding the 2G limit, our binary in most
cases is the best choice.

MySQL uses LinuxThreads on Linux.  If you are using an old Linux
version that doesn't have `glibc2', you must install LinuxThreads
before trying to compile MySQL.   You can get LinuxThreads at
`http://www.mysql.com/downloads/os-linux.html'.

*Note*: we have seen some strange problems with Linux 2.2.14 and MySQL
on SMP systems. If you have a SMP system, we recommend you upgrade to
Linux 2.4 as soon as possible!  Your system will be faster and more
stable by doing this!

Note that `glibc' versions before and including Version 2.1.1 have a
fatal bug in `pthread_mutex_timedwait' handling, which is used when you
do `INSERT DELAYED'.  We recommend that you not use `INSERT DELAYED'
before upgrading glibc.

If you plan to have 1000+ concurrent connections, you will need to make
some changes to LinuxThreads, recompile it, and relink MySQL against
the new `libpthread.a'.  Increase `PTHREAD_THREADS_MAX' in
`sysdeps/unix/sysv/linux/bits/local_lim.h' to 4096 and decrease
`STACK_SIZE' in `linuxthreads/internals.h' to 256 KB. The paths are
relative to the root of `glibc' Note that MySQL will not be stable with
around 600-1000 connections if `STACK_SIZE' is the default of 2 MB.

If MySQL can't open enough files, or connections, it may be that you
haven't configured Linux to handle enough files.

In Linux 2.2 and onward, you can check the number of allocated file
handles by doing:

     cat /proc/sys/fs/file-max
     cat /proc/sys/fs/dquot-max
     cat /proc/sys/fs/super-max

If you have more than 16 MB of memory, you should add something like the
following to your init scripts (e.g. `/etc/init.d/boot.local' on SuSE
Linux):

     echo 65536 > /proc/sys/fs/file-max
     echo 8192 > /proc/sys/fs/dquot-max
     echo 1024 > /proc/sys/fs/super-max

You can also run the preceding commands from the command-line as root,
but these settings will be lost the next time your computer reboots.

Alternatively, you can set these parameters on bootup by using the
`sysctl' tool, which is used by many Linux distributions (SuSE has
added it as well, beginning with SuSE Linux 8.0). Just put the following
values into a file named `/etc/sysctl.conf':

     # Increase some values for MySQL
     fs.file-max = 65536
     fs.dquot-max = 8192
     fs.super-max = 1024

You should also add the following to `/etc/my.cnf':

     [safe_mysqld]
     open-files-limit=8192

This should allow MySQL to create up to 8192 connections + files.

The `STACK_SIZE' constant in LinuxThreads controls the spacing of thread
stacks in the address space.  It needs to be large enough so that there
will be plenty of room for the stack of each individual thread, but
small enough to keep the stack of some threads from running into the
global `mysqld' data.  Unfortunately, the Linux implementation of
`mmap()', as we have experimentally discovered, will successfully unmap
an already mapped region if you ask it to map out an address already in
use, zeroing out the data on the entire page, instead of returning an
error.  So, the safety of `mysqld' or any other threaded application
depends on the "gentleman" behaviour of the code that creates threads.
The user must take measures to make sure the number of running threads
at any time is sufficiently low for thread stacks to stay away from the
global heap.  With `mysqld', you should enforce this "gentleman"
behaviour by setting a reasonable value for the `max_connections'
variable.

If you build MySQL yourself and do not want to mess with patching
LinuxThreads, you should set `max_connections' to a value no higher
than 500.  It should be even less if you have a large key buffer,  large
heap tables, or some other things that make `mysqld' allocate a lot of
memory, or if you are running a 2.2 kernel with a 2G patch. If you are
using our binary or RPM version 3.23.25 or later, you can safely set
`max_connections' at 1500, assuming no large key buffer or heap tables
with lots of data.  The more you reduce `STACK_SIZE' in LinuxThreads
the more threads you can safely create.  We recommend the values between
128K and 256K.

If you use a lot of concurrent connections, you may suffer from a
"feature" in the 2.2 kernel that penalises a process for forking or
cloning a child in an attempt to prevent a fork bomb attack.  This will
cause MySQL not to scale well as you increase the number of concurrent
clients.  On single-CPU systems, we have seen this manifested in a very
slow thread creation, which means it may take a long time to connect to
MySQL (as long as 1 minute), and it may take just as long to shut it
down.  On multiple-CPU systems, we have observed a gradual drop in
query speed as the number of clients increases.  In the process of
trying to find a solution, we have received a kernel patch from one of
our users, who claimed it made a lot of difference for his site.  The
patch is available at
`http://www.mysql.com/Downloads/Patches/linux-fork.patch'. We have now
done rather extensive testing of this patch on both development and
production systems.  It has significantly improved `MySQL' performance
without causing any problems and we now recommend it to our users who
are still running high-load servers on 2.2 kernels.  This issue has
been fixed in the 2.4 kernel, so if you are not satisfied with the
current performance of your system, rather than patching your 2.2
kernel, it might be easier to just upgrade to 2.4, which will also give
you a nice SMP boost in addition to fixing this fairness bug.

We have tested MySQL on the 2.4 kernel on a 2-CPU machine and found
MySQL scales *much* betterthere was virtually no slowdown on queries
throughput all the way up to 1000 clients, and the MySQL scaling factor
(computed as the ratio of maximum throughput to the throughput with one
client) was 180%.  We have observed similar results on a 4-CPU
systemvirtually no slowdown as the number of clients was increased up
to 1000, and 300% scaling factor. So for a high-load SMP server we
would definitely recommend the 2.4 kernel at this point. We have
discovered that it is essential to run `mysqld' process with the
highest possible priority on the 2.4 kernel to achieve maximum
performance.  This can be done by adding `renice -20 $$' command to
`safe_mysqld'. In our testing on a 4-CPU machine, increasing the
priority gave 60% increase in throughput with 400 clients.

We are currently also trying to collect more info on how well `MySQL'
performs on 2.4 kernel on 4-way and 8-way systems. If you have access
such a system and have done some benchmarks, please send a mail to
<[e-mail]> with the results - we will include them in the manual.

There is another issue that greatly hurts MySQL performance, especially
on SMP systems.  The implementation of mutex in LinuxThreads in
`glibc-2.1' is very bad for programs with many threads that only hold
the mutex for a short time. On an SMP system, ironic as it is, if you
link MySQL against unmodified `LinuxThreads', removing processors from
the machine improves MySQL performance in many cases.  We have made a
patch available for `glibc 2.1.3' to correct this behaviour
(`http://www.mysql.com/Downloads/Linux/linuxthreads-2.1-patch').

With `glibc-2.2.2' MySQL version 3.23.36 will use the adaptive mutex,
which is much better than even the patched one in `glibc-2.1.3'. Be
warned, however, that under some conditions, the current mutex code in
`glibc-2.2.2' overspins, which hurts MySQL performance. The chance of
this condition can be reduced by renicing `mysqld' process to the
highest priority. We have also been able to correct the overspin
behaviour with a patch, available at
`http://www.mysql.com/Downloads/Linux/linuxthreads-2.2.2.patch'.  It
combines the correction of overspin, maximum number of threads, and
stack spacing all in one. You will need to apply it in the
`linuxthreads' directory with `patch -p0
</tmp/linuxthreads-2.2.2.patch'.  We hope it will be included in some
form in to the future releases of `glibc-2.2'. In any case, if you link
against `glibc-2.2.2' you still need to correct `STACK_SIZE' and
`PTHREAD_THREADS_MAX'. We hope that the defaults will be corrected to
some more acceptable values for high-load MySQL setup in the future, so
that your own build can be reduced to `./configure; make; make install'.

We recommend that you use the above patches to build a special static
version of `libpthread.a' and use it only for statically linking
against `MySQL'. We know that the patches are safe for `MySQL' and
significantly improve its performance, but we cannot say anything about
other applications. If you link other applications against the patched
version of the library, or build a patched shared version and install
it on your system, you are doing it at your own risk with regard to
other applications that depend on `LinuxThreads'.

If you experience any strange problems during the installation of
MySQL, or with some common utilties hanging, it is very likely that
they are either library or compiler related. If this is the case, using
our binary will resolve them.

One known problem with the binary distribution is that with older Linux
systems that use `libc' (like RedHat 4.x or Slackware), you will get
some non-fatal problems with hostname resolution.  *Note Binary
notes-Linux::.

When using LinuxThreads you will see a minimum of three processes
running.  These are in fact threads.  There will be one thread for the
LinuxThreads manager, one thread to handle connections, and one thread
to handle alarms and signals.

Note that the Linux kernel and the LinuxThread library can by default
only have 1024 threads.  This means that you can only have up to 1021
connections to MySQL on an unpatched system.  The page
`http://www.volano.com/linuxnotes.html' contains information how to go
around this limit.

If you see a dead `mysqld' daemon process with `ps', this usually means
that you have found a bug in MySQL or you have a corrupted table. *Note
Crashing::.

To get a core dump on Linux if `mysqld' dies with a `SIGSEGV' signal,
you can start `mysqld' with the `--core-file' option.  Note that you
also probably need to raise the `core file size' by adding `ulimit -c
1000000' to `safe_mysqld' or starting `safe_mysqld' with
`--core-file-size=1000000'.  *Note `safe_mysqld': safe_mysqld.

If you are linking your own MySQL client and get the error:

     ld.so.1: ./my: fatal: libmysqlclient.so.4:
     open failed: No such file or directory

When executing them, the problem can be avoided by one of the following
methods:

   * Link the client with the following flag (instead of `-Lpath'):
     `-Wl,r/path-libmysqlclient.so'.

   * Copy `libmysqclient.so' to `/usr/lib'.

   * Add the pathname of the directory where `libmysqlclient.so' is
     located to the `LD_RUN_PATH' environment variable before running
     your client.

If you are using the Fujitsu compiler `(fcc / FCC)' you will have some
problems compiling MySQL because the Linux header files are very `gcc'
oriented.

The following `configure' line should work with `fcc/FCC':

     CC=fcc CFLAGS="-O -K fast -K lib -K omitfp -Kpreex -D_GNU_SOURCE \
     -DCONST=const -DNO_STRTOLL_PROTO" CXX=FCC CXXFLAGS="-O -K fast -K lib \
     -K omitfp -K preex --no_exceptions --no_rtti -D_GNU_SOURCE -DCONST=const \
     -Dalloca=__builtin_alloca -DNO_STRTOLL_PROTO \
     '-D_EXTERN_INLINE=static __inline'" ./configure --prefix=/usr/local/mysql \
     --enable-assembler --with-mysqld-ldflags=-all-static --disable-shared \
     --with-low-memory

Linux Notes for Binary Distributions
....................................

MySQL needs at least Linux Version 2.0.

*Warning*: We have reports from some MySQL users that they have got
serious stability problems with MySQL with Linux kernel 2.2.14.  If you
are using this kernel you should upgrade to 2.2.19 (or newer) or to a
2.4 kernel.  If you have a multi-cpu box, then you should seriously
consider using 2.4 as this will give you a significant speed boost.

The binary release is linked with `-static', which means you do not
normally need to worry about which version of the system libraries you
have. You need not install LinuxThreads, either.  A program linked with
`-static' is slightly bigger than a dynamically linked program but also
slightly faster (3-5%).  One problem, however, is that you can't use
user-definable functions (UDFs) with a statically linked program.  If
you are going to write or use UDF functions (this is something only for
C or C++ programmers), you must compile MySQL yourself, using dynamic
linking.

If you are using a `libc'-based system (instead of a `glibc2' system),
you will probably get some problems with hostname resolving and
`getpwnam()' with the binary release. (This is because `glibc'
unfortunately depends on some external libraries to resolve hostnames
and `getpwent()', even when compiled with `-static'). In this case you
probably get the following error message when you run
`mysql_install_db':

     Sorry, the host 'xxxx' could not be looked up

or the following error when you try to run `mysqld' with the `--user'
option:

     getpwnam: No such file or directory

You can solve this problem in one of the following ways:

   * Get a MySQL source distribution (an RPM or the `tar.gz'
     distribution) and install this instead.

   * Execute `mysql_install_db --force'; this will not execute the
     `resolveip' test in `mysql_install_db'.  The downside is that you
     can't use host names in the grant tables; you must use IP numbers
     instead (except for `localhost').  If you are using an old MySQL
     release that doesn't support `--force', you have to remove the
     `resolveip' test in `mysql_install' with an editor.

   * Start `mysqld' with `su' instead of using `--user'.

The Linux-Intel binary and RPM releases of MySQL are configured for the
highest possible speed.  We are always trying to use the fastest stable
compiler available.

MySQL Perl support requires Version Perl 5.004_03 or newer.

On some Linux 2.2 versions, you may get the error `Resource temporarily
unavailable' when you do a lot of new connections to a `mysqld' server
over TCP/IP.

The problem is that Linux has a delay between when you close a TCP/IP
socket and until this is actually freed by the system.  As there is only
room for a finite number of TCP/IP slots, you will get the above error
if you try to do too many new TCP/IP connections during a small time,
like when you run the MySQL `test-connect' benchmark over TCP/IP.

We have mailed about this problem a couple of times to different Linux
mailing lists but have never been able to resolve this properly.

The only known 'fix' to this problem is to use persistent connections in
your clients or use sockets, if you are running the database server and
clients on the same machine.  We hope that the `Linux 2.4' kernel will
fix this problem in the future.

Linux x86 Notes
...............

MySQL requires `libc' Version 5.4.12 or newer. It's known to work with
`libc' 5.4.46.  `glibc' Version 2.0.6 and later should also work. There
have been some problems with the `glibc' RPMs from RedHat, so if you
have problems, check whether there are any updates!  The `glibc'
2.0.7-19 and 2.0.7-29 RPMs are known to work.

If you are using Redhat 8.0 or a new glibc 2.2.x libray you should start
mysqld with the option `--thread-stack=192K'.  If you don't do it
mysqld will die in `gethostbyaddr()' because the new glibc library
requires > 128K memory on stack for this call.  This stack size is
default on MySQL 4.0.10 and above.

If you are using gcc 3.0 and above to compile MySQL, you must install
the `libstdc++v3' library before compiling MySQL; if you don't do this
you will get an error about a missing `__cxa_pure_virtual' symbol
during linking!

On some older Linux distributions, `configure' may produce an error
like this:

     Syntax error in sched.h. Change _P to __P in the /usr/include/sched.h file.
     See the Installation chapter in the Reference Manual.

Just do what the error message says and add an extra underscore to the
`_P' macro that has only one underscore, then try again.

You may get some warnings when compiling; those shown here can be
ignored:

     mysqld.cc -o objs-thread/mysqld.o
     mysqld.cc: In function `void init_signals()':
     mysqld.cc:315: warning: assignment of negative value `-1' to
     `long unsigned int'
     mysqld.cc: In function `void * signal_hand(void *)':
     mysqld.cc:346: warning: assignment of negative value `-1' to
     `long unsigned int'

`mysql.server' can be found in the `share/mysql' directory under the
MySQL installation directory or in the `support-files' directory of the
MySQL source tree.

If `mysqld' always core dumps when it starts up, the problem may be that
you have an old `/lib/libc.a'.  Try renaming it, then remove
`sql/mysqld' and do a new `make install' and try again.  This problem
has been reported on some Slackware installations.

If you get the following error when linking `mysqld', it means that
your `libg++.a' is not installed correctly:

     /usr/lib/libc.a(putc.o): In function `_IO_putc':
     putc.o(.text+0x0): multiple definition of `_IO_putc'

You can avoid using `libg++.a' by running `configure' like this:

     shell> CXX=gcc ./configure

Linux SPARC Notes
.................

In some implementations, `readdir_r()' is broken.  The symptom is that
`SHOW DATABASES' always returns an empty set.  This can be fixed by
removing `HAVE_READDIR_R' from `config.h' after configuring and before
compiling.

Some problems will require patching your Linux installation.  The patch
can be found at
`http://www.mysql.com/Downloads/patches/Linux-sparc-2.0.30.diff'.  This
patch is against the Linux distribution `sparclinux-2.0.30.tar.gz' that
is available at `vger.rutgers.edu' (a version of Linux that was never
merged with the official 2.0.30).  You must also install LinuxThreads
Version 0.6 or newer.

Linux Alpha Notes
.................

MySQL Version 3.23.12 is the first MySQL version that is tested on
Linux-Alpha.  If you plan to use MySQL on Linux-Alpha, you should
ensure that you have this version or newer.

We have tested MySQL on Alpha with our benchmarks and test suite, and
it appears to work nicely.

We currently build the MySQL binary packages on SuSE Linux 7.0 for AXP,
kernel 2.4.4-SMP, Compaq C compiler (V6.2-505) and Compaq C++ compiler
(V6.3-006) on a Compaq DS20 machine with an Alpha EV6 processor.

You can find the above compilers at
`http://www.support.compaq.com/alpha-tools/').  By using these
compilers, instead of gcc, we get about 9-14% better performance with
MySQL.

Note that until MySQL version 3.23.52 and 4.0.2 we optimised the binary
for the current CPU only (by using the `-fast' compile option); this
meant that you could only use our binaries if you had an Alpha EV6
processor.

Starting with all following releases we added the `-arch generic' flag
to our compile options, which makes sure the binary runs on all Alpha
processors. We also compile statically to avoid library problems.

     CC=ccc CFLAGS="-fast -arch generic" CXX=cxx \
     CXXFLAGS="-fast -arch generic -noexceptions -nortti" \
     ./configure --prefix=/usr/local/mysql --disable-shared \
     --with-extra-charsets=complex --enable-thread-safe-client \
     --with-mysqld-ldflags=-non_shared --with-client-ldflags=-non_shared

If you want to use egcs the following configure line worked for us:

     CFLAGS="-O3 -fomit-frame-pointer" CXX=gcc \
     CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors \
     -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql \
     --disable-shared

Some known problems when running MySQL on Linux-Alpha:

   * Debugging threaded applications like MySQL will not work with `gdb
     4.18'.  You should download and use gdb 5.1 instead!

   * If you try linking `mysqld' statically when using `gcc', the
     resulting image will core dump at start.  In other words, *don't*
     use `--with-mysqld-ldflags=-all-static' with `gcc'.

Linux PowerPC Notes
...................

MySQL should work on MkLinux with the newest `glibc' package (tested
with `glibc' 2.0.7).

Linux MIPS Notes
................

To get MySQL to work on Qube2, (Linux Mips), you need the newest
`glibc' libraries (`glibc-2.0.7-29C2' is known to work).  You must also
use the `egcs' C++ compiler (`egcs-1.0.2-9', `gcc 2.95.2' or newer).

Linux IA64 Notes
................

To get MySQL to compile on Linux IA64, we use the following compile
line: Using `gcc-2.96':

     CC=gcc CFLAGS="-O3 -fno-omit-frame-pointer" CXX=gcc \
     CXXFLAGS="-O3 -fno-omit-frame-pointer -felide-constructors \
     -fno-exceptions -fno-rtti" ./configure --prefix=/usr/local/mysql \
     "--with-comment=Official MySQL binary" --with-extra-charsets=complex

On IA64 the MySQL client binaries are using shared libraries. This means
that if you install our binary distribution in some other place than
`/usr/local/mysql' you need to either modify `/etc/ld.so.conf' or add
the path to the directory where you have `libmysqlclient.so' to the
`LD_LIBRARY_PATH' environment variable.

*Note Link errors::.

Windows Notes
-------------

This section describes using MySQL on Windows. This information is also
provided in the `README' file that comes with the MySQL Windows
distribution. *Note Windows installation::.

Starting MySQL on Windows 95, 98 or Me
......................................

MySQL uses TCP/IP to connect a client to a server. (This will allow any
machine on your network to connect to your MySQL server.)  Because of
this, you must install TCP/IP on your machine before starting MySQL.
You can find TCP/IP on your Windows CD-ROM.

Note that if you are using an old Windows 95 release (for example
OSR2), it's likely that you have an old Winsock package; MySQL requires
Winsock 2! You can get the newest Winsock from
`http://www.microsoft.com/'.  Windows 98 has the new Winsock 2 library,
so the above doesn't apply there.

To start the `mysqld' server, you should start an MS-DOS window and
type:

     C:\> C:\mysql\bin\mysqld

This will start `mysqld' in the background without a window.

You can kill the MySQL server by executing:

     C:\> C:\mysql\bin\mysqladmin -u root shutdown

This calls the MySQL administation utility as user `root', which is the
default Administrator in the MySQL grant system. Please note that the
MySQL grant system is wholly independent from any login users under
Windows.

Note that Windows 95/98/Me don't support creation of named pipes.  So
on those platforms, you can only use named pipes to connect to a remote
MySQL server running on a Windows NT/2000/XP server host.  (The MySQL
server must also support named pipes, of course.  For example, using
`mysqld-opt' under NT/2000/XP will not allow named pipe connections.
You should use either `mysqld-nt' or `mysqld-max-nt'.)

If `mysqld' doesn't start, please check the `\mysql\data\mysql.err'
file to see if the server wrote any message there to indicate the cause
of the problem.  You can also try to start the server with `mysqld
--standalone'; in this case, you may get some useful information on the
screen that may help solve the problem.

The last option is to start `mysqld' with `--standalone --debug'.  In
this case `mysqld' will write a log file `C:\mysqld.trace' that should
contain the reason why `mysqld' doesn't start. *Note Making trace
files::.

Use `mysqld --help' to display all the options that `mysqld'
understands!

Starting MySQL on Windows NT, 2000 or XP
........................................

To get MySQL to work with TCP/IP on Windows NT 4, you must install
service pack 3 (or newer)!

Normally you should install MySQL as a service on Windows NT/2000/XP.
In case the server was already running, first stop it using the
following command:

     C:\mysql\bin> mysqladmin -u root shutdown

This calls the MySQL administation utility as user ``root'', which is
the default `Administrator' in the MySQL grant system.  Please note
that the MySQL grant system is wholly independent from any login users
under Windows.

Now install the server service:

     C:\mysql\bin> mysqld-max-nt --install

If any options are required, they must be specified as "`Start
parameters'" in the Windows `Services' utility before you start the
MySQL service.

The `Services' utility (`Windows Service Control Manager') can be found
in the `Windows Control Panel' (under `Administrative Tools' on Windows
2000). It is advisable to close the Services utility while performing
the `--install' or `--remove' operations, this prevents some odd errors.

For information about which server binary to run, see *Note Windows
prepare environment::.

Please note that from MySQL version 3.23.44, you have the choice of set
up the service as `Manual' instead (if you don't wish the service to be
started automatically during the boot process):

     C:\mysql\bin> mysqld-max-nt --install-manual

The service is installed with the name `MySQL'. Once installed, it can
be immediately started from the `Services' utility, or by using the
command `NET START MySQL'.

Once running, `mysqld-max-nt' can be stopped using `mysqladmin', from
the Services utility, or by using the command `NET STOP MySQL'.

When running as a service, the operating system will automatically stop
the MySQL service on computer shutdown. In MySQL versions < 3.23.47,
Windows only waited for a few seconds for the shutdown to complete, and
killed the database server process if the time limit was exceeded
(potentially causing problems). For instance, at the next startup the
`InnoDB' storage engine had to do crash recovery. Starting from MySQL
version 3.23.48, the Windows will wait longer for the MySQL server
shutdown to complete. If you notice this is not enough for your
intallation, it is safest to run the MySQL server not as a service, but
from the Command prompt, and shut it down with `mysqladmin shutdown'.

There is a problem that Windows NT (but not Windows 2000/XP) by default
only waits 20 seconds for a service to shut down, and after that kills
the service process. You can increase this default by opening the
Registry Editor `\winnt\system32\regedt32.exe' and editing the value of
`WaitToKillServiceTimeout' at
`HKEY_LOCAL_MACHINE\SYSTEM\CurrentControlSet\Control' in the Registry
tree. Specify the new larger value in milliseconds, for example 120000
to have Windows NT wait upto 120 seconds.

Please note that when run as a service, `mysqld-max-nt' has no access
to a console and so no messages can be seen.  Errors can be checked in
`c:\mysql\data\mysql.err'.

If you have problems installing `mysqld-max-nt' as a service, try
starting it with the full path:

     C:\> C:\mysql\bin\mysqld-max-nt --install

If this doesn't work, you can get `mysqld-max-nt' to start properly by
fixing the path in the registry!

If you don't want to start `mysqld-max-nt' as a service, you can start
it as follows:

     C:\> C:\mysql\bin\mysqld-max-nt --standalone

or

     C:\> C:\mysql\bin\mysqld --standalone --debug

The last method gives you a debug trace in `C:\mysqld.trace'. *Note
Making trace files::.

Running MySQL on Windows
........................

MySQL supports TCP/IP on all Windows platforms and named pipes on
NT/2000/XP. The default is to use named pipes for local connections on
NT/2000/XP and TCP/IP for all other cases if the client has TCP/IP
installed. The host name specifies which protocol is used:

*Host       *Protocol*
name*
NULL         On NT/2000/XP, try named pipes first; if
(none)      that doesn't work, use TCP/IP.  On 9x/Me,
            TCP/IP is used.
.           Named pipes
localhost    TCP/IP to current host
hostname     TCP/IP

You can force a MySQL client to use named pipes by specifying the
`--pipe' option or by specifying `.' as the host name.  Use the
`--socket' option to specify the name of the pipe.

Note that starting from 3.23.50, named pipes are only enabled if mysqld
is started with `--enable-named-pipe'.  This is because some users have
experienced problems shutting down the MySQL server when one uses named
pipes.

You can test whether MySQL is working by executing the following
commands:

     C:\> C:\mysql\bin\mysqlshow
     C:\> C:\mysql\bin\mysqlshow -u root mysql
     C:\> C:\mysql\bin\mysqladmin version status proc
     C:\> C:\mysql\bin\mysql test

If `mysqld' is slow to answer to connections on Windows 9x/Me, there is
probably a problem with your DNS.  In this case, start `mysqld' with
`--skip-name-resolve' and use only `localhost' and IP numbers in the
MySQL grant tables.  You can also avoid DNS when connecting to a
`mysqld-nt' MySQL server running on NT/2000/XP by using the `--pipe'
argument to specify use of named pipes.  This works for most MySQL
clients.

There are two versions of the MySQL command-line tool:
*Binary**Description*
`mysql' Compiled on native Windows, which offers
        very limited text editing capabilities.
`mysqlc'Compiled with the Cygnus GNU compiler and
        libraries, which offers `readline' editing.

If you want to use `mysqlc.exe', you must copy
`C:\mysql\lib\cygwinb19.dll' to your Windows system directory
(`\windows\system' or similar place).

The default privileges on Windows give all local users full privileges
to all databases without specifying a password.  To make MySQL more
secure, you should set a password for all users and remove the row in
the `mysql.user' table that has `Host='localhost'' and `User='''.

You should also add a password for the `root' user. The following
example starts by removing the anonymous user that has all privileges,
then sets a `root' user password:

     C:\> C:\mysql\bin\mysql mysql
     mysql> DELETE FROM user WHERE Host='localhost' AND User='';
     mysql> QUIT
     C:\> C:\mysql\bin\mysqladmin reload
     C:\> C:\mysql\bin\mysqladmin -u root password your_password

After you've set the password, if you want to take down the `mysqld'
server, you can do so using this command:

     C:\> mysqladmin --user=root --password=your_password shutdown

If you are using the old shareware version of MySQL Version 3.21 under
Windows, the above command will fail with an error: `parse error near
'SET password''.  The solution for this is to download and upgrade to
the latest MySQL version, which is now freely available.

With the current MySQL versions you can easily add new users and change
privileges with `GRANT' and `REVOKE' commands.  *Note GRANT::.

Connecting to a Remote MySQL from Windows with SSH
..................................................

Here is a note about how to connect to get a secure connection to remote
MySQL server with SSH (by David Carlson <[e-mail]>):

   * Install an SSH client on your Windows machine.  As a user, the
     best non-free one I've found is from `SecureCRT' from
     `http://www.vandyke.com/'.  Another option is `f-secure' from
     `http://www.f-secure.com/'. You can also find some free ones on
     `Google' at
     `http://directory.google.com/Top/Computers/Security/Products_and_Tools/Cryptography/SSH/Clients/Windows/'.

   * Start your Windows SSH client.  Set `Host_Name =
     yourmysqlserver_URL_or_IP'.  Set `userid=your_userid' to log in to
     your server (probably not the same as your MySQL login/password.

   * Set up port forwarding. Either do a remote forward (Set
     `local_port: 3306', `remote_host: yourmysqlservername_or_ip',
     `remote_port: 3306' ) or a local forward (Set `port: 3306',
     `host: localhost', `remote port: 3306').

   * Save everything, otherwise you'll have to redo it the next time.

   * Log in to your server with SSH session you just created.

   * On your Windows machine, start some ODBC application (such as
     Access).

   * Create a new file in Windows and link to MySQL using the ODBC
     driver the same way you normally do, except type in `localhost'
     for the MySQL host servernot `yourmysqlservername'.

You should now have an ODBC connection to MySQL, encrypted using SSH.

Splitting Data Across Different Disks on Windows
................................................

Beginning with MySQL Version 3.23.16, the `mysqld-max' and
`mysql-max-nt' servers in the MySQL distribution are compiled with the
`-DUSE_SYMDIR' option.  This allows you to put a database on different
disk by adding a symbolic link to it (in a manner similar to the way
that symbolic links work on Unix).

On Windows, you make a symbolic link to a database by creating a file
that contains the path to the destination directory and saving this in
the `mysql_data' directory under the filename `database.sym'.  Note
that the symbolic link will be used only if the directory
`mysql_data_dir\database' doesn't exist.

For example, if the MySQL data directory is `C:\mysql\data' and you
want to have database `foo' located at `D:\data\foo', you should create
the file `C:\mysql\data\foo.sym' that contains the text `D:\data\foo\'.
After that, all tables created in the database `foo' will be created
in `D:\data\foo'.

Note that because of the speed penalty you get when opening every table,
we have not enabled this by default even if you have compiled MySQL
with support for this. To enable symlinks you should put in your
`my.cnf' or `my.ini' file the following entry:

     [mysqld]
     use-symbolic-links

In MySQL 4.0 we will enable symlinks by default. Then you should
instead use the `skip-symlink' option if you want to disable this.

Compiling MySQL Clients on Windows
..................................

In your source files, you should include `windows.h' before you include
`mysql.h':

     #if defined(_WIN32) || defined(_WIN64)
     #include <windows.h>
     #endif
     #include <mysql.h>

You can either link your code with the dynamic `libmysql.lib' library,
which is just a wrapper to load in `libmysql.dll' on demand, or link
with the static `mysqlclient.lib' library.

Note that as the mysqlclient libraries are compiled as threaded
libraries, you should also compile your code to be multi-threaded!

MySQL-Windows Compared to Unix MySQL
....................................

MySQL-Windows has by now proven itself to be very stable. This version
of MySQL has the same features as the corresponding Unix version with
the following exceptions:

*Windows 95 and threads*
     Windows 95 leaks about 200 bytes of main memory for each thread
     creation.  Each connection in MySQL creates a new thread, so you
     shouldn't run `mysqld' for an extended time on Windows 95 if your
     server handles many connections!  Other versions of Windows don't
     suffer from this bug.

*Concurrent reads*
     MySQL depends on the `pread()' and `pwrite()' calls to be able to
     mix `INSERT' and `SELECT'.  Currently we use mutexes to emulate
     `pread()'/`pwrite()'.  We will, in the long run, replace the file
     level interface with a virtual interface so that we can use the
     `readfile()'/`writefile()' interface on NT/2000/XP to get more
     speed.  The current implementation limits the number of open files
     MySQL can use to 1024, which means that you will not be able to
     run as many concurrent threads on NT/2000/XP as on Unix.

*Blocking read*
     MySQL uses a blocking read for each connection.  This means that:

        * A connection will not be disconnected automatically after 8
          hours, as happens with the Unix version of MySQL.

        * If a connection hangs, it's impossible to break it without
          killing MySQL.

        * `mysqladmin kill' will not work on a sleeping connection.

        * `mysqladmin shutdown' can't abort as long as there are
          sleeping connections.

     We plan to fix this problem when our Windows developers have
     figured out a nice workaround.

*`DROP DATABASE'*
     You can't drop a database that is in use by some thread.

*Killing MySQL from the task manager*
     You can't kill MySQL from the task manager or with the shutdown
     utility in Windows 95.  You must take it down with `mysqladmin
     shutdown'.

*Case-insensitive names*
     Filenames are case-insensitive on Windows, so database and table
     names are also case-insensitive in MySQL for Windows.  The only
     restriction is that database and table names must be specified
     using the same case throughout a given statement.  *Note Name case
     sensitivity::.

*The `\' directory character*
     Pathname components in Windows 95 are separated by the `\'
     character, which is also the escape character in MySQL.  If you
     are using `LOAD DATA INFILE' or `SELECT ... INTO OUTFILE', you
     must double the `\' character:

          mysql> LOAD DATA INFILE "C:\\tmp\\skr.txt" INTO TABLE skr;
          mysql> SELECT * INTO OUTFILE 'C:\\tmp\\skr.txt' FROM skr;

     Alternatively, use Unix style filenames with `/' characters:

          mysql> LOAD DATA INFILE "C:/tmp/skr.txt" INTO TABLE skr;
          mysql> SELECT * INTO OUTFILE 'C:/tmp/skr.txt' FROM skr;

*`Can't open named pipe' error*
     If you use a MySQL 3.22 version on NT with the newest mysql-clients
     you will get the following error:

          error 2017: can't open named pipe to host: . pipe...

     This is because the release version of MySQL uses named pipes on NT
     by default.  You can avoid this error by using the
     `--host=localhost' option to the new MySQL clients or create an
     option file `C:\my.cnf' that contains the following information:

          [client]
          host = localhost

     Starting from 3.23.50, named pipes are only enabled if `mysqld' is
     started with `--enable-named-pipe'.

*`Access denied for user' error*
     If you get the error `Access denied for user: 'some-user@unknown'
     to database 'mysql'' when accessing a MySQL server on the same
     machine, this means that MySQL can't resolve your host name
     properly.

     To fix this, you should create a file `\windows\hosts' with the
     following information:

          127.0.0.1       localhost

*`ALTER TABLE'*
     While you are executing an `ALTER TABLE' statement, the table is
     locked from usage by other threads.  This has to do with the fact
     that on Windows, you can't delete a file that is in use by another
     threads.  (In the future, we may find some way to work around this
     problem.)

**
     `DROP TABLE' on a table that is in use by a `MERGE' table will not
     work on Windows because the `MERGE' handler does the table mapping
     hidden from the upper layer of MySQL.  Because Windows doesn't
     allow you to drop files that are open, you first must flush all
     `MERGE' tables (with `FLUSH TABLES') or drop the `MERGE' table
     before dropping the table.  We will fix this at the same time we
     introduce `VIEW's.

**
     `DATA DIRECTORY' and `INDEX DIRECTORY' directives in `CREATE
     TABLE' is ignored on Windows, because Windows doesn't support
     symbolic links.

Here are some open issues for anyone who might want to help us with the
Windows release:

   * Make a single-user `MYSQL.DLL' server.  This should include
     everything in a standard MySQL server, except thread creation.
     This will make MySQL much easier to use in applications that don't
     need a true client/server and don't need to access the server from
     other hosts.

   * Add some nice start and shutdown icons to the MySQL installation.

   * When registering `mysqld' as a service with `--install' (on NT) it
     would be nice if you could also add default options on the
     command-line.  For the moment, the workaround is to list the
     parameters in the `C:\my.cnf' file instead.

   * It would be really nice to be able to kill `mysqld' from the task
     manager.  For the moment, you must use `mysqladmin shutdown'.

   * Port `readline' to Windows for use in the `mysql' command-line
     tool.

   * GUI versions of the standard MySQL clients (`mysql', `mysqlshow',
     `mysqladmin', and `mysqldump') would be nice.

   * It would be nice if the socket read and write functions in `net.c'
     were interruptible. This would make it possible to kill open
     threads with `mysqladmin kill' on Windows.

   * `mysqld' always starts in the "C" locale and not in the default
     locale.  We would like to have `mysqld' use the current locale for
     the sort order.

   * Add macros to use the faster thread-safe increment/decrement
     methods provided by Windows.

Other Windows-specific issues are described in the `README' file that
comes with the MySQL-Windows distribution.

Solaris Notes
-------------

On Solaris, you may run into trouble even before you get the MySQL
distribution unpacked!  Solaris `tar' can't handle long file names, so
you may see an error like this when you unpack MySQL:

     x mysql-3.22.12-beta/bench/Results/ATIS-mysql_odbc-NT_4.0-cmp-db2,\
     informix,ms-sql,mysql,oracle,solid,sybase, 0 bytes, 0 tape blocks
     tar: directory checksum error

In this case, you must use GNU `tar' (`gtar') to unpack the
distribution.  You can find a precompiled copy for Solaris at
`http://www.mysql.com/downloads/os-solaris.html'.

Sun native threads work only on Solaris 2.5 and higher.  For Version
2.4 and earlier, MySQL will automatically use MIT-pthreads.  *Note
MIT-pthreads::.

If you get the following error from configure:

     checking for restartable system calls... configure: error can not run test
     programs while cross compiling

This means that you have something wrong with your compiler
installation!  In this case you should upgrade your compiler to a newer
version.  You may also be able to solve this problem by inserting the
following row into the `config.cache' file:

     ac_cv_sys_restartable_syscalls=${ac_cv_sys_restartable_syscalls='no'}

If you are using Solaris on a SPARC, the recommended compiler is `gcc'
2.95.2.  You can find this at `http://gcc.gnu.org/'.  Note that `egcs'
1.1.1 and `gcc' 2.8.1 don't work reliably on SPARC!

The recommended `configure' line when using `gcc' 2.95.2 is:

     CC=gcc CFLAGS="-O3" \
     CXX=gcc CXXFLAGS="-O3 -felide-constructors -fno-exceptions -fno-rtti" \
     ./configure --prefix=/usr/local/mysql --with-low-memory --enable-assembler

If you have an UltraSPARC, you can get 4% more performance by adding
"-mcpu=v8 -Wa,-xarch=v8plusa" to CFLAGS and CXXFLAGS.

If you have Sun's Forte 5.0 (or newer) compiler, you can run
`configure' like this:

     CC=cc CFLAGS="-Xa -fast -native -xstrconst -mt" \
     CXX=CC CXXFLAGS="-noex -mt" \
     ./configure --prefix=/usr/local/mysql --enable-assembler

You can create a 64 bit binary with:

     CC=cc CFLAGS="-Xa -fast -native -xstrconst -mt -xarch=v9" \
     CXX=CC CXXFLAGS="-noex -mt -xarch=v9" ASFLAGS="-xarch=v9" \
     ./configure --prefix=/usr/local/mysql --enable-assembler

In the MySQL benchmarks, we got a 4% speedup on an UltraSPARC when using
Forte 5.0 in 32 bit mode compared to using gcc 3.2 with -mcpu flags.

If you create a 64 bit binary, it's 4 % slower than the 32 bit binary,
but mysqld can instead handle more treads and memory.

If you get a problem with `fdatasync' or `sched_yield', you can fix
this by adding `LIBS=-lrt' to the configure line

The following paragraph is only relevant for older compilers than
WorkShop 5.3:

You may also have to edit the `configure' script to change this line:

     #if !defined(__STDC__) || __STDC__ != 1

to this:

     #if !defined(__STDC__)

If you turn on `__STDC__' with the `-Xc' option, the Sun compiler can't
compile with the Solaris `pthread.h' header file.  This is a Sun bug
(broken compiler or broken include file).

If `mysqld' issues the error message shown here when you run it, you
have tried to compile MySQL with the Sun compiler without enabling the
multi-thread option (`-mt'):

     libc internal error: _rmutex_unlock: rmutex not held

Add `-mt' to `CFLAGS' and `CXXFLAGS' and try again.

If you are using the SFW version of gcc (which comes with Solaris 8),
you must add `/opt/sfw/lib' to the environment variable
`LD_LIBRARY_PATH' before running configure.

If you are using the gcc available from `sunfreeware.com', you may have
many problems.  You should recompile gcc and GNU binutils on the
machine you will be running them from to avoid any problems.

If you get the following error when compiling MySQL with `gcc', it
means that your `gcc' is not configured for your version of Solaris:

     shell> gcc -O3 -g -O2 -DDBUG_OFF  -o thr_alarm ...
     ./thr_alarm.c: In function `signal_hand':
     ./thr_alarm.c:556: too many arguments to function `sigwait'

The proper thing to do in this case is to get the newest version of
`gcc' and compile it with your current `gcc' compiler!  At least for
Solaris 2.5, almost all binary versions of `gcc' have old, unusable
include files that will break all programs that use threads (and
possibly other programs)!

Solaris doesn't provide static versions of all system libraries
(`libpthreads' and `libdl'), so you can't compile MySQL with
`--static'.  If you try to do so, you will get the error:

     ld: fatal: library -ldl: not found

     or

     undefined reference to `dlopen'

     or

     cannot find -lrt

If too many processes try to connect very rapidly to `mysqld', you will
see this error in the MySQL log:

     Error in accept: Protocol error

You might try starting the server with the `--set-variable back_log=50'
option as a workaround for this. Please note that `--set-variable' is
deprecated since MySQL 4.0, just use `--back_log=50' on its own.  *Note
Command-line options::.

If you are linking your own MySQL client, you might get the following
error when you try to execute it:

     ld.so.1: ./my: fatal: libmysqlclient.so.#:
     open failed: No such file or directory

The problem can be avoided by one of the following methods:

   * Link the client with the following flag (instead of `-Lpath'):
     `-Wl,r/full-path-to-libmysqlclient.so'.

   * Copy `libmysqclient.so' to `/usr/lib'.

   * Add the pathname of the directory where `libmysqlclient.so' is
     located to the `LD_RUN_PATH' environment variable before running
     your client.

If you have problems with configure trying to link with `-lz' and you
don't have `zlib' installed, you have two options:

   * If you want to be able to use the compressed communication
     protocol, you need to get and install zlib from ftp.gnu.org.

   * Configure with `--with-named-z-libs=no'.

If you are using gcc and have problems with loading `UDF' functions
into MySQL, try adding `-lgcc' to the link line for the `UDF' function.

If you would like MySQL to start automatically, you can copy
`support-files/mysql.server' to `/etc/init.d' and create a symbolic
link to it named `/etc/rc3.d/S99mysql.server'.

As Solaris doesn't support core files for `setuid()' applications, you
can't get a core file from `mysqld' if you are using the `--user'
option.

Solaris 2.7/2.8 Notes
.....................

You can normally use a Solaris 2.6 binary on Solaris 2.7 and 2.8.  Most
of the Solaris 2.6 issues also apply for Solaris 2.7 and 2.8.

Note that MySQL Version 3.23.4 and above should be able to autodetect
new versions of Solaris and enable workarounds for the following
problems!

Solaris 2.7 / 2.8 has some bugs in the include files.  You may see the
following error when you use `gcc':

     /usr/include/widec.h:42: warning: `getwc' redefined
     /usr/include/wchar.h:326: warning: this is the location of the previous
     definition

If this occurs, you can do the following to fix the problem:

Copy `/usr/include/widec.h' to `.../lib/gcc-lib/os/gcc-version/include'
and change line 41 from:

     #if     !defined(lint) && !defined(__lint)

     to

     #if     !defined(lint) && !defined(__lint) && !defined(getwc)

Alternatively, you can edit `/usr/include/widec.h' directly.  Either
way, after you make the fix, you should remove `config.cache' and run
`configure' again!

If you get errors like this when you run `make', it's because
`configure' didn't detect the `curses.h' file (probably because of the
error in `/usr/include/widec.h'):

     In file included from mysql.cc:50:
     /usr/include/term.h:1060: syntax error before `,'
     /usr/include/term.h:1081: syntax error before `;'

The solution to this is to do one of the following:

   * Configure with `CFLAGS=-DHAVE_CURSES_H CXXFLAGS=-DHAVE_CURSES_H
     ./configure'.

   * Edit `/usr/include/widec.h' as indicted above and rerun configure.

   * Remove the `#define HAVE_TERM' line from `config.h' file and run
     `make' again.

If you get a problem that your linker can't find `-lz' when linking
your client program, the problem is probably that your `libz.so' file is
installed in `/usr/local/lib'.  You can fix this by one of the
following methods:

   * Add `/usr/local/lib' to `LD_LIBRARY_PATH'.

   * Add a link to `libz.so' from `/lib'.

   * If you are using Solaris 8, you can install the optional zlib from
     your Solaris 8 CD distribution.

   * Configure MySQL with the `--with-named-z-libs=no' option.

Solaris x86 Notes
.................

On Solaris 2.8 on x86, `mysqld' will core dump if you run 'strip' in.

If you are using `gcc' or `egcs' on Solaris x86 and you experience
problems with core dumps under load, you should use the following
`configure' command:

     CC=gcc CFLAGS="-O3 -fomit-frame-pointer -DHAVE_CURSES_H" \
     CXX=gcc \
     CXXFLAGS="-O3 -fomit-frame-pointer -felide-constructors -fno-exceptions \
     -fno-rtti -DHAVE_CURSES_H" \
     ./configure --prefix=/usr/local/mysql

This will avoid problems with the `libstdc++' library and with C++
exceptions.

If this doesn't help, you should compile a debug version and run it
with a trace file or under `gdb'.  *Note Using gdb on mysqld::.

BSD Notes
---------

This section provides information for the various BSD flavours, as well
as specific versions within those.

FreeBSD Notes
.............

FreeBSD 3.x is recommended for running MySQL since the thread package
is much more integrated.

The easiest and therefore the preferred way to install is to use the
mysql-server and mysql-client ports available on
`http://www.freebsd.org/'.

Using these gives you:
   * A working MySQL with all optimisations known to work on your
     version of FreeBSD enabled.

   * Automatic configuration and build.

   * Startup scripts installed in /usr/local/etc/rc.d.

   * Ability to see which files that are installed with pkg_info -L.
     And to remove them all with pkg_delete if you no longer want MySQL
     on that machine.

It is recommended you use MIT-pthreads on FreeBSD 2.x and native
threads on Versions 3 and up. It is possible to run with  native
threads on some late 2.2.x versions but you may encounter problems
shutting down `mysqld'.

The MySQL `Makefile's require GNU make (`gmake') to work.  If you want
to compile MySQL you need to install GNU `make' first.

Be sure to have your name resolver setup correct.  Otherwise, you may
experience resolver delays or failures when connecting to `mysqld'.

Make sure that the `localhost' entry in the `/etc/hosts' file is
correct (otherwise, you will have problems connecting to the database).
The `/etc/hosts' file should start with a line:

     127.0.0.1       localhost localhost.your.domain

The recommended way to compile and install MySQL on FreeBSD with gcc
(2.95.2 and up) is:

     CC=gcc CFLAGS="-O2 -fno-strength-reduce" \
     CXX=gcc CXXFLAGS="-O2 -fno-rtti -fno-exceptions -felide-constructors \
     -fno-strength-reduce" \
     ./configure --prefix=/usr/local/mysql --enable-assembler
     gmake
     gmake install
     ./scripts/mysql_install_db
     cd /usr/local/mysql
     ./bin/mysqld_safe &

If you notice that `configure' will use MIT-pthreads, you should read
the MIT-pthreads notes.  *Note MIT-pthreads::.

If you get an error from `make install' that it can't find
`/usr/include/pthreads', `configure' didn't detect that you need
MIT-pthreads.  This is fixed by executing these commands:

     shell> rm config.cache
     shell> ./configure --with-mit-threads

FreeBSD is also known to have a very low default file handle limit.
*Note Not enough file handles::.  Uncomment the ulimit -n section in
safe_mysqld or raise the limits for the `mysqld' user in /etc/login.conf
(and rebuild it with cap_mkdb /etc/login.conf).  Also be sure you set
the appropriate class for this user in the password file if you are not
using the default (use: chpass mysqld-user-name).  *Note `safe_mysqld':
safe_mysqld.

If you have a lot of memory you should consider rebuilding the kernel
to allow MySQL to take more than 512M of RAM.  Take a look at `option
MAXDSIZ' in the LINT config file for more info.

If you get problems with the current date in MySQL, setting the `TZ'
variable will probably help.  *Note Environment variables::.

To get a secure and stable system you should only use FreeBSD kernels
that are marked `-RELEASE'.

NetBSD notes
............

To compile on NetBSD you need GNU `make'. Otherwise, the compile will
crash when `make' tries to run `lint' on C++ files.

OpenBSD 2.5 Notes
.................

On OpenBSD Version 2.5, you can compile MySQL with native threads with
the following options:

     CFLAGS=-pthread CXXFLAGS=-pthread ./configure --with-mit-threads=no

OpenBSD 2.8 Notes
.................

Our users have reported that OpenBSD 2.8 has a threading bug which
causes problems with MySQL.  The OpenBSD Developers have fixed the
problem, but as of January 25th, 2001, it's only available in the
"-current" branch.  The symptoms of this threading bug are: slow
response, high load, high CPU usage, and crashes.

If you get an error like `Error in accept:: Bad file descriptor' or
error 9 when trying to open tables or directories, the problem is
probably that you haven't allocated enough file descriptors for MySQL.

In this case try starting `safe_mysqld' as root with the following
options:

`--user=mysql --open-files-limit=2048'

BSD/OS Version 2.x Notes
........................

If you get the following error when compiling MySQL, your `ulimit'
value for virtual memory is too low:

     item_func.h: In method `Item_func_ge::Item_func_ge(const Item_func_ge &)':
     item_func.h:28: virtual memory exhausted
     make[2]: *** [item_func.o] Error 1

Try using `ulimit -v 80000' and run `make' again.  If this doesn't work
and you are using `bash', try switching to `csh' or `sh'; some BSDI
users have reported problems with `bash' and `ulimit'.

If you are using `gcc', you may also use have to use the
`--with-low-memory' flag for `configure' to be able to compile
`sql_yacc.cc'.

If you get problems with the current date in MySQL, setting the `TZ'
variable will probably help.  *Note Environment variables::.

BSD/OS Version 3.x Notes
........................

Upgrade to BSD/OS Version 3.1.  If that is not possible, install
BSDIpatch M300-038.

Use the following command when configuring MySQL:

     shell> env CXX=shlicc++ CC=shlicc2 \
            ./configure \
                --prefix=/usr/local/mysql \
                --localstatedir=/var/mysql \
                --without-perl \
                --with-unix-socket-path=/var/mysql/mysql.sock

The following is also known to work:

     shell> env CC=gcc CXX=gcc CXXFLAGS=-O3 \
            ./configure \
                --prefix=/usr/local/mysql \
                --with-unix-socket-path=/var/mysql/mysql.sock

You can change the directory locations if you wish, or just use the
defaults by not specifying any locations.

If you have problems with performance under heavy load, try using the
`--skip-thread-priority' option to `mysqld'!  This will run all threads
with the same priority; on BSDI Version 3.1, this gives better
performance (at least until BSDI fixes their thread scheduler).

If you get the error `virtual memory exhausted' while compiling, you
should try using `ulimit -v 80000' and run `make' again.  If this
doesn't work and you are using `bash', try switching to `csh' or `sh';
some BSDI users have reported problems with `bash' and `ulimit'.

BSD/OS Version 4.x Notes
........................

BSDI Version 4.x has some thread-related bugs.  If you want to use
MySQL on this, you should install all thread-related patches.  At least
M400-023 should be installed.

On some BSDI Version 4.x systems, you may get problems with shared
libraries.  The symptom is that you can't execute any client programs,
for example, `mysqladmin'.  In this case you need to reconfigure not to
use shared libraries with the `--disable-shared' option to configure.

Some customers have had problems on BSDI 4.0.1 that the `mysqld' binary
after a while can't open tables.  This is because some library/system
related bug causes `mysqld' to change current directory without asking
for this!

The fix is to either upgrade to 3.23.34 or after running `configure'
remove the line `#define HAVE_REALPATH' from `config.h' before running
make.

Note that the above means that you can't symbolic link a database
directories to another database directory or symbolic link a table to
another database on BSDI!  (Making a symbolic link to another disk is
okay).

Mac OS X Notes
--------------

Mac OS X Public Beta
....................

MySQL should work without any problems on Mac OS X Public Beta
(Darwin).  You don't need the pthread patches for this OS!

Mac OS X Server
...............

Before trying to configure MySQL on Mac OS X server you must first
install the pthread package from `http://www.prnet.de/RegEx/mysql.html'.

Our binary for Mac OS X is compiled on Rhapsody 5.5 with the following
configure line:

     CC=gcc CFLAGS="-O2 -fomit-frame-pointer" CXX=gcc CXXFLAGS="-O2 \
     -fomit-frame-pointer" ./configure --prefix=/usr/local/mysql \
     "--with-comment=Official MySQL binary" --with-extra-charsets=complex \
     --disable-shared

You might want to also add aliases to your shell's resource file to
access `mysql' and `mysqladmin' from the command-line:

     alias mysql '/usr/local/mysql/bin/mysql'
     alias mysqladmin '/usr/local/mysql/bin/mysqladmin'

Other Unix Notes
----------------

HP-UX Notes for Binary Distributions
....................................

Some of the binary distributions of MySQL for HP-UX is distributed as
an HP depot file and as a tar file.  To use the depot file you must be
running at least HP-UX 10.x to have access to HP's software depot tools.

The HP version of MySQL was compiled on an HP 9000/8xx server under
HP-UX 10.20, and uses MIT-pthreads.  It is known to work well under
this configuration.  MySQL Version 3.22.26 and newer can also be built
with HP's native thread package.

Other configurations that may work:

   * HP 9000/7xx running HP-UX 10.20+

   * HP 9000/8xx running HP-UX 10.30

The following configurations almost definitely won't work:

   * HP 9000/7xx or 8xx running HP-UX 10.x where x < 2

   * HP 9000/7xx or 8xx running HP-UX 9.x

To install the distribution, use one of the commands here, where
`/path/to/depot' is the full pathname of the depot file:

   * To install everything, including the server, client and
     development tools:

          shell> /usr/sbin/swinstall -s /path/to/depot mysql.full

   * To install only the server:

          shell> /usr/sbin/swinstall -s /path/to/depot mysql.server

   * To install only the client package:

          shell> /usr/sbin/swinstall -s /path/to/depot mysql.client

   * To install only the development tools:

          shell> /usr/sbin/swinstall -s /path/to/depot mysql.developer

The depot places binaries and libraries in `/opt/mysql' and data in
`/var/opt/mysql'. The depot also creates the appropriate entries in
`/etc/init.d' and `/etc/rc2.d' to start the server automatically at
boot time.  Obviously, this entails being `root' to install.

To install the HP-UX tar.gz distribution, you must have a copy of GNU
`tar'.

HP-UX Version 10.20 Notes
.........................

There are a couple of small problems when compiling MySQL on HP-UX.  We
recommend that you use `gcc' instead of the HP-UX native compiler,
because `gcc' produces better code!

We recommend using gcc 2.95 on HP-UX.  Don't use high optimisation
flags (like -O6) as this may not be safe on HP-UX.

The following configure line should work with gcc 2.95:

     CFLAGS="-I/opt/dce/include -fpic" \
     CXXFLAGS="-I/opt/dce/include -felide-constructors -fno-exceptions \
     -fno-rtti" CXX=gcc ./configure --with-pthread \
     --with-named-thread-libs='-ldce' --prefix=/usr/local/mysql --disable-shared

The following configure line should work with gcc 3.1:

     CFLAGS="-DHPUX -I/opt/dce/include -O3 -fPIC" CXX=gcc \
     CXXFLAGS="-DHPUX -I/opt/dce/include -felide-constructors -fno-exceptions \
     -fno-rtti -O3 -fPIC" ./configure --prefix=/usr/local/mysql \
     --with-extra-charsets=complex --enable-thread-safe-client \
     --enable-local-infile  --with-pthread \
     --with-named-thread-libs=-ldce --with-lib-ccflags=-fPIC
     --disable-shared

HP-UX Version 11.x Notes
........................

For HP-UX Version 11.x we recommend MySQL Version 3.23.15 or later.

Because of some critical bugs in the standard HP-UX libraries, you
should install the following patches before trying to run MySQL on
HP-UX 11.0:

     PHKL_22840 Streams cumulative
     PHNE_22397 ARPA cumulative

This will solve the problem of getting `EWOULDBLOCK' from `recv()' and
`EBADF' from `accept()' in threaded applications.

If you are using `gcc' 2.95.1 on an unpatched HP-UX 11.x system, you
will get the error:

     In file included from /usr/include/unistd.h:11,
                      from ../include/global.h:125,
                      from mysql_priv.h:15,
                      from item.cc:19:
     /usr/include/sys/unistd.h:184: declaration of C function ...
     /usr/include/sys/pthread.h:440: previous declaration ...
     In file included from item.h:306,
                      from mysql_priv.h:158,
                      from item.cc:19:

The problem is that HP-UX doesn't define `pthreads_atfork()'
consistently.  It has conflicting prototypes in
`/usr/include/sys/unistd.h':184 and `/usr/include/sys/pthread.h':440
(details below).

One solution is to copy `/usr/include/sys/unistd.h' into
`mysql/include' and edit `unistd.h' and change it to match the
definition in `pthread.h'.  Here's the diff:

     183,184c183,184
     <      extern int pthread_atfork(void (*prepare)(), void (*parent)(),
     <                                                void (*child)());
     ---
     >      extern int pthread_atfork(void (*prepare)(void), void (*parent)(void),
     >                                                void (*child)(void));

After this, the following configure line should work:

     CFLAGS="-fomit-frame-pointer -O3 -fpic" CXX=gcc \
     CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti -O3" \
     ./configure --prefix=/usr/local/mysql --disable-shared

If you are using MySQL 4.0.5 with the HP-UX compiler you can use:
(tested with cc B.11.11.04):

     CC=cc CXX=aCC CFLAGS=+DD64 CXXFLAGS=+DD64 ./configure --with-extra-character-set=complex

You can ignore any errors of the following type:

     aCC: warning 901: unknown option: `-3': use +help for online documentation

If you get the following error from `configure'

     checking for cc option to accept ANSI C... no
     configure: error: MySQL requires a ANSI C compiler (and a C++ compiler).
     Try gcc. See the Installation chapter in the Reference Manual.

Check that you don't have the path to the K&R compiler before the path
to the HP-UX C and C++ compiler.

Another reason for not beeing able to compile is that you didn't define
the `+DD64' flags above.

IBM-AIX notes
.............

Automatic detection of `xlC' is missing from Autoconf, so a `configure'
command something like this is needed when compiling MySQL (This
example uses the IBM compiler):

     export CC="xlc_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192 "
     export CXX="xlC_r -ma -O3 -qstrict -qoptimize=3 -qmaxmem=8192"
     export CFLAGS="-I /usr/local/include"
     export LDFLAGS="-L /usr/local/lib"
     export CPPFLAGS=$CFLAGS
     export CXXFLAGS=$CFLAGS

     ./configure --prefix=/usr/local \
             --localstatedir=/var/mysql \
             --sysconfdir=/etc/mysql \
             --sbindir='/usr/local/bin' \
             --libexecdir='/usr/local/bin' \
             --enable-thread-safe-client \
             --enable-large-files

Above are the options used to compile the MySQL distribution that can
be found at `http://www-frec.bull.com/'.

If you change the `-O3' to `-O2' in the above configure line, you must
also remove the `-qstrict' option (this is a limitation in the IBM C
compiler).

If you are using `gcc' or `egcs' to compile MySQL, you *must* use the
`-fno-exceptions' flag, as the exception handling in `gcc'/`egcs' is
not thread-safe!  (This is tested with `egcs' 1.1.)  There are also
some known problems with IBM's assembler, which may cause it to
generate bad code when used with gcc.

We recommend the following `configure' line with `egcs' and `gcc 2.95'
on AIX:

     CC="gcc -pipe -mcpu=power -Wa,-many" \
     CXX="gcc -pipe -mcpu=power -Wa,-many" \
     CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti" \
     ./configure --prefix=/usr/local/mysql --with-low-memory

The `-Wa,-many' is necessary for the compile to be successful.  IBM is
aware of this problem but is in to hurry to fix it because of the
workaround available.  We don't know if the `-fno-exceptions' is
required with `gcc 2.95', but as MySQL doesn't use exceptions and the
above option generates faster code, we recommend that you should always
use this option with `egcs / gcc'.

If you get a problem with assembler code try changing the -mcpu=xxx to
match your CPU. Typically power2, power, or powerpc may need to be used,
alternatively you might need to use 604 or 604e. I'm not positive but I
would think using "power" would likely be safe most of the time, even on
a power2 machine.

If you don't know what your CPU is then do a "uname -m", this will give
you back a string that looks like "000514676700", with a format of
xxyyyyyymmss where xx and ss are always 0's, yyyyyy is a unique system
id and mm is the id of the CPU Planar. A chart of these values can be
found at
`http://publib.boulder.ibm.com/doc_link/en_US/a_doc_lib/cmds/aixcmds5/uname.htm'.
This will give you a machine type and a machine model you can use to
determine what type of CPU you have.

If you have problems with signals (MySQL dies unexpectedly under high
load) you may have found an OS bug with threads and signals.  In this
case you can tell MySQL not to use signals by configuring with:

     shell> CFLAGS=-DDONT_USE_THR_ALARM CXX=gcc \
            CXXFLAGS="-felide-constructors -fno-exceptions -fno-rtti \
            -DDONT_USE_THR_ALARM" \
            ./configure --prefix=/usr/local/mysql --with-debug --with-low-memory

This doesn't affect the performance of MySQL, but has the side effect
that you can't kill clients that are "sleeping" on a connection with
`mysqladmin kill' or `mysqladmin shutdown'.  Instead, the client will
die when it issues its next command.

On some versions of AIX, linking with `libbind.a' makes `getservbyname'
core dump.  This is an AIX bug and should be reported to IBM.

For AIX 4.2.1 and gcc you have to do the following changes.

After configuring, edit `config.h' and `include/my_config.h' and change
the line that says

     #define HAVE_SNPRINTF 1

to

     #undef HAVE_SNPRINTF

And finally, in `mysqld.cc' you need to add a prototype for initgoups.

     #ifdef _AIX41
     extern "C" int initgroups(const char *,int);
     #endif

If you need to allocate a lot of memory to the mysqld process, it's not
enough to just set 'ulimit -d unlimited'. You may also have to set in
`mysqld_safe' something like:

     export LDR_CNTRL='MAXDATA=0x80000000'

You can find more about using a lot of memory at:
`http://publib16.boulder.ibm.com/pseries/en_US/aixprggd/genprogc/lrg_prg_support.htm'.

SunOS 4 Notes
.............

On SunOS 4, MIT-pthreads is needed to compile MySQL, which in turn
means you will need GNU `make'.

Some SunOS 4 systems have problems with dynamic libraries and `libtool'.
You can use the following `configure' line to avoid this problem:

     shell> ./configure --disable-shared --with-mysqld-ldflags=-all-static

When compiling `readline', you may get warnings about duplicate defines.
These may be ignored.

When compiling `mysqld', there will be some `implicit declaration of
function' warnings. These may be ignored.

Alpha-DEC-UNIX Notes (Tru64)
............................

If you are using egcs 1.1.2 on Digital Unix, you should upgrade to gcc
2.95.2, as egcs on DEC has some serious bugs!

When compiling threaded programs under Digital Unix, the documentation
recommends using the `-pthread' option for `cc' and `cxx' and the
libraries `-lmach -lexc' (in addition to `-lpthread').  You should run
`configure' something like this:

     CC="cc -pthread" CXX="cxx -pthread -O" \
     ./configure --with-named-thread-libs="-lpthread -lmach -lexc -lc"

When compiling `mysqld', you may see a couple of warnings like this:

     mysqld.cc: In function void handle_connections()':
     mysqld.cc:626: passing long unsigned int *' as argument 3 of
     accept(int,sockadddr *, int *)'

You can safely ignore these warnings.  They occur because `configure'
can detect only errors, not warnings.

If you start the server directly from the command-line, you may have
problems with it dying when you log out.  (When you log out, your
outstanding processes receive a `SIGHUP' signal.)  If so, try starting
the server like this:

     shell> nohup mysqld [options] &

`nohup' causes the command following it to ignore any `SIGHUP' signal
sent from the terminal.  Alternatively, start the server by running
`safe_mysqld', which invokes `mysqld' using `nohup' for you.  *Note
`safe_mysqld': safe_mysqld.

If you get a problem when compiling mysys/get_opt.c, just remove the
line #define _NO_PROTO from the start of that file!

If you are using Compac's CC compiler, the following configure line
should work:

     CC="cc -pthread"
     CFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all -arch host"
     CXX="cxx -pthread"
     CXXFLAGS="-O4 -ansi_alias -ansi_args -fast -inline speed all -arch host \
     -noexceptions -nortti"
     export CC CFLAGS CXX CXXFLAGS
     ./configure \
     --prefix=/usr/local/mysql \
     --with-low-memory \
     --enable-large-files \
     --enable-shared=yes \
     --with-named-thread-libs="-lpthread -lmach -lexc -lc"
     gnumake

If you get a problem with libtool, when compiling with shared libraries
as above, when linking `mysql', you should be able to get around this
by issuing:

     cd mysql
     /bin/sh ../libtool --mode=link cxx -pthread  -O3 -DDBUG_OFF \
     -O4 -ansi_alias -ansi_args -fast -inline speed \
     -speculate all \ -arch host  -DUNDEF_HAVE_GETHOSTBYNAME_R \
     -o mysql  mysql.o readline.o sql_string.o completion_hash.o \
     ../readline/libreadline.a -lcurses \
     ../libmysql/.libs/libmysqlclient.so  -lm
     cd ..
     gnumake
     gnumake install
     scripts/mysql_install_db

Alpha-DEC-OSF/1 Notes
.....................

If you have problems compiling and have DEC `CC' and `gcc' installed,
try running `configure' like this:

     CC=cc CFLAGS=-O CXX=gcc CXXFLAGS=-O3 \
     ./configure --prefix=/usr/local/mysql

If you get problems with the `c_asm.h' file, you can create and use a
'dummy' `c_asm.h' file with:

     touch include/c_asm.h
     CC=gcc CFLAGS=-I./include \
     CXX=gcc CXXFLAGS=-O3 \
     ./configure --prefix=/usr/local/mysql

Note that the following problems with the `ld' program can be fixed by
downloading the latest DEC (Compaq) patch kit from:
`http://ftp.support.compaq.com/public/unix/'.

On OSF/1 V4.0D and compiler "DEC C V5.6-071 on Digital Unix V4.0 (Rev.
878)" the compiler had some strange behaviour (undefined `asm' symbols).
`/bin/ld' also appears to be broken (problems with `_exit undefined'
errors occuring while linking `mysqld').  On this system, we have
managed to compile MySQL with the following `configure' line, after
replacing `/bin/ld' with the version from OSF 4.0C:

     CC=gcc CXX=gcc CXXFLAGS=-O3 ./configure --prefix=/usr/local/mysql

With the Digital compiler "C++ V6.1-029", the following should work:

     CC=cc -pthread
     CFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all \
            -arch host
     CXX=cxx -pthread
     CXXFLAGS=-O4 -ansi_alias -ansi_args -fast -inline speed -speculate all \
               -arch host -noexceptions -nortti
     export CC CFLAGS CXX CXXFLAGS
     ./configure --prefix=/usr/mysql/mysql --with-mysqld-ldflags=-all-static \
                 --disable-shared --with-named-thread-libs="-lmach -lexc -lc"

In some versions of OSF/1, the `alloca()' function is broken. Fix this
by removing the line in `config.h' that defines `'HAVE_ALLOCA''.

The `alloca()' function also may have an incorrect prototype in
`/usr/include/alloca.h'.  This warning resulting from this can be
ignored.

`configure' will use the following thread libraries automatically:
`--with-named-thread-libs="-lpthread -lmach -lexc -lc"'.

When using `gcc', you can also try running `configure' like this:

     shell> CFLAGS=-D_PTHREAD_USE_D4 CXX=gcc CXXFLAGS=-O3 ./configure ...

If you have problems with signals (MySQL dies unexpectedly under high
load), you may have found an OS bug with threads and signals. In this
case you can tell MySQL not to use signals by configuring with:

     shell> CFLAGS=-DDONT_USE_THR_ALARM \
            CXXFLAGS=-DDONT_USE_THR_ALARM \
            ./configure ...

This doesn't affect the performance of MySQL, but has the side effect
that you can't kill clients that are "sleeping" on a connection with
`mysqladmin kill' or `mysqladmin shutdown'.  Instead, the client will
die when it issues its next command.

With `gcc' 2.95.2, you will probably run into the following compile
error:

     sql_acl.cc:1456: Internal compiler error in `scan_region', at except.c:2566
     Please submit a full bug report.

To fix this you should change to the `sql' directory and do a "cut and
paste" of the last `gcc' line, but change `-O3' to `-O0' (or add `-O0'
immediately after `gcc' if you don't have any `-O' option on your
compile line).  After this is done you can just change back to the
top-level directly and run `make' again.

SGI Irix Notes
..............

If you are using Irix Version 6.5.3 or newer `mysqld' will only be able
to create threads if you run it as a user with `CAP_SCHED_MGT'
privileges (like `root') or give the `mysqld' server this privilege
with the following shell command:

     shell> chcap "CAP_SCHED_MGT+epi" /opt/mysql/libexec/mysqld

You may have to undefine some things in `config.h' after running
`configure' and before compiling.

In some Irix implementations, the `alloca()' function is broken.  If the
`mysqld' server dies on some `SELECT' statements, remove the lines from
`config.h' that define `HAVE_ALLOC' and `HAVE_ALLOCA_H'.  If
`mysqladmin create' doesn't work, remove the line from `config.h' that
defines `HAVE_READDIR_R'.  You may have to remove the `HAVE_TERM_H'
line as well.

SGI recommends that you install all of the patches on this page as a
set:
`http://support.sgi.com/surfzone/patches/patchset/6.2_indigo.rps.html'

At the very minimum, you should install the latest kernel rollup, the
latest `rld' rollup, and the latest `libc' rollup.

You definitely need all the POSIX patches on this page, for pthreads
support:

`http://support.sgi.com/surfzone/patches/patchset/6.2_posix.rps.html'

If you get the something like the following error when compiling
`mysql.cc':

     "/usr/include/curses.h", line 82: error(1084): invalid combination of type

Type the following in the top-level directory of your MySQL source tree:

     shell> extra/replace bool curses_bool < /usr/include/curses.h \
     > include/curses.h
     shell> make

There have also been reports of scheduling problems.  If only one
thread is running, things go slow.  Avoid this by starting another
client.  This may lead to a 2-to-10-fold increase in execution speed
thereafter for the other thread.  This is a poorly understood problem
with Irix threads; you may have to improvise to find solutions until
this can be fixed.

If you are compiling with `gcc', you can use the following `configure'
command:

     CC=gcc CXX=gcc CXXFLAGS=-O3 \
     ./configure --prefix=/usr/local/mysql --enable-thread-safe-client \
     --with-named-thread-libs=-lpthread

On Irix 6.5.11 with native Irix C and C++ compilers ver. 7.3.1.2, the
following is reported to work

     CC=cc CXX=CC CFLAGS='-O3 -n32 -TARG:platform=IP22 -I/usr/local/include \
     -L/usr/local/lib' CXXFLAGS='-O3 -n32 -TARG:platform=IP22 \
     -I/usr/local/include -L/usr/local/lib' ./configure \
     --prefix=/usr/local/mysql --with-innodb --with-berkeley-db \
     --with-libwrap=/usr/local \
     --with-named-curses-libs=/usr/local/lib/libncurses.a

Caldera (SCO) Notes
...................

The current port is tested only on a "sco3.2v5.0.4" and "sco3.2v5.0.5"
system.  There has also been a lot of progress on a port to "sco
3.2v4.2".

For the moment the recommended compiler on OpenServer is gcc 2.95.2.
With this you should be able to compile MySQL with just:

     CC=gcc CXX=gcc ./configure ... (options)

  1. For OpenServer 5.0.X you need to use gcc-2.95.2p1 or newer from the
     Skunkware.  `http://www.caldera.com/skunkware/' and choose browser
     OpenServer packages or by ftp to ftp2.caldera.com in the
     pub/skunkware/osr5/devtools/gcc directory.

  2. You need the port of GCC 2.5.x for this product and the Development
     system.  They are required on this version of Caldera (SCO) Unix.
     You cannot just use the GCC Dev system.

  3. You should get the FSU Pthreads package and install it first.
     This can be found at
     `http://www.cs.wustl.edu/~schmidt/ACE_wrappers/FSU-threads.tar.gz'.
     You can also get a precompiled package from
     `http://www.mysql.com/Downloads/SCO/FSU-threads-3.5c.tar.gz'.

  4. FSU Pthreads can be compiled with Caldera (SCO) Unix 4.2 with
     tcpip.  Or OpenServer 3.0 or Open Desktop 3.0 (OS 3.0 ODT 3.0),
     with the Caldera (SCO) Development System installed using a good
     port of GCC 2.5.x ODT or OS 3.0 you will need a good port of GCC
     2.5.x There are a lot of problems without a good port.  The port
     for this product requires the SCO Unix Development system.
     Without it, you are missing the libraries and the linker that is
     needed.

  5. To build FSU Pthreads on your system, do the following:

       a. Run `./configure' in the `threads/src' directory and select
          the SCO OpenServer option. This command copies
          `Makefile.SCO5' to `Makefile'.

       b. Run `make'.

       c. To install in the default `/usr/include' directory, login as
          root, then `cd' to the `thread/src' directory, and run `make
          install'.

  6. Remember to use GNU `make' when making MySQL.

  7. If you don't start `safe_mysqld' as root, you probably will get
     only the default 110 open files per process.  `mysqld' will write
     a note about this in the log file.

  8. With SCO 3.2V5.0.5, you should use FSU Pthreads version 3.5c or
     newer.  You should also use gcc 2.95.2 or newer!

     The following `configure' command should work:

          shell> ./configure --prefix=/usr/local/mysql --disable-shared

  9. With SCO 3.2V4.2, you should use FSU Pthreads version 3.5c or
     newer.  The following `configure' command should work:

          shell> CFLAGS="-D_XOPEN_XPG4" CXX=gcc CXXFLAGS="-D_XOPEN_XPG4" \
                 ./configure \
                     --prefix=/usr/local/mysql \
                     --with-named-thread-libs="-lgthreads -lsocket -lgen -lgthreads" \
                     --with-named-curses-libs="-lcurses"

     You may get some problems with some include files. In this case,
     you can find new SCO-specific include files at
     `http://www.mysql.com/Downloads/SCO/SCO-3.2v4.2-includes.tar.gz'.
     You should unpack this file in the `include' directory of your
     MySQL source tree.

Caldera (SCO) development notes:

   * MySQL should automatically detect FSU Pthreads and link `mysqld'
     with `-lgthreads -lsocket -lgthreads'.

   * The Caldera (SCO) development libraries are re-entrant in FSU
     Pthreads.  Caldera claim sthat its libraries' functions are
     re-entrant, so they must be reentrant with FSU Pthreads.  FSU
     Pthreads on OpenServer tries to use the SCO scheme to make
     re-entrant libraries.

   * FSU Pthreads (at least the version at `http://www.mysql.com/')
     comes linked with GNU `malloc'.  If you encounter problems with
     memory usage, make sure that `gmalloc.o' is included in
     `libgthreads.a' and `libgthreads.so'.

   * In FSU Pthreads, the following system calls are pthreads-aware:
     `read()', `write()', `getmsg()', `connect()', `accept()',
     `select()', and `wait()'.

   * The CSSA-2001-SCO.35.2 (the patch is listed in custom as
     erg711905-dscr_remap security patch (version 2.0.0) breaks FSU
     threads and makes mysqld unstable.  You have to remove this one if
     you want to run mysqld on an OpenServer 5.0.6 machine.

If you want to install DBI on Caldera (SCO), you have to edit the
`Makefile' in DBI-xxx and each subdirectory.

Note that the following assumes gcc 2.95.2 or newer:

     OLD:                                  NEW:
     CC = cc                               CC = gcc
     CCCDLFLAGS = -KPIC -W1,-Bexport       CCCDLFLAGS = -fpic
     CCDLFLAGS = -wl,-Bexport              CCDLFLAGS =

     LD = ld                               LD = gcc -G -fpic
     LDDLFLAGS = -G -L/usr/local/lib       LDDLFLAGS = -L/usr/local/lib
     LDFLAGS = -belf -L/usr/local/lib      LDFLAGS = -L/usr/local/lib

     LD = ld                               LD = gcc -G -fpic
     OPTIMISE = -Od                        OPTIMISE = -O1

     OLD:
     CCCFLAGS = -belf -dy -w0 -U M_XENIX -DPERL_SCO5 -I/usr/local/include

     NEW:
     CCFLAGS = -U M_XENIX -DPERL_SCO5 -I/usr/local/include

This is because the Perl dynaloader will not load the `DBI' modules if
they were compiled with `icc' or `cc'.

Perl works best when compiled with `cc'.

Caldera (SCO) Unixware Version 7.0 Notes
........................................

You must use a version of MySQL at least as recent as Version 3.22.13
because that version fixes some portability problems under Unixware.

We have been able to compile MySQL with the following `configure'
command on Unixware Version 7.0.1:

     CC=cc CXX=CC ./configure --prefix=/usr/local/mysql

If you want to use `gcc', you must use `gcc' 2.95.2 or newer.

Caldera provides libsocket.so.2 at
`ftp://stage.caldera.com/pub/security/tools' for pre-OSR506 security
fixes. Also, the telnetd fix at
<ftp://stage.caldera.com/pub/security/openserver/CSSA-2001-SCO.10/> as
both libsocket.so.2 and libresolv.so.1 with instructions for installing
on pre-OSR506 systems.

It's probably a good idea to install the above patches before trying to
compile/use MySQL.

OS/2 Notes
----------

MySQL uses quite a few open files. Because of this, you should add
something like the following to your `CONFIG.SYS' file:

     SET EMXOPT=-c -n -h1024

If you don't do this, you will probably run into the following error:

     File 'xxxx' not found (Errcode: 24)

When using MySQL with OS/2 Warp 3, FixPack 29 or above is required.
With OS/2 Warp 4, FixPack 4 or above is required. This is a requirement
of the Pthreads library.  MySQL must be installed in a partition that
supports long filenames such as HPFS, FAT32, etc.

The `INSTALL.CMD' script must be run from OS/2's own `CMD.EXE' and may
not work with replacement shells such as `4OS2.EXE'.

The `scripts/mysql-install-db' script has been renamed.  It is now
called `install.cmd' and is a REXX script, which will set up the default
MySQL security settings and create the WorkPlace Shell icons for MySQL.

Dynamic module support is compiled in but not fully tested. Dynamic
modules should be compiled using the Pthreads run-time library.

     gcc -Zdll -Zmt -Zcrtdll=pthrdrtl -I../include -I../regex -I.. \
         -o example udf_example.cc -L../lib -lmysqlclient udf_example.def
     mv example.dll example.udf

*Note*: Due to limitations in OS/2, UDF module name stems must not
exceed 8 characters. Modules are stored in the `/mysql2/udf' directory;
the `safe-mysqld.cmd' script will put this directory in the
`BEGINLIBPATH' environment variable. When using UDF modules, specified
extensions are ignoredit is assumed to be `.udf'.  For example, in
Unix, the shared module might be named `example.so' and you would load
a function from it like this:

     mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example.so";

Is OS/2, the module would be named `example.udf', but you would not
specify the module extension:

     mysql> CREATE FUNCTION metaphon RETURNS STRING SONAME "example";

BeOS Notes
----------

We are really interested in getting MySQL to work on BeOS, but
unfortunately we don't have any person who knows BeOS or has time to do
a port.

We are interested in finding someone to do a port, and we will help them
with any technical questions they may have while doing the port.

We have previously talked with some BeOS developers that have said that
MySQL is 80% ported to BeOS, but we haven't heard from them in a while.

Novell NetWare Notes
--------------------

We are really interested in getting MySQL to work on NetWare, but
unfortunately we don't have any person who knows NetWare or has time to
do a port.

We are interested in finding someone to do a port, and we will help them
with any technical questions they may have while doing the port.

Perl Installation Comments
==========================

Installing Perl on Unix
-----------------------

Perl support for MySQL is provided by means of the `DBI'/`DBD' client
interface.  *Note Perl::.  The Perl `DBD'/`DBI' client code requires
Perl Version 5.004 or later.  The interface *will not work* if you have
an older version of Perl.

MySQL Perl support also requires that you've installed MySQL client
programming support.  If you installed MySQL from RPM files, client
programs are in the client RPM, but client programming support is in
the developer RPM.  Make sure you've installed the latter RPM.

As of Version 3.22.8, Perl support is distributed separately from the
main MySQL distribution.  If you want to install Perl support, the files
you will need can be obtained from
`http://www.mysql.com/downloads/api-dbi.html'.

The Perl distributions are provided as compressed `tar' archives and
have names like `MODULE-VERSION.tar.gz', where `MODULE' is the module
name and `VERSION' is the version number.  You should get the
`Data-Dumper', `DBI', and `Msql-Mysql-modules' distributions and
install them in that order.  The installation procedure is shown here.
The example shown is for the `Data-Dumper' module, but the procedure is
the same for all three distributions:

  1. Unpack the distribution into the current directory:
          shell> gunzip < Data-Dumper-VERSION.tar.gz | tar xvf -
     This command creates a directory named `Data-Dumper-VERSION'.

  2. Change into the top-level directory of the unpacked distribution:
          shell> cd Data-Dumper-VERSION

  3. Build the distribution and compile everything:
          shell> perl Makefile.PL
          shell> make
          shell> make test
          shell> make install

The `make test' command is important because it verifies that the
module is working.  Note that when you run that command during the
`Msql-Mysql-modules' installation to exercise the interface code, the
MySQL server must be running or the test will fail.

It is a good idea to rebuild and reinstall the `Msql-Mysql-modules'
distribution whenever you install a new release of MySQL, particularly
if you notice symptoms such as all your `DBI' scripts dumping core
after you upgrade MySQL.

If you don't have the right to install Perl modules in the system
directory or if you to install local Perl modules, the following
reference may help you:

     `http://www.iserver.com/support/contrib/perl5/modules.html'

Look under the heading `Installing New Modules that Require Locally
Installed Modules'.

Installing ActiveState Perl on Windows
--------------------------------------

To install the MySQL `DBD' module with ActiveState Perl on Windows, you
should do the following:

   * Get ActiveState Perl from
     `http://www.activestate.com/Products/ActivePerl/' and install it.

   * Open a DOS shell.

   * If required, set the HTTP_proxy variable. For example, you might
     try:

          set HTTP_proxy=my.proxy.com:3128

   * Start the PPM program:

          C:\> c:\perl\bin\ppm.pl

   * If you have not already done so, install `DBI':

          ppm> install DBI

   * If this succeeds, run the following command:

          install \
          ftp://ftp.de.uu.net/pub/CPAN/authors/id/JWIED/DBD-mysql-1.2212.x86.ppd

The above should work at least with ActiveState Perl Version 5.6.

If you can't get the above to work, you should instead install the
`MyODBC' driver and connect to MySQL server through ODBC:

     use DBI;
     $dbh= DBI->connect("DBI:ODBC:$dsn","$user","$password") ||
       die "Got error $DBI::errstr when connecting to $dsn\n";

Installing the MySQL Perl Distribution on Windows
-------------------------------------------------

The MySQL Perl distribution contains `DBI', `DBD:MySQL' and `DBD:ODBC'.

   * Get the Perl distribution for Windows from
     `http://www.mysql.com/downloads/os-win32.html'.

   * Unzip the distribution in `C:' so that you get a `C:\PERL'
     directory.

   * Add the directory `C:\PERL\BIN' to your path.

   * Add the directory `C:\PERL\BIN\MSWIN32-x86-thread' or
     `C:\PERL\BIN\MSWIN32-x86' to your path.

   * Test that `perl' works by executing `perl -v' in a DOS shell.

Problems Using the Perl `DBI'/`DBD' Interface
---------------------------------------------

If Perl reports that it can't find the `../mysql/mysql.so' module, then
the problem is probably that Perl can't locate the shared library
`libmysqlclient.so'.

You can fix this by any of the following methods:

   * Compile the `Msql-Mysql-modules' distribution with `perl
     Makefile.PL -static -config' rather than `perl Makefile.PL'.

   * Copy `libmysqlclient.so' to the directory where your other shared
     libraries are located (probably `/usr/lib' or `/lib').

   * On Linux you can add the pathname of the directory where
     `libmysqlclient.so' is located to the `/etc/ld.so.conf' file.

   * Add the pathname of the directory where `libmysqlclient.so' is
     located to the `LD_RUN_PATH' environment variable.

If you get the following errors from `DBD-mysql', you are probably
using `gcc' (or using an old binary compiled with `gcc'):

     /usr/bin/perl: can't resolve symbol '__moddi3'
     /usr/bin/perl: can't resolve symbol '__divdi3'

Add `-L/usr/lib/gcc-lib/... -lgcc' to the link command when the
`mysql.so' library gets built (check the output from `make' for
`mysql.so' when you compile the Perl client).  The `-L' option should
specify the pathname of the directory where `libgcc.a' is located on
your system.

Another cause of this problem may be that Perl and MySQL aren't both
compiled with `gcc'.  In this case, you can solve the mismatch by
compiling both with `gcc'.

If you get the following error from `Msql-Mysql-modules' when you run
the tests:

     t/00base............install_driver(mysql) failed:
     Can't load '../blib/arch/auto/DBD/mysql/mysql.so' for module DBD::mysql:
     ../blib/arch/auto/DBD/mysql/mysql.so: undefined symbol:
     uncompress at /usr/lib/perl5/5.00503/i586-linux/DynaLoader.pm line 169.

it means that you need to include the compression library, -lz, to the
link line. This can be doing the following change in the file
`lib/DBD/mysql/Install.pm':

     $sysliblist .= " -lm";

     to

     $sysliblist .= " -lm -lz";

After this, you *must* run 'make realclean' and then proceed with the
installation from the beginning.

If you want to use the Perl module on a system that doesn't support
dynamic linking (like Caldera/SCO) you can generate a static version of
Perl that includes `DBI' and `DBD-mysql'.  The way this works is that
you generate a version of Perl with the `DBI' code linked in and
install it on top of your current Perl.  Then you use that to build a
version of Perl that additionally has the `DBD' code linked in, and
install that.

On Caldera (SCO), you must have the following environment variables set:

     shell> LD_LIBRARY_PATH=/lib:/usr/lib:/usr/local/lib:/usr/progressive/lib
     or
     shell> LD_LIBRARY_PATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:\
     /usr/progressive/lib:/usr/skunk/lib
     shell> LIBPATH=/usr/lib:/lib:/usr/local/lib:/usr/ccs/lib:\
     /usr/progressive/lib:/usr/skunk/lib
     shell> MANPATH=scohelp:/usr/man:/usr/local1/man:/usr/local/man:\
     /usr/skunk/man:

First, create a Perl that includes a statically linked `DBI' by running
these commands in the directory where your `DBI' distribution is
located:

     shell> perl Makefile.PL -static -config
     shell> make
     shell> make install
     shell> make perl

Then you must install the new Perl. The output of `make perl' will
indicate the exact `make' command you will need to execute to perform
the installation.  On Caldera (SCO), this is `make -f Makefile.aperl
inst_perl MAP_TARGET=perl'.

Next, use the just-created Perl to create another Perl that also
includes a statically-linked `DBD::mysql' by running these commands in
the directory where your `Msql-Mysql-modules' distribution is located:

     shell> perl Makefile.PL -static -config
     shell> make
     shell> make install
     shell> make perl

Finally, you should install this new Perl.  Again, the output of `make
perl' indicates the command to use.

Tutorial Introduction
*********************

This chapter provides a tutorial introduction to MySQL by showing how
to use the `mysql' client program to create and use a simple database.
`mysql' (sometimes referred to as the "terminal monitor" or just
"monitor") is an interactive program that allows you to connect to a
MySQL server, run queries, and view the results.  `mysql' may also be
used in batch mode: you place your queries in a file beforehand, then
tell `mysql' to execute the contents of the file.  Both ways of using
`mysql' are covered here.

To see a list of options provided by `mysql', invoke it with the
`--help' option:

     shell> mysql --help

This chapter assumes that `mysql' is installed on your machine and that
a MySQL server is available to which you can connect.  If this is not
true, contact your MySQL administrator.  (If *you* are the
administrator, you will need to consult other sections of this manual.)

This chapter describes the entire process of setting up and using a
database.  If you are interested only in accessing an already-existing
database, you may want to skip over the sections that describe how to
create the database and the tables it contains.

Because this chapter is tutorial in nature, many details are
necessarily left out.  Consult the relevant sections of the manual for
more information on the topics covered here.

Connecting to and Disconnecting from the Server
===============================================

To connect to the server, you'll usually need to provide a MySQL user
name when you invoke `mysql' and, most likely, a password.  If the
server runs on a machine other than the one where you log in, you'll
also need to specify a hostname.  Contact your administrator to find
out what connection parameters you should use to connect (that is, what
host, user name, and password to use).  Once you know the proper
parameters, you should be able to connect like this:

     shell> mysql -h host -u user -p
     Enter password: ********

The `********' represents your password; enter it when `mysql' displays
the `Enter password:' prompt.

If that works, you should see some introductory information followed by
a `mysql>' prompt:

     shell> mysql -h host -u user -p
     Enter password: ********
     Welcome to the MySQL monitor.  Commands end with ; or \g.
     Your MySQL connection id is 459 to server version: 3.22.20a-log

     Type 'help' for help.

     mysql>

The prompt tells you that `mysql' is ready for you to enter commands.

Some MySQL installations allow users to connect as the anonymous
(unnamed) user to the server running on the local host.  If this is the
case on your machine, you should be able to connect to that server by
invoking `mysql' without any options:

     shell> mysql

After you have connected successfully, you can disconnect any time by
typing `QUIT' at the `mysql>' prompt:

     mysql> QUIT
     Bye

You can also disconnect by pressing Control-D.

Most examples in the following sections assume you are connected to the
server.  They indicate this by the `mysql>' prompt.

Entering Queries
================

Make sure you are connected to the server, as discussed in the previous
section.  Doing so will not in itself select any database to work with,
but that's okay.  At this point, it's more important to find out a
little about how to issue queries than to jump right in creating
tables, loading data into them, and retrieving data from them.  This
section describes the basic principles of entering commands, using
several queries you can try out to familiarise yourself with how
`mysql' works.

Here's a simple command that asks the server to tell you its version
number and the current date.  Type it in as shown here following the
`mysql>' prompt and press Enter:

     mysql> SELECT VERSION(), CURRENT_DATE;
     +--------------+--------------+
     | VERSION()    | CURRENT_DATE |
     +--------------+--------------+
     | 3.22.20a-log | 1999-03-19   |
     +--------------+--------------+
     1 row in set (0.01 sec)
     mysql>

This query illustrates several things about `mysql':

   * A command normally consists of a SQL statement followed by a
     semicolon.  (There are some exceptions where a semicolon is not
     needed.  `QUIT', mentioned earlier, is one of them.  We'll get to
     others later.)

   * When you issue a command, `mysql' sends it to the server for
     execution and displays the results, then prints another `mysql>'
     to indicate that it is ready for another command.

   * `mysql' displays query output as a table (rows and columns).  The
     first row contains labels for the columns.  The rows following are
     the query results.  Normally, column labels are the names of the
     columns you fetch from database tables.  If you're retrieving the
     value of an expression rather than a table column (as in the
     example just shown), `mysql' labels the column using the
     expression itself.

   * `mysql' shows how many rows were returned and how long the query
     took to execute, which gives you a rough idea of server
     performance.  These values are imprecise because they represent
     wall clock time (not CPU or machine time), and because they are
     affected by factors such as server load and network latency.  (For
     brevity, the "rows in set" line is not shown in the remaining
     examples in this chapter.)

Keywords may be entered in any lettercase.  The following queries are
equivalent:

     mysql> SELECT VERSION(), CURRENT_DATE;
     mysql> select version(), current_date;
     mysql> SeLeCt vErSiOn(), current_DATE;

Here's another query.  It demonstrates that you can use `mysql' as a
simple calculator:

     mysql> SELECT SIN(PI()/4), (4+1)*5;
     +-------------+---------+
     | SIN(PI()/4) | (4+1)*5 |
     +-------------+---------+
     |    0.707107 |      25 |
     +-------------+---------+

The commands shown thus far have been relatively short, single-line
statements.  You can even enter multiple statements on a single line.
Just end each one with a semicolon:

     mysql> SELECT VERSION(); SELECT NOW();
     +--------------+
     | VERSION()    |
     +--------------+
     | 3.22.20a-log |
     +--------------+

     +---------------------+
     | NOW()               |
     +---------------------+
     | 1999-03-19 00:15:33 |
     +---------------------+

A command need not be given all on a single line, so lengthy commands
that require several lines are not a problem.  `mysql' determines where
your statement ends by looking for the terminating semicolon, not by
looking for the end of the input line.  (In other words, `mysql'
accepts free-format input:  it collects input lines but does not
execute them until it sees the semicolon.)

Here's a simple multiple-line statement:

     mysql> SELECT
         -> USER()
         -> ,
         -> CURRENT_DATE;
     +--------------------+--------------+
     | USER()             | CURRENT_DATE |
     +--------------------+--------------+
     | joesmith@localhost | 1999-03-18   |
     +--------------------+--------------+

In this example, notice how the prompt changes from `mysql>' to `->'
after you enter the first line of a multiple-line query.  This is how
`mysql' indicates that it hasn't seen a complete statement and is
waiting for the rest.  The prompt is your friend, because it provides
valuable feedback.  If you use that feedback, you will always be aware
of what `mysql' is waiting for.

If you decide you don't want to execute a command that you are in the
process of entering, cancel it by typing `\c':

     mysql> SELECT
         -> USER()
         -> \c
     mysql>

Here, too, notice the prompt.  It switches back to `mysql>' after you
type `\c', providing feedback to indicate that `mysql' is ready for a
new command.

The following table shows each of the prompts you may see and
summarises what they mean about the state that `mysql' is in:

*Prompt**Meaning*
`mysql>'Ready for new command.
`       Waiting for next line of multiple-line command.
->'
`       Waiting for next line, collecting a string that begins
'>'     with a single quote (`'').
`       Waiting for next line, collecting a string that begins
">'     with a double quote (`"').

Multiple-line statements commonly occur by accident when you intend to
issue a command on a single line, but forget the terminating semicolon.
In this case, `mysql' waits for more input:

     mysql> SELECT USER()
         ->

If this happens to you (you think you've entered a statement but the
only response is a `->' prompt), most likely `mysql' is waiting for the
semicolon.  If you don't notice what the prompt is telling you, you
might sit there for a while before realising what you need to do.
Enter a semicolon to complete the statement, and `mysql' will execute
it:

     mysql> SELECT USER()
         -> ;
     +--------------------+
     | USER()             |
     +--------------------+
     | joesmith@localhost |
     +--------------------+

The `'>' and `">' prompts occur during string collection.  In MySQL,
you can write strings surrounded by either `'' or `"' characters (for
example, `'hello'' or `"goodbye"'), and `mysql' lets you enter strings
that span multiple lines.  When you see a `'>' or `">' prompt, it means
that you've entered a line containing a string that begins with a `''
or `"' quote character, but have not yet entered the matching quote
that terminates the string.  That's fine if you really are entering a
multiple-line string, but how likely is that?  Not very.  More often,
the `'>' and `">' prompts indicate that you've inadvertantly left out a
quote character.  For example:

     mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
         ">

If you enter this `SELECT' statement, then press Enter and wait for the
result, nothing will happen.  Instead of wondering why this query takes
so long, notice the clue provided by the `">' prompt.  It tells you
that `mysql' expects to see the rest of an unterminated string.  (Do
you see the error in the statement?  The string `"Smith' is missing the
second quote.)

At this point, what do you do?  The simplest thing is to cancel the
command.  However, you cannot just type `\c' in this case, because
`mysql' interprets it as part of the string that it is collecting!
Instead, enter the closing quote character (so `mysql' knows you've
finished the string), then type `\c':

     mysql> SELECT * FROM my_table WHERE name = "Smith AND age < 30;
         "> "\c
     mysql>

The prompt changes back to `mysql>', indicating that `mysql' is ready
for a new command.

It's important to know what the `'>' and `">' prompts signify, because
if you mistakenly enter an unterminated string, any further lines you
type will appear to be ignored by `mysql'including a line containing
`QUIT'!  This can be quite confusing, especially if you don't know that
you need to supply the terminating quote before you can cancel the
current command.

Creating and Using a Database
=============================

Now that you know how to enter commands, it's time to access a database.

Suppose you have several pets in your home (your menagerie) and you'd
like to keep track of various types of information about them.  You can
do so by creating tables to hold your data and loading them with the
desired information.  Then you can answer different sorts of questions
about your animals by retrieving data from the tables.  This section
shows you how to:

   * Create a database

   * Create a table

   * Load data into the table

   * Retrieve data from the table in various ways

   * Use multiple tables

The menagerie database will be simple (deliberately), but it is not
difficult to think of real-world situations in which a similar type of
database might be used.  For example, a database like this could be
used by a farmer to keep track of livestock, or by a veterinarian to
keep track of patient records.  A menagerie distribution containing
some of the queries and sample data used in the following sections can
be obtained from the MySQL web site.  It's available in either
compressed `tar' format
(`http://www.mysql.com/Downloads/Contrib/Examples/menagerie.tar.gz') or
Zip format
(`http://www.mysql.com/Downloads/Contrib/Examples/menagerie.zip').

Use the `SHOW' statement to find out what databases currently exist on
the server:

     mysql> SHOW DATABASES;
     +----------+
     | Database |
     +----------+
     | mysql    |
     | test     |
     | tmp      |
     +----------+

The list of databases is probably different on your machine, but the
`mysql' and `test' databases are likely to be among them.  The `mysql'
database is required because it describes user access privileges.  The
`test' database is often provided as a workspace for users to try
things out.

Note that you may not see all databases if you don't have the `SHOW
DATABASES' privilege. *Note GRANT::.

If the `test' database exists, try to access it:

     mysql> USE test
     Database changed

Note that `USE', like `QUIT', does not require a semicolon.  (You can
terminate such statements with a semicolon if you like; it does no
harm.)  The `USE' statement is special in another way, too:  it must be
given on a single line.

You can use the `test' database (if you have access to it) for the
examples that follow, but anything you create in that database can be
removed by anyone else with access to it.  For this reason, you should
probably ask your MySQL administrator for permission to use a database
of your own.  Suppose you want to call yours `menagerie'.  The
administrator needs to execute a command like this:

     mysql> GRANT ALL ON menagerie.* TO your_mysql_name;

where `your_mysql_name' is the MySQL user name assigned to you.

Creating and Selecting a Database
---------------------------------

If the administrator creates your database for you when setting up your
permissions, you can begin using it.  Otherwise, you need to create it
yourself:

     mysql> CREATE DATABASE menagerie;

Under Unix, database names are case-sensitive (unlike SQL keywords), so
you must always refer to your database as `menagerie', not as
`Menagerie', `MENAGERIE', or some other variant.  This is also true for
table names.  (Under Windows, this restriction does not apply, although
you must refer to databases and tables using the same lettercase
throughout a given query.)

Creating a database does not select it for use; you must do that
explicitly.  To make `menagerie' the current database, use this command:

     mysql> USE menagerie
     Database changed

Your database needs to be created only once, but you must select it for
use each time you begin a `mysql' session.  You can do this by issuing a
`USE' statement as shown above.  Alternatively, you can select the
database on the command-line when you invoke `mysql'.  Just specify its
name after any connection parameters that you might need to provide.
For example:

     shell> mysql -h host -u user -p menagerie
     Enter password: ********

Note that `menagerie' is not your password on the command just shown.
If you want to supply your password on the command-line after the `-p'
option, you must do so with no intervening space (for example, as
`-pmypassword', not as `-p mypassword').  However, putting your
password on the command-line is not recommended, because doing so
exposes it to snooping by other users logged in on your machine.

Creating a Table
----------------

Creating the database is the easy part, but at this point it's empty, as
`SHOW TABLES' will tell you:

     mysql> SHOW TABLES;
     Empty set (0.00 sec)

The harder part is deciding what the structure of your database should
be: what tables you will need and what columns will be in each of them.

You'll want a table that contains a record for each of your pets.  This
can be called the `pet' table, and it should contain, as a bare minimum,
each animal's name.  Because the name by itself is not very
interesting, the table should contain other information.  For example,
if more than one person in your family keeps pets, you might want to
list each animal's owner.  You might also want to record some basic
descriptive information such as species and sex.

How about age?  That might be of interest, but it's not a good thing to
store in a database.  Age changes as time passes, which means you'd
have to update your records often.  Instead, it's better to store a
fixed value such as date of birth.  Then, whenever you need age, you
can calculate it as the difference between the current date and the
birth date.  MySQL provides functions for doing date arithmetic, so
this is not difficult.  Storing birth date rather than age has other
advantages, too:

   * You can use the database for tasks such as generating reminders
     for upcoming pet birthdays.  (If you think this type of query is
     somewhat silly, note that it is the same question you might ask in
     the context of a business database to identify clients to whom
     you'll soon need to send out birthday greetings, for that
     computer-assisted personal touch.)

   * You can calculate age in relation to dates other than the current
     date.  For example, if you store death date in the database, you
     can easily calculate how old a pet was when it died.

You can probably think of other types of information that would be
useful in the `pet' table, but the ones identified so far are
sufficient for now: name, owner, species, sex, birth, and death.

Use a `CREATE TABLE' statement to specify the layout of your table:

     mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20),
         -> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE);

`VARCHAR' is a good choice for the `name', `owner', and `species'
columns because the column values will vary in length.  The lengths of
those columns need not all be the same, and need not be `20'.  You can
pick any length from `1' to `255', whatever seems most reasonable to
you.  (If you make a poor choice and it turns out later that you need a
longer field, MySQL provides an `ALTER TABLE' statement.)

Several types of values can be chosen to represent sex in animal
records, such as `"m"' and `"f"', or perhaps `"male"' and `"female"'.
It's simplest to use the single characters `"m"' and `"f"'.

The use of the `DATE' data type for the `birth' and `death' columns is
a fairly obvious choice.

Now that you have created a table, `SHOW TABLES' should produce some
output:

     mysql> SHOW TABLES;
     +---------------------+
     | Tables in menagerie |
     +---------------------+
     | pet                 |
     +---------------------+

To verify that your table was created the way you expected, use a
`DESCRIBE' statement:

     mysql> DESCRIBE pet;
     +---------+-------------+------+-----+---------+-------+
     | Field   | Type        | Null | Key | Default | Extra |
     +---------+-------------+------+-----+---------+-------+
     | name    | varchar(20) | YES  |     | NULL    |       |
     | owner   | varchar(20) | YES  |     | NULL    |       |
     | species | varchar(20) | YES  |     | NULL    |       |
     | sex     | char(1)     | YES  |     | NULL    |       |
     | birth   | date        | YES  |     | NULL    |       |
     | death   | date        | YES  |     | NULL    |       |
     +---------+-------------+------+-----+---------+-------+

You can use `DESCRIBE' any time, for example, if you forget the names of
the columns in your table or what types they are.

Loading Data into a Table
-------------------------

After creating your table, you need to populate it.  The `LOAD DATA' and
`INSERT' statements are useful for this.

Suppose your pet records can be described as shown here.  (Observe that
MySQL expects dates in `'YYYY-MM-DD'' format; this may be different
from what you are used to.)

*name*  *owner* *species**sex**birth*     *death*
Fluffy  Harold  cat     f    1993-02-04
Claws   Gwen    cat     m    1994-03-17
Buffy   Harold  dog     f    1989-05-13
Fang    Benny   dog     m    1990-08-27
Bowser  Diane   dog     m    1998-08-31  1995-07-29
Chirpy  Gwen    bird    f    1998-09-11
WhistlerGwen    bird         1997-12-09
Slim    Benny   snake   m    1996-04-29

Because you are beginning with an empty table, an easy way to populate
it is to create a text file containing a row for each of your animals,
then load the contents of the file into the table with a single
statement.

You could create a text file `pet.txt' containing one record per line,
with values separated by tabs, and given in the order in which the
columns were listed in the `CREATE TABLE' statement.  For missing
values (such as unknown sexes or death dates for animals that are still
living), you can use `NULL' values.  To represent these in your text
file, use `\N'.  For example, the record for Whistler the bird would
look like this (where the whitespace between values is a single tab
character):

*name*  *owner* *species**sex**birth*     *death*
`Whistler'`Gwen'  `bird'  `\N' `1997-12-09'`\N'

To load the text file `pet.txt' into the `pet' table, use this command:

     mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;

You can specify the column value separator and end of line marker
explicitly in the `LOAD DATA' statement if you wish, but the defaults
are tab and linefeed.  These are sufficient for the statement to read
the file `pet.txt' properly.

When you want to add new records one at a time, the `INSERT' statement
is useful.  In its simplest form, you supply values for each column, in
the order in which the columns were listed in the `CREATE TABLE'
statement.  Suppose Diane gets a new hamster named Puffball.  You could
add a new record using an `INSERT' statement like this:

     mysql> INSERT INTO pet
         -> VALUES ('Puffball','Diane','hamster','f','1999-03-30',NULL);

Note that string and date values are specified as quoted strings here.
Also, with `INSERT', you can insert `NULL' directly to represent a
missing value.  You do not use `\N' like you do with `LOAD DATA'.

From this example, you should be able to see that there would be a lot
more typing involved to load your records initially using several
`INSERT' statements rather than a single `LOAD DATA' statement.

Retrieving Information from a Table
-----------------------------------

The `SELECT' statement is used to pull information from a table.  The
general form of the statement is:

     SELECT what_to_select
     FROM which_table
     WHERE conditions_to_satisfy

`what_to_select' indicates what you want to see.  This can be a list of
columns, or `*' to indicate "all columns." `which_table' indicates the
table from which you want to retrieve data.  The `WHERE' clause is
optional.  If it's present, `conditions_to_satisfy' specifies
conditions that rows must satisfy to qualify for retrieval.

Selecting All Data
..................

The simplest form of `SELECT' retrieves everything from a table:

     mysql> SELECT * FROM pet;
     +----------+--------+---------+------+------------+------------+
     | name     | owner  | species | sex  | birth      | death      |
     +----------+--------+---------+------+------------+------------+
     | Fluffy   | Harold | cat     | f    | 1993-02-04 | NULL       |
     | Claws    | Gwen   | cat     | m    | 1994-03-17 | NULL       |
     | Buffy    | Harold | dog     | f    | 1989-05-13 | NULL       |
     | Fang     | Benny  | dog     | m    | 1990-08-27 | NULL       |
     | Bowser   | Diane  | dog     | m    | 1998-08-31 | 1995-07-29 |
     | Chirpy   | Gwen   | bird    | f    | 1998-09-11 | NULL       |
     | Whistler | Gwen   | bird    | NULL | 1997-12-09 | NULL       |
     | Slim     | Benny  | snake   | m    | 1996-04-29 | NULL       |
     | Puffball | Diane  | hamster | f    | 1999-03-30 | NULL       |
     +----------+--------+---------+------+------------+------------+

This form of `SELECT' is useful if you want to review your entire table,
for instance, after you've just loaded it with your initial dataset.
As it happens, the output just shown reveals an error in your datafile:
Bowser appears to have been born after he died!  Consulting your
original pedigree papers, you find that the correct birth year is 1989,
not 1998.

There are least a couple of ways to fix this:

   * Edit the file `pet.txt' to correct the error, then empty the table
     and reload it using `DELETE' and `LOAD DATA':

          mysql> SET AUTOCOMMIT=1;  # Used for quick re-create of the table
          mysql> DELETE FROM pet;
          mysql> LOAD DATA LOCAL INFILE "pet.txt" INTO TABLE pet;

     However, if you do this, you must also re-enter the record for
     Puffball.

   * Fix only the erroneous record with an `UPDATE' statement:

          mysql> UPDATE pet SET birth = "1989-08-31" WHERE name = "Bowser";

As shown above, it is easy to retrieve an entire table.  But typically
you don't want to do that, particularly when the table becomes large.
Instead, you're usually more interested in answering a particular
question, in which case you specify some constraints on the information
you want.  Let's look at some selection queries in terms of questions
about your pets that they answer.

Selecting Particular Rows
.........................

You can select only particular rows from your table.  For example, if
you want to verify the change that you made to Bowser's birth date,
select Bowser's record like this:

     mysql> SELECT * FROM pet WHERE name = "Bowser";
     +--------+-------+---------+------+------------+------------+
     | name   | owner | species | sex  | birth      | death      |
     +--------+-------+---------+------+------------+------------+
     | Bowser | Diane | dog     | m    | 1989-08-31 | 1995-07-29 |
     +--------+-------+---------+------+------------+------------+

The output confirms that the year is correctly recorded now as 1989,
not 1998.

String comparisons are normally case-insensitive, so you can specify the
name as `"bowser"', `"BOWSER"', etc.  The query result will be the same.

You can specify conditions on any column, not just `name'.  For example,
if you want to know which animals were born after 1998, test the `birth'
column:

     mysql> SELECT * FROM pet WHERE birth >= "1998-1-1";
     +----------+-------+---------+------+------------+-------+
     | name     | owner | species | sex  | birth      | death |
     +----------+-------+---------+------+------------+-------+
     | Chirpy   | Gwen  | bird    | f    | 1998-09-11 | NULL  |
     | Puffball | Diane | hamster | f    | 1999-03-30 | NULL  |
     +----------+-------+---------+------+------------+-------+

You can combine conditions, for example, to locate female dogs:

     mysql> SELECT * FROM pet WHERE species = "dog" AND sex = "f";
     +-------+--------+---------+------+------------+-------+
     | name  | owner  | species | sex  | birth      | death |
     +-------+--------+---------+------+------------+-------+
     | Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |
     +-------+--------+---------+------+------------+-------+

The preceding query uses the `AND' logical operator.  There is also an
`OR' operator:

     mysql> SELECT * FROM pet WHERE species = "snake" OR species = "bird";
     +----------+-------+---------+------+------------+-------+
     | name     | owner | species | sex  | birth      | death |
     +----------+-------+---------+------+------------+-------+
     | Chirpy   | Gwen  | bird    | f    | 1998-09-11 | NULL  |
     | Whistler | Gwen  | bird    | NULL | 1997-12-09 | NULL  |
     | Slim     | Benny | snake   | m    | 1996-04-29 | NULL  |
     +----------+-------+---------+------+------------+-------+

`AND' and `OR' may be intermixed.  If you do that, it's a good idea to
use parentheses to indicate how conditions should be grouped:

     mysql> SELECT * FROM pet WHERE (species = "cat" AND sex = "m")
         -> OR (species = "dog" AND sex = "f");
     +-------+--------+---------+------+------------+-------+
     | name  | owner  | species | sex  | birth      | death |
     +-------+--------+---------+------+------------+-------+
     | Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |
     | Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |
     +-------+--------+---------+------+------------+-------+

Selecting Particular Columns
............................

If you don't want to see entire rows from your table, just name the
columns in which you're interested, separated by commas.  For example,
if you want to know when your animals were born, select the `name' and
`birth' columns:

     mysql> SELECT name, birth FROM pet;
     +----------+------------+
     | name     | birth      |
     +----------+------------+
     | Fluffy   | 1993-02-04 |
     | Claws    | 1994-03-17 |
     | Buffy    | 1989-05-13 |
     | Fang     | 1990-08-27 |
     | Bowser   | 1989-08-31 |
     | Chirpy   | 1998-09-11 |
     | Whistler | 1997-12-09 |
     | Slim     | 1996-04-29 |
     | Puffball | 1999-03-30 |
     +----------+------------+

To find out who owns pets, use this query:

     mysql> SELECT owner FROM pet;
     +--------+
     | owner  |
     +--------+
     | Harold |
     | Gwen   |
     | Harold |
     | Benny  |
     | Diane  |
     | Gwen   |
     | Gwen   |
     | Benny  |
     | Diane  |
     +--------+

However, notice that the query simply retrieves the `owner' field from
each record, and some of them appear more than once.  To minimise the
output, retrieve each unique output record just once by adding the
keyword `DISTINCT':

     mysql> SELECT DISTINCT owner FROM pet;
     +--------+
     | owner  |
     +--------+
     | Benny  |
     | Diane  |
     | Gwen   |
     | Harold |
     +--------+

You can use a `WHERE' clause to combine row selection with column
selection.  For example, to get birth dates for dogs and cats only, use
this query:

     mysql> SELECT name, species, birth FROM pet
         -> WHERE species = "dog" OR species = "cat";
     +--------+---------+------------+
     | name   | species | birth      |
     +--------+---------+------------+
     | Fluffy | cat     | 1993-02-04 |
     | Claws  | cat     | 1994-03-17 |
     | Buffy  | dog     | 1989-05-13 |
     | Fang   | dog     | 1990-08-27 |
     | Bowser | dog     | 1989-08-31 |
     +--------+---------+------------+

Sorting Rows
............

You may have noticed in the preceding examples that the result rows are
displayed in no particular order.  However, it's often easier to examine
query output when the rows are sorted in some meaningful way.  To sort a
result, use an `ORDER BY' clause.

Here are animal birthdays, sorted by date:

     mysql> SELECT name, birth FROM pet ORDER BY birth;
     +----------+------------+
     | name     | birth      |
     +----------+------------+
     | Buffy    | 1989-05-13 |
     | Bowser   | 1989-08-31 |
     | Fang     | 1990-08-27 |
     | Fluffy   | 1993-02-04 |
     | Claws    | 1994-03-17 |
     | Slim     | 1996-04-29 |
     | Whistler | 1997-12-09 |
     | Chirpy   | 1998-09-11 |
     | Puffball | 1999-03-30 |
     +----------+------------+

On character type columns, sortinglike all other comparison
operationsis normally performed in a case-insensitive fashion.  This
means that the order will be undefined for columns that are identical
except for their case. You can force a case-sensitive sort by using the
BINARY cast: `ORDER BY BINARY(field)'.

To sort in reverse order, add the `DESC' (descending) keyword to the
name of the column you are sorting by:

     mysql> SELECT name, birth FROM pet ORDER BY birth DESC;
     +----------+------------+
     | name     | birth      |
     +----------+------------+
     | Puffball | 1999-03-30 |
     | Chirpy   | 1998-09-11 |
     | Whistler | 1997-12-09 |
     | Slim     | 1996-04-29 |
     | Claws    | 1994-03-17 |
     | Fluffy   | 1993-02-04 |
     | Fang     | 1990-08-27 |
     | Bowser   | 1989-08-31 |
     | Buffy    | 1989-05-13 |
     +----------+------------+

You can sort on multiple columns.  For example, to sort by type of
animal, then by birth date within animal type with youngest animals
first, use the following query:

     mysql> SELECT name, species, birth FROM pet ORDER BY species, birth DESC;
     +----------+---------+------------+
     | name     | species | birth      |
     +----------+---------+------------+
     | Chirpy   | bird    | 1998-09-11 |
     | Whistler | bird    | 1997-12-09 |
     | Claws    | cat     | 1994-03-17 |
     | Fluffy   | cat     | 1993-02-04 |
     | Fang     | dog     | 1990-08-27 |
     | Bowser   | dog     | 1989-08-31 |
     | Buffy    | dog     | 1989-05-13 |
     | Puffball | hamster | 1999-03-30 |
     | Slim     | snake   | 1996-04-29 |
     +----------+---------+------------+

Note that the `DESC' keyword applies only to the column name immediately
preceding it (`birth'); `species' values are still sorted in ascending
order.

Date Calculations
.................

MySQL provides several functions that you can use to perform
calculations on dates, for example, to calculate ages or extract parts
of dates.

To determine how many years old each of your pets is, compute the
difference in the year part of the current date and the birth date, then
subtract one if the current date occurs earlier in the calendar year
than the birth date.  The following query shows, for each pet, the
birth date, the current date, and the age in years.

     mysql> SELECT name, birth, CURRENT_DATE,
         -> (YEAR(CURRENT_DATE)-YEAR(birth))
         -> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
         -> AS age
         -> FROM pet;
     +----------+------------+--------------+------+
     | name     | birth      | CURRENT_DATE | age  |
     +----------+------------+--------------+------+
     | Fluffy   | 1993-02-04 | 2001-08-29   |    8 |
     | Claws    | 1994-03-17 | 2001-08-29   |    7 |
     | Buffy    | 1989-05-13 | 2001-08-29   |   12 |
     | Fang     | 1990-08-27 | 2001-08-29   |   11 |
     | Bowser   | 1989-08-31 | 2001-08-29   |   11 |
     | Chirpy   | 1998-09-11 | 2001-08-29   |    2 |
     | Whistler | 1997-12-09 | 2001-08-29   |    3 |
     | Slim     | 1996-04-29 | 2001-08-29   |    5 |
     | Puffball | 1999-03-30 | 2001-08-29   |    2 |
     +----------+------------+--------------+------+

Here, `YEAR()' pulls out the year part of a date and `RIGHT()' pulls
off the rightmost five characters that represent the `MM-DD' (calendar
year) part of the date.  The part of the expression that compares the
`MM-DD' values evaluates to 1 or 0, which adjusts the year difference
down a year if `CURRENT_DATE' occurs earlier in the year than `birth'.
The full expression is somewhat ungainly, so an alias (`age') is used
to make the output column label more meaningful.

The query works, but the result could be scanned more easily if the rows
were presented in some order.  This can be done by adding an `ORDER BY
name' clause to sort the output by name:

     mysql> SELECT name, birth, CURRENT_DATE,
         -> (YEAR(CURRENT_DATE)-YEAR(birth))
         -> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
         -> AS age
         -> FROM pet ORDER BY name;
     +----------+------------+--------------+------+
     | name     | birth      | CURRENT_DATE | age  |
     +----------+------------+--------------+------+
     | Bowser   | 1989-08-31 | 2001-08-29   |   11 |
     | Buffy    | 1989-05-13 | 2001-08-29   |   12 |
     | Chirpy   | 1998-09-11 | 2001-08-29   |    2 |
     | Claws    | 1994-03-17 | 2001-08-29   |    7 |
     | Fang     | 1990-08-27 | 2001-08-29   |   11 |
     | Fluffy   | 1993-02-04 | 2001-08-29   |    8 |
     | Puffball | 1999-03-30 | 2001-08-29   |    2 |
     | Slim     | 1996-04-29 | 2001-08-29   |    5 |
     | Whistler | 1997-12-09 | 2001-08-29   |    3 |
     +----------+------------+--------------+------+

To sort the output by `age' rather than `name', just use a different
`ORDER BY' clause:

     mysql> SELECT name, birth, CURRENT_DATE,
         -> (YEAR(CURRENT_DATE)-YEAR(birth))
         -> - (RIGHT(CURRENT_DATE,5)<RIGHT(birth,5))
         -> AS age
         -> FROM pet ORDER BY age;
     +----------+------------+--------------+------+
     | name     | birth      | CURRENT_DATE | age  |
     +----------+------------+--------------+------+
     | Chirpy   | 1998-09-11 | 2001-08-29   |    2 |
     | Puffball | 1999-03-30 | 2001-08-29   |    2 |
     | Whistler | 1997-12-09 | 2001-08-29   |    3 |
     | Slim     | 1996-04-29 | 2001-08-29   |    5 |
     | Claws    | 1994-03-17 | 2001-08-29   |    7 |
     | Fluffy   | 1993-02-04 | 2001-08-29   |    8 |
     | Fang     | 1990-08-27 | 2001-08-29   |   11 |
     | Bowser   | 1989-08-31 | 2001-08-29   |   11 |
     | Buffy    | 1989-05-13 | 2001-08-29   |   12 |
     +----------+------------+--------------+------+

A similar query can be used to determine age at death for animals that
have died.  You determine which animals these are by checking whether
the `death' value is `NULL'.  Then, for those with non-`NULL' values,
compute the difference between the `death' and `birth' values:

     mysql> SELECT name, birth, death,
         -> (YEAR(death)-YEAR(birth)) - (RIGHT(death,5)<RIGHT(birth,5))
         -> AS age
         -> FROM pet WHERE death IS NOT NULL ORDER BY age;
     +--------+------------+------------+------+
     | name   | birth      | death      | age  |
     +--------+------------+------------+------+
     | Bowser | 1989-08-31 | 1995-07-29 |    5 |
     +--------+------------+------------+------+

The query uses `death IS NOT NULL' rather than `death <> NULL' because
`NULL' is a special value.  This is explained later.  *Note Working
with `NULL': Working with NULL.

What if you want to know which animals have birthdays next month?  For
this type of calculation, year and day are irrelevant; you simply want
to extract the month part of the `birth' column.  MySQL provides several
date-part extraction functions, such as `YEAR()', `MONTH()', and
`DAYOFMONTH()'.  `MONTH()' is the appropriate function here.  To see
how it works, run a simple query that displays the value of both
`birth' and `MONTH(birth)':

     mysql> SELECT name, birth, MONTH(birth) FROM pet;
     +----------+------------+--------------+
     | name     | birth      | MONTH(birth) |
     +----------+------------+--------------+
     | Fluffy   | 1993-02-04 |            2 |
     | Claws    | 1994-03-17 |            3 |
     | Buffy    | 1989-05-13 |            5 |
     | Fang     | 1990-08-27 |            8 |
     | Bowser   | 1989-08-31 |            8 |
     | Chirpy   | 1998-09-11 |            9 |
     | Whistler | 1997-12-09 |           12 |
     | Slim     | 1996-04-29 |            4 |
     | Puffball | 1999-03-30 |            3 |
     +----------+------------+--------------+

Finding animals with birthdays in the upcoming month is easy, too.
Suppose the current month is April.  Then the month value is `4' and
you look for animals born in May (month 5) like this:

     mysql> SELECT name, birth FROM pet WHERE MONTH(birth) = 5;
     +-------+------------+
     | name  | birth      |
     +-------+------------+
     | Buffy | 1989-05-13 |
     +-------+------------+

There is a small complication if the current month is December, of
course.  You don't just add one to the month number (`12') and look for
animals born in month 13, because there is no such month.  Instead, you
look for animals born in January (month 1).

You can even write the query so that it works no matter what the current
month is.  That way you don't have to use a particular month number in
the query.  `DATE_ADD()' allows you to add a time interval to a given
date.  If you add a month to the value of `NOW()', then extract the
month part with `MONTH()', the result produces the month in which to
look for birthdays:

     mysql> SELECT name, birth FROM pet
         -> WHERE MONTH(birth) = MONTH(DATE_ADD(NOW(), INTERVAL 1 MONTH));

A different way to accomplish the same task is to add `1' to get the
next month after the current one (after using the modulo function
(`MOD') to wrap around the month value to `0' if it is currently `12'):

     mysql> SELECT name, birth FROM pet
         -> WHERE MONTH(birth) = MOD(MONTH(NOW()), 12) + 1;

Note that `MONTH' returns a number between 1 and 12. And
`MOD(something,12)' returns a number between 0 and 11. So the addition
has to be after the `MOD()', otherwise we would go from November (11)
to January (1).

Working with `NULL' Values
..........................

The `NULL' value can be surprising until you get used to it.
Conceptually, `NULL' means missing value or unknown value and it is
treated somewhat differently than other values.  To test for `NULL',
you cannot use the arithmetic comparison operators such as `=', `<', or
`<>'.  To demonstrate this for yourself, try the following query:

     mysql> SELECT 1 = NULL, 1 <> NULL, 1 < NULL, 1 > NULL;
     +----------+-----------+----------+----------+
     | 1 = NULL | 1 <> NULL | 1 < NULL | 1 > NULL |
     +----------+-----------+----------+----------+
     |     NULL |      NULL |     NULL |     NULL |
     +----------+-----------+----------+----------+

Clearly you get no meaningful results from these comparisons.  Use the
`IS NULL' and `IS NOT NULL' operators instead:

     mysql> SELECT 1 IS NULL, 1 IS NOT NULL;
     +-----------+---------------+
     | 1 IS NULL | 1 IS NOT NULL |
     +-----------+---------------+
     |         0 |             1 |
     +-----------+---------------+

Note that in MySQL, 0 or `NULL' means false and anything else means
true. The default truth value from a boolean operation is 1.

This special treatment of `NULL' is why, in the previous section, it
was necessary to determine which animals are no longer alive using
`death IS NOT NULL' instead of `death <> NULL'.

Two `NULL' values are regarded as equal in a `GROUP BY'.

When doing an `ORDER BY', `NULL' values are presented first.  In
versions prior to 4.0.2, if you sort in descending order using `DESC',
`NULL' values are presented last.

Pattern Matching
................

MySQL provides standard SQL pattern matching as well as a form of
pattern matching based on extended regular expressions similar to those
used by Unix utilities such as `vi', `grep', and `sed'.

SQL pattern matching allows you to use `_' to match any single
character and `%' to match an arbitrary number of characters (including
zero characters).  In MySQL, SQL patterns are case-insensitive by
default.  Some examples are shown here.  Note that you do not use `='
or `<>' when you use SQL patterns; use the `LIKE' or `NOT LIKE'
comparison operators instead.

To find names beginning with `b':

     mysql> SELECT * FROM pet WHERE name LIKE "b%";
     +--------+--------+---------+------+------------+------------+
     | name   | owner  | species | sex  | birth      | death      |
     +--------+--------+---------+------+------------+------------+
     | Buffy  | Harold | dog     | f    | 1989-05-13 | NULL       |
     | Bowser | Diane  | dog     | m    | 1989-08-31 | 1995-07-29 |
     +--------+--------+---------+------+------------+------------+

To find names ending with `fy':

     mysql> SELECT * FROM pet WHERE name LIKE "%fy";
     +--------+--------+---------+------+------------+-------+
     | name   | owner  | species | sex  | birth      | death |
     +--------+--------+---------+------+------------+-------+
     | Fluffy | Harold | cat     | f    | 1993-02-04 | NULL  |
     | Buffy  | Harold | dog     | f    | 1989-05-13 | NULL  |
     +--------+--------+---------+------+------------+-------+

To find names containing a `w':

     mysql> SELECT * FROM pet WHERE name LIKE "%w%";
     +----------+-------+---------+------+------------+------------+
     | name     | owner | species | sex  | birth      | death      |
     +----------+-------+---------+------+------------+------------+
     | Claws    | Gwen  | cat     | m    | 1994-03-17 | NULL       |
     | Bowser   | Diane | dog     | m    | 1989-08-31 | 1995-07-29 |
     | Whistler | Gwen  | bird    | NULL | 1997-12-09 | NULL       |
     +----------+-------+---------+------+------------+------------+

To find names containing exactly five characters, use the `_' pattern
character:

     mysql> SELECT * FROM pet WHERE name LIKE "_____";
     +-------+--------+---------+------+------------+-------+
     | name  | owner  | species | sex  | birth      | death |
     +-------+--------+---------+------+------------+-------+
     | Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |
     | Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |
     +-------+--------+---------+------+------------+-------+

The other type of pattern matching provided by MySQL uses extended
regular expressions.  When you test for a match for this type of
pattern, use the `REGEXP' and `NOT REGEXP' operators (or `RLIKE' and
`NOT RLIKE', which are synonyms).

Some characteristics of extended regular expressions are:

   * `.' matches any single character.

   * A character class `[...]' matches any character within the
     brackets.  For example, `[abc]' matches `a', `b', or `c'.  To name
     a range of characters, use a dash.  `[a-z]' matches any lowercase
     letter, whereas `[0-9]' matches any digit.

   * `*' matches zero or more instances of the thing preceding it.  For
     example, `x*' matches any number of `x' characters, `[0-9]*'
     matches any number of digits, and `.*' matches any number of
     anything.

   * The pattern matches if it occurs anywhere in the value being
     tested.  (SQL patterns match only if they match the entire value.)

   * To anchor a pattern so that it must match the beginning or end of
     the value being tested, use `^' at the beginning or `$' at the end
     of the pattern.

To demonstrate how extended regular expressions work, the `LIKE' queries
shown previously are rewritten here to use `REGEXP'.

To find names beginning with `b', use `^' to match the beginning of the
name:

     mysql> SELECT * FROM pet WHERE name REGEXP "^b";
     +--------+--------+---------+------+------------+------------+
     | name   | owner  | species | sex  | birth      | death      |
     +--------+--------+---------+------+------------+------------+
     | Buffy  | Harold | dog     | f    | 1989-05-13 | NULL       |
     | Bowser | Diane  | dog     | m    | 1989-08-31 | 1995-07-29 |
     +--------+--------+---------+------+------------+------------+

Prior to MySQL Version 3.23.4, `REGEXP' is case-sensitive, and the
previous query will return no rows. To match either lowercase or
uppercase `b', use this query instead:

     mysql> SELECT * FROM pet WHERE name REGEXP "^[bB]";

From MySQL 3.23.4 on, to force a `REGEXP' comparison to be
case-sensitive, use the `BINARY' keyword to make one of the strings a
binary string. This query will match only lowercase `b' at the
beginning of a name:

     mysql> SELECT * FROM pet WHERE name REGEXP BINARY "^b";

To find names ending with `fy', use `$' to match the end of the name:

     mysql> SELECT * FROM pet WHERE name REGEXP "fy$";
     +--------+--------+---------+------+------------+-------+
     | name   | owner  | species | sex  | birth      | death |
     +--------+--------+---------+------+------------+-------+
     | Fluffy | Harold | cat     | f    | 1993-02-04 | NULL  |
     | Buffy  | Harold | dog     | f    | 1989-05-13 | NULL  |
     +--------+--------+---------+------+------------+-------+

To find names containing a lowercase or uppercase `w', use this query:

     mysql> SELECT * FROM pet WHERE name REGEXP "w";
     +----------+-------+---------+------+------------+------------+
     | name     | owner | species | sex  | birth      | death      |
     +----------+-------+---------+------+------------+------------+
     | Claws    | Gwen  | cat     | m    | 1994-03-17 | NULL       |
     | Bowser   | Diane | dog     | m    | 1989-08-31 | 1995-07-29 |
     | Whistler | Gwen  | bird    | NULL | 1997-12-09 | NULL       |
     +----------+-------+---------+------+------------+------------+

Because a regular expression pattern matches if it occurs anywhere in
the value, it is not necessary in the previous query to put a wildcard
on either side of the pattern to get it to match the entire value like
it would be if you used a SQL pattern.

To find names containing exactly five characters, use `^' and `$' to
match the beginning and end of the name, and five instances of `.' in
between:

     mysql> SELECT * FROM pet WHERE name REGEXP "^.....$";
     +-------+--------+---------+------+------------+-------+
     | name  | owner  | species | sex  | birth      | death |
     +-------+--------+---------+------+------------+-------+
     | Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |
     | Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |
     +-------+--------+---------+------+------------+-------+

You could also write the previous query using the `{n}'
"repeat-`n'-times" operator:

     mysql> SELECT * FROM pet WHERE name REGEXP "^.{5}$";
     +-------+--------+---------+------+------------+-------+
     | name  | owner  | species | sex  | birth      | death |
     +-------+--------+---------+------+------------+-------+
     | Claws | Gwen   | cat     | m    | 1994-03-17 | NULL  |
     | Buffy | Harold | dog     | f    | 1989-05-13 | NULL  |
     +-------+--------+---------+------+------------+-------+

Counting Rows
.............

Databases are often used to answer the question, "How often does a
certain type of data occur in a table?"  For example, you might want to
know how many pets you have, or how many pets each owner has, or you
might want to perform various kinds of censuses on your animals.

Counting the total number of animals you have is the same question as
"How many rows are in the `pet' table?" because there is one record per
pet.  The `COUNT()' function counts the number of non-`NULL' results, so
the query to count your animals looks like this:

     mysql> SELECT COUNT(*) FROM pet;
     +----------+
     | COUNT(*) |
     +----------+
     |        9 |
     +----------+

Earlier, you retrieved the names of the people who owned pets.  You can
use `COUNT()' if you want to find out how many pets each owner has:

     mysql> SELECT owner, COUNT(*) FROM pet GROUP BY owner;
     +--------+----------+
     | owner  | COUNT(*) |
     +--------+----------+
     | Benny  |        2 |
     | Diane  |        2 |
     | Gwen   |        3 |
     | Harold |        2 |
     +--------+----------+

Note the use of `GROUP BY' to group together all records for each
`owner'.  Without it, all you get is an error message:

     mysql> SELECT owner, COUNT(owner) FROM pet;
     ERROR 1140 at line 1: Mixing of GROUP columns (MIN(),MAX(),COUNT()...)
     with no GROUP columns is illegal if there is no GROUP BY clause

`COUNT()' and `GROUP BY' are useful for characterising your data in
various ways.  The following examples show different ways to perform
animal census operations.

Number of animals per species:

     mysql> SELECT species, COUNT(*) FROM pet GROUP BY species;
     +---------+----------+
     | species | COUNT(*) |
     +---------+----------+
     | bird    |        2 |
     | cat     |        2 |
     | dog     |        3 |
     | hamster |        1 |
     | snake   |        1 |
     +---------+----------+

Number of animals per sex:

     mysql> SELECT sex, COUNT(*) FROM pet GROUP BY sex;
     +------+----------+
     | sex  | COUNT(*) |
     +------+----------+
     | NULL |        1 |
     | f    |        4 |
     | m    |        4 |
     +------+----------+

(In this output, `NULL' indicates sex unknown.)

Number of animals per combination of species and sex:

     mysql> SELECT species, sex, COUNT(*) FROM pet GROUP BY species, sex;
     +---------+------+----------+
     | species | sex  | COUNT(*) |
     +---------+------+----------+
     | bird    | NULL |        1 |
     | bird    | f    |        1 |
     | cat     | f    |        1 |
     | cat     | m    |        1 |
     | dog     | f    |        1 |
     | dog     | m    |        2 |
     | hamster | f    |        1 |
     | snake   | m    |        1 |
     +---------+------+----------+

You need not retrieve an entire table when you use `COUNT()'.  For
example, the previous query, when performed just on dogs and cats,
looks like this:

     mysql> SELECT species, sex, COUNT(*) FROM pet
         -> WHERE species = "dog" OR species = "cat"
         -> GROUP BY species, sex;
     +---------+------+----------+
     | species | sex  | COUNT(*) |
     +---------+------+----------+
     | cat     | f    |        1 |
     | cat     | m    |        1 |
     | dog     | f    |        1 |
     | dog     | m    |        2 |
     +---------+------+----------+

Or, if you wanted the number of animals per sex only for known-sex
animals:

     mysql> SELECT species, sex, COUNT(*) FROM pet
         -> WHERE sex IS NOT NULL
         -> GROUP BY species, sex;
     +---------+------+----------+
     | species | sex  | COUNT(*) |
     +---------+------+----------+
     | bird    | f    |        1 |
     | cat     | f    |        1 |
     | cat     | m    |        1 |
     | dog     | f    |        1 |
     | dog     | m    |        2 |
     | hamster | f    |        1 |
     | snake   | m    |        1 |
     +---------+------+----------+

Using More Than one Table
.........................

The `pet' table keeps track of which pets you have.  If you want to
record other information about them, such as events in their lives like
visits to the vet or when litters are born, you need another table.
What should this table look like? It needs:

   * To contain the pet name so you know which animal each event
     pertains to.

   * A date so you know when the event occurred.

   * A field to describe the event.

   * An event type field, if you want to be able to categorise events.

Given these considerations, the `CREATE TABLE' statement for the
`event' table might look like this:

     mysql> CREATE TABLE event (name VARCHAR(20), date DATE,
         -> type VARCHAR(15), remark VARCHAR(255));

As with the `pet' table, it's easiest to load the initial records by
creating a tab-delimited text file containing the information:

*name*  *date*      *type*  *remark*
Fluffy  1995-05-15  litter  4 kittens, 3 female, 1
                            male
Buffy   1993-06-23  litter  5 puppies, 2 female, 3
                            male
Buffy   1994-06-19  litter  3 puppies, 3 female
Chirpy  1999-03-21  vet     needed beak straightened
Slim    1997-08-03  vet     broken rib
Bowser  1991-10-12  kennel
Fang    1991-10-12  kennel
Fang    1998-08-28  birthdayGave him a new chew toy
Claws   1998-03-17  birthdayGave him a new flea
                            collar
Whistler1998-12-09  birthdayFirst birthday

Load the records like this:

     mysql> LOAD DATA LOCAL INFILE "event.txt" INTO TABLE event;

Based on what you've learned from the queries you've run on the `pet'
table, you should be able to perform retrievals on the records in the
`event' table; the principles are the same.  But when is the `event'
table by itself insufficient to answer questions you might ask?

Suppose you want to find out the ages of each pet when they had their
litters.  The `event' table indicates when this occurred, but to
calculate the age of the mother, you need her birth date.  Because that
is stored in the `pet' table, you need both tables for the query:

     mysql> SELECT pet.name,
         -> (TO_DAYS(date) - TO_DAYS(birth))/365 AS age,
         -> remark
         -> FROM pet, event
         -> WHERE pet.name = event.name AND type = "litter";
     +--------+------+-----------------------------+
     | name   | age  | remark                      |
     +--------+------+-----------------------------+
     | Fluffy | 2.27 | 4 kittens, 3 female, 1 male |
     | Buffy  | 4.12 | 5 puppies, 2 female, 3 male |
     | Buffy  | 5.10 | 3 puppies, 3 female         |
     +--------+------+-----------------------------+

There are several things to note about this query:

   * The `FROM' clause lists two tables because the query needs to pull
     information from both of them.

   * When combining (joining) information from multiple tables, you
     need to specify how records in one table can be matched to records
     in the other.  This is easy because they both have a `name'
     column.  The query uses `WHERE' clause to match up records in the
     two tables based on the `name' values.

   * Because the `name' column occurs in both tables, you must be
     specific about which table you mean when referring to the column.
     This is done by prepending the table name to the column name.

You need not have two different tables to perform a join.  Sometimes it
is useful to join a table to itself, if you want to compare records in
a table to other records in that same table.  For example, to find
breeding pairs among your pets, you can join the `pet' table with
itself to pair up males and females of like species:

     mysql> SELECT p1.name, p1.sex, p2.name, p2.sex, p1.species
         -> FROM pet AS p1, pet AS p2
         -> WHERE p1.species = p2.species AND p1.sex = "f" AND p2.sex = "m";
     +--------+------+--------+------+---------+
     | name   | sex  | name   | sex  | species |
     +--------+------+--------+------+---------+
     | Fluffy | f    | Claws  | m    | cat     |
     | Buffy  | f    | Fang   | m    | dog     |
     | Buffy  | f    | Bowser | m    | dog     |
     +--------+------+--------+------+---------+

In this query, we specify aliases for the table name in order to refer
to the columns and keep straight which instance of the table each
column reference is associated with.

Getting Information About Databases and Tables
==============================================

What if you forget the name of a database or table, or what the
structure of a given table is (for example, what its columns are
called)?  MySQL addresses this problem through several statements that
provide information about the databases and tables it supports.

You have already seen `SHOW DATABASES', which lists the databases
managed by the server.  To find out which database is currently
selected, use the `DATABASE()' function:

     mysql> SELECT DATABASE();
     +------------+
     | DATABASE() |
     +------------+
     | menagerie  |
     +------------+

If you haven't selected any database yet, the result is blank.

To find out what tables the current database contains (for example, when
you're not sure about the name of a table), use this command:

     mysql> SHOW TABLES;
     +---------------------+
     | Tables in menagerie |
     +---------------------+
     | event               |
     | pet                 |
     +---------------------+

If you want to find out about the structure of a table, the `DESCRIBE'
command is useful; it displays information about each of a table's
columns:

     mysql> DESCRIBE pet;
     +---------+-------------+------+-----+---------+-------+
     | Field   | Type        | Null | Key | Default | Extra |
     +---------+-------------+------+-----+---------+-------+
     | name    | varchar(20) | YES  |     | NULL    |       |
     | owner   | varchar(20) | YES  |     | NULL    |       |
     | species | varchar(20) | YES  |     | NULL    |       |
     | sex     | char(1)     | YES  |     | NULL    |       |
     | birth   | date        | YES  |     | NULL    |       |
     | death   | date        | YES  |     | NULL    |       |
     +---------+-------------+------+-----+---------+-------+

`Field' indicates the column name, `Type' is the data type for the
column, `NULL' indicates whether the column can contain `NULL' values,
`Key' indicates whether the column is indexed, and `Default' specifies
the column's default value.

If you have indexes on a table, `SHOW INDEX FROM tbl_name' produces
information about them.

Examples of Common Queries
==========================

Here are examples of how to solve some common problems with MySQL.

Some of the examples use the table `shop' to hold the price of each
article (item number) for certain traders (dealers).  Supposing that
each trader has a single fixed price per article, then (`article',
`dealer') is a primary key for the records.

Start the command-line tool `mysql' and select a database:

     mysql your-database-name

(In most MySQL installations, you can use the database-name 'test').

You can create the example table as:

     CREATE TABLE shop (
      article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
      dealer  CHAR(20)                 DEFAULT ''     NOT NULL,
      price   DOUBLE(16,2)             DEFAULT '0.00' NOT NULL,
      PRIMARY KEY(article, dealer));

     INSERT INTO shop VALUES
     (1,'A',3.45),(1,'B',3.99),(2,'A',10.99),(3,'B',1.45),(3,'C',1.69),
     (3,'D',1.25),(4,'D',19.95);

Okay, so the example data is:

     mysql> SELECT * FROM shop;

     +---------+--------+-------+
     | article | dealer | price |
     +---------+--------+-------+
     |    0001 | A      |  3.45 |
     |    0001 | B      |  3.99 |
     |    0002 | A      | 10.99 |
     |    0003 | B      |  1.45 |
     |    0003 | C      |  1.69 |
     |    0003 | D      |  1.25 |
     |    0004 | D      | 19.95 |
     +---------+--------+-------+

The Maximum Value for a Column
------------------------------

"What's the highest item number?"

     SELECT MAX(article) AS article FROM shop

     +---------+
     | article |
     +---------+
     |       4 |
     +---------+

The Row Holding the Maximum of a Certain Column
-----------------------------------------------

"Find number, dealer, and price of the most expensive article."

In ANSI SQL this is easily done with a subquery:

     SELECT article, dealer, price
     FROM   shop
     WHERE  price=(SELECT MAX(price) FROM shop)

In MySQL (which does not yet have subselects), just do it in two steps:

  1. Get the maximum price value from the table with a `SELECT'
     statement.

  2. Using this value compile the actual query:
          SELECT article, dealer, price
          FROM   shop
          WHERE  price=19.95

Another solution is to sort all rows descending by price and only get
the first row using the MySQL-specific `LIMIT' clause:

     SELECT article, dealer, price
     FROM   shop
     ORDER BY price DESC
     LIMIT 1

*NOTE*:  If there are several most expensive articles (for example,
each 19.95) the `LIMIT' solution shows only one of them!

Maximum of Column per Group
---------------------------

"What's the highest price per article?"

     SELECT article, MAX(price) AS price
     FROM   shop
     GROUP BY article

     +---------+-------+
     | article | price |
     +---------+-------+
     |    0001 |  3.99 |
     |    0002 | 10.99 |
     |    0003 |  1.69 |
     |    0004 | 19.95 |
     +---------+-------+

The Rows Holding the Group-wise Maximum of a Certain Field
----------------------------------------------------------

"For each article, find the dealer(s) with the most expensive price."

In ANSI SQL, I'd do it with a subquery like this:

     SELECT article, dealer, price
     FROM   shop s1
     WHERE  price=(SELECT MAX(s2.price)
                   FROM shop s2
                   WHERE s1.article = s2.article);

In MySQL it's best do it in several steps:

  1. Get the list of (article,maxprice).

  2. For each article get the corresponding rows that have the stored
     maximum price.

This can easily be done with a temporary table:

     CREATE TEMPORARY TABLE tmp (
             article INT(4) UNSIGNED ZEROFILL DEFAULT '0000' NOT NULL,
             price   DOUBLE(16,2)             DEFAULT '0.00' NOT NULL);

     LOCK TABLES shop read;

     INSERT INTO tmp SELECT article, MAX(price) FROM shop GROUP BY article;

     SELECT shop.article, dealer, shop.price FROM shop, tmp
     WHERE shop.article=tmp.article AND shop.price=tmp.price;

     UNLOCK TABLES;

     DROP TABLE tmp;

If you don't use a `TEMPORARY' table, you must also lock the 'tmp'
table.

"Can it be done with a single query?"

Yes, but only by using a quite inefficient trick that I call the
"MAX-CONCAT trick":

     SELECT article,
            SUBSTRING( MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 7) AS dealer,
       0.00+LEFT(      MAX( CONCAT(LPAD(price,6,'0'),dealer) ), 6) AS price
     FROM   shop
     GROUP BY article;

     +---------+--------+-------+
     | article | dealer | price |
     +---------+--------+-------+
     |    0001 | B      |  3.99 |
     |    0002 | A      | 10.99 |
     |    0003 | C      |  1.69 |
     |    0004 | D      | 19.95 |
     +---------+--------+-------+

The last example can, of course, be made a bit more efficient by doing
the splitting of the concatenated column in the client.

Using user variables
--------------------

You can use MySQL user variables to remember results without having to
store them in temporary variables in the client.  *Note Variables::.

For example, to find the articles with the highest and lowest price you
can do:

     mysql> SELECT @min_price:=MIN(price),@max_price:=MAX(price) FROM shop;
     mysql> SELECT * FROM shop WHERE price=@min_price OR price=@max_price;
     +---------+--------+-------+
     | article | dealer | price |
     +---------+--------+-------+
     |    0003 | D      |  1.25 |
     |    0004 | D      | 19.95 |
     +---------+--------+-------+

Using Foreign Keys
------------------

In MySQL 3.23.44 and up, `InnoDB' tables supports checking of foreign
key constraints. *Note InnoDB::.  See also *Note ANSI diff Foreign
Keys::.

You don't actually need foreign keys to join 2 tables.  The only thing
MySQL currently doesn't do (in table types other than `InnoDB'), is
`CHECK' to make sure that the keys you use really exist in the table(s)
you're referencing and it doesn't automatically delete rows from a
table with a foreign key definition. If you use your keys like normal,
it'll work just fine:

     CREATE TABLE person (
         id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
         name CHAR(60) NOT NULL,
         PRIMARY KEY (id)
     );

     CREATE TABLE shirt (
         id SMALLINT UNSIGNED NOT NULL AUTO_INCREMENT,
         style ENUM('t-shirt', 'polo', 'dress') NOT NULL,
         color ENUM('red', 'blue', 'orange', 'white', 'black') NOT NULL,
         owner SMALLINT UNSIGNED NOT NULL REFERENCES person(id),
         PRIMARY KEY (id)
     );


     INSERT INTO person VALUES (NULL, 'Antonio Paz');

     INSERT INTO shirt VALUES
     (NULL, 'polo', 'blue', LAST_INSERT_ID()),
     (NULL, 'dress', 'white', LAST_INSERT_ID()),
     (NULL, 't-shirt', 'blue', LAST_INSERT_ID());


     INSERT INTO person VALUES (NULL, 'Lilliana Angelovska');

     INSERT INTO shirt VALUES
     (NULL, 'dress', 'orange', LAST_INSERT_ID()),
     (NULL, 'polo', 'red', LAST_INSERT_ID()),
     (NULL, 'dress', 'blue', LAST_INSERT_ID()),
     (NULL, 't-shirt', 'white', LAST_INSERT_ID());


     SELECT * FROM person;
     +----+---------------------+
     | id | name                |
     +----+---------------------+
     |  1 | Antonio Paz         |
     |  2 | Lilliana Angelovska |
     +----+---------------------+

     SELECT * FROM shirt;
     +----+---------+--------+-------+
     | id | style   | color  | owner |
     +----+---------+--------+-------+
     |  1 | polo    | blue   |     1 |
     |  2 | dress   | white  |     1 |
     |  3 | t-shirt | blue   |     1 |
     |  4 | dress   | orange |     2 |
     |  5 | polo    | red    |     2 |
     |  6 | dress   | blue   |     2 |
     |  7 | t-shirt | white  |     2 |
     +----+---------+--------+-------+


     SELECT s.* FROM person p, shirt s
      WHERE p.name LIKE 'Lilliana%'
        AND s.owner = p.id
        AND s.color <> 'white';

     +----+-------+--------+-------+
     | id | style | color  | owner |
     +----+-------+--------+-------+
     |  4 | dress | orange |     2 |
     |  5 | polo  | red    |     2 |
     |  6 | dress | blue   |     2 |
     +----+-------+--------+-------+

Searching on Two Keys
---------------------

MySQL doesn't yet optimise when you search on two different keys
combined with `OR' (searching on one key with different `OR' parts is
optimised quite well):

     SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1'
     OR  field2_index = '1'

The reason is that we haven't yet had time to come up with an efficient
way to handle this in the general case. (The `AND' handling is, in
comparison, now completely general and works very well.)

For the moment you can solve this very efficiently by using a
`TEMPORARY' table. This type of optimisation is also very good if you
are using very complicated queries where the SQL server does the
optimisations in the wrong order.

     CREATE TEMPORARY TABLE tmp
     SELECT field1_index, field2_index FROM test_table WHERE field1_index = '1';
     INSERT INTO tmp
     SELECT field1_index, field2_index FROM test_table WHERE field2_index = '1';
     SELECT * from tmp;
     DROP TABLE tmp;

The above way to solve this query is in effect a `UNION' of two queries.
*Note UNION::.

Calculating Visits Per Day
--------------------------

The following shows an idea of how you can use the bit group functions
to calculate the number of days per month a user has visited a web page.

     CREATE TABLE t1 (year YEAR(4), month INT(2) UNSIGNED ZEROFILL,
                  day INT(2) UNSIGNED ZEROFILL);
     INSERT INTO t1 VALUES(2000,1,1),(2000,1,20),(2000,1,30),(2000,2,2),
                 (2000,2,23),(2000,2,23);
     SELECT year,month,BIT_COUNT(BIT_OR(1<<day)) AS days FROM t1
            GROUP BY year,month;

     Which returns:

     +------+-------+------+
     | year | month | days |
     +------+-------+------+
     | 2000 |    01 |    3 |
     | 2000 |    02 |    2 |
     +------+-------+------+

The above calculates how many different days was used for a given
year/month combination, with automatic removal of duplicate entries.

Using `AUTO_INCREMENT'
----------------------

The `AUTO_INCREMENT' attribute can be used to generate a unique
identity for new rows:

     CREATE TABLE animals (
                  id MEDIUMINT NOT NULL AUTO_INCREMENT,
                  name CHAR(30) NOT NULL,
                  PRIMARY KEY (id)
                  );
     INSERT INTO animals (name) VALUES ("dog"),("cat"),("penguin"),
                                       ("lax"),("whale");
     SELECT * FROM animals;

     Which returns:

     +----+---------+
     | id | name    |
     +----+---------+
     |  1 | dog     |
     |  2 | cat     |
     |  3 | penguin |
     |  4 | lax     |
     |  5 | whale   |
     +----+---------+

You can retrieve the used `AUTO_INCREMENT' key with the
`LAST_INSERT_ID()' SQL function or the `mysql_insert_id()' API function.
Note: for a multi-row insert, `LAST_INSERT_ID()'/`mysql_insert_id()'
will actually return the `AUTO_INCREMENT' key from the *first* inserted
row. This allows multi-row inserts to be reproduced on other servers.

For MyISAM and BDB tables you can specify `AUTO_INCREMENT' on secondary
column in a multi-column key.  In this case the generated value for the
autoincrement column is calculated as `MAX(auto_increment_column)+1)
WHERE prefix=given-prefix'.  This is useful when you want to put data
into ordered groups.

     CREATE TABLE animals (
                  grp ENUM('fish','mammal','bird') NOT NULL,
                  id MEDIUMINT NOT NULL AUTO_INCREMENT,
                  name CHAR(30) NOT NULL,
                  PRIMARY KEY (grp,id)
                  );
     INSERT INTO animals (grp,name) VALUES("mammal","dog"),("mammal","cat"),
                       ("bird","penguin"),("fish","lax"),("mammal","whale");
     SELECT * FROM animals ORDER BY grp,id;

     Which returns:

     +--------+----+---------+
     | grp    | id | name    |
     +--------+----+---------+
     | fish   |  1 | lax     |
     | mammal |  1 | dog     |
     | mammal |  2 | cat     |
     | mammal |  3 | whale   |
     | bird   |  1 | penguin |
     +--------+----+---------+

Note that in this case, the `AUTO_INCREMENT' value will be reused if you
delete the row with the biggest `AUTO_INCREMENT' value in any group.

Using `mysql' in Batch Mode
===========================

In the previous sections, you used `mysql' interactively to enter
queries and view the results.  You can also run `mysql' in batch mode.
To do this, put the commands you want to run in a file, then tell
`mysql' to read its input from the file:

     shell> mysql < batch-file

If you are running `mysql' under windows and have some special
characters in the file that causes problems, you can do:

     dos> mysql -e "source batch-file"

If you need to specify connection parameters on the command-line, the
command might look like this:

     shell> mysql -h host -u user -p < batch-file
     Enter password: ********

When you use `mysql' this way, you are creating a script file, then
executing the script.

If you want the script to continue even if you have errors, you should
use the `--force' command-line option.

Why use a script?  Here are a few reasons:

   * If you run a query repeatedly (say, every day or every week),
     making it a script allows you to avoid retyping it each time you
     execute it.

   * You can generate new queries from existing ones that are similar
     by copying and editing script files.

   * Batch mode can also be useful while you're developing a query,
     particularly for multiple-line commands or multiple-statement
     sequences of commands.  If you make a mistake, you don't have to
     retype everything.  Just edit your script to correct the error,
     then tell `mysql' to execute it again.

   * If you have a query that produces a lot of output, you can run the
     output through a pager rather than watching it scroll off the top
     of your screen:

          shell> mysql < batch-file | more

   * You can catch the output in a file for further processing:

          shell> mysql < batch-file > mysql.out

   * You can distribute your script to other people so they can run the
     commands, too.

   * Some situations do not allow for interactive use, for example,
     when you run a query from a `cron' job.  In this case, you must
     use batch mode.

The default output format is different (more concise) when you run
`mysql' in batch mode than when you use it interactively.  For example,
the output of `SELECT DISTINCT species FROM pet' looks like this when
run interactively:

     +---------+
     | species |
     +---------+
     | bird    |
     | cat     |
     | dog     |
     | hamster |
     | snake   |
     +---------+

But like this when run in batch mode:

     species
     bird
     cat
     dog
     hamster
     snake

If you want to get the interactive output format in batch mode, use
`mysql -t'.  To echo to the output the commands that are executed, use
`mysql -vvv'.

You can also use scripts in the `mysql' command-line prompt by using
the `source' command:

     mysql> source filename;

Queries from Twin Project
=========================

At Analytikerna and Lentus, we have been doing the systems and field
work for a big research project. This project is a collaboration
between the Institute of Environmental Medicine at Karolinska
Institutet Stockholm and the Section on Clinical Research in Aging and
Psychology at the University of Southern California.

The project involves a screening part where all twins in Sweden older
than 65 years are interviewed by telephone. Twins who meet certain
criteria are passed on to the next stage. In this latter stage, twins
who want to participate are visited by a doctor/nurse team. Some of the
examinations include physical and neuropsychological examination,
laboratory testing, neuroimaging, psychological status assessment, and
family history collection. In addition, data are collected on medical
and environmental risk factors.

More information about Twin studies can be found at:
`http://www.imm.ki.se/TWIN/TWINUKW.HTM'

The latter part of the project is administered with a web interface
written using Perl and MySQL.

Each night all data from the interviews are moved into a MySQL database.

Find all Non-distributed Twins
------------------------------

The following query is used to determine who goes into the second part
of the project:

     SELECT
             CONCAT(p1.id, p1.tvab) + 0 AS tvid,
             CONCAT(p1.christian_name, " ", p1.surname) AS Name,
             p1.postal_code AS Code,
             p1.city AS City,
             pg.abrev AS Area,
             IF(td.participation = "Aborted", "A", " ") AS A,
             p1.dead AS dead1,
             l.event AS event1,
             td.suspect AS tsuspect1,
             id.suspect AS isuspect1,
             td.severe AS tsevere1,
             id.severe AS isevere1,
             p2.dead AS dead2,
             l2.event AS event2,
             h2.nurse AS nurse2,
             h2.doctor AS doctor2,
             td2.suspect AS tsuspect2,
             id2.suspect AS isuspect2,
             td2.severe AS tsevere2,
             id2.severe AS isevere2,
             l.finish_date
     FROM
             twin_project AS tp
             /* For Twin 1 */
             LEFT JOIN twin_data AS td ON tp.id = td.id
                       AND tp.tvab = td.tvab
             LEFT JOIN informant_data AS id ON tp.id = id.id
                       AND tp.tvab = id.tvab
             LEFT JOIN harmony AS h ON tp.id = h.id
                       AND tp.tvab = h.tvab
             LEFT JOIN lentus AS l ON tp.id = l.id
                       AND tp.tvab = l.tvab
             /* For Twin 2 */
             LEFT JOIN twin_data AS td2 ON p2.id = td2.id
                       AND p2.tvab = td2.tvab
             LEFT JOIN informant_data AS id2 ON p2.id = id2.id
                       AND p2.tvab = id2.tvab
             LEFT JOIN harmony AS h2 ON p2.id = h2.id
                       AND p2.tvab = h2.tvab
             LEFT JOIN lentus AS l2 ON p2.id = l2.id
                       AND p2.tvab = l2.tvab,
             person_data AS p1,
             person_data AS p2,
             postal_groups AS pg
     WHERE
             /* p1 gets main twin and p2 gets his/her twin. */
             /* ptvab is a field inverted from tvab */
             p1.id = tp.id AND p1.tvab = tp.tvab AND
             p2.id = p1.id AND p2.ptvab = p1.tvab AND
             /* Just the sceening survey */
             tp.survey_no = 5 AND
             /* Skip if partner died before 65 but allow emigration (dead=9) */
             (p2.dead = 0 OR p2.dead = 9 OR
              (p2.dead = 1 AND
               (p2.death_date = 0 OR
                (((TO_DAYS(p2.death_date) - TO_DAYS(p2.birthday)) / 365)
                 >= 65))))
             AND
             (
             /* Twin is suspect */
             (td.future_contact = 'Yes' AND td.suspect = 2) OR
             /* Twin is suspect - Informant is Blessed */
             (td.future_contact = 'Yes' AND td.suspect = 1
                                        AND id.suspect = 1) OR
             /* No twin - Informant is Blessed */
             (ISNULL(td.suspect) AND id.suspect = 1
                                 AND id.future_contact = 'Yes') OR
             /* Twin broken off - Informant is Blessed */
             (td.participation = 'Aborted'
              AND id.suspect = 1 AND id.future_contact = 'Yes') OR
             /* Twin broken off - No inform - Have partner */
             (td.participation = 'Aborted' AND ISNULL(id.suspect)
                                           AND p2.dead = 0))
             AND
             l.event = 'Finished'
             /* Get at area code */
             AND SUBSTRING(p1.postal_code, 1, 2) = pg.code
             /* Not already distributed */
             AND (h.nurse IS NULL OR h.nurse=00 OR h.doctor=00)
             /* Has not refused or been aborted */
             AND NOT (h.status = 'Refused' OR h.status = 'Aborted'
             OR h.status = 'Died' OR h.status = 'Other')
     ORDER BY
             tvid;

Some explanations:
`CONCAT(p1.id, p1.tvab) + 0 AS tvid'
     We want to sort on the concatenated `id' and `tvab' in numerical
     order. Adding `0' to the result causes MySQL to treat the result
     as a number.

column `id'
     This identifies a pair of twins. It is a key in all tables.

column `tvab'
     This identifies a twin in a pair. It has a value of `1' or `2'.

column `ptvab'
     This is an inverse of `tvab'. When `tvab' is `1' this is `2', and
     vice versa. It exists to save typing and to make it easier for
     MySQL to optimise the query.

This query demonstrates, among other things, how to do lookups on a
table from the same table with a join (`p1' and `p2'). In the example,
this is used to check whether a twin's partner died before the age of
65. If so, the row is not returned.

All of the above exist in all tables with twin-related information. We
have a key on both `id,tvab' (all tables), and `id,ptvab'
(`person_data') to make queries faster.

On our production machine (A 200MHz UltraSPARC), this query returns
about 150-200 rows and takes less than one second.

The current number of records in the tables used above:
*Table*            *Rows*
`person_data'      71074
`lentus'           5291
`twin_project'     5286
`twin_data'        2012
`informant_data'   663
`harmony'          381
`postal_groups'    100

Show a Table on Twin Pair Status
--------------------------------

Each interview ends with a status code called `event'. The query shown
here is used to display a table over all twin pairs combined by event.
This indicates in how many pairs both twins are finished, in how many
pairs one twin is finished and the other refused, and so on.

     SELECT
             t1.event,
             t2.event,
             COUNT(*)
     FROM
             lentus AS t1,
             lentus AS t2,
             twin_project AS tp
     WHERE
             /* We are looking at one pair at a time */
             t1.id = tp.id
             AND t1.tvab=tp.tvab
             AND t1.id = t2.id
             /* Just the sceening survey */
             AND tp.survey_no = 5
             /* This makes each pair only appear once */
             AND t1.tvab='1' AND t2.tvab='2'
     GROUP BY
             t1.event, t2.event;

Using MySQL with Apache
=======================

There are programs that let you authenticate your users from a MySQL
database and also let you log your log files into a MySQL table.

You can change the Apache logging format to be easily readable by MySQL
by putting the following into the Apache configuration file:

     LogFormat \
             "\"%h\",%{%Y%m%d%H%M%S}t,%>s,\"%b\",\"%{Content-Type}o\",  \
             \"%U\",\"%{Referer}i\",\"%{User-Agent}i\""

In MySQL you can do something like this:

     LOAD DATA INFILE '/local/access_log' INTO TABLE table_name
     FIELDS TERMINATED BY ',' OPTIONALLY ENCLOSED BY '"' ESCAPED BY '\\'

Database Administration
***********************

Configuring MySQL
=================

`mysqld' Command-line Options
-----------------------------

In most cases you should manage mysqld options through option files.
*Note Option files::.

`mysqld' and `mysqld.server' reads options from the `mysqld' and
`server' groups. `mysqld_safe' read options from the `mysqld',
`server', `mysqld_safe' and `safe_mysqld' groups.  An embedded MySQL
server usually reads options from the `server', `embedded' and
`xxxxx_SERVER', where `xxxxx' is the name of the application.

`mysqld' accepts the following command-line options:

`--ansi'
     Use ANSI SQL syntax instead of MySQL syntax.  *Note ANSI mode::.

`-b, --basedir=path'
     Path to installation directory. All paths are usually resolved
     relative to this.

`--big-tables'
     Allow big result sets by saving all temporary sets on file.  It
     solves most 'table full' errors, but also slows down the queries
     where in-memory tables would suffice.  Since Version 3.23.2, MySQL
     is able to solve it automatically by using memory for small
     temporary tables and switching to disk tables where necessary.

`--bind-address=IP'
     IP address to bind to.

`--character-sets-dir=path'
     Directory where character sets are.  *Note Character sets::.

`--chroot=path'
     Put `mysqld' daemon in chroot environment at startup. Recommended
     security measure since MySQL 4.0 (MySQL 3.23 is not able to provide
     100% closed chroot jail).  It somewhat limits `LOAD DATA INFILE'
     and `SELECT ... INTO OUTFILE' though.

`--core-file'
     Write a core file if `mysqld' dies.  For some systems you must also
     specify `--core-file-size' to `safe_mysqld'.  *Note `safe_mysqld':
     safe_mysqld.  Note that on some systems, like Solaris, you will
     not get a core file if you are also using the `--user' option.

`-h, --datadir=path'
     Path to the database root.

`--debug[...]='
     If MySQL is configured with `--with-debug', you can use this
     option to get a trace file of what `mysqld' is doing.  *Note
     Making trace files::.

`--default-character-set=charset'
     Set the default character set.  *Note Character sets::.

`--default-table-type=type'
     Set the default table type for tables.  *Note Table types::.

`--delay-key-write[= OFF | ON | ALL]'
     How MyISAM `DELAYED KEYS' should be used. *Note Server
     parameters::.

`--delay-key-write-for-all-tables;  In MySQL 4.0.3 you should use --delay-key-write=ALL instead.'
     Don't flush key buffers between writes for any `MyISAM' table.
     *Note Server parameters::.

`--des-key-file=filename'
     Read the default keys used by `DES_ENCRYPT()' and `DES_DECRYPT()'
     from this file.

`--enable-external-locking (was --enable-locking)'
     Enable system locking.  Note that if you use this option on a
     system on which `lockd' does not fully work (as on Linux), you
     will easily get mysqld to deadlock.

`--enable-named-pipe'
     Enable support for named pipes (only on NT/Win2000/XP).

`-T, --exit-info'
     This is a bit mask of different flags one can use for debugging the
     mysqld server; one should not use this option if one doesn't know
     exactly what it does!

`--flush'
     Flush all changes to disk after each SQL command.  Normally MySQL
     only does a write of all changes to disk after each SQL command
     and lets the operating system handle the syncing to disk.  *Note
     Crashing::.

`-?, --help'
     Display short help and exit.

`--init-file=file'
     Read SQL commands from this file at startup.

`-L, --language=...'
     Client error messages in given language.  May be given as a full
     path.  *Note Languages::.

`-l, --log[=file]'
     Log connections and queries to file. *Note Query log::.

`--log-isam[=file]'
     Log all ISAM/MyISAM changes to file (only used when debugging
     ISAM/MyISAM).

`--log-slow-queries[=file]'
     Log all queries that have taken more than `long_query_time'
     seconds to execute to file.  *Note Slow query log::.

`--log-update[=file]'
     Log updates to `file.#' where `#' is a unique number if not given.
     *Note Update log::.

`--log-long-format'
     Log some extra information to update log.  If you are using
     `--log-slow-queries' then queries that are not using indexes are
     logged to the slow query log.

`--low-priority-updates'
     Table-modifying operations (`INSERT'/`DELETE'/`UPDATE') will have
     lower priority than selects.  It can also be done via `{INSERT |
     REPLACE | UPDATE | DELETE} LOW_PRIORITY ...' to lower the priority
     of only one query, or by `SET LOW_PRIORITY_UPDATES=1' to change
     the priority in one thread.  *Note Table locking::.

`--memlock'
     Lock the `mysqld' process in memory.  This works only if your
     system supports the `mlockall()' system call (like Solaris).  This
     may help if you have a problem where the operating system is
     causing `mysqld' to swap on disk.

`--myisam-recover [=option[,option...]]]'
     Option is any combination of `DEFAULT', `BACKUP', `FORCE' or
     `QUICK'.  You can also set this explicitly to `""' if you want to
     disable this option. If this option is used, `mysqld' will on open
     check if the table is marked as crashed or if the table wasn't
     closed properly.  (The last option only works if you are running
     with `--skip-external-locking'.)  If this is the case `mysqld'
     will run check on the table. If the table was corrupted, `mysqld'
     will attempt to repair it.

     The following options affects how the repair works.

     *Option*   *Description*
     DEFAULT    The same as not giving any option to
                         `--myisam-recover'.
     BACKUP     If the data table was changed during recover,
                save a                     backup of the
                `table_name.MYD' datafile as
                 `table_name-datetime.BAK'.
     FORCE      Run recover even if we will lose more than one
                row                     from the .MYD file.
     QUICK      Don't check the rows in the table if there
                aren't any                     delete blocks.

     Before a table is automatically repaired, MySQL will add a note
     about this in the error log.  If you want to be able to recover
     from most things without user intervention, you should use the
     options `BACKUP,FORCE'.  This will force a repair of a table even
     if some rows would be deleted, but it will keep the old datafile
     as a backup so that you can later examine what happened.

`--pid-file=path'
     Path to pid file used by `safe_mysqld'.

`-P, --port=...'
     Port number to listen for TCP/IP connections.

`-o, --old-protocol'
     Use the 3.20 protocol for compatibility with some very old clients.
     *Note Upgrading-from-3.20::.

`--one-thread'
     Only use one thread (for debugging under Linux).  *Note Debugging
     server::.

`-O, --set-variable var=option'
     Give a variable a value. `--help' lists variables.  You can find a
     full description for all variables in the `SHOW VARIABLES' section
     in this manual.  *Note SHOW VARIABLES::.  The tuning server
     parameters section includes information of how to optimise these.
     Please note that `--set-variable' is deprecated since MySQL 4.0,
     just use `--var=option' on its own.  *Note Server parameters::.

     In MySQL 4.0.2 one can set a variable directly with
     `--variable-name=option' and `set-variable' is not anymore needed
     in option files.

     If you want to restrict the maximum value a startup option can be
     set to with `SET', you can define this by using the
     `--maximum-variable-name' command line option. *Note SET OPTION::.

     Note that when setting a variable to a value, MySQL may
     automatically correct it to stay within a given range and also
     adjusts the value a little to fix for the used algorithm.

`--safe-mode'
     Skip some optimise stages.

`--safe-show-database'
     With this option, the `SHOW DATABASES' command returns only those
     databases for which the user has some kind of privilege.  From
     version 4.0.2 this option is deprecated and doesn't do anything
     (the option is enabled by default) as we now have the `SHOW
     DATABASES' privilege. *Note GRANT::.

`--safe-user-create'
     If this is enabled, a user can't create new users with the GRANT
     command, if the user doesn't have `INSERT' privilege to the
     `mysql.user' table or any column in this table.

`--skip-bdb'
     Disable usage of BDB tables. This will save memory and may speed
     up some things.

`--skip-concurrent-insert'
     Turn off the ability to select and insert at the same time on
     `MyISAM' tables. (This is only to be used if you think you have
     found a bug in this feature.)

`--skip-delay-key-write; In MySQL 4.0.3 you should use --delay-key-write=OFF instead.'
     Ignore the `DELAY_KEY_WRITE' option for all tables.  *Note Server
     parameters::.

`--skip-grant-tables'
     This option causes the server not to use the privilege system at
     all.  This gives everyone *full access* to all databases!  (You
     can tell a running server to start using the grant tables again by
     executing `mysqladmin flush-privileges' or `mysqladmin reload'.)

`--skip-host-cache'
     Never use host name cache for faster name-ip resolution, but query
     DNS server on every connect instead.  *Note DNS::.

`--skip-innodb'
     Disable usage of Innodb tables.  This will save memory and disk
     space and speed up some things.

`--skip-external-locking (was --skip-locking)'
     Don't use system locking.  To use `isamchk' or `myisamchk' you must
     shut down the server.  *Note Stability::.  Note that in MySQL
     Version 3.23 you can use `REPAIR' and `CHECK' to repair/check
     `MyISAM' tables.

`--skip-name-resolve'
     Hostnames are not resolved.  All `Host' column values in the grant
     tables must be IP numbers or `localhost'.  *Note DNS::.

`--skip-networking'
     Don't listen for TCP/IP connections at all.  All interaction with
     `mysqld' must be made via Unix sockets.  This option is highly
     recommended for systems where only local requests are allowed.
     *Note DNS::.

`--skip-new'
     Don't use new, possible wrong routines.

`--skip-symlink'
     Don't delete or rename files that a symlinked file in the data
     directory points to.

`--skip-safemalloc'
     If MySQL is configured with `--with-debug=full', all programs will
     check the memory for overruns for every memory allocation and
     memory freeing.  As this checking is very slow, you can avoid
     this, when you don't need memory checking, by using this option.

`--skip-show-database'
     Don't allow `SHOW DATABASES' command, unless the user has the
     `SHOW DATABASES' privilege. From version 4.0.2 you should no longer
     need this option, since access can now be granted specifically
     with the `SHOW DATABASES' privilege.

`--skip-stack-trace'
     Don't write stack traces.  This option is useful when you are
     running `mysqld' under a debugger. On some systems you also have
     to use this option to get a core file. *Note Debugging server::.

`--skip-thread-priority'
     Disable using thread priorities for faster response time.

`--socket=path'
     Socket file to use for local connections instead of default
     `/tmp/mysql.sock'.

`--sql-mode=option[,option[,option...]]'
     Option can be any combination of: `REAL_AS_FLOAT',
     `PIPES_AS_CONCAT', `ANSI_QUOTES', `IGNORE_SPACE', `SERIALIZE',
     `ONLY_FULL_GROUP_BY'.  It can also be empty (`""') if you want to
     reset this.

     By specifying all of the above options is same as using -ansi.
     With this option one can turn on only needed SQL modes. *Note ANSI
     mode::.

`--temp-pool'
     Using this option will cause most temporary files created to use a
     small set of names, rather than a unique name for each new file.
     This is to work around a problem in the Linux kernel dealing with
     creating a bunch of new files with different names. With the old
     behaviour, Linux seems to 'leak' memory, as it's being allocated
     to the directory entry cache instead of the disk cache.

`--transaction-isolation= { READ-UNCOMMITTED | READ-COMMITTED | REPEATABLE-READ | SERIALIZABLE }'
     Sets the default transaction isolation level.  *Note SET
     TRANSACTION::.

`-t, --tmpdir=path'
     Path for temporary files. It may be useful if your default `/tmp'
     directory resides on a partition too small to hold temporary
     tables.

`-u, --user= [user_name | userid]'
     Run `mysqld' daemon as user `user_name' or `userid' (numeric).
     This option is *mandatory* when starting `mysqld' as root.

`-V, --version'
     Output version information and exit.

`-W, --log-warnings  (Was --warnings)'
     Print out warnings like `Aborted connection...' to the `.err' file.
     *Note Communication errors::.

One can change most values for a running server with the `SET' command.
*Note SET OPTION::.

`my.cnf' Option Files
---------------------

MySQL can, since Version 3.22, read default startup options for the
server and for clients from option files.

MySQL reads default options from the following files on Unix:

*Filename*                *Purpose*
`/etc/my.cnf'             Global options
`DATADIR/my.cnf'          Server-specific options
`defaults-extra-file'     The file specified with
                          -defaults-extra-file=#
`~/.my.cnf'               User-specific options

`DATADIR' is the MySQL data directory (typically
`/usr/local/mysql/data' for a binary installation or `/usr/local/var'
for a source installation).  Note that this is the directory that was
specified at configuration time, not the one specified with `--datadir'
when `mysqld' starts up!  (`--datadir' has no effect on where the
server looks for option files, because it looks for them before it
processes any command-line arguments.)

MySQL reads default options from the following files on Windows:

*Filename*                *Purpose*
`windows-system-directory\my.ini'Global options
`C:\my.cnf'               Global options

Note that on Windows, you should specify all paths with `/' instead of
`\'. If you use `\', you need to specify this twice, as `\' is the
escape character in MySQL.

MySQL tries to read option files in the order listed above.  If
multiple option files exist, an option specified in a file read later
takes precedence over the same option specified in a file read earlier.
Options specified on the command-line take precedence over options
specified in any option file.  Some options can be specified using
environment variables.  Options specified on the command-line or in
option files take precedence over environment variable values. *Note
Environment variables::.

The following programs support option files:  `mysql', `mysqladmin',
`mysqld', `mysqld_safe', `mysql.server', `mysqldump', `mysqlimport',
`mysqlshow', `mysqlcheck', `myisamchk', and `myisampack'.

Any long option that may be given on the command-line when running a
MySQL program can be given in an option file as well (without the
leading double dash).  Run the program with `--help' to get a list of
available options.

An option file can contain lines of the following forms:

`#comment'
     Comment lines start with `#' or `;'. Empty lines are ignored.

`[group]'
     `group' is the name of the program or group for which you want to
     set options.  After a group line, any `option' or `set-variable'
     lines apply to the named group until the end of the option file or
     another group line is given.

`option'
     This is equivalent to `--option' on the command-line.

`option=value'
     This is equivalent to `--option=value' on the command-line.

`set-variable = variable=value'
     This is equivalent to `--set-variable variable=value' on the
     command-line.  This syntax must be used to set a `mysqld' variable.
     Please note that `--set-variable' is deprecated since MySQL 4.0,
     just use `--variable=value' on its own.

The `client' group allows you to specify options that apply to all
MySQL clients (not `mysqld'). This is the perfect group to use to
specify the password you use to connect to the server.  (But make sure
the option file is readable and writable only by yourself.)

Note that for options and values, all leading and trailing blanks are
automatically deleted.  You may use the escape sequences `\b', `\t',
`\n', `\r', `\\', and `\s' in your value string (`\s' == blank).

Here is a typical global option file:

     [client]
     port=3306
     socket=/tmp/mysql.sock

     [mysqld]
     port=3306
     socket=/tmp/mysql.sock
     set-variable = key_buffer_size=16M
     set-variable = max_allowed_packet=1M

     [mysqldump]
     quick

Here is typical user option file:

     [client]
     # The following password will be sent to all standard MySQL clients
     password=my_password

     [mysql]
     no-auto-rehash
     set-variable = connect_timeout=2

     [mysqlhotcopy]
     interactive-timeout

If you have a source distribution, you will find sample configuration
files named `my-xxxx.cnf' in the `support-files' directory.  If you
have a binary distribution, look in the `DIR/support-files' directory,
where `DIR' is the pathname to the MySQL installation directory
(typically `/usr/local/mysql').  Currently there are sample
configuration files for small, medium, large, and very large systems.
You can copy `my-xxxx.cnf' to your home directory (rename the copy to
`.my.cnf') to experiment with this.

All MySQL clients that support option files support the following
options:

*Option*                         *Description*
-no-defaults                     Don't read any option files.
-print-defaults                  Print the program name and all options
                                 that it will get.
-defaults-file=full-path-to-default-fileOnly use the given configuration file.
-defaults-extra-file=full-path-to-default-fileRead this configuration file after the
                                 global configuration file but before
                                 the user configuration file.

Note that the above options must be first on the command-line to work!
`--print-defaults' may however be used directly after the
`--defaults-xxx-file' commands.

Note for developers:  Option file handling is implemented simply by
processing all matching options (that is, options in the appropriate
group) before any command-line arguments. This works nicely for
programs that use the last instance of an option that is specified
multiple times. If you have an old program that handles
multiply-specified options this way but doesn't read option files, you
need add only two lines to give it that capability.  Check the source
code of any of the standard MySQL clients to see how to do this.

In shell scripts you can use the `my_print_defaults' command to parse
the config files:


     shell> my_print_defaults client mysql
     --port=3306
     --socket=/tmp/mysql.sock
     --no-auto-rehash

The above output contains all options for the groups 'client' and
'mysql'.

Installing Many Servers on the Same Machine
-------------------------------------------

In some cases you may want to have many different `mysqld' daemons
(servers) running on the same machine.  You may for example want to run
a new version of MySQL for testing together with an old version that is
in production.  Another case is when you want to give different users
access to different `mysqld' servers that they manage themselves.

One way to get a new server running is by starting it with a different
socket and port as follows:

     shell> MYSQL_UNIX_PORT=/tmp/mysqld-new.sock
     shell> MYSQL_TCP_PORT=3307
     shell> export MYSQL_UNIX_PORT MYSQL_TCP_PORT
     shell> scripts/mysql_install_db
     shell> bin/safe_mysqld &

The environment variables appendix includes a list of other environment
variables you can use to affect `mysqld'. *Note Environment variables::.

The above is the quick and dirty way that one commonly uses for testing.
The nice thing with this is that all connections you do in the above
shell will automatically be directed to the new running server!

If you need to do this more permanently, you should create an option
file for each server. *Note Option files::.  In your startup script that
is executed at boot time you should specify for both servers:

`safe_mysqld --defaults-file=path-to-option-file'

At least the following options should be different per server:

   * port=#

   * socket=path

   * pid-file=path

The following options should be different, if they are used:

   * log=path

   * log-bin=path

   * log-update=path

   * log-isam=path

   * bdb-logdir=path

If you want more performance, you can also specify the following
differently:

   * tmpdir=path

   * bdb-tmpdir=path

*Note Command-line options::.

If you are installing binary MySQL versions (.tar files) and start them
with `./bin/safe_mysqld' then in most cases the only option you need to
add/change is the `socket' and `port' argument to `safe_mysqld'.

*Note Running Multiple MySQL Servers on the Same Machine: Multiple
servers.

Running Multiple MySQL Servers on the Same Machine
--------------------------------------------------

There are circumstances when you might want to run multiple servers on
the same machine.  For example, you might want to test a new MySQL
release while leaving your existing production setup undisturbed.  Or
you might be an Internet service provider that wants to provide
independent MySQL installations for different customers.

If you want to run multiple servers, the easiest way is to compile the
servers with different TCP/IP ports and socket files so they are not
both listening to the same TCP/IP port or socket file. *Note
`mysqld_multi': mysqld_multi.

Assume an existing server is configured for the default port number and
socket file.  Then configure the new server with a `configure' command
something like this:

     shell> ./configure  --with-tcp-port=port_number \
                  --with-unix-socket-path=file_name \
                  --prefix=/usr/local/mysql-3.22.9

Here `port_number' and `file_name' should be different from the default
port number and socket file pathname, and the `--prefix' value should
specify an installation directory different from the one under which
the existing MySQL installation is located.

You can check the socket used by any currently executing MySQL server
with this command:

     shell> mysqladmin -h hostname --port=port_number variables

Note that if you specify "`localhost'" as a hostname, `mysqladmin' will
default to using Unix sockets instead of TCP/IP.

If you have a MySQL server running on the port you used, you will get a
list of some of the most important configurable variables in MySQL,
including the socket name.

You don't have to recompile a new MySQL server just to start with a
different port and socket.  You can change the port and socket to be
used by specifying them at runtime as options to `safe_mysqld':

     shell> /path/to/safe_mysqld --socket=file_name --port=port_number

`mysqld_multi' can also take `safe_mysqld' (or `mysqld') as an argument
and pass the options from a configuration file to `safe_mysqld' and
further to `mysqld'.

If you run the new server on the same database directory as another
server with logging enabled, you should also specify the name of the log
files to `safe_mysqld' with `--log', `--log-update', or
`--log-slow-queries'.  Otherwise, both servers may be trying to write
to the same log file.

*Warning*: normally you should never have two servers that update data
in the same database!  If your OS doesn't support fault-free system
locking, this may lead to unpleasant surprises!

If you want to use another database directory for the second server, you
can use the `--datadir=path' option to `safe_mysqld'.

*Note* also that starting several MySQL servers (`mysqlds') in
different machines and letting them access one data directory over
`NFS' is generally a *bad idea*! The problem is that the `NFS' will
become the bottleneck with the speed. It is not meant for such use. And
last but not least, you would still have to come up with a solution how
to make sure that two or more `mysqlds' are not interfering with each
other. At the moment there is no platform that would 100% reliable do
the file locking (`lockd' daemon usually) in every situation. Yet there
would be one more possible risk with `NFS'; it would make the work even
more complicated for `lockd' daemon to handle. So make it easy for your
self and forget about the idea. The working solution is to have one
computer with an operating system that efficiently handles threads and
have several CPUs in it.

When you want to connect to a MySQL server that is running with a
different port than the port that is compiled into your client, you can
use one of the following methods:

   * Start the client with `--host 'hostname' --port=port_number' to
     connect with TCP/IP, or `[--host localhost] --socket=file_name' to
     connect via a Unix socket.

   * In your C or Perl programs, you can give the port or socket
     arguments when connecting to the MySQL server.

   * If your are using the Perl `DBD::mysql' module you can read the
     options from the MySQL option files.  *Note Option files::.

          $dsn = "DBI:mysql:test;mysql_read_default_group=client;
                  mysql_read_default_file=/usr/local/mysql/data/my.cnf"
          $dbh = DBI->connect($dsn, $user, $password);

   * Set the `MYSQL_UNIX_PORT' and `MYSQL_TCP_PORT' environment
     variables to point to the Unix socket and TCP/IP port before you
     start your clients.  If you normally use a specific socket or
     port, you should place commands to set these environment variables
     in your `.login' file.  *Note Environment variables::.

   * Specify the default socket and TCP/IP port in the `.my.cnf' file
     in your home directory. *Note Option files::.

General Security Issues and the MySQL Access Privilege System
=============================================================

MySQL has an advanced but non-standard security/privilege system.  This
section describes how it works.

General Security Guidelines
---------------------------

Anyone using MySQL on a computer connected to the Internet should read
this section to avoid the most common security mistakes.

In discussing security, we emphasise the necessity of fully protecting
the entire server host (not simply the MySQL server) against all types
of applicable attacks: eavesdropping, altering, playback, and denial of
service. We do not cover all aspects of availability and fault tolerance
here.

MySQL uses security based on Access Control Lists (ACLs) for all
connections, queries, and other operations that a user may attempt to
perform. There is also some support for SSL-encrypted connections
between MySQL clients and servers. Many of the concepts discussed here
are not specific to MySQL at all; the same general ideas apply to
almost all applications.

When running MySQL, follow these guidelines whenever possible:

   * *Do not ever give anyone (except the mysql root user) access to the
     `user' table in the `mysql' database!*  This is critical.  *The
     encrypted password is the real password in MySQL.* Anyone who
     knows the password which is listed in the `user' table and has
     access to the host listed for the account *can easily log in as
     that user*.

   * Learn the MySQL access privilege system. The `GRANT' and `REVOKE'
     commands are used for controlling access to MySQL. Do not grant
     any more privileges than necessary. Never grant privileges to all
     hosts.

     Checklist:
        - Try `mysql -u root'. If you are able to connect successfully
          to the server without being asked for a password, you have
          problems. Anyone can connect to your MySQL server as the MySQL
          `root' user with full privileges!  Review the MySQL
          installation instructions, paying particular attention to the
          item about setting a `root' password.

        - Use the command `SHOW GRANTS' and check to see who has access
          to what. Remove those privileges that are not necessary using
          the `REVOKE' command.

   * Do not keep any plain-text passwords in your database. When your
     computer becomes compromised, the intruder can take the full list
     of passwords and use them. Instead use `MD5()', `SHA1()' or
     another one-way hashing function.

   * Do not choose passwords from dictionaries. There are special
     programs to break them. Even passwords like "xfish98" are very
     bad.  Much better is "duag98" which contains the same word "fish"
     but typed one key to the left on a standard QWERTY keyboard.
     Another method is to use "Mhall" which is taken from the first
     characters of each word in the sentence "Mary had a little lamb."
     This is easy to remember and type, but difficult to guess for
     someone who does not know it.

   * Invest in a firewall. This protects you from at least 50% of all
     types of exploits in any software. Put MySQL behind the firewall
     or in a demilitarised zone (DMZ).

     Checklist:
        - Try to scan your ports from the Internet using a tool such as
          `nmap'. MySQL uses port 3306 by default. This port should be
          inaccessible from untrusted hosts. Another simple way to
          check whether or not your MySQL port is open is to try the
          following command from some remote machine, where
          `server_host' is the hostname of your MySQL server:

               shell> telnet server_host 3306

          If you get a connection and some garbage characters, the port
          is open, and should be closed on your firewall or router,
          unless you really have a good reason to keep it open. If
          `telnet' just hangs or the connection is refused, everything
          is OK; the port is blocked.

   * Do not trust any data entered by your users. They can try to trick
     your code by entering special or escaped character sequences in
     web forms, URLs, or whatever application you have built. Be sure
     that your application remains secure if a user enters something
     like "`; DROP DATABASE mysql;'". This is an extreme example, but
     large security leaks and data loss may occur as a result of
     hackers using similar techniques, if you do not prepare for them.

     Also remember to check numeric data. A common mistake is to
     protect only strings. Sometimes people think that if a database
     contains only publicly available data that it need not be
     protected. This is incorrect. At least denial-of-service type
     attacks can be performed on such databases. The simplest way to
     protect from this type of attack is to use apostrophes around the
     numeric constants: `SELECT * FROM table WHERE ID='234'' rather
     than `SELECT * FROM table WHERE ID=234'.  MySQL automatically
     converts this string to a number and strips all non-numeric
     symbols from it.

     Checklist:
        - All web applications:
             * Try to enter `'' and `"' in all your web forms. If you
               get any kind of MySQL error, investigate the problem
               right away.

             * Try to modify any dynamic URLs by adding `%22' (`"'),
               `%23' (`#'), and `%27' (`'') in the URL.

             * Try to modify datatypes in dynamic URLs from numeric
               ones to character ones containing characters from
               previous examples. Your application should be safe
               against this and similar attacks.

             * Try to enter characters, spaces, and special symbols
               instead of numbers in numeric fields. Your application
               should remove them before passing them to MySQL or your
               application should generate an error. Passing unchecked
               values to MySQL is very dangerous!

             * Check data sizes before passing them to MySQL.

             * Consider having your application connect to the database
               using a different user name than the one you use for
               administrative purposes. Do not give your applications
               any more access privileges than they need.

        - Users of PHP:
             * Check out the `addslashes()' function.  As of PHP 4.0.3,
               a `mysql_escape_string()' function is available that is
               based on the function of the same name in the MySQL C
               API.

        - Users of MySQL C API:
             * Check out the `mysql_real_escape_string()' API call.

        - Users of MySQL++:
             * Check out the `escape' and `quote' modifiers for query
               streams.

        - Users of Perl DBI:
             * Check out the `quote()' method or use placeholders.

        - Users of Java JDBC:
             * Use a `PreparedStatement' object and placeholders.

   * Do not transmit plain (unencrypted) data over the Internet. These
     data are accessible to everyone who has the time and ability to
     intercept it and use it for their own purposes. Instead, use an
     encrypted protocol such as SSL or SSH. MySQL supports internal SSL
     connections as of Version 4.0.0.  SSH port-forwarding can be used
     to create an encrypted (and compressed) tunnel for the
     communication.

   * Learn to use the `tcpdump' and `strings' utilities. For most cases,
     you can check whether MySQL data streams are unencrypted by
     issuing a command like the following:

          shell> tcpdump -l -i eth0 -w - src or dst port 3306 | strings

     (This works under Linux and should work with small modifications
     under other systems.)  Warning: If you do not see data this
     doesn't always actually mean that it is encrypted. If you need
     high security, you should consult with a security expert.

How to Make MySQL Secure Against Crackers
-----------------------------------------

When you connect to a MySQL server, you normally should use a password.
The password is not transmitted in clear text over the connection,
however the encryption algorithm is not very strong, and with some
effort a clever attacker can crack the password if he is able to sniff
the traffic between the client and the server. If the connection
between the client and the server goes through an untrusted network,
you should use an SSH tunnel to encrypt the communication.

All other information is transferred as text that can be read by anyone
who is able to watch the connection.  If you are concerned about this,
you can use the compressed protocol (in MySQL Version 3.22 and above)
to make things much harder.  To make things even more secure you should
use `ssh'.  You can find an `Open Source' `ssh' client at
`http://www.openssh.org/', and a commercial `ssh' client at
`http://www.ssh.com/'.  With this, you can get an encrypted TCP/IP
connection between a MySQL server and a MySQL client.

If you are using MySQL 4.0, you can also use internal OpenSSL support.
*Note Secure connections::.

To make a MySQL system secure, you should strongly consider the
following suggestions:

   * Use passwords for all MySQL users. Remember that anyone can log in
     as any other person as simply as `mysql -u other_user db_name' if
     `other_user' has no password.  It is common behaviour with
     client/server applications that the client may specify any user
     name.  You can change the password of all users by editing the
     `mysql_install_db' script before you run it, or only the password
     for the MySQL `root' user like this:

          shell> mysql -u root mysql
          mysql> UPDATE user SET Password=PASSWORD('new_password')
              ->             WHERE user='root';
          mysql> FLUSH PRIVILEGES;

   * Don't run the MySQL daemon as the Unix `root' user.  This is very
     dangerous, because any user with the `FILE' privilege will be able
     to create files as `root' (for example, `~root/.bashrc'). To
     prevent this, `mysqld' will refuse to run as `root' unless it is
     specified directly using a `--user=root' option.

     `mysqld' can be run as an ordinary unprivileged user instead.  You
     can also create a new Unix user `mysql' to make everything even
     more secure.  If you run `mysqld' as another Unix user, you don't
     need to change the `root' user name in the `user' table, because
     MySQL user names have nothing to do with Unix user names.  To
     start `mysqld' as another Unix user, add a `user' line that
     specifies the user name to the `[mysqld]' group of the
     `/etc/my.cnf' option file or the `my.cnf' option file in the
     server's data directory. For example:

          [mysqld]
          user=mysql

     This will cause the server to start as the designated user whether
     you start it manually or by using `safe_mysqld' or `mysql.server'.
     For more details, see *Note Changing MySQL user::.

   * Don't support symlinks to tables (this can be disabled with the
     `--skip-symlink' option). This is especially important if you run
     `mysqld' as root as anyone that has write access to the mysqld data
     directories could then delete any file in the system!  *Note
     Symbolic links to tables::.

   * Check that the Unix user that `mysqld' runs as is the only user
     with read/write privileges in the database directories.

   * Don't give the `PROCESS' privilege to all users.  The output of
     `mysqladmin processlist' shows the text of the currently executing
     queries, so any user who is allowed to execute that command might
     be able to see if another user issues an `UPDATE user SET
     password=PASSWORD('not_secure')' query.

     `mysqld' reserves an extra connection for users who have the
     `PROCESS' privilege, so that a MySQL `root' user can log in and
     check things even if all normal connections are in use.

   * Don't give the `FILE' privilege to all users.  Any user that has
     this privilege can write a file anywhere in the filesystem with
     the privileges of the `mysqld' daemon!  To make this a bit safer,
     all files generated with `SELECT ... INTO OUTFILE' are readable to
     everyone, and you cannot overwrite existing files.

     The `FILE' privilege may also be used to read any file accessible
     to the Unix user that the server runs as.  This could be abused,
     for example, by using `LOAD DATA' to load `/etc/passwd' into a
     table, which can then be read with `SELECT'.

   * If you don't trust your DNS, you should use IP numbers instead of
     hostnames in the grant tables. In any case, you should be very
     careful about creating grant table entries using hostname values
     that contain wildcards!

   * If you want to restrict the number of connections for a single
     user, you can do this by setting the `max_user_connections'
     variable in `mysqld'.

Startup Options for `mysqld' Concerning Security
------------------------------------------------

The following `mysqld' options affect security:

`--local-infile[=(0|1)]'
     If one uses `--local-infile=0' then one can't use `LOAD DATA LOCAL
     INFILE'.

`--safe-show-database'
     With this option, the `SHOW DATABASES' command returns only those
     databases for which the user has some kind of privilege.  From
     version 4.0.2 this option is deprecated and doesn't do anything
     (the option is enabled by default) as we now have the `SHOW
     DATABASES' privilege. *Note GRANT::.

`--safe-user-create'
     If this is enabled, an user can't create new users with the `GRANT'
     command, if the user doesn't have the `INSERT' privilege for the
     `mysql.user' table.  If you want to give a user access to just
     create new users with those privileges that the user has right to
     grant, you should give the user the following privilege:

          mysql> GRANT INSERT(user) ON mysql.user TO 'user'@'hostname';

     This will ensure that the user can't change any privilege columns
     directly, but has to use the `GRANT' command to give privileges to
     other users.

`--skip-grant-tables'
     This option causes the server not to use the privilege system at
     all. This gives everyone *full access* to all databases!  (You can
     tell a running server to start using the grant tables again by
     executing `mysqladmin flush-privileges' or `mysqladmin reload'.)

`--skip-name-resolve'
     Hostnames are not resolved.  All `Host' column values in the grant
     tables must be IP numbers or `localhost'.

`--skip-networking'
     Don't allow TCP/IP connections over the network.  All connections
     to `mysqld' must be made via Unix sockets.  This option is
     unsuitable when using a MySQL version prior to 3.23.27 with the
     MIT-pthreads package, because Unix sockets were not supported by
     MIT-pthreads at that time.

`--skip-show-database'
     Don't allow `SHOW DATABASES' command, unless the user has the
     `SHOW DATABASES' privilege. From version 4.0.2 you should no longer
     need this option, since access can now be granted specifically
     with the `SHOW DATABASES' privilege.

Security issues with LOAD DATA LOCAL
------------------------------------

In MySQL 3.23.49 and MySQL 4.0.2, we added some new options to deal with
possible security issues when it comes to `LOAD DATA LOCAL'.

There are two possible problems with supporting this command:

As the reading of the file is initiated from the server, one could
theoretically create a patched MySQL server that could read any file on
the client machine that the current user has read access to, when the
client issues a query against the table.

In a web environment where the clients are connecting from a web
server, a user could use `LOAD DATA LOCAL' to read any files that the
web server process has read access to (assuming a user could run any
command against the SQL server).

There are two separate fixes for this:

If you don't configure MySQL with `--enable-local-infile', then `LOAD
DATA LOCAL' will be disabled by all clients, unless one calls
`mysql_options(... MYSQL_OPT_LOCAL_INFILE, 0)' in the client.  *Note
`mysql_options()': mysql_options.

For the `mysql' command-line client, `LOAD DATA LOCAL' can be enabled
by specifying the option `--local-infile[=1]', or disabled with
`--local-infile=0'.

By default, all MySQL clients and libraries are compiled with
`--enable-local-infile', to be compatible with MySQL 3.23.48 and before.

One can disable all `LOAD DATA LOCAL' commands in the MySQL server by
starting `mysqld' with `--local-infile=0'.

In the case that `LOAD DATA LOCAL INFILE' is disabled in the server or
the client, you will get the error message (1148):

     The used command is not allowed with this MySQL version

What the Privilege System Does
------------------------------

The primary function of the MySQL privilege system is to authenticate a
user connecting from a given host, and to associate that user with
privileges on a database such as `SELECT', `INSERT', `UPDATE' and
`DELETE'.

Additional functionality includes the ability to have an anonymous user
and to grant privileges for MySQL-specific functions such as `LOAD DATA
INFILE' and administrative operations.

How the Privilege System Works
------------------------------

The MySQL privilege system ensures that all users may do exactly the
things that they are supposed to be allowed to do.  When you connect to
a MySQL server, your identity is determined by *the host from which you
connect* and *the user name you specify*.  The system grants privileges
according to your identity and *what you want to do*.

MySQL considers both your hostname and user name in identifying you
because there is little reason to assume that a given user name belongs
to the same person everywhere on the Internet.  For example, the user
`joe' who connects from `office.com' need not be the same person as the
user `joe' who connects from `elsewhere.com'.  MySQL handles this by
allowing you to distinguish users on different hosts that happen to
have the same name:  you can grant `joe' one set of privileges for
connections from `office.com', and a different set of privileges for
connections from `elsewhere.com'.

MySQL access control involves two stages:

   * Stage 1: The server checks whether you are even allowed to connect.

   * Stage 2: Assuming you can connect, the server checks each request
     you issue to see whether you have sufficient privileges to perform
     it.  For example, if you try to select rows from a table in a
     database or drop a table from the database, the server makes sure
     you have the `SELECT' privilege for the table or the `DROP'
     privilege for the database.

The server uses the `user', `db', and `host' tables in the `mysql'
database at both stages of access control.  The fields in these grant
tables are shown here:

*Table name*   `user'         `db'           `host'
*Scope         `Host'         `Host'         `Host'
fields*
               `User'         `Db'           `Db'
               `Password'     `User'
*Privilege     `Select_priv'  `Select_priv'  `Select_priv'
fields*
               `Insert_priv'  `Insert_priv'  `Insert_priv'
               `Update_priv'  `Update_priv'  `Update_priv'
               `Delete_priv'  `Delete_priv'  `Delete_priv'
               `Index_priv'   `Index_priv'   `Index_priv'
               `Alter_priv'   `Alter_priv'   `Alter_priv'
               `Create_priv'  `Create_priv'  `Create_priv'
               `Drop_priv'    `Drop_priv'    `Drop_priv'
               `Grant_priv'   `Grant_priv'   `Grant_priv'
               `References_priv'
               `Reload_priv'
               `Shutdown_priv'
               `Process_priv'
               `File_priv'

For the second stage of access control (request verification), the
server may, if the request involves tables, additionally consult the
`tables_priv' and `columns_priv' tables.  The fields in these tables
are shown here:

*Table name*   `tables_priv'  `columns_priv'
*Scope         `Host'         `Host'
fields*
               `Db'           `Db'
               `User'         `User'
               `Table_name'   `Table_name'
                              `Column_name'
*Privilege     `Table_priv'   `Column_priv'
fields*
               `Column_priv'
*Other         `Timestamp'    `Timestamp'
fields*
               `Grantor'

Each grant table contains scope fields and privilege fields.

Scope fields determine the scope of each entry in the tables, that is,
the context in which the entry applies.  For example, a `user' table
entry with `Host' and `User' values of `'thomas.loc.gov'' and `'bob''
would be used for authenticating connections made to the server by
`bob' from the host `thomas.loc.gov'.  Similarly, a `db' table entry
with `Host', `User', and `Db' fields of `'thomas.loc.gov'', `'bob'' and
`'reports'' would be used when `bob' connects from the host
`thomas.loc.gov' to access the `reports' database.  The `tables_priv'
and `columns_priv' tables contain scope fields indicating tables or
table/column combinations to which each entry applies.

For access-checking purposes, comparisons of `Host' values are
case-insensitive.  `User', `Password', `Db', and `Table_name' values
are case-sensitive.  `Column_name' values are case-insensitive in MySQL
Version 3.22.12 or later.

Privilege fields indicate the privileges granted by a table entry, that
is, what operations can be performed.  The server combines the
information in the various grant tables to form a complete description
of a user's privileges.  The rules used to do this are described in
*Note Request access::.

Scope fields are strings, declared as shown here; the default value for
each is the empty string:

*Field name*   *Type*      *Notes*
`Host'         `CHAR(60)'
`User'         `CHAR(16)'
`Password'     `CHAR(16)'
`Db'           `CHAR(64)'  (`CHAR(60)' for the `tables_priv' and
                           `columns_priv' tables)
`Table_name'   `CHAR(60)'
`Column_name'  `CHAR(60)'

In the `user', `db' and `host' tables, all privilege fields are
declared as `ENUM('N','Y')'each can have a value of `'N'' or `'Y'', and
the default value is `'N''.

In the `tables_priv' and `columns_priv' tables, the privilege fields
are declared as `SET' fields:

*Table      *Field      *Possible set elements*
name*       name*
`tables_priv'`Table_priv'`'Select', 'Insert', 'Update',
                        'Delete', 'Create', 'Drop', 'Grant',
                        'References', 'Index', 'Alter''
`tables_priv'`Column_priv'`'Select', 'Insert', 'Update',
                        'References''
`columns_priv'`Column_priv'`'Select', 'Insert', 'Update',
                        'References''

Briefly, the server uses the grant tables like this:

   * The `user' table scope fields determine whether to allow or reject
     incoming connections.  For allowed connections, any privileges
     granted in the `user' table indicate the user's global (superuser)
     privileges.  These privileges apply to *all* databases on the
     server.

   * The `db' and `host' tables are used together:

        - The `db' table scope fields determine which users can access
          which databases from which hosts.  The privilege fields
          determine which operations are allowed.

        - The `host' table is used as an extension of the `db' table
          when you want a given `db' table entry to apply to several
          hosts.  For example, if you want a user to be able to use a
          database from several hosts in your network, leave the `Host'
          value empty in the user's `db' table entry, then populate the
          `host' table with an entry for each of those hosts.  This
          mechanism is described more detail in *Note Request access::.

   * The `tables_priv' and `columns_priv' tables are similar to the
     `db' table, but are more fine-grained: they apply at the table and
     column levels rather than at the database level.

Note that administrative privileges (`RELOAD', `SHUTDOWN', etc.) are
specified only in the `user' table.  This is because administrative
operations are operations on the server itself and are not
database-specific, so there is no reason to list such privileges in the
other grant tables.  In fact, only the `user' table need be consulted
to determine whether you can perform an administrative operation.

The `FILE' privilege is specified only in the `user' table, too.  It is
not an administrative privilege as such, but your ability to read or
write files on the server host is independent of the database you are
accessing.

The `mysqld' server reads the contents of the grant tables once, when it
starts up.  Changes to the grant tables take effect as indicated in
*Note Privilege changes::.

When you modify the contents of the grant tables, it is a good idea to
make sure that your changes set up privileges the way you want.  For
help in diagnosing problems, see *Note Access denied::.  For advice on
security issues, see *Note Security::.

A useful diagnostic tool is the `mysqlaccess' script, which Yves
Carlier has provided for the MySQL distribution.  Invoke `mysqlaccess'
with the `--help' option to find out how it works.  Note that
`mysqlaccess' checks access using only the `user', `db' and `host'
tables.  It does not check table- or column-level privileges.

Privileges Provided by MySQL
----------------------------

Information about user privileges is stored in the `user', `db',
`host', `tables_priv', and `columns_priv' tables in the `mysql'
database (that is, in the database named `mysql').  The MySQL server
reads the contents of these tables when it starts up and under the
circumstances indicated in *Note Privilege changes::.

The names used in this manual to refer to the privileges provided by
MySQL version 4.0.2 are shown here, along with the table column name
associated with each privilege in the grant tables and the context in
which the privilege applies:

*Privilege* *Column*       *Context*
`ALTER'     `Alter_priv'   tables
`DELETE'    `Delete_priv'  tables
`INDEX'     `Index_priv'   tables
`INSERT'    `Insert_priv'  tables
`SELECT'    `Select_priv'  tables
`UPDATE'    `Update_priv'  tables
`CREATE'    `Create_priv'  databases, tables, or
                           indexes
`DROP'      `Drop_priv'    databases or tables
`GRANT'     `Grant_priv'   databases or tables
`REFERENCES'`References_priv'databases or tables
`CREATE     `Create_tmp_table_priv'server administration
TEMPORARY
TABLES'
`EXECUTE'   `Execute_priv' server administration
`FILE'      `File_priv'    file access on server
`LOCK       `Lock_tables_priv'server administration
TABLES'
`PROCESS'   `Process_priv' server administration
`RELOAD'    `Reload_priv'  server administration
`REPLICATION`Repl_client_priv'server administration
CLIENT'
`REPLICATION`Repl_slave_priv'server administration
SLAVE'
`SHOW       `Show_db_priv' server administration
DATABASES'
`SHUTDOWN'  `Shutdown_priv'server administration
`SUPER'     `Super_priv'   server administration

The `SELECT', `INSERT', `UPDATE', and `DELETE' privileges allow you to
perform operations on rows in existing tables in a database.

`SELECT' statements require the `SELECT' privilege only if they
actually retrieve rows from a table.  You can execute certain `SELECT'
statements even without permission to access any of the databases on the
server.  For example, you could use the `mysql' client as a simple
calculator:

     mysql> SELECT 1+1;
     mysql> SELECT PI()*2;

The `INDEX' privilege allows you to create or drop (remove) indexes.

The `ALTER' privilege allows you to use `ALTER TABLE'.

The `CREATE' and `DROP' privileges allow you to create new databases
and tables, or to drop (remove) existing databases and tables.

Note that if you grant the `DROP' privilege for the `mysql' database to
a user, that user can drop the database in which the MySQL access
privileges are stored!

The `GRANT' privilege allows you to give to other users those
privileges you yourself possess.

The `FILE' privilege gives you permission to read and write files on
the server using the `LOAD DATA INFILE' and `SELECT ... INTO OUTFILE'
statements.  Any user to whom this privilege is granted can read or
write any file that the MySQL server can read or write.

The remaining privileges are used for administrative operations, which
are performed using the `mysqladmin' program.  The table here shows
which `mysqladmin' commands each administrative privilege allows you to
execute:

*Privilege* *Commands permitted to privilege holders*
`RELOAD'    `reload', `refresh', `flush-privileges',
            `flush-hosts', `flush-logs', and `flush-tables'
`SHUTDOWN'  `shutdown'
`PROCESS'   `processlist'
`SUPER'     `kill'

The `reload' command tells the server to re-read the grant tables.  The
`refresh' command flushes all tables and opens and closes the log
files.  `flush-privileges' is a synonym for `reload'.  The other
`flush-*' commands perform functions similar to `refresh' but are more
limited in scope, and may be preferable in some instances.  For example,
if you want to flush just the log files, `flush-logs' is a better choice
than `refresh'.

The `shutdown' command shuts down the server.

The `processlist' command displays information about the threads
executing within the server.  The `kill' command kills server threads.
You can always display or kill your own threads, but you need the
`PROCESS' privilege to display and `SUPER' privilege to kill threads
initiated by other users. *Note KILL::.

It is a good idea in general to grant privileges only to those users
who need them, but you should exercise particular caution in granting
certain privileges:

   * The `GRANT' privilege allows users to give away their privileges to
     other users.  Two users with different privileges and with the
     `GRANT' privilege are able to combine privileges.

   * The `ALTER' privilege may be used to subvert the privilege system
     by renaming tables.

   * The `FILE' privilege can be abused to read any world-readable file
     on the server into a database table, the contents of which can
     then be accessed using `SELECT'. This includes the contents of all
     databases hosted by the server!

   * The `SHUTDOWN' privilege can be abused to deny service to other
     users entirely, by terminating the server.

   * The `PROCESS' privilege can be used to view the plain text of
     currently executing queries, including queries that set or change
     passwords.

   * Privileges on the `mysql' database can be used to change passwords
     and other access privilege information.  (Passwords are stored
     encrypted, so a malicious user cannot simply read them to know the
     plain text password.)  If they can access the `mysql.user' password
     column, they can use it to log into the MySQL server for the given
     user.  (With sufficient privileges, the same user can replace a
     password with a different one.)

There are some things that you cannot do with the MySQL privilege
system:

   * You cannot explicitly specify that a given user should be denied
     access.  That is, you cannot explicitly match a user and then
     refuse the connection.

   * You cannot specify that a user has privileges to create or drop
     tables in a database but not to create or drop the database itself.

Connecting to the MySQL Server
------------------------------

MySQL client programs generally require that you specify connection
parameters when you want to access a MySQL server: the host you want to
connect to, your user name, and your password.  For example, the
`mysql' client can be started like this (optional arguments are enclosed
between `[' and `]'):

     shell> mysql [-h host_name] [-u user_name] [-pyour_pass]

Alternate forms of the `-h', `-u', and `-p' options are
`--host=host_name', `--user=user_name', and `--password=your_pass'.
Note that there is _no space_ between `-p' or `--password=' and the
password following it.

*Note*: Specifying a password on the command-line is not secure!  Any
user on your system may then find out your password by typing a command
like: `ps auxww'.  *Note Option files::.

`mysql' uses default values for connection parameters that are missing
from the command-line:

   * The default hostname is `localhost'.

   * The default user name is your Unix login name.

   * No password is supplied if `-p' is missing.

Thus, for a Unix user `joe', the following commands are equivalent:

     shell> mysql -h localhost -u joe
     shell> mysql -h localhost
     shell> mysql -u joe
     shell> mysql

Other MySQL clients behave similarly.

On Unix systems, you can specify different default values to be used
when you make a connection, so that you need not enter them on the
command-line each time you invoke a client program.  This can be done
in a couple of ways:

   * You can specify connection parameters in the `[client]' section of
     the `.my.cnf' configuration file in your home directory.  The
     relevant section of the file might look like this:

          [client]
          host=host_name
          user=user_name
          password=your_pass

     *Note Option files::.

   * You can specify connection parameters using environment variables.
     The host can be specified for `mysql' using `MYSQL_HOST'.  The
     MySQL user name can be specified using `USER' (this is for Windows
     only).  The password can be specified using `MYSQL_PWD' (but this
     is insecure; see the next section).  *Note Environment variables::.

Access Control, Stage 1: Connection Verification
------------------------------------------------

When you attempt to connect to a MySQL server, the server accepts or
rejects the connection based on your identity and whether you can
verify your identity by supplying the correct password.  If not, the
server denies access to you completely.  Otherwise, the server accepts
the connection, then enters Stage 2 and waits for requests.

Your identity is based on two pieces of information:

   * The host from which you connect

   * Your MySQL user name

Identity checking is performed using the three `user' table scope fields
(`Host', `User', and `Password').  The server accepts the connection
only if a `user' table entry matches your hostname and user name, and
you supply the correct password.

Values in the `user' table scope fields may be specified as follows:

   * A `Host' value may be a hostname or an IP number, or `'localhost''
     to indicate the local host.

   * You can use the wildcard characters `%' and `_' in the `Host'
     field.

   * A `Host' value of `'%'' matches any hostname.

   * A blank `Host' value means that the privilege should be anded with
     the entry in the `host' table that matches the given host name.
     You can find more information about this in the next chapter.

   * As of MySQL Version 3.23, for `Host' values specified as IP
     numbers, you can specify a netmask indicating how many address
     bits to use for the network number. For example:

          mysql> GRANT ALL PRIVILEGES ON db.*
              -> TO david@'192.58.197.0/255.255.255.0';

     This will allow everyone to connect from an IP where the following
     is true:

          user_ip & netmask = host_ip.

     In the above example all IP:s in the interval 192.58.197.0 -
     192.58.197.255 can connect to the MySQL server.

   * Wildcard characters are not allowed in the `User' field, but you
     can specify a blank value, which matches any name.  If the `user'
     table entry that matches an incoming connection has a blank user
     name, the user is considered to be the anonymous user (the user
     with no name), rather than the name that the client actually
     specified.  This means that a blank user name is used for all
     further access checking for the duration of the connection (that
     is, during Stage 2).

   * The `Password' field can be blank.  This does not mean that any
     password matches, it means the user must connect without
     specifying a password.

Non-blank `Password' values represent encrypted passwords.  MySQL does
not store passwords in plaintext form for anyone to see.  Rather, the
password supplied by a user who is attempting to connect is encrypted
(using the `PASSWORD()' function). The encrypted password is then used
when the client/server is checking if the password is correct. (This is
done without the encrypted password ever traveling over the
connection.)  Note that from MySQL's point of view the encrypted
password is the REAL password, so you should not give anyone access to
it!  In particular, don't give normal users read access to the tables
in the `mysql' database!

The examples here show how various combinations of `Host' and `User'
values in `user' table entries apply to incoming connections:

`Host' *value*            `User'      *Connections matched by entry*
                          *value*
`'thomas.loc.gov''        `'fred''    `fred', connecting from
                                      `thomas.loc.gov'
`'thomas.loc.gov''        `'''        Any user, connecting from
                                      `thomas.loc.gov'
`'%''                     `'fred''    `fred', connecting from any host
`'%''                     `'''        Any user, connecting from any host
`'%.loc.gov''             `'fred''    `fred', connecting from any host in
                                      the `loc.gov' domain
`'x.y.%''                 `'fred''    `fred', connecting from `x.y.net',
                                      `x.y.com',`x.y.edu', etc. (this is
                                      probably not useful)
`'144.155.166.177''       `'fred''    `fred', connecting from the host
                                      with IP address `144.155.166.177'
`'144.155.166.%''         `'fred''    `fred', connecting from any host in
                                      the `144.155.166' class C subnet
`'144.155.166.0/255.255.255.0''`'fred''    Same as previous example

Because you can use IP wildcard values in the `Host' field (for example,
`'144.155.166.%'' to match every host on a subnet), there is the
possibility that someone might try to exploit this capability by naming
a host `144.155.166.somewhere.com'.  To foil such attempts, MySQL
disallows matching on hostnames that start with digits and a dot. Thus,
if you have a host named something like `1.2.foo.com', its name will
never match the `Host' column of the grant tables.  Only an IP number
can match an IP wildcard value.

An incoming connection may be matched by more than one entry in the
`user' table.  For example, a connection from `thomas.loc.gov' by
`fred' would be matched by several of the entries just shown above.  How
does the server choose which entry to use if more than one matches?  The
server resolves this question by sorting the `user' table after reading
it at startup time, then looking through the entries in sorted order
when a user attempts to connect.  The first matching entry is the one
that is used.

`user' table sorting works as follows.  Suppose the `user' table looks
like this:

     +-----------+----------+-
     | Host      | User     | ...
     +-----------+----------+-
     | %         | root     | ...
     | %         | jeffrey  | ...
     | localhost | root     | ...
     | localhost |          | ...
     +-----------+----------+-

When the server reads in the table, it orders the entries with the
most-specific `Host' values first (`'%'' in the `Host' column means
"any host" and is least specific).  Entries with the same `Host' value
are ordered with the most-specific `User' values first (a blank `User'
value means "any user" and is least specific).  The resulting sorted
`user' table looks like this:

     +-----------+----------+-
     | Host      | User     | ...
     +-----------+----------+-
     | localhost | root     | ...
     | localhost |          | ...
     | %         | jeffrey  | ...
     | %         | root     | ...
     +-----------+----------+-

When a connection is attempted, the server looks through the sorted
entries and uses the first match found.  For a connection from
`localhost' by `jeffrey', the entries with `'localhost'' in the `Host'
column match first.  Of those, the entry with the blank user name
matches both the connecting hostname and user name.  (The
`'%'/'jeffrey'' entry would have matched, too, but it is not the first
match in the table.)

Here is another example.  Suppose the `user' table looks like this:

     +----------------+----------+-
     | Host           | User     | ...
     +----------------+----------+-
     | %              | jeffrey  | ...
     | thomas.loc.gov |          | ...
     +----------------+----------+-

The sorted table looks like this:

     +----------------+----------+-
     | Host           | User     | ...
     +----------------+----------+-
     | thomas.loc.gov |          | ...
     | %              | jeffrey  | ...
     +----------------+----------+-

A connection from `thomas.loc.gov' by `jeffrey' is matched by the first
entry, whereas a connection from `whitehouse.gov' by `jeffrey' is
matched by the second.

A common misconception is to think that for a given user name, all
entries that explicitly name that user will be used first when the
server attempts to find a match for the connection.  This is simply not
true.  The previous example illustrates this, where a connection from
`thomas.loc.gov' by `jeffrey' is first matched not by the entry
containing `'jeffrey'' as the `User' field value, but by the entry with
no user name!

If you have problems connecting to the server, print out the `user'
table and sort it by hand to see where the first match is being made.
If connection was successful, but your privileges are not what you
expected you may use `CURRENT_USER()' function (new in version 4.0.6)
to see what user/host combination your connection actually matched.
*Note `CURRENT_USER()': Miscellaneous functions.

Access Control, Stage 2: Request Verification
---------------------------------------------

Once you establish a connection, the server enters Stage 2.  For each
request that comes in on the connection, the server checks whether you
have sufficient privileges to perform it, based on the type of
operation you wish to perform.  This is where the privilege fields in
the grant tables come into play.  These privileges can come from any of
the `user', `db', `host', `tables_priv', or `columns_priv' tables.  The
grant tables are manipulated with `GRANT' and `REVOKE' commands.  *Note
`GRANT': GRANT.  (You may find it helpful to refer to *Note
Privileges::, which lists the fields present in each of the grant
tables.)

The `user' table grants privileges that are assigned to you on a global
basis and that apply no matter what the current database is.  For
example, if the `user' table grants you the `DELETE' privilege, you can
delete rows from any database on the server host!  In other words,
`user' table privileges are superuser privileges.  It is wise to grant
privileges in the `user' table only to superusers such as server or
database administrators.  For other users, you should leave the
privileges in the `user' table set to `'N'' and grant privileges on a
database-specific basis only, using the `db' and `host' tables.

The `db' and `host' tables grant database-specific privileges.  Values
in the scope fields may be specified as follows:

   * The wildcard characters `%' and `_' can be used in the `Host' and
     `Db' fields of either table. If you wish to use for instance a `_'
     character as part of a database name, specify it as `\_' in the
     `GRANT' command.

   * A `'%'' `Host' value in the `db' table means "any host." A blank
     `Host' value in the `db' table means "consult the `host' table for
     further information."

   * A `'%'' or blank `Host' value in the `host' table means "any host."

   * A `'%'' or blank `Db' value in either table means "any database."

   * A blank `User' value in either table matches the anonymous user.

The `db' and `host' tables are read in and sorted when the server
starts up (at the same time that it reads the `user' table).  The `db'
table is sorted on the `Host', `Db', and `User' scope fields, and the
`host' table is sorted on the `Host' and `Db' scope fields.  As with
the `user' table, sorting puts the most-specific values first and
least-specific values last, and when the server looks for matching
entries, it uses the first match that it finds.

The `tables_priv' and `columns_priv' tables grant table- and
column-specific privileges.  Values in the scope fields may be
specified as follows:

   * The wildcard characters `%' and `_' can be used in the `Host'
     field of either table.

   * A `'%'' or blank `Host' value in either table means "any host."

   * The `Db', `Table_name' and `Column_name' fields cannot contain
     wildcards or be blank in either table.

The `tables_priv' and `columns_priv' tables are sorted on the `Host',
`Db', and `User' fields.  This is similar to `db' table sorting,
although the sorting is simpler because only the `Host' field may
contain wildcards.

The request verification process is described here.  (If you are
familiar with the access-checking source code, you will notice that the
description here differs slightly from the algorithm used in the code.
The description is equivalent to what the code actually does; it
differs only to make the explanation simpler.)

For administrative requests (`SHUTDOWN', `RELOAD', etc.), the server
checks only the `user' table entry, because that is the only table that
specifies administrative privileges.  Access is granted if the entry
allows the requested operation and denied otherwise.  For example, if
you want to execute `mysqladmin shutdown' but your `user' table entry
doesn't grant the `SHUTDOWN' privilege to you, access is denied without
even checking the `db' or `host' tables.  (They contain no
`Shutdown_priv' column, so there is no need to do so.)

For database-related requests (`INSERT', `UPDATE', etc.), the server
first checks the user's global (superuser) privileges by looking in the
`user' table entry.  If the entry allows the requested operation,
access is granted.  If the global privileges in the `user' table are
insufficient, the server determines the user's database-specific
privileges by checking the `db' and `host' tables:

  1. The server looks in the `db' table for a match on the `Host',
     `Db', and `User' fields.  The `Host' and `User' fields are matched
     to the connecting user's hostname and MySQL user name.  The `Db'
     field is matched to the database the user wants to access.  If
     there is no entry for the `Host' and `User', access is denied.

  2. If there is a matching `db' table entry and its `Host' field is
     not blank, that entry defines the user's database-specific
     privileges.

  3. If the matching `db' table entry's `Host' field is blank, it
     signifies that the `host' table enumerates which hosts should be
     allowed access to the database.  In this case, a further lookup is
     done in the `host' table to find a match on the `Host' and `Db'
     fields.  If no `host' table entry matches, access is denied.  If
     there is a match, the user's database-specific privileges are
     computed as the intersection (*not* the union!) of the privileges
     in the `db' and `host' table entries, that is, the privileges that
     are `'Y'' in both entries.  (This way you can grant general
     privileges in the `db' table entry and then selectively restrict
     them on a host-by-host basis using the `host' table entries.)

After determining the database-specific privileges granted by the `db'
and `host' table entries, the server adds them to the global privileges
granted by the `user' table.  If the result allows the requested
operation, access is granted.  Otherwise, the server checks the user's
table and column privileges in the `tables_priv' and `columns_priv'
tables and adds those to the user's privileges.  Access is allowed or
denied based on the result.

Expressed in boolean terms, the preceding description of how a user's
privileges are calculated may be summarised like this:

     global privileges
     OR (database privileges AND host privileges)
     OR table privileges
     OR column privileges

It may not be apparent why, if the global `user' entry privileges are
initially found to be insufficient for the requested operation, the
server adds those privileges to the database-, table-, and
column-specific privileges later. The reason is that a request might
require more than one type of privilege.  For example, if you execute
an `INSERT ...  SELECT' statement, you need both `INSERT' and `SELECT'
privileges.  Your privileges might be such that the `user' table entry
grants one privilege and the `db' table entry grants the other.  In
this case, you have the necessary privileges to perform the request,
but the server cannot tell that from either table by itself; the
privileges granted by the entries in both tables must be combined.

The `host' table can be used to maintain a list of secure servers.

At TcX, the `host' table contains a list of all machines on the local
network. These are granted all privileges.

You can also use the `host' table to indicate hosts that are *not*
secure.  Suppose you have a machine `public.your.domain' that is located
in a public area that you do not consider secure.  You can allow access
to all hosts on your network except that machine by using `host' table
entries like this:

     +--------------------+----+-
     | Host               | Db | ...
     +--------------------+----+-
     | public.your.domain | %  | ... (all privileges set to 'N')
     | %.your.domain      | %  | ... (all privileges set to 'Y')
     +--------------------+----+-

Naturally, you should always test your entries in the grant tables (for
example, using `mysqlaccess') to make sure your access privileges are
actually set up the way you think they are.

Causes of `Access denied' Errors
--------------------------------

If you encounter `Access denied' errors when you try to connect to the
MySQL server, the following list indicates some courses of action you
can take to correct the problem:

   * After installing MySQL, did you run the `mysql_install_db' script
     to set up the initial grant table contents?  If not, do so.  *Note
     Default privileges::.  Test the initial privileges by executing
     this command:

          shell> mysql -u root test

     The server should let you connect without error.  You should also
     make sure you have a file `user.MYD' in the MySQL database
     directory.  Ordinarily, this is `PATH/var/mysql/user.MYD', where
     `PATH' is the pathname to the MySQL installation root.

   * After a fresh installation, you should connect to the server and
     set up your users and their access permissions:

          shell> mysql -u root mysql

     The server should let you connect because the MySQL `root' user
     has no password initially.  That is also a security risk, so
     setting the `root' password is something you should do while
     you're setting up your other MySQL users.

     If you try to connect as `root' and get this error:

          Access denied for user: '@unknown' to database mysql

     this means that you don't have an entry in the `user' table with a
     `User' column value of `'root'' and that `mysqld' cannot resolve
     the hostname for your client.  In this case, you must restart the
     server with the `--skip-grant-tables' option and edit your
     `/etc/hosts' or `\windows\hosts' file to add an entry for your
     host.

   * If you get an error like the following:

          shell> mysqladmin -u root -pxxxx ver
          Access denied for user: 'root@localhost' (Using password: YES)

     It means that you are using a wrong password. *Note Passwords::.

     If you have forgot the root password, you can restart `mysqld' with
     `--skip-grant-tables' to change the password.  *Note Resetting
     permissions::.

     If you get the above error even if you haven't specified a
     password, this means that you a wrong password in some `my.ini'
     file. *Note Option files::.  You can avoid using option files with
     the `--no-defaults' option, as follows:

          shell> mysqladmin --no-defaults -u root ver

   * If you updated an existing MySQL installation from a version
     earlier than Version 3.22.11 to Version 3.22.11 or later, did you
     run the `mysql_fix_privilege_tables' script?  If not, do so.  The
     structure of the grant tables changed with MySQL Version 3.22.11
     when the `GRANT' statement became functional.

   * If your privileges seem to have changed in the middle of a
     session, it may be that a superuser has changed them.  Reloading
     the grant tables affects new client connections, but it also
     affects existing connections as indicated in *Note Privilege
     changes::.

   * If you can't get your password to work, remember that you must use
     the `PASSWORD()' function if you set the password with the
     `INSERT', `UPDATE', or `SET PASSWORD' statements.  The
     `PASSWORD()' function is unnecessary if you specify the password
     using the `GRANT ... INDENTIFIED BY' statement or the `mysqladmin
     password' command.  *Note Passwords::.

   * `localhost' is a synonym for your local hostname, and is also the
     default host to which clients try to connect if you specify no host
     explicitly.  However, connections to `localhost' do not work if
     you are using a MySQL version prior to 3.23.27 that uses
     MIT-pthreads (`localhost' connections are made using Unix sockets,
     which were not supported by MIT-pthreads at that time).  To avoid
     this problem on such systems, you should use the `--host' option
     to name the server host explicitly.  This will make a TCP/IP
     connection to the `mysqld' server.  In this case, you must have
     your real hostname in `user' table entries on the server host.
     (This is true even if you are running a client program on the same
     host as the server.)

   * If you get an `Access denied' error when trying to connect to the
     database with `mysql -u user_name db_name', you may have a problem
     with the `user' table. Check this by executing `mysql -u root
     mysql' and issuing this SQL statement:

          mysql> SELECT * FROM user;

     The result should include an entry with the `Host' and `User'
     columns matching your computer's hostname and your MySQL user name.

   * The `Access denied' error message will tell you who you are trying
     to log in as, the host from which you are trying to connect, and
     whether or not you were using a password. Normally, you should
     have one entry in the `user' table that exactly matches the
     hostname and user name that were given in the error message. For
     example if you get an error message that contains `Using password:
     NO', this means that you tried to login without an password.

   * If you get the following error when you try to connect from a
     different host than the one on which the MySQL server is running,
     then there is no row in the `user' table that matches that host:

          Host ... is not allowed to connect to this MySQL server

     You can fix this by using the command-line tool `mysql' (on the
     server host!) to add a row to the `user', `db', or `host' table
     for the user/hostname combination from which you are trying to
     connect and then execute `mysqladmin flush-privileges'.  If you are
     not running MySQL Version 3.22 and you don't know the IP number or
     hostname of the machine from which you are connecting, you should
     put an entry with `'%'' as the `Host' column value in the `user'
     table and restart `mysqld' with the `--log' option on the server
     machine.  After trying to connect from the client machine, the
     information in the MySQL log will indicate how you really did
     connect.  (Then replace the `'%'' in the `user' table entry with
     the actual hostname that shows up in the log.  Otherwise, you'll
     have a system that is insecure.)

     Another reason for this error on Linux is that you are using a
     binary MySQL version that is compiled with a different glibc
     version than the one you are using.  In this case you should
     either upgrade your OS/glibc or download the source MySQL version
     and compile this yourself.  A source RPM is normally trivial to
     compile and install, so this isn't a big problem.

   * If you get an error message where the hostname is not shown or
     where the hostname is an IP, even if you try to connect with a
     hostname:

          shell> mysqladmin -u root -pxxxx -h some-hostname ver
          Access denied for user: 'root@' (Using password: YES)

     This means that MySQL got some error when trying to resolve the IP
     to a hostname.  In this case you can execute `mysqladmin
     flush-hosts' to reset the internal DNS cache. *Note DNS::.

     Some permanent solutions are:

        - Try to find out what is wrong with your DNS server and fix
          this.

        - Specify IPs instead of hostnames in the MySQL privilege
          tables.

        - Start `mysqld' with `--skip-name-resolve'.

        - Start `mysqld' with `--skip-host-cache'.

        - Connect to `localhost' if you are running the server and the
          client on the same machine.

        - Put the client machine names in `/etc/hosts'.

   * If `mysql -u root test' works but `mysql -h your_hostname -u root
     test' results in `Access denied', then you may not have the
     correct name for your host in the `user' table.  A common problem
     here is that the `Host' value in the user table entry specifies an
     unqualified hostname, but your system's name resolution routines
     return a fully qualified domain name (or vice-versa).  For
     example, if you have an entry with host `'tcx'' in the `user'
     table, but your DNS tells MySQL that your hostname is
     `'tcx.subnet.se'', the entry will not work. Try adding an entry to
     the `user' table that contains the IP number of your host as the
     `Host' column value.  (Alternatively, you could add an entry to the
     `user' table with a `Host' value that contains a wildcard--for
     example, `'tcx.%''.  However, use of hostnames ending with `%' is
     *insecure* and is *not* recommended!)

   * If `mysql -u user_name test' works but `mysql -u user_name
     other_db_name' doesn't work, you don't have an entry for
     `other_db_name' listed in the `db' table.

   * If `mysql -u user_name db_name' works when executed on the server
     machine, but `mysql -u host_name -u user_name db_name' doesn't
     work when executed on another client machine, you don't have the
     client machine listed in the `user' table or the `db' table.

   * If you can't figure out why you get `Access denied', remove from
     the `user' table all entries that have `Host' values containing
     wildcards (entries that contain `%' or `_').  A very common error
     is to insert a new entry with `Host'=`'%'' and `User'=`'some
     user'', thinking that this will allow you to specify `localhost'
     to connect from the same machine.  The reason that this doesn't
     work is that the default privileges include an entry with
     `Host'=`'localhost'' and `User'=`'''.  Because that entry has a
     `Host' value `'localhost'' that is more specific than `'%'', it is
     used in preference to the new entry when connecting from
     `localhost'!  The correct procedure is to insert a second entry
     with `Host'=`'localhost'' and `User'=`'some_user'', or to remove
     the entry with `Host'=`'localhost'' and `User'=`'''.

   * If you get the following error, you may have a problem with the
     `db' or `host' table:

          Access to database denied

     If the entry selected from the `db' table has an empty value in the
     `Host' column, make sure there are one or more corresponding
     entries in the `host' table specifying which hosts the `db' table
     entry applies to.

     If you get the error when using the SQL commands `SELECT ...  INTO
     OUTFILE' or `LOAD DATA INFILE', your entry in the `user' table
     probably doesn't have the `FILE' privilege enabled.

   * Remember that client programs will use connection parameters
     specified in configuration files or environment variables.  *Note
     Environment variables::.  If a client seems to be sending the
     wrong default connection parameters when you don't specify them on
     the command-line, check your environment and the `.my.cnf' file in
     your home directory.  You might also check the system-wide MySQL
     configuration files, though it is far less likely that client
     connection parameters will be specified there. *Note Option
     files::.  If you get `Access denied' when you run a client without
     any options, make sure you haven't specified an old password in
     any of your option files!  *Note Option files::.

   * If you make changes to the grant tables directly (using an
     `INSERT' or `UPDATE' statement) and your changes seem to be
     ignored, remember that you must issue a `FLUSH PRIVILEGES'
     statement or execute a `mysqladmin flush-privileges' command to
     cause the server to re-read the privilege tables. Otherwise, your
     changes have no effect until the next time the server is
     restarted.  Remember that after you set the `root' password with
     an `UPDATE' command, you won't need to specify it until after you
     flush the privileges, because the server won't know you've changed
     the password yet!

   * If you have access problems with a Perl, PHP, Python, or ODBC
     program, try to connect to the server with `mysql -u user_name
     db_name' or `mysql -u user_name -pyour_pass db_name'.  If you are
     able to connect using the `mysql' client, there is a problem with
     your program and not with the access privileges.  (Note that there
     is no space between `-p' and the password; you can also use the
     `--password=your_pass' syntax to specify the password. If you use
     the `-p' option alone, MySQL will prompt you for the password.)

   * For testing, start the `mysqld' daemon with the
     `--skip-grant-tables' option.  Then you can change the MySQL grant
     tables and use the `mysqlaccess' script to check whether your
     modifications have the desired effect.  When you are satisfied
     with your changes, execute `mysqladmin flush-privileges' to tell
     the `mysqld' server to start using the new grant tables.  *Note*:
     reloading the grant tables overrides the `--skip-grant-tables'
     option.  This allows you to tell the server to begin using the
     grant tables again without bringing it down and restarting it.

   * If everything else fails, start the `mysqld' daemon with a
     debugging option (for example, `--debug=d,general,query'). This
     will print host and user information about attempted connections,
     as well as information about each command issued. *Note Making
     trace files::.

   * If you have any other problems with the MySQL grant tables and
     feel you must post the problem to the mailing list, always provide
     a dump of the MySQL grant tables. You can dump the tables with the
     `mysqldump mysql' command. As always, post your problem using the
     `mysqlbug' script.  *Note Bug reports::.  In some cases you may
     need to restart `mysqld' with `--skip-grant-tables' to run
     `mysqldump'.

MySQL User Account Management
=============================

`GRANT' and `REVOKE' Syntax
---------------------------

     GRANT priv_type [(column_list)] [, priv_type [(column_list)] ...]
         ON {tbl_name | * | *.* | db_name.*}
         TO user_name [IDENTIFIED BY [PASSWORD] 'password']
             [, user_name [IDENTIFIED BY 'password'] ...]
         [REQUIRE
             NONE |
             [{SSL| X509}]
         [CIPHER cipher [AND]]
         [ISSUER issuer [AND]]
         [SUBJECT subject]]
         [WITH [GRANT OPTION | MAX_QUERIES_PER_HOUR # |
                               MAX_UPDATES_PER_HOUR # |
                               MAX_CONNECTIONS_PER_HOUR #]]

     REVOKE priv_type [(column_list)] [, priv_type [(column_list)] ...]
         ON {tbl_name | * | *.* | db_name.*}
         FROM user_name [, user_name ...]

`GRANT' is implemented in MySQL Version 3.22.11 or later. For earlier
MySQL versions, the `GRANT' statement does nothing.

The `GRANT' and `REVOKE' commands allow system administrators to create
users and grant and revoke rights to MySQL users at four privilege
levels:

*Global level*
     Global privileges apply to all databases on a given server. These
     privileges are stored in the `mysql.user' table.

*Database level*
     Database privileges apply to all tables in a given database. These
     privileges are stored in the `mysql.db' and `mysql.host' tables.

*Table level*
     Table privileges apply to all columns in a given table. These
     privileges are stored in the `mysql.tables_priv' table.

*Column level*
     Column privileges apply to single columns in a given table. These
     privileges are stored in the `mysql.columns_priv' table.

If you give a grant for a users that doesn't exists, that user is
created.  For examples of how `GRANT' works, see *Note Adding users::.

For the `GRANT' and `REVOKE' statements, `priv_type' may be specified
as any of the following:

`ALL [PRIVILEGES]'     Sets all simple privileges except `WITH GRANT
                       OPTION'
`ALTER'                Allows usage of `ALTER TABLE'
`CREATE'               Allows usage of `CREATE TABLE'
`CREATE TEMPORARY      Allows usage of `CREATE TEMPORARY TABLE'
TABLES'
`DELETE'               Allows usage of `DELETE'
`DROP'                 Allows usage of `DROP TABLE'.
`EXECUTE'              Allows the user to run stored procedures (for
                       MySQL 5.0)
`FILE'                 Allows usage of `SELECT ... INTO OUTFILE' and
                       `LOAD DATA INFILE'.
`INDEX'                Allows usage of `CREATE INDEX' and `DROP INDEX'
`INSERT'               Allows usage of `INSERT'
`LOCK TABLES'          Allows usage of `LOCK TABLES' on tables for which
                       one has the `SELECT' privilege.
`PROCESS'              Allows usage of `SHOW FULL PROCESSLIST'
`REFERENCES'           For the future
`RELOAD'               Allows usage of `FLUSH'
`REPLICATION CLIENT'   Gives the right to the user to ask where the
                       slaves/masters are.
`REPLICATION SLAVE'    Needed for the replication slaves (to read
                       binlogs from master).
`SELECT'               Allows usage of `SELECT'
`SHOW DATABASES'       `SHOW DATABASES' shows all databases.
`SHUTDOWN'             Allows usage of `mysqladmin shutdown'
`SUPER'                Allows one connect (once) even if max_connections
                       is reached and execute commands `CHANGE MASTER',
                       `KILL thread', `mysqladmin debug', `PURGE MASTER
                       LOGS' and `SET GLOBAL'
`UPDATE'               Allows usage of `UPDATE'
`USAGE'                Synonym for "no privileges."
`GRANT OPTION'         Synonym for `WITH GRANT OPTION'

`USAGE' can be used when you want to create a user that has no
privileges.

The privileges `CREATE TEMPORARY TABLES', `EXECUTE', `LOCK TABLES',
`REPLICATION ...', `SHOW DATABASES' and `SUPER' are new for in version
4.0.2.  To use these new privileges after upgrading to 4.0.2, you have
to run the `mysql_fix_privilege_tables' script.

In older MySQL versions, the `PROCESS' privilege gives the same rights
as the new `SUPER' privilege.

To revoke the `GRANT' privilege from a user, use a `priv_type' value of
`GRANT OPTION':

     mysql> REVOKE GRANT OPTION ON ... FROM ...;

The only `priv_type' values you can specify for a table are `SELECT',
`INSERT', `UPDATE', `DELETE', `CREATE', `DROP', `GRANT OPTION',
`INDEX', and `ALTER'.

The only `priv_type' values you can specify for a column (that is, when
you use a `column_list' clause) are `SELECT', `INSERT', and `UPDATE'.

You can set global privileges by using `ON *.*' syntax.  You can set
database privileges by using `ON db_name.*' syntax. If you specify `ON
*' and you have a current database, you will set the privileges for
that database.  (*Warning*: if you specify `ON *' and you *don't* have
a current database, you will affect the global privileges!)

*Please note*: the `_' and `%' wildcards are allowed when specifying
database names in `GRANT' commands. This means that if you wish to use
for instance a `_' character as part of a database name, you should
specify it as `\_' in the `GRANT' command, to prevent the user from
being able to access additional databases matching the wildcard
pattern, e.g., `GRANT ... ON `foo\_bar`.* TO ...'.

In order to accommodate granting rights to users from arbitrary hosts,
MySQL supports specifying the `user_name' value in the form
`user@host'.  If you want to specify a `user' string containing special
characters (such as `-'), or a `host' string containing special
characters or wildcard characters (such as `%'), you can quote the user
or host name (for example, `'test-user'@'test-hostname'').

You can specify wildcards in the hostname.  For example,
`user@'%.loc.gov'' applies to `user' for any host in the `loc.gov'
domain, and `user@'144.155.166.%'' applies to `user' for any host in
the `144.155.166' class C subnet.

The simple form `user' is a synonym for `user@"%"'.

MySQL doesn't support wildcards in user names.  Anonymous users are
defined by inserting entries with `User=''' into the `mysql.user' table
or creating an user with an empty name with the `GRANT' command.

*Note*: if you allow anonymous users to connect to the MySQL server,
you should also grant privileges to all local users as `user@localhost'
because otherwise the anonymous user entry for the local host in the
`mysql.user' table will be used when the user tries to log into the
MySQL server from the local machine!

You can verify if this applies to you by executing this query:

     mysql> SELECT Host,User FROM mysql.user WHERE User='';

For the moment, `GRANT' only supports host, table, database, and column
names up to 60 characters long. A user name can be up to 16 characters.

The privileges for a table or column are formed from the logical OR of
the privileges at each of the four privilege levels.  For example, if
the `mysql.user' table specifies that a user has a global `SELECT'
privilege, this can't be denied by an entry at the database, table, or
column level.

The privileges for a column can be calculated as follows:

     global privileges
     OR (database privileges AND host privileges)
     OR table privileges
     OR column privileges

In most cases, you grant rights to a user at only one of the privilege
levels, so life isn't normally as complicated as above. The details of
the privilege-checking procedure are presented in *Note Privilege
system::.

If you grant privileges for a user/hostname combination that does not
exist in the `mysql.user' table, an entry is added and remains there
until deleted with a `DELETE' command.  In other words, `GRANT' may
create `user' table entries, but `REVOKE' will not remove them; you
must do that explicitly using `DELETE'.

In MySQL Version 3.22.12 or later, if a new user is created or if you
have global grant privileges, the user's password will be set to the
password specified by the `IDENTIFIED BY' clause, if one is given.  If
the user already had a password, it is replaced by the new one.

If you don't want to send the password in clear text you can use the
`PASSWORD' option followed by a scrambled password from SQL function
`PASSWORD()' or the C API function `make_scrambled_password(char *to,
const char *password)'.

*Warning*: if you create a new user but do not specify an `IDENTIFIED
BY' clause, the user has no password.  This is insecure.

Passwords can also be set with the `SET PASSWORD' command.  *Note
`SET': SET OPTION.

If you grant privileges for a database, an entry in the `mysql.db'
table is created if needed. When all privileges for the database have
been removed with `REVOKE', this entry is deleted.

If a user doesn't have any privileges on a table, the table is not
displayed when the user requests a list of tables (for example, with a
`SHOW TABLES' statement).

The `WITH GRANT OPTION' clause gives the user the ability to give to
other users any privileges the user has at the specified privilege
level.  You should be careful to whom you give the `GRANT' privilege,
as two users with different privileges may be able to join privileges!

`MAX_QUERIES_PER_HOUR #', `MAX_UPDATES_PER_HOUR #' and
`MAX_CONNECTIONS_PER_HOUR #' are new in MySQL version 4.0.2.  These
options limit the number of queries/updates and logins the user can do
during one hour. If `#' is 0 (default), then this means that there are
no limitations for that user. *Note User resources::.  Note: to specify
any of these options for an existing user without adding other
additional privileges, use `GRANT USAGE ... WITH MAX_...'.

You cannot grant another user a privilege you don't have yourself; the
`GRANT' privilege allows you to give away only those privileges you
possess.

Be aware that when you grant a user the `GRANT' privilege at a
particular privilege level, any privileges the user already possesses
(or is given in the future!) at that level are also grantable by that
user.  Suppose you grant a user the `INSERT' privilege on a database.
If you then grant the `SELECT' privilege on the database and specify
`WITH GRANT OPTION', the user can give away not only the `SELECT'
privilege, but also `INSERT'.  If you then grant the `UPDATE' privilege
to the user on the database, the user can give away the `INSERT',
`SELECT' and `UPDATE'.

You should not grant `ALTER' privileges to a normal user.  If you do
that, the user can try to subvert the privilege system by renaming
tables!

Note that if you are using table or column privileges for even one
user, the server examines table and column privileges for all users and
this will slow down MySQL a bit.

When `mysqld' starts, all privileges are read into memory.  Database,
table, and column privileges take effect at once, and user-level
privileges take effect the next time the user connects.  Modifications
to the grant tables that you perform using `GRANT' or `REVOKE' are
noticed by the server immediately.  If you modify the grant tables
manually (using `INSERT', `UPDATE', etc.), you should execute a `FLUSH
PRIVILEGES' statement or run `mysqladmin flush-privileges' to tell the
server to reload the grant tables.  *Note Privilege changes::.

The biggest differences between the ANSI SQL and MySQL versions of
`GRANT' are:

   * In MySQL privileges are given for an username + hostname
     combination and not only for an username.

   * ANSI SQL doesn't have global or database-level privileges, and
     ANSI SQL doesn't support all privilege types that MySQL supports.
     MySQL doesn't support the ANSI SQL `TRIGGER' or `UNDER' privileges.

   * ANSI SQL privileges are structured in a hierarchal manner. If you
     remove an user, all privileges the user has granted are revoked. In
     MySQL the granted privileges are not automatically revoked, but
     you have to revoke these yourself if needed.

   * In MySQL, if you have the `INSERT' privilege on only some of the
     columns in a table, you can execute `INSERT' statements on the
     table; the columns for which you don't have the `INSERT' privilege
     will be set to their default values. ANSI SQL requires you to have
     the `INSERT' privilege on all columns.

   * When you drop a table in ANSI SQL, all privileges for the table
     are revoked.  If you revoke a privilege in ANSI SQL, all
     privileges that were granted based on this privilege are also
     revoked. In MySQL, privileges can be dropped only with explicit
     `REVOKE' commands or by manipulating the MySQL grant tables.

For a description of using `REQUIRE', see *Note Secure connections::.

MySQL User Names and Passwords
------------------------------

There are several distinctions between the way user names and passwords
are used by MySQL and the way they are used by Unix or Windows:

   * User names, as used by MySQL for authentication purposes, have
     nothing to do with Unix user names (login names) or Windows user
     names.  Most MySQL clients by default try to log in using the
     current Unix user name as the MySQL user name, but that is for
     convenience only.  Client programs allow a different name to be
     specified with the `-u' or `--user' options. This means that you
     can't make a database secure in any way unless all MySQL user
     names have passwords.  Anyone may attempt to connect to the server
     using any name, and they will succeed if they specify any name
     that doesn't have a password.

   * MySQL user names can be up to 16 characters long; Unix user names
     typically are limited to 8 characters.

   * MySQL passwords have nothing to do with Unix passwords.  There is
     no necessary connection between the password you use to log in to
     a Unix machine and the password you use to access a database on
     that machine.

   * MySQL encrypts passwords using a different algorithm than the one
     used during the Unix login process.  See the descriptions of the
     `PASSWORD()' and `ENCRYPT()' functions in *Note Miscellaneous
     functions::.  Note that even if the password is stored
     'scrambled', and knowing your 'scrambled' password is enough to be
     able to connect to the MySQL server!

MySQL users and their privileges are normally created with the `GRANT'
command. *Note GRANT::.

When you login to a MySQL server with a command-line client you should
specify the password with `--password=your-password'.  *Note
Connecting::.

     mysql --user=monty --password=guess database_name

If you want the client to prompt for a password, you should use
`--password' without any argument

     mysql --user=monty --password database_name

or the short form:

     mysql -u monty -p database_name

Note that in the last example the password is *not* 'database_name'.

If you want to use the `-p' option to supply a password you should do so
like this:

     mysql -u monty -pguess database_name

On some systems, the library call that MySQL uses to prompt for a
password will automatically cut the password to 8 characters. Internally
MySQL doesn't have any limit for the length of the password.

When Privilege Changes Take Effect
----------------------------------

When `mysqld' starts, all grant table contents are read into memory and
become effective at that point.

Modifications to the grant tables that you perform using `GRANT',
`REVOKE', or `SET PASSWORD' are noticed by the server immediately.

If you modify the grant tables manually (using `INSERT', `UPDATE',
etc.), you should execute a `FLUSH PRIVILEGES' statement or run
`mysqladmin flush-privileges' or `mysqladmin reload' to tell the server
to reload the grant tables. Otherwise, your changes will have _no
effect_ until you restart the server. If you change the grant tables
manually but forget to reload the privileges, you will be wondering why
your changes don't seem to make any difference!

When the server notices that the grant tables have been changed,
existing client connections are affected as follows:

   * Table and column privilege changes take effect with the client's
     next request.

   * Database privilege changes take effect at the next `USE db_name'
     command.

   * Global privilege changes and password changes take effect the next
     time the client connects.

Setting Up the Initial MySQL Privileges
---------------------------------------

After installing MySQL, you set up the initial access privileges by
running `scripts/mysql_install_db'.  *Note Quick install::.  The
`mysql_install_db' script starts up the `mysqld' server, then
initialises the grant tables to contain the following set of privileges:

   * The MySQL `root' user is created as a superuser who can do
     anything.  Connections must be made from the local host.

     *Note*: The initial `root' password is empty, so anyone can
     connect as `root' _without a password_ and be granted all
     privileges.

   * An anonymous user is created that can do anything with databases
     that have a name of `'test'' or starting with `'test_''.
     Connections must be made from the local host.  This means any
     local user can connect without a password and be treated as the
     anonymous user.

   * Other privileges are denied.  For example, normal users can't use
     `mysqladmin shutdown' or `mysqladmin processlist'.

*Note*: the default privileges are different for Windows.  *Note
Windows running::.

Because your installation is initially wide open, one of the first
things you should do is specify a password for the MySQL `root' user.
You can do this as follows (note that you specify the password using
the `PASSWORD()' function):

     shell> mysql -u root mysql
     mysql> SET PASSWORD FOR root@localhost=PASSWORD('new_password');

If you know what you are doing, you can also directly manipulate the
privilege tables:

     shell> mysql -u root mysql
     mysql> UPDATE user SET Password=PASSWORD('new_password')
         ->     WHERE user='root';
     mysql> FLUSH PRIVILEGES;

Another way to set the password is by using the `mysqladmin' command:

     shell> mysqladmin -u root password new_password

Only users with write/update access to the `mysql' database can change
the password for others users.  All normal users (not anonymous ones)
can only change their own password with either of the above commands or
with `SET PASSWORD=PASSWORD('new password')'.

Note that if you update the password in the `user' table directly using
the first method, you must tell the server to re-read the grant tables
(with `FLUSH PRIVILEGES'), because the change will go unnoticed
otherwise.

Once the `root' password has been set, thereafter you must supply that
password when you connect to the server as `root'.

You may wish to leave the `root' password blank so that you don't need
to specify it while you perform additional setup or testing. However,
be sure to set it before using your installation for any real
production work.

See the `scripts/mysql_install_db' script to see how it sets up the
default privileges.  You can use this as a basis to see how to add
other users.

If you want the initial privileges to be different from those just
described above, you can modify `mysql_install_db' before you run it.

To re-create the grant tables completely, remove all the `.frm',
`.MYI', and `.MYD' files in the directory containing the `mysql'
database.  (This is the directory named `mysql' under the database
directory, which is listed when you run `mysqld --help'.) Then run the
`mysql_install_db' script, possibly after editing it first to have the
privileges you want.

*Note*: for MySQL versions older than Version 3.22.10, you should not
delete the `.frm' files.  If you accidentally do this, you should copy
them back from your MySQL distribution before running
`mysql_install_db'.

Adding New Users to MySQL
-------------------------

You can add users two different ways: by using `GRANT' statements or by
manipulating the MySQL grant tables directly.  The preferred method is
to use `GRANT' statements, because they are more concise and less
error-prone. *Note GRANT::.

There are also a lot of contributed programs like `phpmyadmin' that can
be used to create and administrate users.

The following examples show how to use the `mysql' client to set up new
users.  These examples assume that privileges are set up according to
the defaults described in the previous section.  This means that to
make changes, you must be on the same machine where `mysqld' is
running, you must connect as the MySQL `root' user, and the `root' user
must have the `INSERT' privilege for the `mysql' database and the
`RELOAD' administrative privilege.  Also, if you have changed the
`root' user password, you must specify it for the `mysql' commands here.

You can add new users by issuing `GRANT' statements:

     shell> mysql --user=root mysql
     mysql> GRANT ALL PRIVILEGES ON *.* TO monty@localhost
         ->     IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
     mysql> GRANT ALL PRIVILEGES ON *.* TO monty@"%"
         ->     IDENTIFIED BY 'some_pass' WITH GRANT OPTION;
     mysql> GRANT RELOAD,PROCESS ON *.* TO admin@localhost;
     mysql> GRANT USAGE ON *.* TO dummy@localhost;

These `GRANT' statements set up three new users:

`monty'
     A full superuser who can connect to the server from anywhere, but
     who must use a password `'some_pass'' to do so.  Note that we must
     issue `GRANT' statements for both `monty@localhost' and
     `monty@"%"'.  If we don't add the entry with `localhost', the
     anonymous user entry for `localhost' that is created by
     `mysql_install_db' will take precedence when we connect from the
     local host, because it has a more specific `Host' field value and
     thus comes earlier in the `user' table sort order.

`admin'
     A user who can connect from `localhost' without a password and who
     is granted the `RELOAD' and `PROCESS' administrative privileges.
     This allows the user to execute the `mysqladmin reload',
     `mysqladmin refresh', and `mysqladmin flush-*' commands, as well as
     `mysqladmin processlist' .  No database-related privileges are
     granted.  (They can be granted later by issuing additional `GRANT'
     statements.)

`dummy'
     A user who can connect without a password, but only from the local
     host.  The global privileges are all set to `'N''the `USAGE'
     privilege type allows you to create a user with no privileges.  It
     is assumed that you will grant database-specific privileges later.

You can also add the same user access information directly by issuing
`INSERT' statements and then telling the server to reload the grant
tables:

     shell> mysql --user=root mysql
     mysql> INSERT INTO user VALUES('localhost','monty',PASSWORD('some_pass'),
         ->          'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
     mysql> INSERT INTO user VALUES('%','monty',PASSWORD('some_pass'),
         ->          'Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y','Y');
     mysql> INSERT INTO user SET Host='localhost',User='admin',
         ->           Reload_priv='Y', Process_priv='Y';
     mysql> INSERT INTO user (Host,User,Password)
         ->                  VALUES('localhost','dummy','');
     mysql> FLUSH PRIVILEGES;

Depending on your MySQL version, you may have to use a different number
of `'Y'' values above (versions prior to Version 3.22.11 had fewer
privilege columns).  For the `admin' user, the more readable extended
`INSERT' syntax that is available starting with Version 3.22.11 is used.

Note that to set up a superuser, you need only create a `user' table
entry with the privilege fields set to `'Y''.  No `db' or `host' table
entries are necessary.

The privilege columns in the `user' table were not set explicitly in the
last `INSERT' statement (for the `dummy' user), so those columns are
assigned the default value of `'N''.  This is the same thing that
`GRANT USAGE' does.

The following example adds a user `custom' who can connect from hosts
`localhost', `server.domain', and `whitehouse.gov'.  He wants to access
the `bankaccount' database only from `localhost', the `expenses'
database only from `whitehouse.gov', and the `customer' database from
all three hosts.  He wants to use the password `stupid' from all three
hosts.

To set up this user's privileges using `GRANT' statements, run these
commands:

     shell> mysql --user=root mysql
     mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
         ->     ON bankaccount.*
         ->     TO custom@localhost
         ->     IDENTIFIED BY 'stupid';
     mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
         ->     ON expenses.*
         ->     TO [e-mail]
         ->     IDENTIFIED BY 'stupid';
     mysql> GRANT SELECT,INSERT,UPDATE,DELETE,CREATE,DROP
         ->     ON customer.*
         ->     TO custom@'%'
         ->     IDENTIFIED BY 'stupid';

The reason that we do to grant statements for the user 'custom' is that
we want the give the user access to MySQL both from the local machine
with Unix sockets and from the remote machine 'whitehouse.gov' over
TCP/IP.

To set up the user's privileges by modifying the grant tables directly,
run these commands (note the `FLUSH PRIVILEGES' at the end):

     shell> mysql --user=root mysql
     mysql> INSERT INTO user (Host,User,Password)
         -> VALUES('localhost','custom',PASSWORD('stupid'));
     mysql> INSERT INTO user (Host,User,Password)
         -> VALUES('server.domain','custom',PASSWORD('stupid'));
     mysql> INSERT INTO user (Host,User,Password)
         -> VALUES('whitehouse.gov','custom',PASSWORD('stupid'));
     mysql> INSERT INTO db
         -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
         ->  Create_priv,Drop_priv)
         -> VALUES
         -> ('localhost','bankaccount','custom','Y','Y','Y','Y','Y','Y');
     mysql> INSERT INTO db
         -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
         ->  Create_priv,Drop_priv)
         -> VALUES
         -> ('whitehouse.gov','expenses','custom','Y','Y','Y','Y','Y','Y');
     mysql> INSERT INTO db
         -> (Host,Db,User,Select_priv,Insert_priv,Update_priv,Delete_priv,
         ->  Create_priv,Drop_priv)
         -> VALUES('%','customer','custom','Y','Y','Y','Y','Y','Y');
     mysql> FLUSH PRIVILEGES;

The first three `INSERT' statements add `user' table entries that allow
user `custom' to connect from the various hosts with the given
password, but grant no permissions to him (all privileges are set to the
default value of `'N'').  The next three `INSERT' statements add `db'
table entries that grant privileges to `custom' for the `bankaccount',
`expenses', and `customer' databases, but only when accessed from the
proper hosts.  As usual, when the grant tables are modified directly,
the server must be told to reload them (with `FLUSH PRIVILEGES') so
that the privilege changes take effect.

If you want to give a specific user access from any machine in a given
domain, you can issue a `GRANT' statement like the following:

     mysql> GRANT ...
         ->     ON *.*
         ->     TO myusername@"%.mydomainname.com"
         ->     IDENTIFIED BY 'mypassword';

To do the same thing by modifying the grant tables directly, do this:

     mysql> INSERT INTO user VALUES ('%.mydomainname.com', 'myusername',
         ->             PASSWORD('mypassword'),...);
     mysql> FLUSH PRIVILEGES;

Limiting user resources
-----------------------

Starting from MySQL 4.0.2 one can limit certain resources per user.

So far, the only available method of limiting usage of MySQL server
resources has been setting the `max_user_connections' startup variable
to a non-zero value. But this method is strictly global and does not
allow for management of individual users, which could be of particular
interest to Internet Service Providers.

Therefore, management of three resources is introduced on the
individual user level:

   * Number of all queries per hour: All commands that could be run by
     a user.

   * Number of all updates per hour: Any command that changes any table
     or database.

   * Number of connections made per hour: New connections opened per
     hour.

A user in the aforementioned context is a single entry in the `user'
table, which is uniquely identified by its `user' and `host' columns.

All users are by default not limited in using the above resources,
unless the limits are granted to them. These limits can be granted
*only* via global `GRANT (*.*)', using this syntax:

     GRANT ... WITH MAX_QUERIES_PER_HOUR N1
                    MAX_UPDATES_PER_HOUR N2
                    MAX_CONNECTIONS_PER_HOUR N3;

One can specify any combination of the above resources.  N1, N2 and N3
are integers and stands for count / hour.

If user reaches any of the above limits withing one hour, his
connection will be terminated or refused and the appropriate error
message shall be issued.

Current usage values for a particular user can be flushed (set to zero)
by issuing a `GRANT' statement with any of the above clauses, including
a `GRANT' statement with the current values.

Also, current values for all users will be flushed if privileges are
reloaded (in the server or using `mysqladmin reload') or if the `FLUSH
USER_RESOURCES' command is issued.

The feature is enabled as soon as a single user is granted with any of
the limiting `GRANT' clauses.

As a prerequisite for enabling this feature, the `user' table in the
`mysql' database must contain the additional columns, as defined in the
table creation scripts `mysql_install_db' and `mysql_install_db.sh' in
`scripts' subdirectory.

Setting Up Passwords
--------------------

In most cases you should use `GRANT' to set up your users/passwords, so
the following only applies for advanced users. *Note `GRANT': GRANT.

The examples in the preceding sections illustrate an important
principle: when you store a non-empty password using `INSERT' or
`UPDATE' statements, you must use the `PASSWORD()' function to encrypt
it.  This is because the `user' table stores passwords in encrypted
form, not as plaintext.  If you forget that fact, you are likely to
attempt to set passwords like this:

     shell> mysql -u root mysql
     mysql> INSERT INTO user (Host,User,Password)
         -> VALUES('%','jeffrey','biscuit');
     mysql> FLUSH PRIVILEGES;

The result is that the plaintext value `'biscuit'' is stored as the
password in the `user' table.  When the user `jeffrey' attempts to
connect to the server using this password, the `mysql' client encrypts
it with `PASSWORD()', generates an authentification vector based on
*encrypted* password and a random number, obtained from server, and
sends the result to the server.  The server uses the `password' value
in the `user' table (that is *not encrypted* value `'biscuit'') to
perform the same calculations, and compares results.  The comparison
fails and the server rejects the connection:

     shell> mysql -u jeffrey -pbiscuit test
     Access denied

Passwords must be encrypted when they are inserted in the `user' table,
so the `INSERT' statement should have been specified like this instead:

     mysql> INSERT INTO user (Host,User,Password)
         -> VALUES('%','jeffrey',PASSWORD('biscuit'));

You must also use the `PASSWORD()' function when you use `SET PASSWORD'
statements:

     mysql> SET PASSWORD FOR jeffrey@"%" = PASSWORD('biscuit');

If you set passwords using the `GRANT ... IDENTIFIED BY' statement or
the `mysqladmin password' command, the `PASSWORD()' function is
unnecessary.  They both take care of encrypting the password for you,
so you would specify a password of `'biscuit'' like this:

     mysql> GRANT USAGE ON *.* TO jeffrey@"%" IDENTIFIED BY 'biscuit';

or

     shell> mysqladmin -u jeffrey password biscuit

*Note*: `PASSWORD()' does not perform password encryption in the same
way that Unix passwords are encrypted.  You should not assume that if
your Unix password and your MySQL password are the same, that
`PASSWORD()' will result in the same encrypted value as is stored in the
Unix password file. *Note User names::.

Keeping Your Password Secure
----------------------------

It is inadvisable to specify your password in a way that exposes it to
discovery by other users.  The methods you can use to specify your
password when you run client programs are listed here, along with an
assessment of the risks of each method:

   * Never give a normal user access to the `mysql.user' table. Knowing
     the encrypted password for a user makes it possible to login as
     this user.  The passwords are only scrambled so that one shouldn't
     be able to see the real password you used (if you happen to use a
     similar password with your other applications).

   * Use a `-pyour_pass' or `--password=your_pass' option on the command
     line.  This is convenient but insecure, because your password
     becomes visible to system status programs (such as `ps') that may
     be invoked by other users to display command-lines.  (MySQL
     clients typically overwrite the command-line argument with zeroes
     during their initialisation sequence, but there is still a brief
     interval during which the value is visible.)

   * Use a `-p' or `--password' option (with no `your_pass' value
     specified).  In this case, the client program solicits the
     password from the terminal:

          shell> mysql -u user_name -p
          Enter password: ********

     The `*' characters represent your password.

     It is more secure to enter your password this way than to specify
     it on the command-line because it is not visible to other users.
     However, this method of entering a password is suitable only for
     programs that you run interactively.  If you want to invoke a
     client from a script that runs non-interactively, there is no
     opportunity to enter the password from the terminal. On some
     systems, you may even find that the first line of your script is
     read and interpreted (incorrectly) as your password!

   * Store your password in a configuration file.  For example, you can
     list your password in the `[client]' section of the `.my.cnf' file
     in your home directory:

          [client]
          password=your_pass

     If you store your password in `.my.cnf', the file should not be
     group or world readable or writable.  Make sure the file's access
     mode is `400' or `600'.

     *Note Option files::.

   * You can store your password in the `MYSQL_PWD' environment
     variable, but this method must be considered extremely insecure
     and should not be used.  Some versions of `ps' include an option
     to display the environment of running processes; your password
     will be in plain sight for all to see if you set `MYSQL_PWD'.
     Even on systems without such a version of `ps', it is unwise to
     assume there is no other method to observe process environments.
     *Note Environment variables::.

All in all, the safest methods are to have the client program prompt
for the password or to specify the password in a properly protected
`.my.cnf' file.

Using Secure Connections
------------------------

Basics
......

Beginning with version 4.0.0, MySQL has support for SSL encrypted
connections. To understand how MySQL uses SSL, it's necessary to
explain some basic SSL and X509 concepts. People who are already
familiar with them can skip this part.

By default, MySQL uses unencrypted connections between the client and
the server. This means that someone could watch all your traffic and
look at the data being sent or received.  They could even change the
data while it is in transit between client and server. Sometimes you
need to move information over public networks in a secure fashion; in
such cases, using an unencrypted connection is unacceptable.

SSL is a protocol that uses different encryption algorithms to ensure
that data received over a public network can be trusted. It has
mechanisms to detect any change, loss or replay of data. SSL also
incorporates algorithms to recognise and provide identity verification
using the X509 standard.

Encryption is the way to make any kind of data unreadable. In fact,
today's practice requires many additional security elements from
encryption algorithms.  They should resist many kind of known attacks
like just messing with the order of encrypted messages or replaying data
twice.

X509 is a standard that makes it possible to identify someone on the
Internet.  It is most commonly used in e-commerce applications. In basic
terms, there should be some company (called a "Certificate Authority")
that assigns electronic certificates to anyone who needs them.
Certificates rely on asymmetric encryption algorithms that have two
encryption keys (a public key and a secret key). A certificate owner
can prove his identity by showing his certificate to other party. A
certificate consists of its owner's public key. Any data encrypted with
this public key can be decrypted only using the corresponding secret
key, which is held by the owner of the certificate.

MySQL doesn't use encrypted connections by default, because doing so
would make the client/server protocol much slower. Any kind of
additional functionality requires the computer to do additional work and
encrypting data is a CPU-intensive operation that requires time and can
delay MySQL main tasks. By default MySQL is tuned to be fast as
possible.

If you need more information about SSL, X509, or encryption, you should
use your favourite Internet search engine and search for keywords in
which you are interested.

Requirements
............

To get secure connections to work with MySQL you must do the following:

  1. Install the OpenSSL library. We have tested MySQL with OpenSSL
     0.9.6.  `http://www.openssl.org/'.

  2. Configure MySQL with `--with-vio --with-openssl'.

  3. If you are using an old MySQL installation, you have to update your
     `mysql.user' table with some new SSL-related columns. You can do
     this by running the `mysql_fix_privilege_tables.sh' script.  This
     is necessary if your grant tables date from a version prior to
     MySQL 4.0.0.

  4. You can check if a running `mysqld' server supports OpenSSL by
     examining if `SHOW VARIABLES LIKE 'have_openssl'' returns `YES'.

`GRANT' Options
...............

MySQL can check X509 certificate attributes in addition to the normal
username/password scheme. All the usual options are still required
(username, password, IP address mask, database/table name).

There are different possibilities to limit connections:

   * Without any SSL or X509 options, all kind of encrypted/unencrypted
     connections are allowed if the username and password are valid.

   * `REQUIRE SSL' option limits the server to allow only SSL encrypted
     connections. Note that this option can be omitted if there are any
     ACL records which allow non-SSL connections.

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret" REQUIRE SSL;

   * `REQUIRE X509' means that the client should have a valid
     certificate but we do not care about the exact certificate, issuer
     or subject.  The only restriction is that it should be possible to
     verify its signature with one of the CA certificates.

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret" REQUIRE X509;

   * `REQUIRE ISSUER "issuer"' places a restriction on connection
     attempts: The client must present a valid X509 certificate issued
     by CA `"issuer"'.  Using X509 certificates always implies
     encryption, so the `SSL' option is unneccessary.

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret"
              -> REQUIRE ISSUER "C=FI, ST=Some-State, L=Helsinki,
              "> O=MySQL Finland AB, CN=Tonu Samuel/Email=[e-mail]";

   * `REQUIRE SUBJECT "subject"' requires clients to have valid X509
     certificate with subject `"subject"' on it. If the client presents
     a certificate that is valid but has a different `"subject"', the
     connection is disallowed.

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret"
              -> REQUIRE SUBJECT "C=EE, ST=Some-State, L=Tallinn,
              "> O=MySQL demo client certificate,
              "> CN=Tonu Samuel/Email=[e-mail]";

   * `REQUIRE CIPHER "cipher"' is needed to assure enough strong ciphers
     and keylengths will be used. SSL itself can be weak if old
     algorithms with short encryption keys are used. Using this option,
     we can ask for some exact cipher method to allow a connection.

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret"
              -> REQUIRE CIPHER "EDH-RSA-DES-CBC3-SHA";

     The `SUBJECT', `ISSUER', and `CIPHER' options can be combined in
     the `REQUIRE' clause like this:

          mysql> GRANT ALL PRIVILEGES ON test.* TO root@localhost
              -> IDENTIFIED BY "goodsecret"
              -> REQUIRE SUBJECT "C=EE, ST=Some-State, L=Tallinn,
              "> O=MySQL demo client certificate,
              "> CN=Tonu Samuel/Email=[e-mail]"
              -> AND ISSUER "C=FI, ST=Some-State, L=Helsinki,
              "> O=MySQL Finland AB, CN=Tonu Samuel/Email=[e-mail]"
              -> AND CIPHER "EDH-RSA-DES-CBC3-SHA";

     Starting from MySQL 4.0.4 the `AND' keyword is optional between
     `REQUIRE' options.

     The order of the options does not matter, but no option can be
     specified twice.

Disaster Prevention and Recovery
================================

Database Backups
----------------

Because MySQL tables are stored as files, it is easy to do a backup. To
get a consistent backup, do a `LOCK TABLES' on the relevant tables
followed by `FLUSH TABLES' for the tables.  *Note `LOCK TABLES': LOCK
TABLES.  *Note `FLUSH': FLUSH.  You only need a read lock; this allows
other threads to continue to query the tables while you are making a
copy of the files in the database directory.  The `FLUSH TABLE' is
needed to ensure that the all active index pages is written to disk
before you start the backup.

If you want to make a SQL level backup of a table, you can use `SELECT
INTO OUTFILE' or `BACKUP TABLE'. *Note SELECT::.  *Note BACKUP TABLE::.

Another way to back up a database is to use the `mysqldump' program or
the `mysqlhotcopy script'. *Note `mysqldump': mysqldump.  *Note
`mysqlhotcopy': mysqlhotcopy.

  1. Do a full backup of your databases:

          shell> mysqldump --tab=/path/to/some/dir --opt --all

          or

          shell> mysqlhotcopy database /path/to/some/dir

     You can also simply copy all table files (`*.frm', `*.MYD', and
     `*.MYI' files) as long as the server isn't updating anything.  The
     script `mysqlhotcopy' does use this method.

  2. Stop `mysqld' if it's running, then start it with the
     `--log-update[=file_name]' option.  *Note Update log::. The update
     log file(s) provide you with the information you need to replicate
     changes to the database that are made subsequent to the point at
     which you executed `mysqldump'.

If you have to restore something, try to recover your tables using
`REPAIR TABLE' or `myisamchk -r' first.  That should work in 99.9% of
all cases.  If `myisamchk' fails, try the following procedure (this
will only work if you have started MySQL with `--log-update', *note
Update log::):

  1. Restore the original `mysqldump' backup.

  2. Execute the following command to re-run the updates in the binary
     log:

          shell> mysqlbinlog hostname-bin.[0-9]* | mysql

     If you are using the update log you can use:

          shell> ls -1 -t -r hostname.[0-9]* | xargs cat | mysql

`ls' is used to get all the update log files in the right order.

You can also do selective backups with `SELECT * INTO OUTFILE
'file_name' FROM tbl_name' and restore with `LOAD DATA INFILE
'file_name' REPLACE ...' To avoid duplicate records, you need a
`PRIMARY KEY' or a `UNIQUE' key in the table. The `REPLACE' keyword
causes old records to be replaced with new ones when a new record
duplicates an old record on a unique key value.

If you get performance problems in making backups on your system, you
can solve this by setting up replication and do the backups on the slave
instead of on the master. *Note Replication Intro::.

If you are using a Veritas filesystem, you can do:

  1. From a client (or Perl), execute: `FLUSH TABLES WITH READ LOCK'.

  2. From another shell, execute: `mount vxfs snapshot'.

  3. From the first client, execute: `UNLOCK TABLES'.

  4. Copy files from snapshot.

  5. Unmount snapshot.

`BACKUP TABLE' Syntax
---------------------

     BACKUP TABLE tbl_name[,tbl_name...] TO '/path/to/backup/directory'

Copies to the backup directory the minimum number of table files needed
to restore the table, after flushing any buffered changes to disk.
Currently works only for `MyISAM' tables.  For `MyISAM' tables, copies
`.frm' (definition)  and `.MYD' (data) files. The index file can be
rebuilt from those two.

Before using this command, please see *Note Backup::.

During the backup, a read lock will be held for each table, one at time,
as they are being backed up. If you want to back up several tables as a
snapshot, you must first issue `LOCK TABLES' obtaining a read lock for
each table in the group.

The command returns a table with the following columns:

*Column*    *Value*
Table       Table name
Op          Always "backup"
Msg_type    One of `status', `error',
            `info' or `warning'.
Msg_text    The message.

Note that `BACKUP TABLE' is only available in MySQL version 3.23.25 and
later.

`RESTORE TABLE' Syntax
----------------------

     RESTORE TABLE tbl_name[,tbl_name...] FROM '/path/to/backup/directory'

Restores the table(s) from the backup that was made with `BACKUP
TABLE'. Existing tables will not be overwritten; if you try to restore
over an existing table, you will get an error. Restoring will take
longer than backing up due to the need to rebuild the index. The more
keys you have, the longer it will take. Just as `BACKUP TABLE',
`RESTORE TABLE' currently works only for `MyISAM' tables.

The command returns a table with the following columns:

*Column*    *Value*
Table       Table name
Op          Always "restore"
Msg_type    One of `status', `error',
            `info' or `warning'.
Msg_text    The message.

`CHECK TABLE' Syntax
--------------------

     CHECK TABLE tbl_name[,tbl_name...] [option [option...]]

     option = QUICK | FAST | MEDIUM | EXTENDED | CHANGED

`CHECK TABLE' works only on `MyISAM' and `InnoDB' tables. On `MyISAM'
tables it's the same thing as running `myisamchk -m table_name' on the
table.

If you don't specify any option `MEDIUM' is used.

Checks the table(s) for errors. For `MyISAM' tables the key statistics
are updated. The command returns a table with the following columns:

*Column*    *Value*
Table       Table name.
Op          Always "check".
Msg_type    One of `status', `error',
            `info', or `warning'.
Msg_text    The message.

Note that you can get many rows of information for each checked table.
The last row will be of `Msg_type status' and should normally be `OK'.
If you don't get `OK', or `Table is already up to date' you should
normally run a repair of the table. *Note Table maintenance::. `Table
is already up to date' means that the table the given `TYPE' told MySQL
that there wasn't any need to check the table.

The different check types stand for the following:

*Type*      *Meaning*
`QUICK'     Don't scan the rows to check for wrong links.
`FAST'      Only check tables which haven't been closed properly.
`CHANGED'   Only check tables which have been changed since last check
            or haven't been closed properly.
`MEDIUM'    Scan rows to verify that deleted links are okay. This also
            calculates a key checksum for the rows and verifies this
            with a calculated checksum for the keys.
`EXTENDED'  Do a full key lookup for all keys for each row.  This
            ensures that the table is 100% consistent, but will take a
            long time!

For dynamically sized `MyISAM' tables a started check will always do a
`MEDIUM' check. For statically sized rows we skip the row scan for
`QUICK' and `FAST' as the rows are very seldom corrupted.

You can combine check options as in:

     CHECK TABLE test_table FAST QUICK;

Which would simply do a quick check on the table to see whether it was
closed properly.

*Note*: that in some case `CHECK TABLE' will change the table!  This
happens if the table is marked as 'corrupted' or 'not closed properly'
but `CHECK TABLE' didn't find any problems in the table.  In this case
`CHECK TABLE' will mark the table as okay.

If a table is corrupted, then it's most likely that the problem is in
the indexes and not in the data part.  All of the above check types
checks the indexes thoroughly and should thus find most errors.

If you just want to check a table that you assume is okay, you should
use no check options or the `QUICK' option. The latter should be used
when you are in a hurry and can take the very small risk that `QUICK'
didn't find an error in the datafile. (In most cases MySQL should find,
under normal usage, any error in the data file. If this happens then
the table will be marked as 'corrupted', in which case the table can't
be used until it's repaired.)

`FAST' and `CHANGED' are mostly intended to be used from a script (for
example to be executed from `cron') if you want to check your table
from time to time. In most cases you `FAST' is to be prefered over
`CHANGED'.  (The only case when it isn't is when you suspect a bug you
have found a bug in the `MyISAM' code.)

`EXTENDED' is only to be used after you have run a normal check but
still get strange errors from a table when MySQL tries to update a row
or find a row by key (this is very unlikely if a normal check has
succeeded!).

Some things reported by check table, can't be corrected automatically:

   * `Found row where the auto_increment column has the value 0'.

     This means that you have in the table a row where the
     `AUTO_INCREMENT' index column contains the value 0.  (It's
     possible to create a row where the `AUTO_INCREMENT' column is 0 by
     explicitly setting the column to 0 with an `UPDATE' statement)

     This isn't an error in itself, but could cause trouble if you
     decide to dump the table and restore it or do an `ALTER TABLE' on
     the table. In this case the `AUTO_INCREMENT' column will change
     value, according to the rules of `AUTO_INCREMENT' columns, which
     could cause problems like a duplicate key error.

     To get rid of the warning, just execute an `UPDATE' statement to
     set the column to some other value than 0.

`REPAIR TABLE' Syntax
---------------------

     REPAIR TABLE tbl_name[,tbl_name...] [QUICK] [EXTENDED] [USE_FRM]

`REPAIR TABLE' works only on `MyISAM' tables and is the same as running
`myisamchk -r table_name' on the table.

Normally you should never have to run this command, but if disaster
strikes you are very likely to get back all your data from a MyISAM
table with `REPAIR TABLE'. If your tables get corrupted a lot you should
try to find the reason for this! *Note Crashing::. *Note MyISAM table
problems::.

`REPAIR TABLE' repairs a possible corrupted table. The command returns a
table with the following columns:

*Column*    *Value*
Table       Table name
Op          Always "repair"
Msg_type    One of `status', `error',
            `info' or `warning'.
Msg_text    The message.

Note that you can get many rows of information for each repaired table.
The last one row will be of `Msg_type status' and should normally be
`OK'.  If you don't get `OK', you should try repairing the table with
`myisamchk -o', as `REPAIR TABLE' does not yet implement all the
options of `myisamchk'. In the near future, we will make it more
flexible.

If `QUICK' is given then MySQL will try to do a `REPAIR' of only the
index tree.

If you use `EXTENDED' then MySQL will create the index row by row
instead of creating one index at a time with sorting; this may be
better than sorting on fixed-length keys if you have long `CHAR' keys
that compress very well.  This type of repair is like that done by
`myisamchk --safe-recover'.

As of `MySQL' 4.0.2, there is a `USE_FRM' mode for `REPAIR'.  Use it if
the `.MYI' file is missing or if its header is corrupted.  In this mode
MySQL will recreate the table, using information from the `.frm' file.
This kind of repair cannot be done with `myisamchk'.

Using `myisamchk' for Table Maintenance and Crash Recovery
----------------------------------------------------------

Starting with MySQL Version 3.23.13, you can check MyISAM tables with
the `CHECK TABLE' command. *Note CHECK TABLE::.  You can repair tables
with the `REPAIR TABLE' command. *Note REPAIR TABLE::.

To check/repair MyISAM tables (`.MYI' and `.MYD') you should use the
`myisamchk' utility. To check/repair ISAM tables (`.ISM' and `.ISD')
you should use the `isamchk' utility. *Note Table types::.

In the following text we will talk about `myisamchk', but everything
also applies to the old `isamchk'.

You can use the `myisamchk' utility to get information about your
database tables, check and repair them, or optimise them.  The following
sections describe how to invoke `myisamchk' (including a description of
its options), how to set up a table maintenance schedule, and how to
use `myisamchk' to perform its various functions.

You can, in most cases, also use the command `OPTIMIZE TABLES' to
optimise and repair tables, but this is not as fast or reliable (in case
of real fatal errors) as `myisamchk'.  On the other hand, `OPTIMIZE
TABLE' is easier to use and you don't have to worry about flushing
tables.  *Note `OPTIMIZE TABLE': OPTIMIZE TABLE.

Even that the repair in `myisamchk' is quite secure, it's always a good
idea to make a backup _before_ doing a repair (or anything that could
make a lot of changes to a table)

`myisamchk' Invocation Syntax
.............................

`myisamchk' is invoked like this:

     shell> myisamchk [options] tbl_name

The `options' specify what you want `myisamchk' to do.  They are
described here.  (You can also get a list of options by invoking
`myisamchk --help'.)  With no options, `myisamchk' simply checks your
table.  To get more information or to tell `myisamchk' to take
corrective action, specify options as described here and in the
following sections.

`tbl_name' is the database table you want to check/repair.  If you run
`myisamchk' somewhere other than in the database directory, you must
specify the path to the file, because `myisamchk' has no idea where your
database is located.  Actually, `myisamchk' doesn't care whether the
files you are working on are located in a database directory; you can
copy the files that correspond to a database table into another
location and perform recovery operations on them there.

You can name several tables on the `myisamchk' command-line if you
wish.  You can also specify a name as an index file name (with the
`.MYI' suffix), which allows you to specify all tables in a directory
by using the pattern `*.MYI'.  For example, if you are in a database
directory, you can check all the tables in the directory like this:

     shell> myisamchk *.MYI

If you are not in the database directory, you can check all the tables
there by specifying the path to the directory:

     shell> myisamchk /path/to/database_dir/*.MYI

You can even check all tables in all databases by specifying a wildcard
with the path to the MySQL data directory:

     shell> myisamchk /path/to/datadir/*/*.MYI

The recommended way to quickly check all tables is:

     myisamchk --silent --fast /path/to/datadir/*/*.MYI
     isamchk --silent /path/to/datadir/*/*.ISM

If you want to check all tables and repair all tables that are
corrupted, you can use the following line:

     myisamchk --silent --force --fast --update-state -O key_buffer=64M \
               -O sort_buffer=64M -O read_buffer=1M -O write_buffer=1M \
               /path/to/datadir/*/*.MYI
     isamchk --silent --force -O key_buffer=64M -O sort_buffer=64M \
             -O read_buffer=1M -O write_buffer=1M /path/to/datadir/*/*.ISM

The above assumes that you have more than 64 M free.

Note that if you get an error like:

     myisamchk: warning: 1 clients is using or hasn't closed the table properly

This means that you are trying to check a table that has been updated by
the another program (like the `mysqld' server) that hasn't yet closed
the file or that has died without closing the file properly.

If you `mysqld' is running, you must force a sync/close of all tables
with `FLUSH TABLES' and ensure that no one is using the tables while
you are running `myisamchk'.  In MySQL Version 3.23 the easiest way to
avoid this problem is to use `CHECK TABLE' instead of `myisamchk' to
check tables.

General Options for `myisamchk'
...............................

`myisamchk' supports the following options.

`-# or --debug=debug_options'
     Output debug log. The `debug_options' string often is
     `'d:t:o,filename''.

`-? or --help'
     Display a help message and exit.

`-O var=option, --set-variable var=option'
     Set the value of a variable.  Please note that `--set-variable' is
     deprecated since MySQL 4.0, just use `--var=option' on its own.
     The possible variables and their default values for myisamchk can
     be examined with `myisamchk --help':
     *Variable*    *Value*
     key_buffer_size523264
     read_buffer_size262136
     write_buffer_size262136
     sort_buffer_size2097144
     sort_key_blocks16
     decode_bits   9

     `sort_buffer_size' is used when the keys are repaired by sorting
     keys, which is the normal case when you use `--recover'.

     `key_buffer_size' is used when you are checking the table with
     `--extended-check' or when the keys are repaired by inserting key
     row by row in to the table (like when doing normal inserts).
     Repairing through the key buffer is used in the following cases:

        * If you use `--safe-recover'.

        * If the temporary files needed to sort the keys would be more
          than twice as big as when creating the key file directly.
          This is often the case when you have big `CHAR', `VARCHAR' or
          `TEXT' keys as the sort needs to store the whole keys during
          sorting. If you have lots of temporary space and you can
          force `myisamchk' to repair by sorting you can use the
          `--sort-recover' option.

     Reparing through the key buffer takes much less disk space than
     using sorting, but is also much slower.

     If you want a faster repair, set the above variables to about 1/4
     of your available memory.  You can set both variables to big
     values, as only one of the above buffers will be used at a time.

`-s or --silent'
     Silent mode.  Write output only when errors occur. You can use `-s'
     twice (`-ss') to make `myisamchk' very silent.

`-v or --verbose'
     Verbose mode.  Print more information. This can be used with `-d'
     and `-e'. Use `-v' multiple times (`-vv', `-vvv') for more
     verbosity!

`-V or --version'
     Print the `myisamchk' version and exit.

`-w or, --wait'
     Instead of giving an error if the table is locked, wait until the
     table is unlocked before continuing.  Note that if you are running
     `mysqld' on the table with `--skip-external-locking', the table
     can only be locked by another `myisamchk' command.

Check Options for `myisamchk'
.............................

`-c or --check'
     Check table for errors. This is the default operation if you are
     not giving `myisamchk' any options that override this.

`-e or --extend-check'
     Check the table very thoroughly (which is quite slow if you have
     many indexes).  This option should only be used in extreme cases.
     Normally, `myisamchk' or `myisamchk --medium-check' should, in most
     cases, be able to find out if there are any errors in the table.

     If you are using `--extended-check' and have much memory, you
     should increase the value of `key_buffer_size' a lot!

`-F or --fast'
     Check only tables that haven't been closed properly.

`-C or --check-only-changed'
     Check only tables that have changed since the last check.

`-f or --force'
     Restart `myisamchk' with `-r' (repair) on the table, if
     `myisamchk' finds any errors in the table.

`-i or --information'
     Print informational statistics about the table that is checked.

`-m or --medium-check'
     Faster than extended-check, but only finds 99.99% of all errors.
     Should, however, be good enough for most cases.

`-U or --update-state'
     Store in the `.MYI' file when the table was checked and if the
     table crashed.  This should be used to get full benefit of the
     `--check-only-changed' option, but you shouldn't use this option
     if the `mysqld' server is using the table and you are running
     `mysqld' with `--skip-external-locking'.

`-T or --read-only'
     Don't mark table as checked. This is useful if you use `myisamchk'
     to check a table that is in use by some other application that
     doesn't use locking (like `mysqld --skip-external-locking').

Repair Options for myisamchk
............................

The following options are used if you start `myisamchk' with `-r' or
`-o':

`-D # or --data-file-length=#'
     Max length of datafile (when re-creating datafile when it's
     'full').

`-e or --extend-check'
     Try to recover every possible row from the datafile.  Normally
     this will also find a lot of garbage rows. Don't use this option
     if you are not totally desperate.

`-f or --force'
     Overwrite old temporary files (`table_name.TMD') instead of
     aborting.

`-k # or keys-used=#'
     If you are using ISAM, tells the ISAM storage engine to update
     only the first `#' indexes.  If you are using `MyISAM', tells
     which keys to use, where each binary bit stands for one key (first
     key is bit 0).  This can be used to get faster inserts!
     Deactivated indexes can be reactivated by using `myisamchk -r'.
     keys.

`-l or --no-symlinks'
     Do not follow symbolic links. Normally `myisamchk' repairs the
     table a symlink points at.  This option doesn't exist in MySQL 4.0,
     as MySQL 4.0 will not remove symlinks during repair.

`-r or --recover'
     Can fix almost anything except unique keys that aren't unique
     (which is an extremely unlikely error with ISAM/MyISAM tables).
     If you want to recover a table, this is the option to try first.
     Only if myisamchk reports that the table can't be recovered by
     `-r', you should then try `-o'.  (Note that in the unlikely case
     that `-r' fails, the datafile is still intact.)  If you have lots
     of memory, you should increase the size of `sort_buffer_size'!

`-o or --safe-recover'
     Uses an old recovery method (reads through all rows in order and
     updates all index trees based on the found rows); this is an order
     of magnitude slower than `-r', but can handle a couple of very
     unlikely cases that `-r' cannot handle.  This recovery method also
     uses much less disk space than `-r'. Normally one should always
     first repair with `-r', and only if this fails use `-o'.

     If you have lots of memory, you should increase the size of
     `key_buffer_size'!

`-n or --sort-recover'
     Force `myisamchk' to use sorting to resolve the keys even if the
     temporary files should be very big.

`--character-sets-dir=...'
     Directory where character sets are stored.

`--set-character-set=name'
     Change the character set used by the index

`-t or --tmpdir=path'
     Path for storing temporary files. If this is not set, `myisamchk'
     will use the environment variable `TMPDIR' for this.

`-q or --quick'
     Faster repair by not modifying the datafile. One can give a second
     `-q' to force `myisamchk' to modify the original datafile in case
     of duplicate keys

`-u or --unpack'
     Unpack file packed with myisampack.

Other Options for `myisamchk'
.............................

Other actions that `myisamchk' can do, besides repair and check tables:

`-a or --analyze'
     Analyse the distribution of keys. This improves join performance by
     enabling the join optimiser to better choose in which order it
     should join the tables and which keys it should use: `myisamchk
     --describe --verbose table_name'' or using `SHOW KEYS' in MySQL.

`-d or --description'
     Prints some information about table.

`-A or --set-auto-increment[=value]'
     Force `AUTO_INCREMENT' to start at this or higher value. If no
     value is given, then sets the next `AUTO_INCREMENT' value to the
     highest used value for the auto key + 1.

`-S or --sort-index'
     Sort the index tree blocks in high-low order.  This will optimise
     seeks and will make table scanning by key faster.

`-R or --sort-records=#'
     Sorts records according to an index.  This makes your data much
     more localised and may speed up ranged `SELECT' and `ORDER BY'
     operations on this index. (It may be very slow to do a sort the
     first time!)  To find out a table's index numbers, use `SHOW
     INDEX', which shows a table's indexes in the same order that
     `myisamchk' sees them.  Indexes are numbered beginning with 1.

`myisamchk' Memory Usage
........................

Memory allocation is important when you run `myisamchk'.  `myisamchk'
uses no more memory than you specify with the `-O' options.  If you are
going to use `myisamchk' on very large files, you should first decide
how much memory you want it to use.  The default is to use only about
3M to fix things.  By using larger values, you can get `myisamchk' to
operate faster.  For example, if you have more than 32M RAM, you could
use options such as these (in addition to any other options you might
specify):

     shell> myisamchk -O sort=16M -O key=16M -O read=1M -O write=1M ...

Using `-O sort=16M' should probably be enough for most cases.

Be aware that `myisamchk' uses temporary files in `TMPDIR'. If `TMPDIR'
points to a memory filesystem, you may easily get out of memory errors.
If this happens, set `TMPDIR' to point at some directory with more
space and restart `myisamchk'.

When repairing, `myisamchk' will also need a lot of disk space:

   * Double the size of the record file (the original one and a copy).
     This space is not needed if one does a repair with `--quick', as
     in this case only the index file will be re-created.  This space
     is needed on the same disk as the original record file!

   * Space for the new index file that replaces the old one. The old
     index file is truncated at start, so one usually ignore this space.
     This space is needed on the same disk as the original index file!

   * When using `--recover' or `--sort-recover' (but not when using
     `--safe-recover'), you will need space for a sort buffer for:
     `(largest_key + row_pointer_length)*number_of_rows * 2'.  You can
     check the length of the keys and the row_pointer_length with
     `myisamchk -dv table'.  This space is allocated on the temporary
     disk (specified by `TMPDIR' or `--tmpdir=#').

If you have a problem with disk space during repair, you can try to use
`--safe-recover' instead of `--recover'.

Using `myisamchk' for Crash Recovery
....................................

If you run `mysqld' with `--skip-external-locking' (which is the
default on some systems, like Linux), you can't reliably use `myisamchk'
to check a table when `mysqld' is using the same table.  If you can be
sure that no one is accessing the tables through `mysqld' while you run
`myisamchk', you only have to do `mysqladmin flush-tables' before you
start checking the tables.  If you can't guarantee the above, then you
must take down `mysqld' while you check the tables.  If you run
`myisamchk' while `mysqld' is updating the tables, you may get a
warning that a table is corrupt even if it isn't.

If you are not using `--skip-external-locking', you can use `myisamchk'
to check tables at any time.  While you do this, all clients that try
to update the table will wait until `myisamchk' is ready before
continuing.

If you use `myisamchk' to repair or optimise tables, you *must* always
ensure that the `mysqld' server is not using the table (this also
applies if you are using `--skip-external-locking').  If you don't take
down `mysqld' you should at least do a `mysqladmin flush-tables' before
you run `myisamchk'.  Your tables *may be corrupted* if the server and
`myisamchk' access the tables simultaneously.

This chapter describes how to check for and deal with data corruption
in MySQL databases.  If your tables get corrupted frequently you should
try to find the reason for this! *Note Crashing::.

The `MyISAM' table section contains reason for why a table could be
corrupted. *Note MyISAM table problems::.

When performing crash recovery, it is important to understand that each
table `tbl_name' in a database corresponds to three files in the
database directory:

*File*         *Purpose*
`tbl_name.frm' Table definition
               (form) file
`tbl_name.MYD' Datafile
`tbl_name.MYI' Index file

Each of these three file types is subject to corruption in various
ways, but problems occur most often in datafiles and index files.

`myisamchk' works by creating a copy of the `.MYD' (data) file row by
row. It ends the repair stage by removing the old `.MYD' file and
renaming the new file to the original file name.  If you use `--quick',
`myisamchk' does not create a temporary `.MYD' file, but instead
assumes that the `.MYD' file is correct and only generates a new index
file without touching the `.MYD' file. This is safe, because
`myisamchk' automatically detects if the `.MYD' file is corrupt and
aborts the repair in this case.  You can also give two `--quick'
options to `myisamchk'.  In this case, `myisamchk' does not abort on
some errors (like duplicate key) but instead tries to resolve them by
modifying the `.MYD' file. Normally the use of two `--quick' options is
useful only if you have too little free disk space to perform a normal
repair.  In this case you should at least make a backup before running
`myisamchk'.

How to Check Tables for Errors
..............................

To check a MyISAM table, use the following commands:

`myisamchk tbl_name'
     This finds 99.99% of all errors. What it can't find is corruption
     that involves *only* the datafile (which is very unusual). If you
     want to check a table, you should normally run `myisamchk' without
     options or with either the `-s' or `--silent' option.

`myisamchk -m tbl_name'
     This finds 99.999% of all errors. It checks first all index
     entries for errors and then it reads through all rows. It
     calculates a checksum for all keys in the rows and verifies that
     they checksum matches the checksum for the keys in the index tree.

`myisamchk -e tbl_name'
     This does a complete and thorough check of all data (`-e' means
     "extended check"). It does a check-read of every key for each row
     to verify that they indeed point to the correct row.  This may
     take a long time on a big table with many keys.  `myisamchk' will
     normally stop after the first error it finds. If you want to
     obtain more information, you can add the `--verbose' (`-v')
     option.  This causes `myisamchk' to keep going, up through a
     maximum of 20 errors.  In normal usage, a simple `myisamchk' (with
     no arguments other than the table name) is sufficient.

`myisamchk -e -i tbl_name'
     Like the previous command, but the `-i' option tells `myisamchk' to
     print some informational statistics, too.

How to Repair Tables
....................

In the following section we only talk about using `myisamchk' on
`MyISAM' tables (extensions `.MYI' and `.MYD').  If you are using
`ISAM' tables (extensions `.ISM' and `.ISD'), you should use `isamchk'
instead.

Starting with MySQL Version 3.23.14, you can repair MyISAM tables with
the `REPAIR TABLE' command. *Note REPAIR TABLE::.

The symptoms of a corrupted table include queries that abort
unexpectedly and observable errors such as these:

   * `tbl_name.frm' is locked against change

   * Can't find file `tbl_name.MYI' (Errcode: ###)

   * Unexpected end of file

   * Record file is crashed

   * Got error ### from table handler

     To get more information about the error you can run `perror ###'.
     Here is the most common errors that indicates a problem with the
     table:

          shell> perror 126 127 132 134 135 136 141 144 145
          126 = Index file is crashed / Wrong file format
          127 = Record-file is crashed
          132 = Old database file
          134 = Record was already deleted (or record file crashed)
          135 = No more room in record file
          136 = No more room in index file
          141 = Duplicate unique key or constraint on write or update
          144 = Table is crashed and last repair failed
          145 = Table was marked as crashed and should be repaired

     Note that error 135, no more room in record file, is not an error
     that can be fixed by a simple repair. In this case you have to do:

          ALTER TABLE table MAX_ROWS=xxx AVG_ROW_LENGTH=yyy;


In the other cases, you must repair your tables. `myisamchk' can
usually detect and fix most things that go wrong.

The repair process involves up to four stages, described here. Before
you begin, you should `cd' to the database directory and check the
permissions of the table files. Make sure they are readable by the Unix
user that `mysqld' runs as (and to you, because you need to access the
files you are checking).  If it turns out you need to modify files,
they must also be writable by you.

If you are using MySQL Version 3.23.16 and above, you can (and should)
use the `CHECK' and `REPAIR' commands to check and repair `MyISAM'
tables.  *Note CHECK TABLE::.  *Note REPAIR TABLE::.

The manual section about table maintenance includes the options to
`isamchk'/`myisamchk'.  *Note Table maintenance::.

The following section is for the cases where the above command fails or
if you want to use the extended features that `isamchk'/`myisamchk'
provides.

If you are going to repair a table from the command-line, you must first
take down the `mysqld' server. Note that when you do `mysqladmin
shutdown' on a remote server, the `mysqld' server will still be alive
for a while after `mysqladmin' returns, until all queries are stopped
and all keys have been flushed to disk.

*Stage 1: Checking your tables*

Run `myisamchk *.MYI' or `myisamchk -e *.MYI' if you have more time.
Use the `-s' (silent) option to suppress unnecessary information.

If the `mysqld' server is done you should use the -update option to tell
`myisamchk' to mark the table as 'checked'.

You have to repair only those tables for which `myisamchk' announces an
error.  For such tables, proceed to Stage 2.

If you get weird errors when checking (such as `out of memory' errors),
or if `myisamchk' crashes, go to Stage 3.

*Stage 2: Easy safe repair*

Note: If you want repairing to go much faster, you should add: `-O
sort_buffer=# -O key_buffer=#' (where # is about 1/4 of the available
memory) to all `isamchk/myisamchk' commands.

First, try `myisamchk -r -q tbl_name' (`-r -q' means "quick recovery
mode"). This will attempt to repair the index file without touching the
datafile.  If the datafile contains everything that it should and the
delete links point at the correct locations within the datafile, this
should work, and the table is fixed. Start repairing the next table.
Otherwise, use the following procedure:

  1. Make a backup of the datafile before continuing.

  2. Use `myisamchk -r tbl_name' (`-r' means "recovery mode"). This will
     remove incorrect records and deleted records from the datafile and
     reconstruct the index file.

  3. If the preceding step fails, use `myisamchk --safe-recover
     tbl_name'.  Safe recovery mode uses an old recovery method that
     handles a few cases that regular recovery mode doesn't (but is
     slower).

If you get weird errors when repairing (such as `out of memory'
errors), or if `myisamchk' crashes, go to Stage 3.

*Stage 3: Difficult repair*

You should only reach this stage if the first 16K block in the index
file is destroyed or contains incorrect information, or if the index
file is missing.  In this case, it's necessary to create a new index
file. Do so as follows:

  1. Move the datafile to some safe place.

  2. Use the table description file to create new (empty) data and
     index files:

          shell> mysql db_name
          mysql> SET AUTOCOMMIT=1;
          mysql> TRUNCATE TABLE table_name;
          mysql> quit

     If your SQL version doesn't have `TRUNCATE TABLE', use `DELETE FROM
     table_name' instead.

  3. Copy the old datafile back onto the newly created datafile.
     (Don't just move the old file back onto the new file; you want to
     retain a copy in case something goes wrong.)

Go back to Stage 2.  `myisamchk -r -q' should work now.  (This shouldn't
be an endless loop.)

As of `MySQL' 4.0.2 you can also use `REPAIR ... USE_FRM' which
performs the whole procedure automatically.

*Stage 4: Very difficult repair*

You should reach this stage only if the description file has also
crashed. That should never happen, because the description file isn't
changed after the table is created:

  1. Restore the description file from a backup and go back to Stage 3.
     You can also restore the index file and go back to Stage 2.  In
     the latter case, you should start with `myisamchk -r'.

  2. If you don't have a backup but know exactly how the table was
     created, create a copy of the table in another database.  Remove
     the new datafile, then move the description and index files from
     the other database to your crashed database.  This gives you new
     description and index files, but leaves the datafile alone.  Go
     back to Stage 2 and attempt to reconstruct the index file.

Table Optimisation
..................

To coalesce fragmented records and eliminate wasted space resulting from
deleting or updating records, run `myisamchk' in recovery mode:

     shell> myisamchk -r tbl_name

You can optimise a table in the same way using the SQL `OPTIMIZE TABLE'
statement.  `OPTIMIZE TABLE' does a repair of the table and a key
analysis, and also sorts the index tree to give faster key lookups.
There is also no possibility of unwanted interaction between a utility
and the server, because the server does all the work when you use
`OPTIMIZE TABLE'. *Note OPTIMIZE TABLE::.

`myisamchk' also has a number of other options you can use to improve
the performance of a table:

   * `-S', `--sort-index'

   * `-R index_num', `--sort-records=index_num'

   * `-a', `--analyze'

For a full description of the option. *Note myisamchk syntax::.

Setting Up a Table Maintenance Regimen
--------------------------------------

Starting with MySQL Version 3.23.13, you can check MyISAM tables with
the `CHECK TABLE' command. *Note CHECK TABLE::.  You can repair tables
with the `REPAIR TABLE' command. *Note REPAIR TABLE::.

It is a good idea to perform table checks on a regular basis rather than
waiting for problems to occur.  For maintenance purposes, you can use
`myisamchk -s' to check tables.  The `-s' option (short for `--silent')
causes `myisamchk' to run in silent mode, printing messages only when
errors occur.

It's also a good idea to check tables when the server starts up.  For
example, whenever the machine has done a reboot in the middle of an
update, you usually need to check all the tables that could have been
affected. (This is an "expected crashed table".) You could add a test to
`safe_mysqld' that runs `myisamchk' to check all tables that have been
modified during the last 24 hours if there is an old `.pid' (process
ID) file left after a reboot.  (The `.pid' file is created by `mysqld'
when it starts up and removed when it terminates normally.  The
presence of a `.pid' file at system startup time indicates that
`mysqld' terminated abnormally.)

An even better test would be to check any table whose last-modified time
is more recent than that of the `.pid' file.

You should also check your tables regularly during normal system
operation.  At MySQL AB, we run a `cron' job to check all our important
tables once a week, using a line like this in a `crontab' file:

     35 0 * * 0 /path/to/myisamchk --fast --silent /path/to/datadir/*/*.MYI

This prints out information about crashed tables so we can examine and
repair them when needed.

As we haven't had any unexpectedly crashed tables (tables that become
corrupted for reasons other than hardware trouble) for a couple of
years now (this is really true), once a week is more than enough for us.

We recommend that to start with, you execute `myisamchk -s' each night
on all tables that have been updated during the last 24 hours, until
you come to trust MySQL as much as we do.

Normally you don't need to maintain MySQL tables that much.  If you are
changing tables with dynamic size rows (tables with `VARCHAR', `BLOB'
or `TEXT' columns) or have tables with many deleted rows you may want
to from time to time (once a month?) defragment/reclaim space from the
tables.

You can do this by using `OPTIMIZE TABLE' on the tables in question or
if you can take the `mysqld' server down for a while do:

     isamchk -r --silent --sort-index -O sort_buffer_size=16M */*.ISM
     myisamchk -r --silent --sort-index  -O sort_buffer_size=16M */*.MYI

Getting Information About a Table
---------------------------------

To get a description of a table or statistics about it, use the
commands shown here. We explain some of the information in more detail
later:

   * myisamchk -d tbl_name Runs `myisamchk' in "describe mode" to
     produce a description of your table. If you start the MySQL server
     using the `--skip-external-locking' option, `myisamchk' may report
     an error for a table that is updated while it runs.  However,
     because `myisamchk' doesn't change the table in describe mode,
     there isn't any risk of destroying data.

   * myisamchk -d -v tbl_name To produce more information about what
     `myisamchk' is doing, add `-v' to tell it to run in verbose mode.

   * myisamchk -eis tbl_name Shows only the most important information
     from a table. It is slow because it must read the whole table.

   * myisamchk -eiv tbl_name This is like `-eis', but tells you what is
     being done.

Example of `myisamchk -d' output:
     MyISAM file:     company.MYI
     Record format:   Fixed length
     Data records:    1403698  Deleted blocks:         0
     Recordlength:    226

     table description:
     Key Start Len Index   Type
     1   2     8   unique  double
     2   15    10  multip. text packed stripped
     3   219   8   multip. double
     4   63    10  multip. text packed stripped
     5   167   2   multip. unsigned short
     6   177   4   multip. unsigned long
     7   155   4   multip. text
     8   138   4   multip. unsigned long
     9   177   4   multip. unsigned long
         193   1           text

Example of `myisamchk -d -v' output:
     MyISAM file:         company
     Record format:       Fixed length
     File-version:        1
     Creation time:       1999-10-30 12:12:51
     Recover time:        1999-10-31 19:13:01
     Status:              checked
     Data records:           1403698  Deleted blocks:              0
     Datafile parts:         1403698  Deleted data:                0
     Datafilepointer (bytes):      3  Keyfile pointer (bytes):     3
     Max datafile length: 3791650815  Max keyfile length: 4294967294
     Recordlength:               226

     table description:
     Key Start Len Index   Type                  Rec/key     Root Blocksize
     1   2     8   unique  double                      1 15845376      1024
     2   15    10  multip. text packed stripped        2 25062400      1024
     3   219   8   multip. double                     73 40907776      1024
     4   63    10  multip. text packed stripped        5 48097280      1024
     5   167   2   multip. unsigned short           4840 55200768      1024
     6   177   4   multip. unsigned long            1346 65145856      1024
     7   155   4   multip. text                     4995 75090944      1024
     8   138   4   multip. unsigned long              87 85036032      1024
     9   177   4   multip. unsigned long             178 96481280      1024
         193   1           text

Example of `myisamchk -eis' output:
     Checking MyISAM file: company
     Key:  1:  Keyblocks used:  97%  Packed:    0%  Max levels:  4
     Key:  2:  Keyblocks used:  98%  Packed:   50%  Max levels:  4
     Key:  3:  Keyblocks used:  97%  Packed:    0%  Max levels:  4
     Key:  4:  Keyblocks used:  99%  Packed:   60%  Max levels:  3
     Key:  5:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     Key:  6:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     Key:  7:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     Key:  8:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     Key:  9:  Keyblocks used:  98%  Packed:    0%  Max levels:  4
     Total:    Keyblocks used:  98%  Packed:   17%

     Records:          1403698    M.recordlength:     226
     Packed:             0%
     Recordspace used:     100%   Empty space:          0%
     Blocks/Record:   1.00
     Record blocks:    1403698    Delete blocks:        0
     Recorddata:     317235748    Deleted data:         0
     Lost space:             0    Linkdata:             0

     User time 1626.51, System time 232.36
     Maximum resident set size 0, Integral resident set size 0
     Non physical pagefaults 0, Physical pagefaults 627, Swaps 0
     Blocks in 0 out 0, Messages in 0 out 0, Signals 0
     Voluntary context switches 639, Involuntary context switches 28966

Example of `myisamchk -eiv' output:
     Checking MyISAM file: company
     Data records: 1403698   Deleted blocks:       0
     - check file-size
     - check delete-chain
     block_size 1024:
     index  1:
     index  2:
     index  3:
     index  4:
     index  5:
     index  6:
     index  7:
     index  8:
     index  9:
     No recordlinks
     - check index reference
     - check data record references index: 1
     Key:  1:  Keyblocks used:  97%  Packed:    0%  Max levels:  4
     - check data record references index: 2
     Key:  2:  Keyblocks used:  98%  Packed:   50%  Max levels:  4
     - check data record references index: 3
     Key:  3:  Keyblocks used:  97%  Packed:    0%  Max levels:  4
     - check data record references index: 4
     Key:  4:  Keyblocks used:  99%  Packed:   60%  Max levels:  3
     - check data record references index: 5
     Key:  5:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     - check data record references index: 6
     Key:  6:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     - check data record references index: 7
     Key:  7:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     - check data record references index: 8
     Key:  8:  Keyblocks used:  99%  Packed:    0%  Max levels:  3
     - check data record references index: 9
     Key:  9:  Keyblocks used:  98%  Packed:    0%  Max levels:  4
     Total:    Keyblocks used:   9%  Packed:   17%

     - check records and index references
     [LOTS OF ROW NUMBERS DELETED]

     Records:          1403698    M.recordlength:     226   Packed:             0%
     Recordspace used:     100%   Empty space:          0%  Blocks/Record:   1.00
     Record blocks:    1403698    Delete blocks:        0
     Recorddata:     317235748    Deleted data:         0
     Lost space:             0    Linkdata:             0

     User time 1639.63, System time 251.61
     Maximum resident set size 0, Integral resident set size 0
     Non physical pagefaults 0, Physical pagefaults 10580, Swaps 0
     Blocks in 4 out 0, Messages in 0 out 0, Signals 0
     Voluntary context switches 10604, Involuntary context switches 122798

Here are the sizes of the data and index files for the table used in the
preceding examples:

     -rw-rw-r--   1 monty    tcx     317235748 Jan 12 17:30 company.MYD
     -rw-rw-r--   1 davida   tcx      96482304 Jan 12 18:35 company.MYM

Explanations for the types of information `myisamchk' produces are
given here.  The "keyfile" is the index file.  "Record" and "row" are
synonymous:

   * ISAM file Name of the ISAM (index) file.

   * Isam-version Version of ISAM format. Currently always 2.

   * Creation time When the datafile was created.

   * Recover time When the index/datafile was last reconstructed.

   * Data records How many records are in the table.

   * Deleted blocks How many deleted blocks still have reserved space.
     You can optimise your table to minimise this space.  *Note
     Optimisation::.

   * Data file: Parts For dynamic record format, this indicates how
     many data blocks there are. For an optimised table without
     fragmented records, this is the same as `Data records'.

   * Deleted data How many bytes of non-reclaimed deleted data there
     are.  You can optimise your table to minimise this space.  *Note
     Optimisation::.

   * Data file pointer The size of the datafile pointer, in bytes. It
     is usually 2, 3, 4, or 5 bytes. Most tables manage with 2 bytes,
     but this cannot be controlled from MySQL yet. For fixed tables,
     this is a record address. For dynamic tables, this is a byte
     address.

   * Keyfile pointer The size of the index file pointer, in bytes. It
     is usually 1, 2, or 3 bytes. Most tables manage with 2 bytes, but
     this is calculated automatically by MySQL. It is always a block
     address.

   * Max datafile length How long the table's datafile (`.MYD' file)
     can become, in bytes.

   * Max keyfile length How long the table's key file (`.MYI' file) can
     become, in bytes.

   * Recordlength How much space each record takes, in bytes.

   * Record format The format used to store table rows.  The examples
     shown above use `Fixed length'.  Other possible values are
     `Compressed' and `Packed'.

   * table description A list of all keys in the table. For each key,
     some low-level information is presented:

        - Key This key's number.

        - Start Where in the record this index part starts.

        - Len How long this index part is. For packed numbers, this
          should always be the full length of the column. For strings,
          it may be shorter than the full length of the indexed column,
          because you can index a prefix of a string column.

        - Index `unique' or `multip.' (multiple). Indicates whether one
          value can exist multiple times in this index.

        - Type What data-type this index part has. This is an ISAM
          data-type with the options `packed', `stripped' or `empty'.

        - Root Address of the root index block.

        - Blocksize The size of each index block. By default this is
          1024, but the value may be changed at compile time.

        - Rec/key This is a statistical value used by the optimiser. It
          tells how many records there are per value for this key. A
          unique key always has a value of 1. This may be updated after
          a table is loaded (or greatly changed) with `myisamchk -a'.
          If this is not updated at all, a default value of 30 is given.

   * In the first example above, the 9th key is a multi-part key with
     two parts.

   * Keyblocks used What percentage of the keyblocks are used. Because
     the table used in the examples had just been reorganised with
     `myisamchk', the values are very high (very near the theoretical
     maximum).

   * Packed MySQL tries to pack keys with a common suffix. This can
     only be used for `CHAR'/`VARCHAR'/`DECIMAL' keys. For long strings
     like names, this can significantly reduce the space used. In the
     third example above, the 4th key is 10 characters long and a 60%
     reduction in space is achieved.

   * Max levels How deep the B-tree for this key is. Large tables with
     long keys get high values.

   * Records How many rows are in the table.

   * M.recordlength The average record length. For tables with
     fixed-length records, this is the exact record length.

   * Packed MySQL strips spaces from the end of strings. The `Packed'
     value indicates the percentage of savings achieved by doing this.

   * Recordspace used What percentage of the datafile is used.

   * Empty space What percentage of the datafile is unused.

   * Blocks/Record Average number of blocks per record (that is, how
     many links a fragmented record is composed of). This is always 1.0
     for fixed-format tables. This value should stay as close to 1.0 as
     possible. If it gets too big, you can reorganise the table with
     `myisamchk'.  *Note Optimisation::.

   * Recordblocks How many blocks (links) are used. For fixed format,
     this is the same as the number of records.

   * Deleteblocks How many blocks (links) are deleted.

   * Recorddata How many bytes in the datafile are used.

   * Deleted data How many bytes in the datafile are deleted (unused).

   * Lost space If a record is updated to a shorter length, some space
     is lost. This is the sum of all such losses, in bytes.

   * Linkdata When the dynamic table format is used, record fragments
     are linked with pointers (4 to 7 bytes each). `Linkdata' is the
     sum of the amount of storage used by all such pointers.

If a table has been compressed with `myisampack', `myisamchk -d' prints
additional information about each table column.  See *Note
`myisampack': myisampack, for an example of this information and a
description of what it means.

Database Administration Language Reference
==========================================

`OPTIMIZE TABLE' Syntax
-----------------------

     OPTIMIZE TABLE tbl_name[,tbl_name]...

`OPTIMIZE TABLE' should be used if you have deleted a large part of a
table or if you have made many changes to a table with variable-length
rows (tables that have `VARCHAR', `BLOB', or `TEXT' columns).  Deleted
records are maintained in a linked list and subsequent `INSERT'
operations reuse old record positions. You can use `OPTIMIZE TABLE' to
reclaim the unused space and to defragment the datafile.

For the moment, `OPTIMIZE TABLE' works only on `MyISAM' and `BDB'
tables. For `BDB' tables, `OPTIMIZE TABLE' is currently mapped to
`ANALYZE TABLE'.  *Note `ANALYZE TABLE': ANALYZE TABLE.

You can get `OPTIMIZE TABLE' to work on other table types by starting
`mysqld' with `--skip-new' or `--safe-mode', but in this case `OPTIMIZE
TABLE' is just mapped to `ALTER TABLE'.

`OPTIMIZE TABLE' works the following way:
   * If the table has deleted or split rows, repair the table.

   * If the index pages are not sorted, sort them.

   * If the statistics are not up to date (and the repair couldn't be
     done by sorting the index), update them.

`OPTIMIZE TABLE' for a `MyISAM' table is equivalent to running
`myisamchk --quick --check-only-changed --sort-index --analyze' on the
table.

Note that the table is locked during the time `OPTIMIZE TABLE' is
running!

`ANALYZE TABLE' Syntax
----------------------

     ANALYZE TABLE tbl_name[,tbl_name...]

Analyse and store the key distribution for the table.  During the
analysis, the table is locked with a read lock.  This works on `MyISAM'
and `BDB' tables.

This is equivalent to running `myisamchk -a' on the table.

MySQL uses the stored key distribution to decide in which order tables
should be joined when one does a join on something else than a constant.

The command returns a table with the following columns:

*Column*    *Value*
Table       Table name
Op          Always "analyze"
Msg_type    One of `status', `error',
            `info' or `warning'.
Msg_text    The message.

You can check the stored key distribution with the `SHOW INDEX' command.
*Note SHOW DATABASE INFO::.

If the table hasn't changed since the last `ANALYZE TABLE' command, the
table will not be analysed again.

`FLUSH' Syntax
--------------

     FLUSH flush_option [,flush_option] ...

You should use the `FLUSH' command if you want to clear some of the
internal caches MySQL uses.  To execute `FLUSH', you must have the
`RELOAD' privilege.

`flush_option' can be any of the following:

*Option*           *Description*
`HOSTS'            Empties the host cache tables.  You should flush the
                   host tables if some of your hosts change IP number or
                   if you get the error message `Host ... is blocked'.
                   When more than `max_connect_errors' errors occur in a
                   row for a given host while connection to the MySQL
                   server, MySQL assumes something is wrong and blocks
                   the host from further connection requests.  Flushing
                   the host tables allows the host to attempt to connect
                   again. *Note Blocked host::. You can start `mysqld'
                   with `-O max_connect_errors=999999999' to avoid this
                   error message.
`DES_KEY_FILE'     Reloads the DES keys from the file that was specified
                   with the `--des-key-file' option at server startup
                   time.
`LOGS'             Closes and reopens all log files.  If you have
                   specified the update log file or a binary log file
                   without an extension, the extension number of the log
                   file will be incremented by one relative to the
                   previous file.  If you have used an extension in the
                   file name, MySQL will close and reopen the update log
                   file.  *Note Update log::. This is the same thing as
                   sending the `SIGHUP' signal to the `mysqld' server.
`PRIVILEGES'       Reloads the privileges from the grant tables in the
                   `mysql' database.
`QUERY CACHE'      Defragment the query cache to better utilise its
                   memory.  This command will not remove any queries
                   from the cache, unlike `RESET QUERY CACHE'.
`TABLES'           Closes all open tables and force all tables in use to
                   be closed. This also flushes the query cache.
`[TABLE | TABLES]  Flushes only the given tables.
tbl_name
[,tbl_name...]'
`TABLES WITH READ  Closes all open tables and locks all tables for all
LOCK'              databases with a read lock until you execute `UNLOCK
                   TABLES'. This is very convenient way to get backups
                   if you have a filesystem, like Veritas, that can take
                   snapshots in time.
`STATUS'           Resets most status variables to zero. This is
                   something one should only use when debugging a query.
`USER_RESOURCES'   Resets all user resources to zero. This will enable
                   blocked users to login again. *Note User resources::.

You can also access each of the commands shown above with the
`mysqladmin' utility, using the `flush-hosts', `flush-logs', `reload',
or `flush-tables' commands.

Take also a look at the `RESET' command used with replication.  *Note
`RESET': RESET.

`RESET' Syntax
--------------

     RESET reset_option [,reset_option] ...

The `RESET' command is used to clear things. It also acts as an stronger
version of the `FLUSH' command.  *Note `FLUSH': FLUSH.

To execute `RESET', you must have the `RELOAD' privilege.

*Option*           *Description*
`MASTER'           Deletes all binary logs listed in the index file,
                   resetting the binlog index file to be empty. In
                   pre-3.23.26 versions, `FLUSH MASTER' (Master)
`SLAVE'            Makes the slave forget its replication position in
                   the master logs. In pre 3.23.26 versions the command
                   was called `FLUSH SLAVE'(Slave)
`QUERY CACHE'      Removes all query results from the query cache.

`KILL' Syntax
-------------

     KILL thread_id

Each connection to `mysqld' runs in a separate thread.  You can see
which threads are running with the `SHOW PROCESSLIST' command and kill
a thread with the `KILL thread_id' command.

If you have the `PROCESS' privilege, you can see all threads.  If you
have the `SUPER' privilege, you can kill all threads.  Otherwise, you
can only see and kill your own threads.

You can also use the `mysqladmin processlist' and `mysqladmin kill'
commands to examine and kill threads.

When you do a `KILL', a thread-specific `kill flag' is set for the
thread.

In most cases it may take some time for the thread to die as the kill
flag is only checked at specific intervals.

   * In `SELECT', `ORDER BY' and `GROUP BY' loops, the flag is checked
     after reading a block of rows. If the kill flag is set the
     statement is aborted

   * When doing an `ALTER TABLE' the kill flag is checked before each
     block of rows are read from the original table. If the kill flag
     was set the command is aborted and the temporary table is deleted.

   * When doing an `UPDATE TABLE' and `DELETE TABLE', the kill flag is
     checked after each block read and after each updated or delete
     row. If the kill flag is set the statement is aborted.  Note that
     if you are not using transactions, the changes will not be rolled
     back!

   * `GET_LOCK()' will abort with `NULL'.

   * An `INSERT DELAYED' thread will quickly flush all rows it has in
     memory and die.

   * If the thread is in the table lock handler (state: `Locked'), the
     table lock will be quickly aborted.

   * If the thread is waiting for free disk space in a `write' call, the
     write is aborted with an disk full error message.

`SHOW' Syntax
-------------

        SHOW DATABASES [LIKE wild]
     or SHOW [OPEN] TABLES [FROM db_name] [LIKE wild]
     or SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [LIKE wild]
     or SHOW INDEX FROM tbl_name [FROM db_name]
     or SHOW TABLE STATUS [FROM db_name] [LIKE wild]
     or SHOW STATUS [LIKE wild]
     or SHOW VARIABLES [LIKE wild]
     or SHOW LOGS
     or SHOW [FULL] PROCESSLIST
     or SHOW GRANTS FOR user
     or SHOW CREATE TABLE table_name
     or SHOW MASTER STATUS
     or SHOW MASTER LOGS
     or SHOW SLAVE STATUS
     or SHOW WARNINGS [LIMIT #]
     or SHOW ERRORS [LIMIT #]

`SHOW' provides information about databases, tables, columns, or status
information about the server. If the `LIKE wild' part is used, the
`wild' string can be a string that uses the SQL `%' and `_' wildcard
characters.

Retrieving information about Database, Tables, Columns, and Indexes
...................................................................

You can use `db_name.tbl_name' as an alternative to the `tbl_name FROM
db_name' syntax.  These two statements are equivalent:

     mysql> SHOW INDEX FROM mytable FROM mydb;
     mysql> SHOW INDEX FROM mydb.mytable;

`SHOW DATABASES' lists the databases on the MySQL server host.  You can
also get this list using the `mysqlshow' command line tool.  In version
4.0.2 you will only see those databases for which you have some kind of
privilege, if you don't have the global `SHOW DATABASES' privilege.

`SHOW TABLES' lists the tables in a given database.  You can also get
this list using the `mysqlshow db_name' command.

*Note*: if a user doesn't have any privileges for a table, the table
will not show up in the output from `SHOW TABLES' or `mysqlshow
db_name'.

`SHOW OPEN TABLES' lists the tables that are currently open in the
table cache. *Note Table cache::.  The `Comment' field tells how many
times the table is `cached' and `in_use'.

`SHOW COLUMNS' lists the columns in a given table.  If you specify the
`FULL' option, you will also get the privileges you have for each
column.  If the column types are different from what you expect them to
be based on a `CREATE TABLE' statement, note that MySQL sometimes
changes column types.  *Note Silent column changes::.

The `DESCRIBE' statement provides information similar to `SHOW COLUMNS'.
*Note `DESCRIBE': DESCRIBE.

`SHOW FIELDS' is a synonym for `SHOW COLUMNS', and `SHOW KEYS' is a
synonym for `SHOW INDEX'.  You can also list a table's columns or
indexes with `mysqlshow db_name tbl_name' or `mysqlshow -k db_name
tbl_name'.

`SHOW INDEX' returns the index information in a format that closely
resembles the `SQLStatistics' call in ODBC. The following columns are
returned:

*Column*    *Meaning*
`Table'     Name of the table.
`Non_unique'0 if the index can't contain duplicates.
`Key_name'  Name of the index.
`Seq_in_index'Column sequence number in index,
                                          starting
            with 1.
`Column_name'Column name.
`Collation' How the column is sorted in the index.
            In MySQL, this can have values
                                        `A'
            (Ascending) or `NULL' (Not
                                    sorted).
`Cardinality'Number of unique values in the index.
            This is updated by running
                                    `isamchk -a'.
`Sub_part'  Number of indexed characters if the
            column is only partly indexed.
                                         `NULL' if
            the entire key is indexed.
`Null'      Contains 'YES' if the column may
            contain `NULL'.
`Index_type'Index method used.
`Comment'   Various remarks.  For now, it tells in
            MySQL < 4.0.2 whether index is
            `FULLTEXT' or not.

Note that as the `Cardinality' is counted based on statistics stored as
integers, it's not necessarily accurate for small tables.

The `Null' and `Index_type' columns were added in MySQL 4.0.2.

`SHOW TABLE STATUS'
...................

     SHOW TABLE STATUS [FROM db_name] [LIKE wild]

`SHOW TABLE STATUS' (new in Version 3.23) works likes `SHOW STATUS',
but provides a lot of information about each table. You can also get
this list using the `mysqlshow --status db_name' command.  The
following columns are returned:

*Column*       *Meaning*
`Name'         Name of the table.
`Type'         Type of table. *Note Table types::.
`Row_format'   The row storage format (Fixed, Dynamic, or
               Compressed).
`Rows'         Number of rows.
`Avg_row_length'Average row length.
`Data_length'  Length of the datafile.
`Max_data_length'Max length of the datafile.
`Index_length' Length of the index file.
`Data_free'    Number of allocated but not used bytes.
`Auto_increment'Next autoincrement value.
`Create_time'  When the table was created.
`Update_time'  When the datafile was last updated.
`Check_time'   When the table was last checked.
`Create_options'Extra options used with `CREATE TABLE'.
`Comment'      The comment used when creating the table (or some
               information why MySQL couldn't access the table
               information).

`InnoDB' tables will report the free space in the tablespace in the
table comment.

`SHOW STATUS'
.............

`SHOW STATUS' provides server status information (like `mysqladmin
extended-status'). The output resembles that shown here, though the
format and numbers probably differ:

     +--------------------------+------------+
     | Variable_name            | Value      |
     +--------------------------+------------+
     | Aborted_clients          | 0          |
     | Aborted_connects         | 0          |
     | Bytes_received           | 155372598  |
     | Bytes_sent               | 1176560426 |
     | Connections              | 30023      |
     | Created_tmp_disk_tables  | 0          |
     | Created_tmp_tables       | 8340       |
     | Created_tmp_files        | 60         |
     | Delayed_insert_threads   | 0          |
     | Delayed_writes           | 0          |
     | Delayed_errors           | 0          |
     | Flush_commands           | 1          |
     | Handler_delete           | 462604     |
     | Handler_read_first       | 105881     |
     | Handler_read_key         | 27820558   |
     | Handler_read_next        | 390681754  |
     | Handler_read_prev        | 6022500    |
     | Handler_read_rnd         | 30546748   |
     | Handler_read_rnd_next    | 246216530  |
     | Handler_update           | 16945404   |
     | Handler_write            | 60356676   |
     | Key_blocks_used          | 14955      |
     | Key_read_requests        | 96854827   |
     | Key_reads                | 162040     |
     | Key_write_requests       | 7589728    |
     | Key_writes               | 3813196    |
     | Max_used_connections     | 0          |
     | Not_flushed_key_blocks   | 0          |
     | Not_flushed_delayed_rows | 0          |
     | Open_tables              | 1          |
     | Open_files               | 2          |
     | Open_streams             | 0          |
     | Opened_tables            | 44600      |
     | Questions                | 2026873    |
     | Select_full_join         | 0          |
     | Select_full_range_join   | 0          |
     | Select_range             | 99646      |
     | Select_range_check       | 0          |
     | Select_scan              | 30802      |
     | Slave_running            | OFF        |
     | Slave_open_temp_tables   | 0          |
     | Slow_launch_threads      | 0          |
     | Slow_queries             | 0          |
     | Sort_merge_passes        | 30         |
     | Sort_range               | 500        |
     | Sort_rows                | 30296250   |
     | Sort_scan                | 4650       |
     | Table_locks_immediate    | 1920382    |
     | Table_locks_waited       | 0          |
     | Threads_cached           | 0          |
     | Threads_created          | 30022      |
     | Threads_connected        | 1          |
     | Threads_running          | 1          |
     | Uptime                   | 80380      |
     +--------------------------+------------+

The status variables listed above have the following meaning:

*Variable*             *Meaning*
`Aborted_clients'      Number of connections aborted because the client
                       died without closing the connection properly.
                       *Note Communication errors::.
`Aborted_connects'     Number of tries to connect to the MySQL server
                       that failed. *Note Communication errors::.
`Bytes_received'       Number of bytes received from all clients.
`Bytes_sent'           Number of bytes sent to all clients.
`Com_xxx'              Number of times each xxx command has been
                       executed.
`Connections'          Number of connection attempts to the MySQL server.
`Created_tmp_disk_tables'Number of implicit temporary tables on disk
                       created while executing statements.
`Created_tmp_tables'   Number of implicit temporary tables in memory
                       created while executing statements.
`Created_tmp_files'    How many temporary files `mysqld' has created.
`Delayed_insert_threads'Number of delayed insert handler threads in use.
`Delayed_writes'       Number of rows written with `INSERT DELAYED'.
`Delayed_errors'       Number of rows written with `INSERT DELAYED' for
                       which some error occurred (probably `duplicate
                       key').
`Flush_commands'       Number of executed `FLUSH' commands.
`Handler_commit'       Number of internal `COMMIT' commands.
`Handler_delete'       Number of times a row was deleted from a table.
`Handler_read_first'   Number of times the first entry was read from an
                       index.  If this is high, it suggests that the
                       server is doing a lot of full index scans, for
                       example, `SELECT col1 FROM foo', assuming that
                       col1 is indexed.
`Handler_read_key'     Number of requests to read a row based on a key.
                       If this is high, it is a good indication that
                       your queries and tables are properly indexed.
`Handler_read_next'    Number of requests to read next row in key order.
                       This will be incremented if you are querying an
                       index column with a range constraint. This also
                       will be incremented if you are doing an index
                       scan.
`Handler_read_prev'    Number of requests to read previous row in key
                       order.  This is mainly used to optimise `ORDER BY
                       ... DESC'.
`Handler_read_rnd'     Number of requests to read a row based on a fixed
                       position.  This will be high if you are doing a
                       lot of queries that require sorting of the result.
`Handler_read_rnd_next'Number of requests to read the next row in the
                       datafile.  This will be high if you are doing a
                       lot of table scans. Generally this suggests that
                       your tables are not properly indexed or that your
                       queries are not written to take advantage of the
                       indexes you have.
`Handler_rollback'     Number of internal `ROLLBACK' commands.
`Handler_update'       Number of requests to update a row in a table.
`Handler_write'        Number of requests to insert a row in a table.
`Key_blocks_used'      The number of used blocks in the key cache.
`Key_read_requests'    The number of requests to read a key block from
                       the cache.
`Key_reads'            The number of physical reads of a key block from
                       disk.
`Key_write_requests'   The number of requests to write a key block to
                       the cache.
`Key_writes'           The number of physical writes of a key block to
                       disk.
`Max_used_connections' The maximum number of connections in use
                       simultaneously.
`Not_flushed_key_blocks'Keys blocks in the key cache that has changed but
                       hasn't yet been flushed to disk.
`Not_flushed_delayed_rows'Number of rows waiting to be written in `INSERT
                       DELAY' queues.
`Open_tables'          Number of tables that are open.
`Open_files'           Number of files that are open.
`Open_streams'         Number of streams that are open (used mainly for
                       logging).
`Opened_tables'        Number of tables that have been opened.
`Rpl_status'           Status of failsafe replication. (Not yet in use).
`Select_full_join'     Number of joins without keys (If this is 0, you
                       should carefully check the index of your tables).
`Select_full_range_join'Number of joins where we used a range search on
                       reference table.
`Select_range'         Number of joins where we used ranges on the first
                       table. (It's normally not critical even if this
                       is big.)
`Select_scan'          Number of joins where we did a full scan of the
                       first table.
`Select_range_check'   Number of joins without keys where we check for
                       key usage after each row (If this is 0, you
                       should carefully check the index of your tables).
`Questions'            Number of queries sent to the server.
`Slave_open_temp_tables'Number of temporary tables currently open by the
                       slave thread
`Slave_running'        Is `ON' if this is a slave that is connected to a
                       master.
`Slow_launch_threads'  Number of threads that have taken more than
                       `slow_launch_time' to create.
`Slow_queries'         Number of queries that have taken more than
                       `long_query_time'. *Note Slow query log::.
`Sort_merge_passes'    Number of merges passes the sort algoritm have
                       had to do. If this value is large you should
                       consider increasing `sort_buffer'.
`Sort_range'           Number of sorts that where done with ranges.
`Sort_rows'            Number of sorted rows.
`Sort_scan'            Number of sorts that where done by scanning the
                       table.
`ssl_xxx'              Variables used by SSL; Not yet implemented.
`Table_locks_immediate'Number of times a table lock was acquired
                       immediately. Available after 3.23.33.
`Table_locks_waited'   Number of times a table lock could not be
                       acquired immediately and a wait was needed. If
                       this is high, and you have performance problems,
                       you should first optimise your queries, and then
                       either split your table(s) or use replication.
                       Available after 3.23.33.
`Threads_cached'       Number of threads in the thread cache.
`Threads_connected'    Number of currently open connections.
`Threads_created'      Number of threads created to handle connections.
`Threads_running'      Number of threads that are not sleeping.
`Uptime'               How many seconds the server has been up.

Some comments about the above:

   * If `Opened_tables' is big, then your `table_cache' variable is
     probably too small.

   * If `Key_reads' is big, then your `key_buffer_size' variable is
     probably too small.  The cache hit rate can be calculated with
     `Key_reads'/`Key_read_requests'.

   * If `Handler_read_rnd' is big, then you probably have a lot of
     queries that require MySQL to scan whole tables or you have joins
     that don't use keys properly.

   * If `Threads_created' is big, you may want to increase the
     `thread_cache_size' variable.  The cache hit rate can be calculated
     with `Threads_created'/`Connections'.

   * If `Created_tmp_disk_tables' is big, you may want to increase the
     `tmp_table_size' variable to get the temporary tables memory-based
     instead of disk based.

`SHOW VARIABLES'
................

     SHOW [GLOBAL | SESSION] VARIABLES [LIKE wild]

`SHOW VARIABLES' shows the values of some MySQL system variables.  You
can also get this information using the `mysqladmin variables' command.
If the default values are unsuitable, you can set most of these
variables using command-line options when `mysqld' starts up.  *Note
Command-line options::.

The options `GLOBAL' and `SESSION' are new in MySQL 4.0.3.  With
`GLOBAL' you will get the variables that will be used for new
connections to MySQL. With `SESSION' you will get the values that are
in effect for the current connection. If you are not using either
option, `SESSION' is used.

You can change most options with the  `SET' command.  *Note `SET': SET
OPTION.

The output resembles that shown here, though the format and numbers may
differ somewhat:

     +---------------------------------+------------------------------+
     | Variable_name                   | Value                        |
     +---------------------------------+------------------------------|
     | back_log                        | 50                           |
     | basedir                         | /usr/local/mysql             |
     | bdb_cache_size                  | 8388572                      |
     | bdb_log_buffer_size             | 32768                        |
     | bdb_home                        | /usr/local/mysql             |
     | bdb_max_lock                    | 10000                        |
     | bdb_logdir                      |                              |
     | bdb_shared_data                 | OFF                          |
     | bdb_tmpdir                      | /tmp/                        |
     | bdb_version                     | Sleepycat Software: ...     |
     | binlog_cache_size               | 32768                        |
     | bulk_insert_buffer_size         | 8388608                      |
     | character_set                   | latin1                       |
     | character_sets                  | latin1 big5 czech euc_kr     |
     | concurrent_insert               | ON                           |
     | connect_timeout                 | 5                            |
     | convert_character_set           |                              |
     | datadir                         | /usr/local/mysql/data/       |
     | delay_key_write                 | ON                           |
     | delayed_insert_limit            | 100                          |
     | delayed_insert_timeout          | 300                          |
     | delayed_queue_size              | 1000                         |
     | flush                           | OFF                          |
     | flush_time                      | 0                            |
     | ft_min_word_len                 | 4                            |
     | ft_max_word_len                 | 254                          |
     | ft_max_word_len_for_sort        | 20                           |
     | ft_boolean_syntax               | + -><()~*:""&|               |
     | have_bdb                        | YES                          |
     | have_innodb                     | YES                          |
     | have_isam                       | YES                          |
     | have_raid                       | NO                           |
     | have_symlink                    | DISABLED                     |
     | have_openssl                    | YES                          |
     | have_query_cache                | YES                          |
     | init_file                       |                              |
     | innodb_additional_mem_pool_size | 1048576                      |
     | innodb_buffer_pool_size         | 8388608                      |
     | innodb_data_file_path           | ibdata1:10M:autoextend       |
     | innodb_data_home_dir            |                              |
     | innodb_file_io_threads          | 4                            |
     | innodb_force_recovery           | 0                            |
     | innodb_thread_concurrency       | 8                            |
     | innodb_flush_log_at_trx_commit  | 0                            |
     | innodb_fast_shutdown            | ON                           |
     | innodb_flush_method             |                              |
     | innodb_lock_wait_timeout        | 50                           |
     | innodb_log_arch_dir             |                              |
     | innodb_log_archive              | OFF                          |
     | innodb_log_buffer_size          | 1048576                      |
     | innodb_log_file_size            | 5242880                      |
     | innodb_log_files_in_group       | 2                            |
     | innodb_log_group_home_dir       | ./                           |
     | innodb_mirrored_log_groups      | 1                            |
     | interactive_timeout             | 28800                        |
     | join_buffer_size                | 131072                       |
     | key_buffer_size                 | 16773120                     |
     | language                        | /usr/local/mysql/share/...   |
     | large_files_support             | ON                           |
     | local_infile                    | ON                           |
     | locked_in_memory                | OFF                          |
     | log                             | OFF                          |
     | log_update                      | OFF                          |
     | log_bin                         | OFF                          |
     | log_slave_updates               | OFF                          |
     | log_slow_queries                | OFF                          |
     | log_warnings                    | OFF                          |
     | long_query_time                 | 10                           |
     | low_priority_updates            | OFF                          |
     | lower_case_table_names          | OFF                          |
     | max_allowed_packet              | 1047552                      |
     | max_binlog_cache_size           | 4294967295                   |
     | max_binlog_size                 | 1073741824                   |
     | max_connections                 | 100                          |
     | max_connect_errors              | 10                           |
     | max_delayed_threads             | 20                           |
     | max_heap_table_size             | 16777216                     |
     | max_join_size                   | 4294967295                   |
     | max_sort_length                 | 1024                         |
     | max_user_connections            | 0                            |
     | max_tmp_tables                  | 32                           |
     | max_write_lock_count            | 4294967295                   |
     | myisam_max_extra_sort_file_size | 268435456                    |
     | myisam_max_sort_file_size       | 2147483647                   |
     | myisam_recover_options          | force                        |
     | myisam_sort_buffer_size         | 8388608                      |
     | net_buffer_length               | 16384                        |
     | net_read_timeout                | 30                           |
     | net_retry_count                 | 10                           |
     | net_write_timeout               | 60                           |
     | open_files_limit                | 0                            |
     | pid_file                        | /usr/local/mysql/name.pid    |
     | port                            | 3306                         |
     | protocol_version                | 10                           |
     | read_buffer_size                | 131072                       |
     | read_rnd_buffer_size            | 262144                       |
     | rpl_recovery_rank               | 0                            |
     | query_cache_limit               | 1048576                      |
     | query_cache_size                | 0                            |
     | query_cache_type                | ON                           |
     | safe_show_database              | OFF                          |
     | server_id                       | 0                            |
     | slave_net_timeout               | 3600                         |
     | skip_external_locking           | ON                           |
     | skip_networking                 | OFF                          |
     | skip_show_database              | OFF                          |
     | slow_launch_time                | 2                            |
     | socket                          | /tmp/mysql.sock              |
     | sort_buffer_size                | 2097116                      |
     | sql_mode                        | 0                            |
     | table_cache                     | 64                           |
     | table_type                      | MYISAM                       |
     | thread_cache_size               | 3                            |
     | thread_stack                    | 131072                       |
     | tx_isolation                    | READ-COMMITTED               |
     | timezone                        | EEST                         |
     | tmp_table_size                  | 33554432                     |
     | tmpdir                          | /tmp/                        |
     | version                         | 4.0.4-beta                   |
     | wait_timeout                    | 28800                        |
     +---------------------------------+------------------------------+

Each option is described here. Values for buffer sizes, lengths, and
stack sizes are given in bytes.  You can specify values with a suffix
of `K' or `M' to indicate kilobytes or megabytes. For example, `16M'
indicates 16 megabytes.  The case of suffix letters does not matter;
`16M' and `16m' are equivalent:

   * `ansi_mode'.  Is `ON' if `mysqld' was started with `--ansi'.
     *Note ANSI mode::.

   * `back_log' The number of outstanding connection requests MySQL can
     have. This comes into play when the main MySQL thread gets *very*
     many connection requests in a very short time. It then takes some
     time (although very little) for the main thread to check the
     connection and start a new thread. The `back_log' value indicates
     how many requests can be stacked during this short time before
     MySQL momentarily stops answering new requests. You need to
     increase this only if you expect a large number of connections in
     a short period of time.

     In other words, this value is the size of the listen queue for
     incoming TCP/IP connections.  Your operating system has its own
     limit on the size of this queue.  The manual page for the Unix
     `listen(2)' system call should have more details.  Check your OS
     documentation for the maximum value for this variable.  Attempting
     to set `back_log' higher than your operating system limit will be
     ineffective.

   * `basedir' The value of the `--basedir' option.

   * `bdb_cache_size' The buffer that is allocated to cache index and
     rows for `BDB' tables.  If you don't use `BDB' tables, you should
     start `mysqld' with `--skip-bdb' to not waste memory for this
     cache.

   * `bdb_log_buffer_size' The buffer that is allocated to cache index
     and rows for `BDB' tables.  If you don't use `BDB' tables, you
     should set this to 0 or start `mysqld' with `--skip-bdb' to not
     waste memory for this cache.

   * `bdb_home' The value of the `--bdb-home' option.

   * `bdb_max_lock' The maximum number of locks (10,000 by default) you
     can have active on a BDB table. You should increase this if you
     get errors of type `bdb: Lock table is out of available locks' or
     `Got error 12 from ...' when you have do long transactions or when
     `mysqld' has to examine a lot of rows to calculate the query.

   * `bdb_logdir' The value of the `--bdb-logdir' option.

   * `bdb_shared_data' Is `ON' if you are using `--bdb-shared-data'.

   * `bdb_tmpdir' The value of the `--bdb-tmpdir' option.

   * `binlog_cache_size'.  The size of the cache to hold the SQL
     statements for the binary log during a transaction.  If you often
     use big, multi-statement transactions you can increase this to get
     more performance. *Note COMMIT::.

   * `bulk_insert_buffer_size' (was `myisam_bulk_insert_tree_size')
     MyISAM uses special tree-like cache to make bulk inserts (that is,
     `INSERT ... SELECT', `INSERT ... VALUES (...), (...), ...', and
     `LOAD DATA INFILE') faster. This variable limits the size of the
     cache tree in bytes per thread. Setting it to 0 will disable this
     optimisation.  *Note*: this cache is only used when adding data to
     non-empty table.  Default value is 8 MB.

   * `character_set' The default character set.

   * `character_sets' The supported character sets.

   * `concurrent_inserts' If `ON' (the default), MySQL will allow you
     to use `INSERT' on `MyISAM' tables at the same time as you run
     `SELECT' queries on them.  You can turn this option off by
     starting `mysqld' with `--safe' or `--skip-new'.

   * `connect_timeout' The number of seconds the `mysqld' server is
     waiting for a connect packet before responding with `Bad
     handshake'.

   * `datadir' The value of the `--datadir' option.

   * `delay_key_write' Option for MyISAM tables. Can have one of the
     following values:

     OFF                  All CREATE TABLE ... DELAYED_KEY_WRITES are
                          ignored.
     ON                   (default)  MySQL will honor the
                          `DELAY_KEY_WRITE' option for `CREATE TABLE'.
     ALL                  All new opened tables are treated as if they
                          were created with the `DELAY_KEY_WRITE' option.

     If `DELAY_KEY_WRITE' is enabled this means that the key buffer for
     tables with this option will not get flushed on every index
     update, but only when a table is closed.  This will speed up
     writes on keys a lot, but you should add automatic checking of all
     tables with `myisamchk --fast --force' if you use this.

   * `delayed_insert_limit' After inserting `delayed_insert_limit'
     rows, the `INSERT DELAYED' handler will check if there are any
     `SELECT' statements pending. If so, it allows these to execute
     before continuing.

   * `delayed_insert_timeout' How long a `INSERT DELAYED' thread should
     wait for `INSERT' statements before terminating.

   * `delayed_queue_size' What size queue (in rows) should be allocated
     for handling `INSERT DELAYED'.  If the queue becomes full, any
     client that does `INSERT DELAYED' will wait until there is room in
     the queue again.

   * `flush' This is `ON' if you have started MySQL with the `--flush'
     option.

   * `flush_time' If this is set to a non-zero value, then every
     `flush_time' seconds all tables will be closed (to free up
     resources and sync things to disk). We only recommend this option
     on Windows 9x/Me, or on systems where you have very little
     resources.

   * `ft_min_word_len' The minimum length of the word to be included in
     a `FULLTEXT' index.  *Note: `FULLTEXT' indexes must be rebuilt
     after changing this variable.* (This option is new for MySQL 4.0.)

   * `ft_max_word_len' The maximum length of the word to be included in
     a `FULLTEXT' index.  *Note: `FULLTEXT' indexes must be rebuilt
     after changing this variable.* (This option is new for MySQL 4.0.)

   * `ft_max_word_len_for_sort' The maximum length of the word in a
     `FULLTEXT' index to be used in fast index recreation method in
     `REPAIR', `CREATE INDEX',  or `ALTER TABLE'.  Longer words are
     inserted the slow way.  The rule of the thumb is as follows: with
     `ft_max_word_len_for_sort' increasing, *MySQL* will create bigger
     temporary files (thus slowing the process down, due to disk I/O),
     and will put fewer keys in one sort block (again, decreasing the
     efficiency).  When `ft_max_word_len_for_sort' is too small,
     instead, *MySQL* will insert a lot of words into index the slow
     way, but short words will be inserted very quickly.

   * `ft_boolean_syntax' List of operators supported by `MATCH ...
     AGAINST(... IN BOOLEAN MODE)'.  *Note Fulltext Search::.

   * `have_innodb' `YES' if `mysqld' supports InnoDB tables. `DISABLED'
     if `--skip-innodb' is used.

   * `have_bdb' `YES' if `mysqld' supports Berkeley DB tables.
     `DISABLED' if `--skip-bdb' is used.

   * `have_raid' `YES' if `mysqld' supports the `RAID' option.

   * `have_openssl' `YES' if `mysqld' supports SSL (encryption) on the
     client/server protocol.

   * `init_file' The name of the file specified with the `--init-file'
     option when you start the server.  This is a file of SQL
     statements you want the server to execute when it starts.

   * `interactive_timeout' The number of seconds the server waits for
     activity on an interactive connection before closing it.  An
     interactive client is defined as a client that uses the
     `CLIENT_INTERACTIVE' option to `mysql_real_connect()'.  See also
     `wait_timeout'.

   * `join_buffer_size' The size of the buffer that is used for full
     joins (joins that do not use indexes).  The buffer is allocated
     one time for each full join between two tables. Increase this
     value to get a faster full join when adding indexes is not
     possible. (Normally the best way to get fast joins is to add
     indexes.)

   * `key_buffer_size' Index blocks are buffered and are shared by all
     threads.  `key_buffer_size' is the size of the buffer used for
     index blocks.

     Increase this to get better index handling (for all reads and
     multiple writes) to as much as you can afford; 64M on a 256M
     machine that mainly runs MySQL is quite common.  If you, however,
     make this too big (for instance more than 50% of your total
     memory) your system may start to page and become extremely slow.
     Remember that because MySQL does not cache data reads, you will
     have to leave some room for the OS filesystem cache.

     You can check the performance of the key buffer by doing `SHOW
     STATUS' and examine the variables `Key_read_requests',
     `Key_reads', `Key_write_requests', and `Key_writes'.  The
     `Key_reads/Key_read_request' ratio should normally be < 0.01.  The
     `Key_write/Key_write_requests' is usually near 1 if you are using
     mostly updates/deletes but may be much smaller if you tend to do
     updates that affect many at the same time or if you are using
     `DELAY_KEY_WRITE'. *Note `SHOW': SHOW.

     To get even more speed when writing many rows at the same time, use
     `LOCK TABLES'.  *Note `LOCK TABLES': LOCK TABLES.

   * `language' The language used for error messages.

   * `large_file_support' If `mysqld' was compiled with options for big
     file support.

   * `locked_in_memory' If `mysqld' was locked in memory with
     `--memlock'

   * `log' If logging of all queries is enabled.

   * `log_update' If the update log is enabled.

   * `log_bin' If the binary log is enabled.

   * `log_slave_updates' If the updates from the slave should be logged.

   * `long_query_time' If a query takes longer than this (in seconds),
     the `Slow_queries' counter will be incremented. If you are using
     `--log-slow-queries', the query will be logged to the slow query
     logfile. This value is measured in real time, not CPU time, so a
     query that may be under the threshold on a lightly loaded system
     may be above the threshold on a heavily loaded one.  *Note Slow
     query log::.

   * `lower_case_table_names' If set to 1 table names are stored in
     lowercase on disk and table name comparisons will be
     case-insensitive.  From version 4.0.2, this option also applies to
     database names.  *Note Name case sensitivity::.

   * `max_allowed_packet' The maximum size of one packet. The message
     buffer is initialised to `net_buffer_length' bytes, but can grow
     up to `max_allowed_packet' bytes when needed.  This value by
     default is small, to catch big (possibly wrong) packets.  You must
     increase this value if you are using big `BLOB' columns. It should
     be as big as the biggest `BLOB' you want to use.  The protocol
     limits for `max_allowed_packet' is 16M in MySQL 3.23 and 1G in
     MySQL 4.0.

   * `max_binlog_cache_size' If a multi-statement transaction requires
     more than this amount of memory, one will get the error
     "Multi-statement transaction required more than
     'max_binlog_cache_size' bytes of storage".

   * `max_binlog_size' Available after 3.23.33. If a write to the
     binary (replication) log exceeds the given value, rotate the logs.
     You cannot set it to less than 1024 bytes, or more than 1 GB.
     Default is 1 GB.

   * `max_connections' The number of simultaneous clients allowed.
     Increasing this value increases the number of file descriptors
     that `mysqld' requires.  See below for comments on file descriptor
     limits. *Note Too many connections::.

   * `max_connect_errors' If there is more than this number of
     interrupted connections from a host this host will be blocked from
     further connections.  You can unblock a host with the command
     `FLUSH HOSTS'.

   * `max_delayed_threads' Don't start more than this number of threads
     to handle `INSERT DELAYED' statements.  If you try to insert data
     into a new table after all `INSERT DELAYED' threads are in use,
     the row will be inserted as if the `DELAYED' attribute wasn't
     specified.

   * `max_heap_table_size' Don't allow creation of heap tables bigger
     than this.

   * `max_join_size' Joins that are probably going to read more than
     `max_join_size' records return an error. Set this value if your
     users tend to perform joins that lack a `WHERE' clause, that take
     a long time, and that return millions of rows.

   * `max_sort_length' The number of bytes to use when sorting `BLOB'
     or `TEXT' values (only the first `max_sort_length' bytes of each
     value are used; the rest are ignored).

   * `max_user_connections' The maximum number of active connections
     for a single user (0 = no limit).

   * `max_tmp_tables' (This option doesn't yet do anything.)  Maximum
     number of temporary tables a client can keep open at the same time.

   * `max_write_lock_count' After this many write locks, allow some
     read locks to run in between.

   * `myisam_recover_options' The value of the `--myisam-recover'
     option.

   * `myisam_sort_buffer_size' The buffer that is allocated when
     sorting the index when doing a `REPAIR' or when creating indexes
     with `CREATE INDEX' or `ALTER TABLE'.

   * `myisam_max_extra_sort_file_size'.  If the temporary file used for
     fast index creation would be bigger than using the key cache by
     the amount specified here, then prefer the key cache method.  This
     is mainly used to force long character keys in large tables to use
     the slower key cache method to create the index.  *Note* that this
     parameter is given in megabytes before 4.0.3 and in bytes starting
     from this version.

   * `myisam_max_sort_file_size' The maximum size of the temporary file
     MySQL is allowed to use while recreating the index (during
     `REPAIR', `ALTER TABLE' or `LOAD DATA INFILE'.  If the file-size
     would be bigger than this, the index will be created through the
     key cache (which is slower).  *Note* that this parameter is given
     in megabytes before 4.0.3 and in bytes starting from this version.

   * `net_buffer_length' The communication buffer is reset to this size
     between queries. This should not normally be changed, but if you
     have very little memory, you can set it to the expected size of a
     query.  (That is, the expected length of SQL statements sent by
     clients.  If statements exceed this length, the buffer is
     automatically enlarged, up to `max_allowed_packet' bytes.)

   * `net_read_timeout' Number of seconds to wait for more data from a
     connection before aborting the read.  Note that when we don't
     expect data from a connection, the timeout is defined by
     `write_timeout'. See also `slave_net_timeout'.

   * `net_retry_count' If a read on a communication port is
     interrupted, retry this many times before giving up.  This value
     should be quite high on `FreeBSD' as internal interrupts are sent
     to all threads.

   * `net_write_timeout' Number of seconds to wait for a block to be
     written to a connection before aborting the write.

   * `open_files_limit' If this is not 0, then `mysqld' will use this
     value to reserve file descriptors to use with `setrlimit()'.  If
     this value is 0 then `mysqld' will reserve `max_connections*5' or
     `max_connections + table_cache*2' (whichever is larger) number of
     files.  You should try increasing this if `mysqld' gives you the
     error 'Too many open files'.

   * `pid_file' The value of the `--pid-file' option.

   * `port' The value of the `--port' option.

   * `protocol_version' The protocol version used by the MySQL server.

   * `read_buffer_size' (was `record_buffer') Each thread that does a
     sequential scan allocates a buffer of this size for each table it
     scans. If you do many sequential scans, you may want to increase
     this value.

   * `record_rnd_buffer_size' When reading rows in sorted order after a
     sort, the rows are read through this buffer to avoid a disk seeks.
     Can improve `ORDER BY' by a lot if set to a high value.  As this
     is a thread-specific variable, one should not set this big
     globally, but just change this when running some specific big
     queries.

   * `query_cache_limit' Don't cache results that are bigger than this.
     (Default 1M).

   * `query_cache_size' The memory allocated to store results from old
     queries.  If this is 0, the query cache is disabled (default).

   * `query_cache_type' This may be set (only numeric) to
     *Value**Alias*   *Comment*
     0      OFF       Don't cache or retrieve results.
     1      ON        Cache all results except `SELECT SQL_NO_CACHE
                      ...' queries.
     2      DEMAND    Cache only `SELECT SQL_CACHE ...' queries.

   * `safe_show_database' Don't show databases for which the user
     doesn't have any database or table privileges. This can improve
     security if you're concerned about people being able to see what
     databases other users have. See also `skip_show_database'.

   * `server_id' The value of the `--server-id' option.

   * `skip_locking' Is OFF if `mysqld' uses external locking.

   * `skip_networking' Is ON if we only allow local (socket)
     connections.

   * `skip_show_database' This prevents people from doing `SHOW
     DATABASES' if they don't have the `PROCESS' privilege. This can
     improve security if you're concerned about people being able to
     see what databases other users have. See also `safe_show_database'.

   * `slave_net_timeout' Number of seconds to wait for more data from a
     master/slave connection before aborting the read.

   * `slow_launch_time' If creating the thread takes longer than this
     value (in seconds), the `Slow_launch_threads' counter will be
     incremented.

   * `socket' The Unix socket used by the server.

   * `sort_buffer' Each thread that needs to do a sort allocates a
     buffer of this size. Increase this value for faster `ORDER BY' or
     `GROUP BY' operations.  *Note Temporary files::.

   * `table_cache' The number of open tables for all threads.
     Increasing this value increases the number of file descriptors
     that `mysqld' requires.  You can check if you need to increase the
     table cache by checking the `Opened_tables' variable.  *Note
     `Opened_tables': SHOW STATUS.  If this variable is big and you
     don't do `FLUSH TABLES' a lot (which just forces all tables to be
     closed and reopenend), then you should increase the value of this
     variable.

     For more information about the table cache, see *Note Table
     cache::.

   * `table_type' The default table type.

   * `thread_cache_size' How many threads we should keep in a cache for
     reuse.  When a client disconnects, the client's threads are put in
     the cache if there aren't more than `thread_cache_size' threads
     from before.  All new threads are first taken from the cache, and
     only when the cache is empty is a new thread created.  This
     variable can be increased to improve performance if you have a lot
     of new connections. (Normally this doesn't give a notable
     performance improvement if you have a good thread implementation.)
     By examing the difference between the `Connections' and
     `Threads_created' status variables (*note SHOW STATUS:: for
     details) you can see how efficient thread cache is.

   * `thread_concurrency' On Solaris, `mysqld' will call
     `thr_setconcurrency()' with this value.  `thr_setconcurrency()'
     permits the application to give the threads system a hint for the
     desired number of threads that should be run at the same time.

   * `thread_stack' The stack size for each thread.  Many of the limits
     detected by the `crash-me' test are dependent on this value. The
     default is large enough for normal operation.  *Note MySQL
     Benchmarks::.

   * `timezone' The timezone for the server.

   * `tmp_table_size' If an in-memory temporary table exceeds this
     size, MySQL will automatically convert it to an on-disk `MyISAM'
     table.  Increase the value of `tmp_table_size' if you do many
     advanced `GROUP BY' queries and you have lots of memory.

   * `tmpdir' The directory used for temporary files and temporary
     tables.

   * `version' The version number for the server.

   * `wait_timeout' The number of seconds the server waits for activity
     on a not interactive connection before closing it.

     On thread startup `SESSION.WAIT_TIMEOUT' is initialised from
     `GLOBAL.WAIT_TIMEOUT' or `GLOBAL.INTERACTIVE_TIMEOUT' depending on
     the type of client (as defined by the `CLIENT_INTERACTIVE' connect
     option). See also `interactive_timeout'.

The manual section that describes tuning MySQL contains some
information of how to tune the above variables. *Note Server
parameters::.

`SHOW LOGS'
...........

`SHOW LOGS' shows you status information about existing log files.  It
currently only displays information about Berkeley DB log files.

   * `File' shows the full path to the log file

   * `Type' shows the type of the log file (`BDB' for Berkeley DB log
     files)

   * `Status' shows the status of the log file (`FREE' if the file can
     be removed, or `IN USE' if the file is needed by the transaction
     subsystem)

`SHOW PROCESSLIST'
..................

`SHOW [FULL] PROCESSLIST' shows you which threads are running.  You can
also get this information using the `mysqladmin processlist' command.
If you have the `SUPER' privilege, you can see all threads.  Otherwise,
you can see only your own threads.  *Note `KILL': KILL.  If you don't
use the `FULL' option, then only the first 100 characters of each query
will be shown.

This command is very useful if you get the 'too many connections' error
message and want to find out what's going on. MySQL reserves one extra
connection for a client with the `SUPER' privilege to ensure that you
should always be able to login and check the system (assuming you are
not giving this privilege to all your users).

Some states commonly seen in `mysqladmin processlist'

   * `Checking table' The thread is performing [automatic] checking of
     the table.

   * `Closing tables' Means that the thread is flushing the changed
     table data to disk and closing the used tables. This should be a
     fast operation.  If not, then you should check that you don't have
     a full disk or that the disk is not in very heavy use.

   * `Connect Out' Slave connecting to master.

   * `Copying to tmp table on disk' The temporary result set was larger
     than `tmp_table_size' and the thread is now changing the in
     memory-based temporary table to a disk based one to save memory.

   * `Creating tmp table' The thread is creating a temporary table to
     hold a part of the result for the query.

   * `deleting from main table' When executing the first part of a
     multi-table delete and we are only deleting from the first table.

   * `deleting from reference tables' When executing the second part of
     a multi-table delete and we are deleting the matched rows from the
     other tables.

   * `Flushing tables' The thread is executing `FLUSH TABLES' and is
     waiting for all threads to close their tables.

   * `Killed' Someone has sent a kill to the thread and it should abort
     next time it checks the kill flag.  The flag is checked in each
     major loop in MySQL, but in some cases it may still take a short
     time for the thread to die.  If the thread is locked by some other
     thread, the kill will take affect as soon as the other thread
     releases it's lock.

   * `Sending data' The thread is processing rows for a `SELECT'
     statement and is also sending data to the client.

   * `Sorting for group' The thread is doing a sort to satsify a `GROUP
     BY'.

   * `Sorting for order' The thread is doing a sort to satsify a `ORDER
     BY'.

   * `Opening tables' This simply means that the thread is trying to
     open a table. This is should be very fast procedure, unless
     something prevents opening. For example an `ALTER TABLE' or a
     `LOCK TABLE' can prevent opening a table until the command is
     finished.

   * `Removing duplicates' The query was using `SELECT DISTINCT' in
     such a way that MySQL couldn't optimise that distinct away at an
     early stage. Because of this MySQL has to do an extra stage to
     remove all duplicated rows before sending the result to the client.

   * `Reopen table' The thread got a lock for the table, but noticed
     after getting the lock that the underlying table structure
     changed. It has freed the lock, closed the table and is now trying
     to reopen it.

   * `Repair by sorting' The repair code is using sorting to create
     indexes.

   * `Repair with keycache' The repair code is using creating keys one
     by one through the key cache.  This is much slower than `Repair by
     sorting'.

   * `Searching rows for update' The thread is doing a first phase to
     find all matching rows before updating them.  This has to be done
     if the `UPDATE' is changing the index that is used to find the
     involved rows.

   * `Sleeping' The thread is wating for the client to send a new
     command to it.

   * `System lock' The thread is waiting for getting to get a external
     system lock for the table. If you are not using multiple mysqld
     servers that are accessing the same tables, you can disable system
     locks with the `--skip-external-locking' option.

   * `Upgrading lock' The `INSERT DELAYED' handler is trying to get a
     lock for the table to insert rows.

   * `Updating' The thread is searching for rows to update and updating
     them.

   * `User Lock' The thread is waiting on a `GET_LOCK()'.

   * `Waiting for tables' The thread got a notification that the
     underlying structure for a table has changed and it needs to
     reopen the table to get the new structure.  To be able to reopen
     the table it must however wait until all other threads have closed
     the table in question.

     This notification happens if another thread has used `FLUSH TABLES'
     or one of the following commands on the table in question: `FLUSH
     TABLES table_name', `ALTER TABLE', `RENAME TABLE', `REPAIR TABLE',
     `ANALYZE TABLE' or `OPTIMIZE TABLE'.

   * `waiting for handler insert' The `INSERT DELAYED' handler has
     processed all inserts and are waiting to get new ones.

Most states are very quick operations. If threads last in any of these
states for many seconds, there may be a problem around that needs to be
investigated.

There are some other states that are not mentioned previously, but most
of these are only useful to find bugs in `mysqld'.

`SHOW GRANTS'
.............

`SHOW GRANTS FOR user' lists the grant commands that must be issued to
duplicate the grants for a user.

     mysql> SHOW GRANTS FOR root@localhost;
     +---------------------------------------------------------------------+
     | Grants for root@localhost                                           |
     +---------------------------------------------------------------------+
     | GRANT ALL PRIVILEGES ON *.* TO 'root'@'localhost' WITH GRANT OPTION |
     +---------------------------------------------------------------------+

To list grants for the current session one may use `CURRENT_USER()'
function (new in version 4.0.6) to find out what user the session was
authentificated as.  *Note `CURRENT_USER()': Miscellaneous functions.

`SHOW CREATE TABLE'
...................

Shows a `CREATE TABLE' statement that will create the given table:

     mysql> SHOW CREATE TABLE t\G
     *************************** 1. row ***************************
            Table: t
     Create Table: CREATE TABLE t (
       id int(11) default NULL auto_increment,
       s char(60) default NULL,
       PRIMARY KEY (id)
     ) TYPE=MyISAM

`SHOW CREATE TABLE' will quote table and column names according to
`SQL_QUOTE_SHOW_CREATE' option.  *Note `SET SQL_QUOTE_SHOW_CREATE': SET
OPTION.

`SHOW WARNINGS | ERRORS'
........................

     SHOW WARNINGS [LIMIT #]
     SHOW ERRORS [LIMIT #]

This command is implemented in MySQL 4.1.0.

It shows the errors, warnings and notes that one got for the last
command.  The errors/warnings are reset for each new command that uses
a table.

The MySQL server sends back the total number of warnings and errors you
got for the last commend; This can be retrieved by calling
`mysql_warning_count()'.

Up to `max_error_count' messages are stored (Global and thread specific
variable).

You can retrieve the number of errors from `@error_count' and warnings
from `@warning_count'.

`SHOW WARNINGS' shows all errors, warnings and notes you got for the
last command while `SHOW ERRORS' only shows you the errors.

     mysql> DROP TABLE IF EXISTS no_such_table;
     mysql> SHOW WARNINGS;

     +-------+------+-------------------------------+
     | Level | Code | Message                       |
     +-------+------+-------------------------------+
     | Note  | 1051 | Unknown table 'no_such_table' |
     +-------+------+-------------------------------+

MySQL Localisation and International Usage
==========================================

The Character Set Used for Data and Sorting
-------------------------------------------

By default, MySQL uses the ISO-8859-1 (Latin1) character set with
sorting according to Swedish/Finnish. This is the character set suitable
in the USA and western Europe.

All standard MySQL binaries are compiled with
`--with-extra-charsets=complex'.  This will add code to all standard
programs to be able to handle `latin1' and all multi-byte character
sets within the binary. Other character sets will be loaded from a
character-set definition file when needed.

The character set determines what characters are allowed in names and
how things are sorted by the `ORDER BY' and `GROUP BY' clauses of the
`SELECT' statement.

You can change the character set with the `--default-character-set'
option when you start the server.  The character sets available depend
on the `--with-charset=charset' and `--with-extra-charsets=
list-of-charset | complex | all' options to `configure', and the
character set configuration files listed in `SHAREDIR/charsets/Index'.
*Note configure options::.

If you change the character set when running MySQL (which may also
change the sort order), you must run `myisamchk -r -q
--set-character-set=charset' on all tables. Otherwise, your indexes may
not be ordered correctly.

When a client connects to a MySQL server, the server sends the default
character set in use to the client.  The client will switch to use this
character set for this connection.

One should use `mysql_real_escape_string()' when escaping strings for a
SQL query.  `mysql_real_escape_string()' is identical to the old
`mysql_escape_string()' function, except that it takes the `MYSQL'
connection handle as the first parameter.

If the client is compiled with different paths than where the server is
installed and the user who configured MySQL didn't include all
character sets in the MySQL binary, one must specify for the client
where it can find the additional character sets it will need if the
server runs with a different character set than the client.

One can specify this by putting in a MySQL option file:

     [client]
     character-sets-dir=/usr/local/mysql/share/mysql/charsets

where the path points to the directory in which the dynamic MySQL
character sets are stored.

One can force the client to use specific character set by specifying:

     [client]
     default-character-set=character-set-name

but normally this is never needed.

German character set
....................

To get German sorting order, you should start `mysqld' with
`--default-character-set=latin1_de'.  This will give you the following
characteristics.

When sorting and comparing string's the following mapping is done on the
strings before doing the comparison:

     Σ  ->  ae
     ÷  ->  oe
     ⁿ  ->  ue
     ▀  ->  ss

All accented characters, are converted to their un-accented uppercase
counterpart.  All letters are converted to uppercase.

When comparing strings with `LIKE' the one -> two character mapping is
not done. All letters are converted to uppercase. Accent are removed
from all letters except: `▄', `ⁿ', `╓', `÷', `─' and `Σ'.

Non-English Error Messages
--------------------------

`mysqld' can issue error messages in the following languages: Czech,
Danish, Dutch, English (the default), Estonian, French, German, Greek,
Hungarian, Italian, Japanese, Korean, Norwegian, Norwegian-ny, Polish,
Portuguese, Romanian, Russian, Slovak, Spanish, and Swedish.

To start `mysqld' with a particular language, use either the
`--language=lang' or `-L lang' options. For example:

     shell> mysqld --language=swedish

or:

     shell> mysqld --language=/usr/local/share/swedish

Note that all language names are specified in lowercase.

The language files are located (by default) in
`MYSQL_BASE_DIR/share/LANGUAGE/'.

To update the error message file, you should edit the `errmsg.txt' file
and execute the following command to generate the `errmsg.sys' file:

     shell> comp_err errmsg.txt errmsg.sys

If you upgrade to a newer version of MySQL, remember to repeat your
changes with the new `errmsg.txt' file.

Adding a New Character Set
--------------------------

To add another character set to MySQL, use the following procedure.

Decide if the set is simple or complex.  If the character set does not
need to use special string collating routines for sorting and does not
need multi-byte character support, it is simple.  If it needs either of
those features, it is complex.

For example, `latin1' and `danish' are simple charactersets while
`big5' or `czech' are complex character sets.

In the following section, we have assumed that you name your character
set `MYSET'.

For a simple character set do the following:

  1. Add MYSET to the end of the `sql/share/charsets/Index' file Assign
     a unique number to it.

  2. Create the file `sql/share/charsets/MYSET.conf'.  (You can use
     `sql/share/charsets/latin1.conf' as a base for this.)

     The syntax for the file very simple:

        * Comments start with a '#' character and proceed to the end of
          the line.

        * Words are separated by arbitrary amounts of whitespace.

        * When defining the character set, every word must be a number
          in hexadecimal format

        * The `ctype' array takes up the first 257 words. The
          `to_lower[]', `to_upper[]' and `sort_order[]' arrays take up
          256 words each after that.

     *Note Character arrays::.

  3. Add the character set name to the `CHARSETS_AVAILABLE' and
     `COMPILED_CHARSETS' lists in `configure.in'.

  4. Reconfigure, recompile, and test.


For a complex character set do the following:

  1. Create the file `strings/ctype-MYSET.c' in the MySQL source
     distribution.

  2. Add MYSET to the end of the `sql/share/charsets/Index' file.
     Assign a unique number to it.

  3. Look at one of the existing `ctype-*.c' files to see what needs to
     be defined, for example `strings/ctype-big5.c'. Note that the
     arrays in your file must have names like `ctype_MYSET',
     `to_lower_MYSET', and so on.  This corresponds to the arrays in
     the simple character set. *Note Character arrays::.  For a complex
     character set

  4. Near the top of the file, place a special comment like this:

          /*
           * This comment is parsed by configure to create ctype.c,
           * so don't change it unless you know what you are doing.
           *
           * .configure. number_MYSET=MYNUMBER
           * .configure. strxfrm_multiply_MYSET=N
           * .configure. mbmaxlen_MYSET=N
           */

     The `configure' program uses this comment to include the character
     set into the MySQL library automatically.

     The strxfrm_multiply and mbmaxlen lines will be explained in the
     following sections.  Only include these if you need the string
     collating functions or the multi-byte character set functions,
     respectively.

  5. You should then create some of the following functions:

        * `my_strncoll_MYSET()'

        * `my_strcoll_MYSET()'

        * `my_strxfrm_MYSET()'

        * `my_like_range_MYSET()'

     *Note String collating::.

  6. Add the character set name to the `CHARSETS_AVAILABLE' and
     `COMPILED_CHARSETS' lists in `configure.in'.

  7. Reconfigure, recompile, and test.

The file `sql/share/charsets/README' includes some more instructions.

If you want to have the character set included in the MySQL
distribution, mail a patch to <[e-mail]>.

The Character Definition Arrays
-------------------------------

`to_lower[]' and `to_upper[]' are simple arrays that hold the lowercase
and uppercase characters corresponding to each member of the character
set.  For example:

     to_lower['A'] should contain 'a'
     to_upper['a'] should contain 'A'

`sort_order[]' is a map indicating how characters should be ordered for
comparison and sorting purposes.  For many character sets, this is the
same as `to_upper[]' (which means sorting will be case-insensitive).
MySQL will sort characters based on the value of
`sort_order[character]'.  For more complicated sorting rules, see the
discussion of string collating below. *Note String collating::.

`ctype[]' is an array of bit values, with one element for one character.
(Note that `to_lower[]', `to_upper[]', and `sort_order[]' are indexed
by character value, but `ctype[]' is indexed by character value + 1.
This is an old legacy to be able to handle `EOF'.)

You can find the following bitmask definitions in `m_ctype.h':

     #define _U      01      /* Uppercase */
     #define _L      02      /* Lowercase */
     #define _N      04      /* Numeral (digit) */
     #define _S      010     /* Spacing character */
     #define _P      020     /* Punctuation */
     #define _C      040     /* Control character */
     #define _B      0100    /* Blank */
     #define _X      0200    /* heXadecimal digit */

The `ctype[]' entry for each character should be the union of the
applicable bitmask values that describe the character.  For example,
`'A'' is an uppercase character (`_U') as well as a hexadecimal digit
(`_X'), so `ctype['A'+1]' should contain the value:

     _U + _X = 01 + 0200 = 0201

String Collating Support
------------------------

If the sorting rules for your language are too complex to be handled
with the simple `sort_order[]' table, you need to use the string
collating functions.

Right now the best documentation on this is the character sets that are
already implemented.  Look at the `big5', `czech', `gbk', `sjis', and
`tis160' character sets for examples.

You must specify the `strxfrm_multiply_MYSET=N' value in the special
comment at the top of the file.  `N' should be set to the maximum ratio
the strings may grow during `my_strxfrm_MYSET' (it must be a positive
integer).

Multi-byte Character Support
----------------------------

If your want to add support for a new character set that includes
multi-byte characters, you need to use the multi-byte character
functions.

Right now the best documentation on this is the character sets that are
already implemented.  Look at the `euc_kr', `gb2312', `gbk', `sjis',
and `ujis' character sets for examples. These are implemented in the
`ctype-'charset'.c' files in the `strings' directory.

You must specify the `mbmaxlen_MYSET=N' value in the special comment at
the top of the source file.  `N' should be set to the size in bytes of
the largest character in the set.

Problems With Character Sets
----------------------------

If you try to use a character set that is not compiled into your binary,
you can run into a couple of different problems:

   * Your program has a wrong path to where the character sets are
     stored.  (Default `/usr/local/mysql/share/mysql/charsets').  This
     can be fixed by using the `--character-sets-dir' option to the
     program in question.

   * The character set is a multi-byte character set that can't be
     loaded dynamically.  In this case you have to recompile the
     program with the support for the character set.

   * The character set is a dynamic character set, but you don't have a
     configure file for it.  In this case you should install the
     configure file for the character set from a new MySQL distribution.

   * Your `Index' file doesn't contain the name for the character set.

          ERROR 1105: File '/usr/local/share/mysql/charsets/?.conf' not found
          (Errcode: 2)

     In this case you should either get a new `Index' file or add by
     hand the name of any missing character sets.

For `MyISAM' tables, you can check the character set name and number
for a table with `myisamchk -dvv table_name'.

MySQL Server-Side Scripts and Utilities
=======================================

Overview of the Server-Side Scripts and Utilities
-------------------------------------------------

All MySQL programs take many different options. However, every MySQL
program provides a `--help' option that you can use to get a full
description of the program's different options. For example, try `mysql
--help'.

You can override default options for all standard programs with an
option file. *Note Option files::.

The following list briefly describes the server-side MySQL programs:

`myisamchk'
     Utility to describe, check, optimise, and repair MySQL tables.
     Because `myisamchk' has many functions, it is described in its own
     chapter. *Note MySQL Database Administration::.

`make_binary_distribution'
     Makes a binary release of a compiled MySQL. This could be sent by
     FTP to `/pub/mysql/Incoming' on `support.mysql.com' for the
     convenience of other MySQL users.

`mysqlbug'
     The MySQL bug report script.  This script should always be used
     when filing a bug report to the MySQL list.

`mysqld'
     The SQL daemon. This should always be running.

`mysql_install_db'
     Creates the MySQL grant tables with default privileges. This is
     usually executed only once, when first installing MySQL on a
     system.

`safe_mysqld', The Wrapper Around `mysqld'
------------------------------------------

`safe_mysqld' is the recommended way to start a `mysqld' daemon on
Unix.  `safe_mysqld' adds some safety features such as restarting the
server when an error occurs and logging run-time information to a log
file.

If you don't use `--mysqld=#' or `--mysqld-version=#' `safe_mysqld'
will use an executable named `mysqld-max' if it exists. If not,
`safe_mysqld' will start `mysqld'.  This makes it very easy to test to
use `mysqld-max' instead of `mysqld'; just copy `mysqld-max' to where
you have `mysqld' and it will be used.

Normally one should never edit the `safe_mysqld' script, but instead
put the options to `safe_mysqld' in the `[safe_mysqld]' section in the
`my.cnf' file. `safe_mysqld' will read all options from the `[mysqld]',
`[server]' and `[safe_mysqld]' sections from the option files.  *Note
Option files::.

Note that all options on the command-line to `safe_mysqld' are passed
to `mysqld'.  If you wants to use any options in `safe_mysqld' that
`mysqld' doesn't support, you must specify these in the option file.

Most of the options to `safe_mysqld' are the same as the options to
`mysqld'. *Note Command-line options::.

`safe_mysqld' supports the following options:

`--basedir=path'

`--core-file-size=#'
     Size of the core file `mysqld' should be able to create. Passed to
     `ulimit -c'.

`--datadir=path'

`--defaults-extra-file=path'

`--defaults-file=path'

`--err-log=path'

`--ledir=path'
     Path to `mysqld'

`--log=path'

`--mysqld=mysqld-version'
     Name of the `mysqld' version in the `ledir' directory you want to
     start.

`--mysqld-version=version'
     Similar to `--mysqld=' but here you only give the suffix for
     `mysqld'.  For example if you use `--mysqld-version=max',
     `safe_mysqld' will start the `ledir/mysqld-max' version.  If the
     argument to `--mysqld-version' is empty, `ledir/mysqld' will be
     used.

`--no-defaults'

`--open-files-limit=#'
     Number of files `mysqld' should be able to open. Passed to `ulimit
     -n'. Note that you need to start `safe_mysqld' as root for this to
     work properly!

`--pid-file=path'

`--port=#'

`--socket=path'

`--timezone=#'
     Set the timezone (the `TZ') variable to the value of this
     parameter.

`--user=#'
The `safe_mysqld' script is written so that it normally is able to start
a server that was installed from either a source or a binary version of
MySQL, even if these install the server in slightly different
locations.  `safe_mysqld' expects one of these conditions to be true:

   * The server and databases can be found relative to the directory
     from which `safe_mysqld' is invoked.  `safe_mysqld' looks under
     its working directory for `bin' and `data' directories (for binary
     distributions) or for `libexec' and `var' directories (for source
     distributions).  This condition should be met if you execute
     `safe_mysqld' from your MySQL installation directory (for example,
     `/usr/local/mysql' for a binary distribution).

   * If the server and databases cannot be found relative to the
     working directory, `safe_mysqld' attempts to locate them by
     absolute pathnames.  Typical locations are `/usr/local/libexec'
     and `/usr/local/var'.  The actual locations are determined when
     the distribution was built from which `safe_mysqld' comes.  They
     should be correct if MySQL was installed in a standard location.

Because `safe_mysqld' will try to find the server and databases relative
to its own working directory, you can install a binary distribution of
MySQL anywhere, as long as you start `safe_mysqld' from the MySQL
installation directory:

     shell> cd mysql_installation_directory
     shell> bin/safe_mysqld &

If `safe_mysqld' fails, even when invoked from the MySQL installation
directory, you can modify it to use the path to `mysqld' and the
pathname options that are correct for your system.  Note that if you
upgrade MySQL in the future, your modified version of `safe_mysqld'
will be overwritten, so you should make a copy of your edited version
that you can reinstall.

`mysqld_multi', A Program for Managing Multiple MySQL Servers
-------------------------------------------------------------

`mysqld_multi' is meant for managing several `mysqld' processes that
listen for connections on different Unix sockets and TCP/IP ports.

The program will search for group(s) named `[mysqld#]' from `my.cnf'
(or the file named by the `--config-file=...' option), where `#' can be
any positive number starting from 1.  This number is referred to in the
following discussion as the option group number, or GNR.  Group numbers
distinquish option groups from one another and are used as arguments to
`mysqld_multi' to specify which servers you want to start, stop, or
obtain status for.  Options listed in these groups should be the same
as you would use in the usual `[mysqld]' group used for starting
`mysqld'.  (See, for example, *Note Automatic start::.)  However, for
`mysqld_multi', be sure that each group includes options for values
such as the port, socket, etc., to be used for each individual `mysqld'
process.

`mysqld_multi' is invoked using the following syntax:

     Usage: mysqld_multi [OPTIONS] {start|stop|report} [GNR,GNR,GNR...]
     or     mysqld_multi [OPTIONS] {start|stop|report} [GNR-GNR,GNR,GNR-GNR,...]

Each GNR represents an option group number. You can start, stop or
report any GNR, or several of them at the same time. For an example of
how you might set up an option file, use this command:

     shell> mysqld_multi --example

The GNR values in the list can be comma-separated or combined with a
dash; in the latter case, all the GNRs between GNR1-GNR2 will be
affected. With no GNR argument, all groups listed in the option file
will be either started, stopped, or reported. Note that you must not
have any white spaces in the GNR list. Anything after a white space is
ignored.

`mysqld_multi' supports the following options:

`--config-file=...'
     Alternative config file. Note: This will not affect this program's
     own options (group `[mysqld_multi]'), but only groups `[mysqld#]'.
     Without this option, everything will be searched from the ordinary
     `my.cnf' file.

`--example'
     Display an example option file.

`--help'
     Print this help and exit.

`--log=...'
     Log file. Full path to and the name for the log file. Note: If the
     file exists, everything will be appended.

`--mysqladmin=...'
     `mysqladmin' binary to be used for a server shutdown.

`--mysqld=...'
     `mysqld' binary to be used. Note that you can give `safe_mysqld'
     to this option also. The options are passed to `mysqld'. Just make
     sure you have `mysqld' in your environment variable `PATH' or fix
     `safe_mysqld'.

`--no-log'
     Print to stdout instead of the log file. By default the log file is
     turned on.

`--password=...'
     Password for user for `mysqladmin'.

`--tcp-ip'
     Connect to the MySQL server(s) via the TCP/IP port instead of the
     Unix socket. This affects stopping and reporting.  If a socket file
     is missing, the server may still be running, but can be accessed
     only via the TCP/IP port.  By default, connections are made using
     the Unix socket.

`--user=...'
     MySQL user for `mysqladmin'.

`--version'
     Print the version number and exit.

Some notes about `mysqld_multi':

   * Make sure that the MySQL user, who is stopping the `mysqld'
     services (e.g using the `mysqladmin' program) have the same
     password and username for all the data directories accessed (to the
     `mysql' database) And make sure that the user has the `SHUTDOWN'
     privilege! If you have many data directories and many different
     `mysql' databases with different passwords for the MySQL `root'
     user, you may want to create a common `multi_admin' user for each
     using the same password (see below). Example how to do it:
          shell> mysql -u root -S /tmp/mysql.sock -proot_password -e
          "GRANT SHUTDOWN ON *.* TO multi_admin@localhost IDENTIFIED BY 'multipass'"
     *Note Privileges::.  You will have to do the above for each
     `mysqld' running in each data directory, that you have (just
     change the socket, `-S=...').

   * `pid-file' is very important, if you are using `safe_mysqld' to
     start `mysqld' (e.g., `--mysqld=safe_mysqld') Every `mysqld'
     should have its own `pid-file'. The advantage using `safe_mysqld'
     instead of `mysqld' directly here is, that `safe_mysqld' "guards"
     every `mysqld' process and will restart it, if a `mysqld' process
     terminates due to a signal sent using `kill -9', or for other
     reasons such as a segmentation fault (which MySQL should never do,
     of course ;). Please note that the `safe_mysqld' script may
     require that you start it from a certain place. This means that
     you may have to `cd' to a certain directory, before you start the
     `mysqld_multi'. If you have problems starting, please see the
     `safe_mysqld' script. Check especially the lines:

          --------------------------------------------------------------------------
          MY_PWD=`pwd` Check if we are starting this relative (for the binary
          release) if test -d /data/mysql -a -f ./share/mysql/english/errmsg.sys
          -a -x ./bin/mysqld
          --------------------------------------------------------------------------

     *Note `safe_mysqld': safe_mysqld.  The above test should be
     successful, or you may encounter problems.

   * Beware of the dangers starting multiple `mysqld's in the same data
     directory.  Use separate data directories, unless you *know* what
     you are doing!

   * The socket file and the TCP/IP port must be different for every
     `mysqld'.

   * The first and fifth `mysqld' group were intentionally left out from
     the example.  You may have 'gaps' in the config file. This gives
     you more flexibility.  The order in which the `mysqlds' are
     started or stopped depends on the order in which they appear in
     the config file.

   * When you want to refer to a certain group using GNR with this
     program, just use the number in the end of the group name.  For
     example, the GNR for a group named `[mysqld17]' is 17.

   * You may want to use option `--user' for `mysqld', but in order to
     do this you need to run the `mysqld_multi' script as the Unix
     `root' user. Having the option in the config file doesn't matter;
     you will just get a warning, if you are not the superuser and the
     `mysqlds' are started under *your* Unix account. *Important*: Make
     sure that the `pid-file' and the data directory are
     read+write(+execute for the latter one) accessible for *that* Unix
     user, who the specific `mysqld' process is started as. *Do not*
     use the Unix root account for this, unless you *know* what you are
     doing!

   * *Most important*: Make sure that you understand the meanings of
     the options that are passed to the `mysqld's and *why one would
     want* to have separate `mysqld' processes. Starting multiple
     `mysqld's in one data directory *will not* give you extra
     performance in a threaded system!

*Note Multiple servers::.

This is an example of the config file on behalf of `mysqld_multi'.

     # This file should probably be in your home dir (~/.my.cnf) or /etc/my.cnf
     # Version 2.1 by Jani Tolonen

     [mysqld_multi]
     mysqld     = /usr/local/bin/safe_mysqld
     mysqladmin = /usr/local/bin/mysqladmin
     user       = multi_admin
     password   = multipass

     [mysqld2]
     socket     = /tmp/mysql.sock2
     port       = 3307
     pid-file   = /usr/local/mysql/var2/hostname.pid2
     datadir    = /usr/local/mysql/var2
     language   = /usr/local/share/mysql/english
     user       = john

     [mysqld3]
     socket     = /tmp/mysql.sock3
     port       = 3308
     pid-file   = /usr/local/mysql/var3/hostname.pid3
     datadir    = /usr/local/mysql/var3
     language   = /usr/local/share/mysql/swedish
     user       = monty

     [mysqld4]
     socket     = /tmp/mysql.sock4
     port       = 3309
     pid-file   = /usr/local/mysql/var4/hostname.pid4
     datadir    = /usr/local/mysql/var4
     language   = /usr/local/share/mysql/estonia
     user       = tonu

     [mysqld6]
     socket     = /tmp/mysql.sock6
     port       = 3311
     pid-file   = /usr/local/mysql/var6/hostname.pid6
     datadir    = /usr/local/mysql/var6
     language   = /usr/local/share/mysql/japanese
     user       = jani

*Note Option files::.

`myisampack', The MySQL Compressed Read-only Table Generator
------------------------------------------------------------

`myisampack' is used to compress MyISAM tables, and `pack_isam' is used
to compress ISAM tables. Because ISAM tables are deprecated, we will
only discuss `myisampack' here, but everything said about `myisampack'
should also be true for `pack_isam'.

`myisampack' works by compressing each column in the table separately.
The information needed to decompress columns is read into memory when
the table is opened. This results in much better performance when
accessing individual records, because you only have to uncompress
exactly one record, not a much larger disk block as when using Stacker
on MS-DOS.  Usually, `myisampack' packs the datafile 40%-70%.

MySQL uses memory mapping (`mmap()') on compressed tables and falls
back to normal read/write file usage if `mmap()' doesn't work.

Please note the following:
   * After packing, the table is read-only. This is generally intended
     (such as when accessing packed tables on a CD). Also allowing
     writes to a packed table is on our TODO list but with low priority.

   * `myisampack' can also pack `BLOB' or `TEXT' columns.  The older
     `pack_isam' (for `ISAM' tables) can not do this.

`myisampack' is invoked like this:

     shell> myisampack [options] filename ...

Each filename should be the name of an index (`.MYI') file.  If you are
not in the database directory, you should specify the pathname to the
file.  It is permissible to omit the `.MYI' extension.

`myisampack' supports the following options:

`-b, --backup'
     Make a backup of the table as `tbl_name.OLD'.

`-#, --debug=debug_options'
     Output debug log. The `debug_options' string often is
     `'d:t:o,filename''.

`-f, --force'
     Force packing of the table even if it becomes bigger or if the
     temporary file exists.  `myisampack' creates a temporary file
     named `tbl_name.TMD' while it compresses the table.  If you kill
     `myisampack', the `.TMD' file may not be deleted.  Normally,
     `myisampack' exits with an error if it finds that `tbl_name.TMD'
     exists.  With `--force', `myisampack' packs the table anyway.

`-?, --help'
     Display a help message and exit.

`-j big_tbl_name, --join=big_tbl_name'
     Join all tables named on the command-line into a single table
     `big_tbl_name'.  All tables that are to be combined *must* be
     identical (same column names and types, same indexes, etc.).

`-p #, --packlength=#'
     Specify the record length storage size, in bytes.  The value
     should be 1, 2, or 3.  (`myisampack' stores all rows with length
     pointers of 1, 2, or 3 bytes.  In most normal cases, `myisampack'
     can determine the right length value before it begins packing the
     file, but it may notice during the packing process that it could
     have used a shorter length. In this case, `myisampack' will print
     a note that the next time you pack the same file, you could use a
     shorter record length.)

`-s, --silent'
     Silent mode.  Write output only when errors occur.

`-t, --test'
     Don't actually pack table, just test packing it.

`-T dir_name, --tmp_dir=dir_name'
     Use the named directory as the location in which to write the
     temporary table.

`-v, --verbose'
     Verbose mode.  Write information about progress and packing result.

`-V, --version'
     Display version information and exit.

`-w, --wait'
     Wait and retry if table is in use.  If the `mysqld' server was
     invoked with the `--skip-external-locking' option, it is not a
     good idea to invoke `myisampack' if the table might be updated
     during the packing process.

The sequence of commands shown here illustrates a typical table
compression session:

     shell> ls -l station.*
     -rw-rw-r--   1 monty    my         994128 Apr 17 19:00 station.MYD
     -rw-rw-r--   1 monty    my          53248 Apr 17 19:00 station.MYI
     -rw-rw-r--   1 monty    my           5767 Apr 17 19:00 station.frm

     shell> myisamchk -dvv station

     MyISAM file:     station
     Isam-version:  2
     Creation time: 1996-03-13 10:08:58
     Recover time:  1997-02-02  3:06:43
     Data records:              1192  Deleted blocks:              0
     Datafile: Parts:           1192  Deleted data:                0
     Datafile pointer (bytes):     2  Keyfile pointer (bytes):     2
     Max datafile length:   54657023  Max keyfile length:   33554431
     Recordlength:               834
     Record format: Fixed length

     table description:
     Key Start Len Index   Type                       Root  Blocksize    Rec/key
     1   2     4   unique  unsigned long              1024       1024          1
     2   32    30  multip. text                      10240       1024          1

     Field Start Length Type
     1     1     1
     2     2     4
     3     6     4
     4     10    1
     5     11    20
     6     31    1
     7     32    30
     8     62    35
     9     97    35
     10    132   35
     11    167   4
     12    171   16
     13    187   35
     14    222   4
     15    226   16
     16    242   20
     17    262   20
     18    282   20
     19    302   30
     20    332   4
     21    336   4
     22    340   1
     23    341   8
     24    349   8
     25    357   8
     26    365   2
     27    367   2
     28    369   4
     29    373   4
     30    377   1
     31    378   2
     32    380   8
     33    388   4
     34    392   4
     35    396   4
     36    400   4
     37    404   1
     38    405   4
     39    409   4
     40    413   4
     41    417   4
     42    421   4
     43    425   4
     44    429   20
     45    449   30
     46    479   1
     47    480   1
     48    481   79
     49    560   79
     50    639   79
     51    718   79
     52    797   8
     53    805   1
     54    806   1
     55    807   20
     56    827   4
     57    831   4

     shell> myisampack station.MYI
     Compressing station.MYI: (1192 records)
     - Calculating statistics

     normal:     20  empty-space:      16  empty-zero:        12  empty-fill:  11
     pre-space:   0  end-space:        12  table-lookups:      5  zero:         7
     Original trees:  57  After join: 17
     - Compressing file
     87.14%

     shell> ls -l station.*
     -rw-rw-r--   1 monty    my         127874 Apr 17 19:00 station.MYD
     -rw-rw-r--   1 monty    my          55296 Apr 17 19:04 station.MYI
     -rw-rw-r--   1 monty    my           5767 Apr 17 19:00 station.frm

     shell> myisamchk -dvv station

     MyISAM file:     station
     Isam-version:  2
     Creation time: 1996-03-13 10:08:58
     Recover time:  1997-04-17 19:04:26
     Data records:              1192  Deleted blocks:              0
     Datafile: Parts:           1192  Deleted data:                0
     Datafilepointer (bytes):      3  Keyfile pointer (bytes):     1
     Max datafile length:   16777215  Max keyfile length:     131071
     Recordlength:               834
     Record format: Compressed

     table description:
     Key Start Len Index   Type                       Root  Blocksize    Rec/key
     1   2     4   unique  unsigned long             10240       1024          1
     2   32    30  multip. text                      54272       1024          1

     Field Start Length Type                         Huff tree  Bits
     1     1     1      constant                             1     0
     2     2     4      zerofill(1)                          2     9
     3     6     4      no zeros, zerofill(1)                2     9
     4     10    1                                           3     9
     5     11    20     table-lookup                         4     0
     6     31    1                                           3     9
     7     32    30     no endspace, not_always              5     9
     8     62    35     no endspace, not_always, no empty    6     9
     9     97    35     no empty                             7     9
     10    132   35     no endspace, not_always, no empty    6     9
     11    167   4      zerofill(1)                          2     9
     12    171   16     no endspace, not_always, no empty    5     9
     13    187   35     no endspace, not_always, no empty    6     9
     14    222   4      zerofill(1)                          2     9
     15    226   16     no endspace, not_always, no empty    5     9
     16    242   20     no endspace, not_always              8     9
     17    262   20     no endspace, no empty                8     9
     18    282   20     no endspace, no empty                5     9
     19    302   30     no endspace, no empty                6     9
     20    332   4      always zero                          2     9
     21    336   4      always zero                          2     9
     22    340   1                                           3     9
     23    341   8      table-lookup                         9     0
     24    349   8      table-lookup                        10     0
     25    357   8      always zero                          2     9
     26    365   2                                           2     9
     27    367   2      no zeros, zerofill(1)                2     9
     28    369   4      no zeros, zerofill(1)                2     9
     29    373   4      table-lookup                        11     0
     30    377   1                                           3     9
     31    378   2      no zeros, zerofill(1)                2     9
     32    380   8      no zeros                             2     9
     33    388   4      always zero                          2     9
     34    392   4      table-lookup                        12     0
     35    396   4      no zeros, zerofill(1)               13     9
     36    400   4      no zeros, zerofill(1)                2     9
     37    404   1                                           2     9
     38    405   4      no zeros                             2     9
     39    409   4      always zero                          2     9
     40    413   4      no zeros                             2     9
     41    417   4      always zero                          2     9
     42    421   4      no zeros                             2     9
     43    425   4      always zero                          2     9
     44    429   20     no empty                             3     9
     45    449   30     no empty                             3     9
     46    479   1                                          14     4
     47    480   1                                          14     4
     48    481   79     no endspace, no empty               15     9
     49    560   79     no empty                             2     9
     50    639   79     no empty                             2     9
     51    718   79     no endspace                         16     9
     52    797   8      no empty                             2     9
     53    805   1                                          17     1
     54    806   1                                           3     9
     55    807   20     no empty                             3     9
     56    827   4      no zeros, zerofill(2)                2     9
     57    831   4      no zeros, zerofill(1)                2     9

The information printed by `myisampack' is described here:

`normal'
     The number of columns for which no extra packing is used.

`empty-space'
     The number of columns containing values that are only spaces;
     these will occupy 1 bit.

`empty-zero'
     The number of columns containing values that are only binary 0's;
     these will occupy 1 bit.

`empty-fill'
     The number of integer columns that don't occupy the full byte
     range of their type; these are changed to a smaller type (for
     example, an `INTEGER' column may be changed to `MEDIUMINT').

`pre-space'
     The number of decimal columns that are stored with leading spaces.
     In this case, each value will contain a count for the number of
     leading spaces.

`end-space'
     The number of columns that have a lot of trailing spaces.  In this
     case, each value will contain a count for the number of trailing
     spaces.

`table-lookup'
     The column had only a small number of different values, which were
     converted to an `ENUM' before Huffman compression.

`zero'
     The number of columns for which all values are zero.

`Original trees'
     The initial number of Huffman trees.

`After join'
     The number of distinct Huffman trees left after joining trees to
     save some header space.

After a table has been compressed, `myisamchk -dvv' prints additional
information about each field:

`Type'
     The field type may contain the following descriptors:

    `constant'
          All rows have the same value.

    `no endspace'
          Don't store endspace.

    `no endspace, not_always'
          Don't store endspace and don't do end space compression for
          all values.

    `no endspace, no empty'
          Don't store endspace. Don't store empty values.

    `table-lookup'
          The column was converted to an `ENUM'.

    `zerofill(n)'
          The most significant `n' bytes in the value are always 0 and
          are not stored.

    `no zeros'
          Don't store zeros.

    `always zero'
          0 values are stored in 1 bit.

`Huff tree'
     The Huffman tree associated with the field.

`Bits'
     The number of bits used in the Huffman tree.

After you have run `pack_isam'/`myisampack' you must run
`isamchk'/`myisamchk' to re-create the index.  At this time you can
also sort the index blocks and create statistics needed for the MySQL
optimiser to work more efficiently:

     myisamchk -rq --analyze --sort-index table_name.MYI
     isamchk   -rq --analyze --sort-index table_name.ISM

After you have installed the packed table into the MySQL database
directory you should do `mysqladmin flush-tables' to force `mysqld' to
start using the new table.

If you want to unpack a packed table, you can do this with the
`--unpack' option to `isamchk' or `myisamchk'.

`mysqld-max', An Extended `mysqld' Server
-----------------------------------------

`mysqld-max' is the MySQL server (`mysqld') configured with the
following configure options:

*Option*               *Comment*
-with-server-suffix=-maxAdd a suffix to the `mysqld'
                       version string.
-with-innodb           Support for InnoDB tables.
-with-bdb              Support for Berkeley DB (BDB)
                       tables
CFLAGS=-DUSE_SYMDIR    Symbolic links support for
                       Windows.

You can find the MySQL-max binaries at
`http://www.mysql.com/downloads/mysql-max-3.23.html'.

The Windows MySQL binary distributions includes both the standard
`mysqld.exe' binary and the `mysqld-max.exe' binary.
`http://www.mysql.com/downloads/mysql-3.23.html'.  *Note Windows
installation::.

Note that as InnoDB and Berkeley DB are not available for all platforms,
some of the `Max' binaries may not have support for both of these.  You
can check which table types are supported by doing the following query:

     mysql> SHOW VARIABLES LIKE "have_%";
     +---------------+-------+
     | Variable_name | Value |
     +---------------+-------+
     | have_bdb      | YES   |
     | have_innodb   | NO    |
     | have_isam     | YES   |
     | have_raid     | NO    |
     | have_openssl  | NO    |
     +---------------+-------+

The meaning of the values are:

*Value*     *Meaning*
`YES'       The option is activated and usable.
`NO'        MySQL is not compiled with support for this option.
`DISABLED'  The xxxx option is disabled because one started `mysqld'
            with `--skip-xxxx' or because one didn't start `mysqld' with
            all needed options to enable the option.  In this case the
            `hostname.err' file should contain a reason for why the
            option is disabled.

*Note*:  To be able to create InnoDB tables you *must* edit your
startup options to include at least the `innodb_data_file_path' option.
*Note InnoDB start::.

To get better performance for BDB tables, you should add some
configuration options for these too. *Note BDB start::.

`safe_mysqld' will automatically try to start any `mysqld' binary with
the `-max' suffix. This makes it very easy to test out a another
`mysqld' binary in an existing installation.  Just run `configure' with
the options you want and then install the new `mysqld' binary as
`mysqld-max' in the same directory where your old `mysqld' binary is.
*Note `safe_mysqld': safe_mysqld.

The `mysqld-max' RPM uses the above mentioned `safe_mysqld' feature. It
just installs the `mysqld-max' executable and `safe_mysqld' will
automatically use this executable when `safe_mysqld' is restarted.

The following table shows which table types our standard MySQL-Max
binaries includes:

*System*    `BDB'   `InnoDB'
AIX 4.3     N       Y
HP-UX 11.0  N       Y
Linux-Alpha N       Y
Linux-Intel Y       Y
Linux-IA64  N       Y
Solaris-IntelN       Y
Solaris-SPARCY       Y
Caldera     Y       Y
(SCO) OSR5
UnixWare    Y       Y
Windows/NT  Y       Y

MySQL Client-Side Scripts and Utilities
=======================================

Overview of the Client-Side Scripts and Utilities
-------------------------------------------------

All MySQL clients that communicate with the server using the
`mysqlclient' library use the following environment variables:

*Name*             *Description*
`MYSQL_UNIX_PORT'  The default socket; used for connections
                   to `localhost'
`MYSQL_TCP_PORT'   The default TCP/IP port
`MYSQL_PWD'        The default password
`MYSQL_DEBUG'      Debug-trace options when debugging
`TMPDIR'           The directory where temporary tables/files
                   are created

Use of `MYSQL_PWD' is insecure.  *Note Connecting::.

The `mysql' client uses the file named in the `MYSQL_HISTFILE'
environment variable to save the command-line history. The default
value for the history file is `$HOME/.mysql_history', where `$HOME' is
the value of the `HOME' environment variable. *Note Environment
variables::.

All MySQL programs take many different options. However, every MySQL
program provides a `--help' option that you can use to get a full
description of the program's different options. For example, try `mysql
--help'.

You can override default options for all standard client programs with
an option file. *Note Option files::.

The following list briefly describes the client-side MySQL programs:

`msql2mysql'
     A shell script that converts `mSQL' programs to MySQL. It doesn't
     handle all cases, but it gives a good start when converting.

`mysqlaccess'
     A script that checks the access privileges for a host, user, and
     database combination.

`mysqladmin'
     Utility for performing administrative operations, such as creating
     or dropping databases, reloading the grant tables, flushing tables
     to disk, and reopening log files.  `mysqladmin' can also be used
     to retrieve version, process, and status information from the
     server.  *Note `mysqladmin': mysqladmin.

`mysqldump'
     Dumps a MySQL database into a file as SQL statements or as
     tab-separated text files. Enhanced freeware originally by Igor
     Romanenko.  *Note `mysqldump': mysqldump.

`mysqlimport'
     Imports text files into their respective tables using `LOAD DATA
     INFILE'. *Note `mysqlimport': mysqlimport.

`mysqlshow'
     Displays information about databases, tables, columns, and indexes.

`replace'
     A utility program that is used by `msql2mysql', but that has more
     general applicability as well.  `replace' changes strings in place
     in files or on the standard input. Uses a finite state machine to
     match longer strings first. Can be used to swap strings. For
     example, this command swaps `a' and `b' in the given files:

          shell> replace a b b a -- file1 file2 ...

`mysql', The Command-line Tool
------------------------------

`mysql' is a simple SQL shell (with GNU `readline' capabilities).  It
supports interactive and non-interactive use. When used interactively,
query results are presented in an ASCII-table format. When used
non-interactively (for example, as a filter), the result is presented in
tab-separated format.  (The output format can be changed using
command-line options.)  You can run scripts simply like this:

     shell> mysql database < script.sql > output.tab

If you have problems due to insufficient memory in the client, use the
`--quick' option!  This forces `mysql' to use `mysql_use_result()'
rather than `mysql_store_result()' to retrieve the result set.

Using `mysql' is very easy. Just start it as follows: `mysql database'
or `mysql --user=user_name --password=your_password database'. Type a
SQL statement, end it with `;', `\g', or `\G' and press Enter.

`mysql' supports the following options:

`-?, --help'
     Display this help and exit.

`-A, --no-auto-rehash'
     No automatic rehashing. One has to use 'rehash' to get table and
     field completion. This gives a quicker start of mysql.

`--prompt=...'
     Set the mysql prompt to specified format.

`-b, --no-beep'
     Turn off beep-on-error.

`-B, --batch'
     Print results with a tab as separator, each row on a new line.
     Doesn't use history file.

`--character-sets-dir=...'
     Directory where character sets are located.

`-C, --compress'
     Use compression in server/client protocol.

`-#, --debug[=...]'
     Debug log. Default is 'd:t:o,/tmp/mysql.trace'.

`-D, --database=...'
     Database to use. This is mainly useful in the `my.cnf' file.

`--default-character-set=...'
     Set the default character set.

`-e, --execute=...'
     Execute command and quit. (Output like with -batch)

`-E, --vertical'
     Print the output of a query (rows) vertically. Without this option
     you can also force this output by ending your statements with `\G'.

`-f, --force'
     Continue even if we get a SQL error.

`-g, --no-named-commands'
     Named commands are disabled. Use \* form only, or use named
     commands only in the beginning of a line ending with a semicolon
     (`;'). Since Version 10.9, the client now starts with this option
     *enabled* by default!  With the -g option, long format commands
     will still work from the first line, however.

`-G, --enable-named-commands'
     Named commands are *enabled*.  Long format commands are allowed as
     well as shortened \* commands.

`-i, --ignore-space'
     Ignore space after function names.

`-h, --host=...'
     Connect to the given host.

`-H, --html'
     Produce HTML output.

`-X, --xml'
     Produce XML output.

`-L, --skip-line-numbers'
     Don't write line number for errors. Useful when one wants to
     compare result files that includes error messages

`--no-pager'
     Disable pager and print to stdout. See interactive help (\h) also.

`--no-tee'
     Disable outfile. See interactive help (\h) also.

`-n, --unbuffered'
     Flush buffer after each query.

`-N, --skip-column-names'
     Don't write column names in results.

`-O, --set-variable var=option'
     Give a variable a value. `--help' lists variables.  Please note
     that `--set-variable' is deprecated since MySQL 4.0, just use
     `--var=option' on its own.

`-o, --one-database'
     Only update the default database. This is useful for skipping
     updates to other database in the update log.

``--pager[=...]''
     Output type. Default is your `ENV' variable `PAGER'. Valid pagers
     are less, more, cat [> filename], etc.  See interactive help (\h)
     also. This option does not work in batch mode. Pager works only in
     Unix.

`-p[password], --password[=...]'
     Password to use when connecting to server. If a password is not
     given on the command-line, you will be prompted for it.  Note that
     if you use the short form `-p' you can't have a space between the
     option and the password.

`-P  --port=...'
     TCP/IP port number to use for connection.

`-q, --quick'
     Don't cache result, print it row-by-row. This may slow down the
     server if the output is suspended. Doesn't use history file.

`-r, --raw'
     Write column values without escape conversion. Used with `--batch'

`-s, --silent'
     Be more silent.

`-S  --socket=...'
     Socket file to use for connection.

`-t  --table'
     Output in table format. This is default in non-batch mode.

`-T, --debug-info'
     Print some debug information at exit.

`--tee=...'
     Append everything into outfile. See interactive help (\h) also.
     Does not work in batch mode.

`-u, --user=#'
     User for login if not current user.

`-U, --safe-updates[=#], --i-am-a-dummy[=#]'
     Only allow `UPDATE' and `DELETE' that uses keys. See below for
     more information about this option.  You can reset this option if
     you have it in your `my.cnf' file by using `--safe-updates=0'.

`-v, --verbose'
     More verbose output (-v -v -v gives the table output format).

`-V, --version'
     Output version information and exit.

`-w, --wait'
     Wait and retry if connection is down instead of aborting.

You can also set the following variables with `-O' or `--set-variable';
please note that `--set-variable' is deprecated since MySQL 4.0, just
use `--var=option' on its own:

*Variable Name*    *Default**Description*
connect_timeout    0       Number of seconds before timeout connection.
max_allowed_packet 16777216Max packetlength to send/receive from to server
net_buffer_length  16384   Buffer for TCP/IP and socket communication
select_limit       1000    Automatic limit for SELECT when using
                           -i-am-a-dummy
max_join_size      1000000 Automatic limit for rows in a join when using
                           -i-am-a-dummy.

If you type 'help' on the command-line, `mysql' will print out the
commands that it supports:

     mysql> help

     MySQL commands:
     help    (\h)    Display this text.
     ?       (\h)    Synonym for `help'.
     clear   (\c)    Clear command.
     connect (\r)    Reconnect to the server.
                     Optional arguments are db and host.
     edit    (\e)    Edit command with $EDITOR.
     ego     (\G)    Send command to mysql server,
                     display result vertically.
     exit    (\q)    Exit mysql. Same as quit.
     go      (\g)    Send command to mysql server.
     nopager (\n)    Disable pager, print to stdout.
     notee   (\t)    Don't write into outfile.
     pager   (\P)    Set PAGER [to_pager].
                     Print the query results via PAGER.
     print   (\p)    Print current command.
     prompt  (\R)    Change your mysql prompt.
     quit    (\q)    Quit mysql.
     rehash  (\#)    Rebuild completion hash.
     source  (\.)    Execute a SQL script file.
                     Takes a file name as an argument.
     status  (\s)    Get status information from the server.
     tee     (\T)    Set outfile [to_outfile].
                     Append everything into given outfile.
     use     (\u)    Use another database.
                     Takes database name as argument.

The `pager' command works only in Unix.

The `status' command gives you some information about the connection
and the server you are using. If you are running in the
`--safe-updates' mode, `status' will also print the values for the
`mysql' variables that affect your queries.

A useful startup option for beginners (introduced in MySQL Version
3.23.11) is `--safe-updates' (or `--i-am-a-dummy' for users that has at
some time done a `DELETE FROM table_name' but forgot the `WHERE'
clause).  When using this option, `mysql' sends the following command
to the MySQL server when opening the connection:

     SET SQL_SAFE_UPDATES=1,SQL_SELECT_LIMIT=#select_limit#,
         SQL_MAX_JOIN_SIZE=#max_join_size#"

where `#select_limit#' and `#max_join_size#' are variables that can be
set from the `mysql' command-line. *Note `SET': SET OPTION.

The effect of the above is:

   * You are not allowed to do an `UPDATE' or `DELETE' statement if you
     don't have a key constraint in the `WHERE' part. One can, however,
     force an `UPDATE/DELETE' by using `LIMIT':
          UPDATE table_name SET not_key_column=# WHERE not_key_column=# LIMIT 1;

   * All big results are automatically limited to `#select_limit#' rows.

   * `SELECT's that will probably need to examine more than
     `#max_join_size' row combinations will be aborted.

Some useful hints about the `mysql' client:

Some data is much more readable when displayed vertically, instead of
the usual horizontal box type output. For example longer text, which
includes new lines, is often much easier to be read with vertical
output.

     mysql> SELECT * FROM mails WHERE LENGTH(txt) < 300 lIMIT 300,1\G
     *************************** 1. row ***************************
       msg_nro: 3068
          date: 2000-03-01 23:29:50
     time_zone: +0200
     mail_from: Monty
         reply: [e-mail]
       mail_to: "Thimble Smith" <[e-mail]>
           sbj: UTF-8
           txt: >>>>> "Thimble" == Thimble Smith writes:

     Thimble> Hi.  I think this is a good idea.  Is anyone familiar with UTF-8
     Thimble> or Unicode? Otherwise, I'll put this on my TODO list and see what
     Thimble> happens.

     Yes, please do that.

     Regards,
     Monty
          file: inbox-jani-1
          hash: 190402944
     1 row in set (0.09 sec)

For logging, you can use the `tee' option. The `tee' can be started
with option `--tee=...', or from the command-line interactively with
command `tee'. All the data displayed on the screen will also be
appended into a given file. This can be very useful for debugging
purposes also. The `tee' can be disabled from the command-line with
command `notee'. Executing `tee' again starts logging again. Without a
parameter the previous file will be used. Note that `tee' will flush
the results into the file after each command, just before the
command-line appears again waiting for the next command.

Browsing, or searching the results in the interactive mode in Unix less,
more, or any other similar program, is now possible with option
`--pager[=...]'. Without argument, `mysql' client will look for
environment variable PAGER and set `pager' to that.  `pager' can be
started from the interactive command-line with command `pager' and
disabled with command `nopager'.  The command takes an argument
optionally and the `pager' will be set to that. Command `pager' can be
called without an argument, but this requires that the option `--pager'
was used, or the `pager' will default to stdout. `pager' works only in
Unix, since it uses the popen() function, which doesn't exist in
Windows. In Windows, the `tee' option can be used instead, although it
may not be as handy as `pager' can be in some situations.

A few tips about `pager':
   * You can use it to write to a file:
          mysql> pager cat > /tmp/log.txt
     and the results will only go to a file. You can also pass any
     options for the programs that you want to use with the `pager':
          mysql> pager less -n -i -S

   * From the above do note the option '-S'. You may find it very
     useful when browsing the results; try the option with horizontal
     output (end commands with '\g', or ';') and with vertical output
     (end commands with '\G'). Sometimes a very wide result set is hard
     to be read from the screen, with option -S to less you can browse
     the results within the interactive less from left to right,
     preventing lines longer than your screen from being continued to
     the next line. This can make the result set much more readable.
     You can swith the mode between on and off within the interactive
     less with '-S'. See the 'h' for more help about less.

   * You can combine very complex ways to handle the results, for
     example the following would send the results to two files in two
     different directories, on two different hard-disks mounted on /dr1
     and /dr2, yet let the results still be seen on the screen via less:
          mysql> pager cat | tee /dr1/tmp/res.txt | \
          tee /dr2/tmp/res2.txt | less -n -i -S


You can also combine the two functions above; have the `tee' enabled,
`pager' set to 'less' and you will be able to browse the results in
unix 'less' and still have everything appended into a file the same
time. The difference between Unix `tee' used with the `pager' and the
`mysql' client in-built `tee', is that the in-built `tee' works even if
you don't have the Unix `tee' available. The in-built `tee' also logs
everything that is printed on the screen, where the Unix `tee' used
with `pager' doesn't log quite that much. Last, but not least, the
interactive `tee' is more handy to switch on and off, when you want to
log something into a file, but want to be able to turn the feature off
sometimes.

From MySQL version 4.0.2 it is possible to change the prompt in the
`mysql' command-line client.

You can use the following prompt options:
*Option**Description*
\v      mysqld version
\d      database in use
\h      host connected to
\p      port connected on
\u      username
\U      full username@host
\\      `\'
\n      new line break
\t      tab
\       space
\_      space
\R      military hour time (0-23)
\r      standard hour time (1-12)
\m      minutes
\y      two digit year
\Y      four digit year
\D      full date format
\s      seconds
\w      day of the week in three letter
        format (Mon, Tue, ...)
\P      am/pm
\o      month in number format
\O      month in three letter format (Jan,
        Feb, ...)
\c      counter that counts up for each
        command you do

`\' followed by any other letter just becomes that letter.

You may set the prompt in the following places:

*Environment Variable*
     You may set the `MYSQL_PS1' environment variable to a prompt
     string.  For example:

          shell> export MYSQL_PS1="(\u@\h) [\d]> "

*`my.cnf'*

*`.my.cnf'*
     You may set the `prompt' option in any MySQL configuration file,
     in the `mysql' group.  For example:

          [mysql]
          prompt=(\u@\h) [\d]>\_

*Command Line*
     You may set the `--prompt' option on the command line to `mysql'.
     For example:

          shell> mysql --prompt="(\u@\h) [\d]> "

          (user@host) [database]>

*Interactively*
     You may also use the `prompt' (or `\R') command to change your
     prompt interactively.  For example:

          mysql> prompt (\u@\h) [\d]>\_
          PROMPT set to '(\u@\h) [\d]>\_'
          (user@host) [database]>
          (user@host) [database]> prompt
          Returning to default PROMPT of mysql>
          mysql>

`mysqladmin', Administrating a MySQL Server
-------------------------------------------

A utility for performing administrative operations. The syntax is:

     shell> mysqladmin [OPTIONS] command [command-option] command ...

You can get a list of the options your version of `mysqladmin' supports
by executing `mysqladmin --help'.

The current `mysqladmin' supports the following commands:

`create databasename'
     Create a new database.

`drop databasename'
     Delete a database and all its tables.

`extended-status'
     Gives an extended status message from the server.

`flush-hosts'
     Flush all cached hosts.

`flush-logs'
     Flush all logs.

`flush-tables'
     Flush all tables.

`flush-privileges'
     Reload grant tables (same as reload).

`kill id,id,...'
     Kill mysql threads.

`password'
     Set a new password. Change old password to new-password.

`ping'
     Check if mysqld is alive.

`processlist'
     Show list of active threads in server.

`reload'
     Reload grant tables.

`refresh'
     Flush all tables and close and open logfiles.

`shutdown'
     Take server down.

`slave-start'
     Start slave replication thread.

`slave-stop'
     Stop slave replication thread.

`status'
     Gives a short status message from the server.

`variables'
     Prints variables available.

`version'
     Get version info from server.

All commands can be shortened to their unique prefix.  For example:

     shell> mysqladmin proc stat
     +----+-------+-----------+----+-------------+------+-------+------+
     | Id | User  | Host      | db | Command     | Time | State | Info |
     +----+-------+-----------+----+-------------+------+-------+------+
     | 6  | monty | localhost |    | Processlist | 0    |       |      |
     +----+-------+-----------+----+-------------+------+-------+------+
     Uptime: 10077  Threads: 1  Questions: 9  Slow queries: 0
     Opens: 6 Flush tables: 1  Open tables: 2
     Memory in use: 1092K  Max memory used: 1116K

The `mysqladmin status' command result has the following columns:

*Column*       *Description*
Uptime         Number of seconds the MySQL server has been up.
Threads        Number of active threads (clients).
Questions      Number of questions from clients since
               `mysqld' was started.
Slow queries   Queries that have taken more than
               `long_query_time' seconds. *Note Slow query
               log::.
Opens          How many tables `mysqld' has opened.
Flush tables   Number of `flush ...', `refresh', and `reload'
               commands.
Open tables    Number of tables that are open now.
Memory in use  Memory allocated directly by the `mysqld' code
               (only available when MySQL is compiled with
               -with-debug=full).
Max memory     Maximum memory allocated directly by the
used           `mysqld' code (only available when MySQL is
               compiled with -with-debug=full).

If you do `mysqladmin shutdown' on a socket (in other words, on a the
computer where `mysqld' is running), `mysqladmin' will wait until the
MySQL `pid-file' is removed to ensure that the `mysqld' server has
stopped properly.

Using `mysqlcheck' for Table Maintenance and Crash Recovery
-----------------------------------------------------------

Since MySQL version 3.23.38 you will be able to use a new checking and
repairing tool for `MyISAM' tables. The difference to `myisamchk' is
that `mysqlcheck' should be used when the `mysqld' server is running,
where as `myisamchk' should be used when it is not. The benefit is that
you no longer have to take the server down for checking or repairing
your tables.

`mysqlcheck' uses MySQL server commands `CHECK', `REPAIR', `ANALYZE'
and `OPTIMIZE' in a convenient way for the user.

There are three alternative ways to invoke `mysqlcheck':

     shell> mysqlcheck [OPTIONS] database [tables]
     shell> mysqlcheck [OPTIONS] --databases DB1 [DB2 DB3...]
     shell> mysqlcheck [OPTIONS] --all-databases

So it can be used in a similar way as `mysqldump' when it comes to what
databases and tables you want to choose.

`mysqlcheck' does have a special feature compared to the other clients;
the default behaviour, checking tables (-c), can be changed by renaming
the binary. So if you want to have a tool that repairs tables by
default, you should just copy `mysqlcheck' to your harddrive with a new
name, `mysqlrepair', or alternatively make a symbolic link to
`mysqlrepair' and name the symbolic link as `mysqlrepair'. If you
invoke `mysqlrepair' now, it will repair tables by default.

The names that you can use to change `mysqlcheck' default behaviour are
here:

     mysqlrepair:   The default option will be -r
     mysqlanalyze:  The default option will be -a
     mysqloptimize: The default option will be -o

The options available for `mysqlcheck' are listed here, please check
what your version supports with `mysqlcheck --help'.

`-A, --all-databases'
     Check all the databases. This will be same as -databases with all
     databases selected

`-1, --all-in-1'
     Instead of making one query for each table, execute all queries in
     1 query separately for each database. Table names will be in a
     comma separated list.

`-a, --analyze'
     Analyse given tables.

`--auto-repair'
     If a checked table is corrupted, automatically fix it. Repairing
     will be done after all tables have been checked, if corrupted ones
     were found.

`-#, --debug=...'
     Output debug log. Often this is 'd:t:o,filename'

`--character-sets-dir=...'
     Directory where character sets are

`-c, --check'
     Check table for errors

`-C, --check-only-changed'
     Check only tables that have changed since last check or haven't
     been closed properly.

`--compress'
     Use compression in server/client protocol.

`-?, --help'
     Display this help message and exit.

`-B, --databases'
     To check several databases. Note the difference in usage; in this
     case no tables are given. All name arguments are regarded as
     database names.

`--default-character-set=...'
     Set the default character set

`-F, --fast'
     Check only tables that hasn't been closed properly

`-f, --force'
     Continue even if we get an sql-error.

`-e, --extended'
     If you are using this option with CHECK TABLE, it will ensure that
     the table is 100 percent consistent, but will take a long time.

     If you are using this option with REPAIR TABLE, it will run an
     extended repair on the table, which may not only take a long time
     to execute, but may produce a lot of garbage rows also!

`-h, --host=...'
     Connect to host.

`-m, --medium-check'
     Faster than extended-check, but only finds 99.99 percent of all
     errors. Should be good enough for most cases.

`-o, --optimize'
     Optimise table

`-p, --password[=...]'
     Password to use when connecting to server. If password is not given
     it's solicited on the tty.

`-P, --port=...'
     Port number to use for connection.

`-q, --quick'
     If you are using this option with CHECK TABLE, it prevents the
     check from scanning the rows to check for wrong links. This is the
     fastest check.

     If you are using this option with REPAIR TABLE, it will try to
     repair only the index tree. This is the fastest repair method for
     a table.

`-r, --repair'
     Can fix almost anything except unique keys that aren't unique.

`-s, --silent'
     Print only error messages.

`-S, --socket=...'
     Socket file to use for connection.

`--tables'
     Overrides option -databases (-B).

`-u, --user=#'
     User for login if not current user.

`-v, --verbose'
     Print info about the various stages.

`-V, --version'
     Output version information and exit.

`mysqldump', Dumping Table Structure and Data
---------------------------------------------

Utility to dump a database or a collection of database for backup or for
transferring the data to another SQL server (not necessarily a MySQL
server).  The dump will contain SQL statements to create the table
and/or populate the table.

If you are doing a backup on the server, you should consider using the
`mysqlhotcopy' instead. *Note `mysqlhotcopy': mysqlhotcopy.

     shell> mysqldump [OPTIONS] database [tables]
     OR     mysqldump [OPTIONS] --databases [OPTIONS] DB1 [DB2 DB3...]
     OR     mysqldump [OPTIONS] --all-databases [OPTIONS]

If you don't give any tables or use the `--databases' or
`--all-databases', the whole database(s) will be dumped.

You can get a list of the options your version of `mysqldump' supports
by executing `mysqldump --help'.

Note that if you run `mysqldump' without `--quick' or `--opt',
`mysqldump' will load the whole result set into memory before dumping
the result.  This will probably be a problem if you are dumping a big
database.

Note that if you are using a new copy of the `mysqldump' program and
you are going to do a dump that will be read into a very old MySQL
server, you should not use the `--opt' or `-e' options.

`mysqldump' supports the following options:

`--add-locks'
     Add `LOCK TABLES' before and `UNLOCK TABLE' after each table dump.
     (To get faster inserts into MySQL.)

`--add-drop-table'
     Add a `drop table' before each create statement.

`-A, --all-databases'
     Dump all the databases. This will be same as `--databases' with all
     databases selected.

`-a, --all'
     Include all MySQL-specific create options.

`--allow-keywords'
     Allow creation of column names that are keywords.  This works by
     prefixing each column name with the table name.

`-c, --complete-insert'
     Use complete insert statements (with column names).

`-C, --compress'
     Compress all information between the client and the server if both
     support compression.

`-B, --databases'
     To dump several databases. Note the difference in usage. In this
     case no tables are given. All name arguments are regarded as
     database names.  `USE db_name;' will be included in the output
     before each new database.

`--delayed'
     Insert rows with the `INSERT DELAYED' command.

`-e, --extended-insert'
     Use the new multiline `INSERT' syntax. (Gives more compact and
     faster inserts statements.)

`-#, --debug[=option_string]'
     Trace usage of the program (for debugging).

`--help'
     Display a help message and exit.

`--fields-terminated-by=...'
`--fields-enclosed-by=...'
`--fields-optionally-enclosed-by=...'
`--fields-escaped-by=...'
`--lines-terminated-by=...'
     These options are used with the `-T' option and have the same
     meaning as the corresponding clauses for `LOAD DATA INFILE'.
     *Note `LOAD DATA': LOAD DATA.

`-F, --flush-logs'
     Flush log file in the MySQL server before starting the dump.

`-f, --force,'
     Continue even if we get a SQL error during a table dump.

`-h, --host=..'
     Dump data from the MySQL server on the named host. The default host
     is `localhost'.

`-l, --lock-tables.'
     Lock all tables before starting the dump.  The tables are locked
     with `READ LOCAL' to allow concurrent inserts in the case of
     `MyISAM' tables.

     Please note that when dumping multiple databases, `--lock-tables'
     will lock tables for each database separately. So using this
     option will not guarantee your tables will be logically consistent
     between databases.  Tables in different databases may be dumped in
     completely different states.

`-K, --disable-keys'
     `/*!40000 ALTER TABLE tb_name DISABLE KEYS */;' and `/*!40000
     ALTER TABLE tb_name ENABLE KEYS */;' will be put in the output.
     This will make loading the data into a MySQL 4.0 server faster as
     the indexes are created after all data are inserted.

`-n, --no-create-db'
     `CREATE DATABASE /*!32312 IF NOT EXISTS*/ db_name;' will not be
     put in the output. The above line will be added otherwise, if a
     `--databases' or `--all-databases' option was given.

`-t, --no-create-info'
     Don't write table creation information (the `CREATE TABLE'
     statement).

`-d, --no-data'
     Don't write any row information for the table.  This is very
     useful if you just want to get a dump of the structure for a table!

`--opt'
     Same as `--quick --add-drop-table --add-locks --extended-insert
     --lock-tables'.  Should give you the fastest possible dump for
     reading into a MySQL server.

`-pyour_pass, --password[=your_pass]'
     The password to use when connecting to the server. If you specify
     no `=your_pass' part, `mysqldump' you will be prompted for a
     password.

`-P port_num, --port=port_num'
     The TCP/IP port number to use for connecting to a host.  (This is
     used for connections to hosts other than `localhost', for which
     Unix sockets are used.)

`-q, --quick'
     Don't buffer query, dump directly to stdout. Uses
     `mysql_use_result()' to do this.

`-Q, --quote-names'
     Quote table and column names within ``' characters.

`-r, --result-file=...'
     Direct output to a given file. This option should be used in MSDOS,
     because it prevents new line `\n' from being converted to `\n\r'
     (new line + carriage return).

`--single-transaction'
     This option issues a `BEGIN' SQL command before dumping data from
     server. It is mostly useful with `InnoDB' tables and
     `READ_COMMITTED' transaction isolation level, as in this mode it
     will dump the consistent state of the database at the time then
     `BEGIN' was issued without blocking any applications.

     When using this option you should keep in mind that only
     transactional tables will be dumped in a consistent state, e.g.,
     any `MyISAM' or `HEAP' tables dumped while using this option may
     still change state.

     The `--single-transaction' option was added in version 4.0.2.
     This option is mutually exclusive with the `--lock-tables' option
     as `LOCK TABLES' already commits a previous transaction internally.

`-S /path/to/socket, --socket=/path/to/socket'
     The socket file to use when connecting to `localhost' (which is the
     default host).

`--tables'
     Overrides option -databases (-B).

`-T, --tab=path-to-some-directory'
     Creates a `table_name.sql' file, that contains the SQL CREATE
     commands, and a `table_name.txt' file, that contains the data, for
     each give table.  The format of the `.txt' file is made according
     to the `--fields-xxx' and `--lines--xxx' options.  *Note*: This
     option only works if `mysqldump' is run on the same machine as the
     `mysqld' daemon, and the user/group that `mysqld' is running as
     (normally user `mysql', group `mysql') needs to have permission to
     create/write a file at the location you specify.

`-u user_name, --user=user_name'
     The MySQL user name to use when connecting to the server. The
     default value is your Unix login name.

`-O var=option, --set-variable var=option'
     Set the value of a variable.  The possible variables are listed
     below.  Please note that `--set-variable' is deprecated since
     MySQL 4.0, just use `--var=option' on its own.

`-v, --verbose'
     Verbose mode.  Print out more information on what the program does.

`-V, --version'
     Print version information and exit.

`-w, --where='where-condition''
     Dump only selected records. Note that quotes are mandatory:

`-X, --xml'
     Dumps a database as well formed XML

`-x, --first-slave'
     Locks all tables across all databases.

          "--where=user='jimf'" "-wuserid>1" "-wuserid<1"

`-O net_buffer_length=#, where # < 16M'
     When creating multi-row-insert statements (as with option
     `--extended-insert' or `--opt'), `mysqldump' will create rows up
     to `net_buffer_length' length. If you increase this variable, you
     should also ensure that the `max_allowed_packet' variable in the
     MySQL server is bigger than the `net_buffer_length'.

The most normal use of `mysqldump' is probably for making a backup of
whole databases. *Note Backup::.

     mysqldump --opt database > backup-file.sql

You can read this back into MySQL with:

     mysql database < backup-file.sql

or

     mysql -e "source /patch-to-backup/backup-file.sql" database

However, it's also very useful to populate another MySQL server with
information from a database:

     mysqldump --opt database | mysql ---host=remote-host -C database

It is possible to dump several databases with one command:

     mysqldump --databases database1 [database2 ...] > my_databases.sql

If all the databases are wanted, one can use:

     mysqldump --all-databases > all_databases.sql

`mysqlhotcopy', Copying MySQL Databases and Tables
--------------------------------------------------

`mysqlhotcopy' is a Perl script that uses `LOCK TABLES', `FLUSH TABLES'
and `cp' or `scp' to quickly make a backup of a database.  It's the
fastest way to make a backup of the database or single tables, but it
can only be run on the same machine where the database directories are.

     mysqlhotcopy db_name [/path/to/new_directory]

     mysqlhotcopy db_name_1 ... db_name_n /path/to/new_directory

     mysqlhotcopy db_name./regex/

`mysqlhotcopy' supports the following options:

`-?, --help'
     Display a help screen and exit

`-u, --user=#'
     User for database login

`-p, --password=#'
     Password to use when connecting to server

`-P, --port=#'
     Port to use when connecting to local server

`-S, --socket=#'
     Socket to use when connecting to local server

`--allowold'
     Don't abort if target already exists (rename it _old)

`--keepold'
     Don't delete previous (now renamed) target when done

`--noindices'
     Don't include full index files in copy to make the backup smaller
     and faster The indexes can later be reconstructed with `myisamchk
     -rq.'.

`--method=#'
     Method for copy (`cp' or `scp').

`-q, --quiet'
     Be silent except for errors

`--debug'
     Enable debug

`-n, --dryrun'
     Report actions without doing them

`--regexp=#'
     Copy all databases with names matching regexp

`--suffix=#'
     Suffix for names of copied databases

`--checkpoint=#'
     Insert checkpoint entry into specified db.table

`--flushlog'
     Flush logs once all tables are locked.

`--tmpdir=#'
     Temporary directory (instead of /tmp).

You can use `perldoc mysqlhotcopy' to get more complete documentation
for `mysqlhotcopy'.

`mysqlhotcopy' reads the groups `[client]' and  `[mysqlhotcopy]' from
the option files.

To be able to execute `mysqlhotcopy' you need write access to the
backup directory, the `SELECT' privilege for the tables you are about to
copy and the MySQL `RELOAD' privilege (to be able to execute `FLUSH
TABLES').

`mysqlimport', Importing Data from Text Files
---------------------------------------------

`mysqlimport' provides a command-line interface to the `LOAD DATA
INFILE' SQL statement.  Most options to `mysqlimport' correspond
directly to the same options to `LOAD DATA INFILE'.  *Note `LOAD DATA':
LOAD DATA.

`mysqlimport' is invoked like this:

     shell> mysqlimport [options] database textfile1 [textfile2 ...]

For each text file named on the command-line, `mysqlimport' strips any
extension from the filename and uses the result to determine which
table to import the file's contents into.  For example, files named
`patient.txt', `patient.text', and `patient' would all be imported into
a table named `patient'.

`mysqlimport' supports the following options:

`-c, --columns=...'
     This option takes a comma-separated list of field names as an
     argument.  The field list is used to create a proper `LOAD DATA
     INFILE' command, which is then passed to MySQL. *Note `LOAD DATA':
     LOAD DATA.

`-C, --compress'
     Compress all information between the client and the server if both
     support compression.

`-#, --debug[=option_string]'
     Trace usage of the program (for debugging).

`-d, --delete'
     Empty the table before importing the text file.

`--fields-terminated-by=...'
`--fields-enclosed-by=...'
`--fields-optionally-enclosed-by=...'
`--fields-escaped-by=...'
`--lines-terminated-by=...'
     These options have the same meaning as the corresponding clauses
     for `LOAD DATA INFILE'. *Note `LOAD DATA': LOAD DATA.

`-f, --force'
     Ignore errors.  For example, if a table for a text file doesn't
     exist, continue processing any remaining files.  Without `--force',
     `mysqlimport' exits if a table doesn't exist.

`--help'
     Display a help message and exit.

`-h host_name, --host=host_name'
     Import data to the MySQL server on the named host. The default host
     is `localhost'.

`-i, --ignore'
     See the description for the `--replace' option.

`-l, --lock-tables'
     Lock *all* tables for writing before processing any text files.
     This ensures that all tables are synchronised on the server.

`-L, --local'
     Read input files from the client.  By default, text files are
     assumed to be on the server if you connect to `localhost' (which
     is the default host).

`-pyour_pass, --password[=your_pass]'
     The password to use when connecting to the server. If you specify
     no `=your_pass' part, `mysqlimport' you will be prompted for a
     password.

`-P port_num, --port=port_num'
     The TCP/IP port number to use for connecting to a host.  (This is
     used for connections to hosts other than `localhost', for which
     Unix sockets are used.)

`-r, --replace'
     The `--replace' and `--ignore' options control handling of input
     records that duplicate existing records on unique key values.  If
     you specify `--replace', new rows replace existing rows that have
     the same unique key value. If you specify `--ignore', input rows
     that duplicate an existing row on a unique key value are skipped.
     If you don't specify either option, an error occurs when a
     duplicate key value is found, and the rest of the text file is
     ignored.

`-s, --silent'
     Silent mode.  Write output only when errors occur.

`-S /path/to/socket, --socket=/path/to/socket'
     The socket file to use when connecting to `localhost' (which is the
     default host).

`-u user_name, --user=user_name'
     The MySQL user name to use when connecting to the server. The
     default value is your Unix login name.

`-v, --verbose'
     Verbose mode.  Print out more information what the program does.

`-V, --version'
     Print version information and exit.

Here is a sample run using `mysqlimport':

     $ mysql --version
     mysql  Ver 9.33 Distrib 3.22.25, for pc-linux-gnu (i686)
     $ uname -a
     Linux xxx.com 2.2.5-15 #1 Mon Apr 19 22:21:09 EDT 1999 i586 unknown
     $ mysql -e 'CREATE TABLE imptest(id INT, n VARCHAR(30))' test
     $ ed
     a
     100     Max Sydow
     101     Count Dracula
     .
     w imptest.txt
     32
     q
     $ od -c imptest.txt
     0000000   1   0   0  \t   M   a   x       S   y   d   o   w  \n   1   0
     0000020   1  \t   C   o   u   n   t       D   r   a   c   u   l   a  \n
     0000040
     $ mysqlimport --local test imptest.txt
     test.imptest: Records: 2  Deleted: 0  Skipped: 0  Warnings: 0
     $ mysql -e 'SELECT * FROM imptest' test
     +------+---------------+
     | id   | n             |
     +------+---------------+
     |  100 | Max Sydow     |
     |  101 | Count Dracula |
     +------+---------------+

Showing Databases, Tables, and Columns
--------------------------------------

`mysqlshow' can be used to quickly look at which databases exist, their
tables, and the table's columns.

With the `mysql' program you can get the same information with the
`SHOW' commands.  *Note SHOW::.

`mysqlshow' is invoked like this:

     shell> mysqlshow [OPTIONS] [database [table [column]]]

   * If no database is given, all matching databases are shown.

   * If no table is given, all matching tables in the database are
     shown.

   * If no column is given, all matching columns and column types in
     the table are shown.

Note that in newer MySQL versions, you only see those
database/tables/columns for which you have some privileges.

If the last argument contains a shell or SQL wildcard (`*', `?', `%' or
`_') then only what's matched by the wildcard is shown.  If a database
contains underscore(s), those should be escaped with backslash (some
Unix shells will require two), in order to get tables / columns
properly. '*' are converted into SQL '%' wildcard and '?' into SQL '_'
wildcard.  This may cause some confusion when you try to display the
columns for a table with a `_' as in this case `mysqlshow' only shows
you the table names that match the pattern.  This is easily fixed by
adding an extra `%' last on the command-line (as a separate argument).

perror, Explaining Error Codes
------------------------------

For most system errors MySQL will, in addition to a internal text
message, also print the system error code in one of the following
styles: `message ... (errno: #)' or `message ... (Errcode: #)'.

You can find out what the error code means by either examining the
documentation for your system or use the `perror' utility.

`perror' prints a description for a system error code, or an MyISAM/ISAM
storage engine (table handler) error code.

`perror' is invoked like this:

     shell> perror [OPTIONS] [ERRORCODE [ERRORCODE...]]

     Example:

     shell> perror 13 64
     Error code  13:  Permission denied
     Error code  64:  Machine is not on the network

Note that the error messages are mostly system dependent!

How to Run SQL Commands from a Text File
----------------------------------------

The `mysql' client typically is used interactively, like this:

     shell> mysql database

However, it's also possible to put your SQL commands in a file and tell
`mysql' to read its input from that file.  To do so, create a text file
`text_file' that contains the commands you wish to execute.  Then
invoke `mysql' as shown here:

     shell> mysql database < text_file

You can also start your text file with a `USE db_name' statement.  In
this case, it is unnecessary to specify the database name on the command
line:

     shell> mysql < text_file

If you are already running `mysql', you can execute a SQL script file
using the `source' command:

     mysql> source filename;

For more information about batch mode, *Note Batch mode::.

The MySQL Log Files
===================

MySQL has several different log files that can help you find out what's
going on inside `mysqld':

*Log file*     *Description*
The error log  Problems encountering starting, running or stopping
               `mysqld'.
The isam log   Logs all changes to the ISAM tables. Used only for
               debugging the isam code.
The query log  Established connections and executed queries.
The update     Deprecated: Stores all statements that changes data
log
The binary     Stores all statements that changes something. Used also
log            for replication
The slow log   Stores all queries that took more than `long_query_time'
               to execute or didn't use indexes.

All logs can be found in the `mysqld' data directory.  You can force
`mysqld' to reopen the log files (or in some cases switch to a new log)
by executing `FLUSH LOGS'. *Note FLUSH::.

The Error Log
-------------

`mysqld' writes all errors to the stderr, which the `safe_mysqld'
script redirects to a file called `'hostname'.err'.  (On Windows,
`mysqld' writes this directly to `\mysql\data\mysql.err'.)

This contains information indicating when `mysqld' was started and
stopped and also any critical errors found when running.  If `mysqld'
dies unexpectedly and `safe_mysqld' needs to restart `mysqld',
`safe_mysqld' will write a `restarted mysqld' row in this file.  This
log also holds a warning if `mysqld' notices a table that needs to be
automatically checked or repaired.

On some operating systems, the error log will contain a stack trace for
where `mysqld' died. This can be used to find out where `mysqld' died.
*Note Using stack trace::.

The General Query Log
---------------------

If you want to know what happens within `mysqld', you should start it
with `--log[=file]'.  This will log all connections and queries to the
log file (by default named `'hostname'.log').  This log can be very
useful when you suspect an error in a client and want to know exactly
what `mysqld' thought the client sent to it.

Older versions of the `mysql.server' script (from MySQL 3.23.4 to
3.23.8) pass `safe_mysqld' a `--log' option (enable general query log).
If you need better performance when you start using MySQL in a
production environment, you can remove the `--log' option from
`mysql.server' or change it to `--log-bin'. *Note Binary log::.

The entries in this log are written as `mysqld' receives the questions.
This may be different from the order in which the statements are
executed.  This is in contrast to the update log and the binary log
which are written after the query is executed, but before any locks are
released.

The Update Log
--------------

*Note*: the update log is replaced by the binary log. *Note Binary
log::.  With this you can do anything that you can do with the update
log.

When started with the `--log-update[=file_name]' option, `mysqld'
writes a log file containing all SQL commands that update data. If no
filename is given, it defaults to the name of the host machine. If a
filename is given, but it doesn't contain a path, the file is written
in the data directory. If `file_name' doesn't have an extension,
`mysqld' will create log file names like so: `file_name.###', where
`###' is a number that is incremented each time you execute `mysqladmin
refresh', execute `mysqladmin flush-logs', execute the `FLUSH LOGS'
statement, or restart the server.

*Note*: for the above scheme to work, you must not create your own
files with the same filename as the update log + some extensions that
may be regarded as a number, in the directory used by the update log!

If you use the `--log' or `-l' options, `mysqld' writes a general log
with a filename of `hostname.log', and restarts and refreshes do not
cause a new log file to be generated (although it is closed and
reopened). In this case you can copy it (on Unix) by doing:

     mv hostname.log hostname-old.log
     mysqladmin flush-logs
     cp hostname-old.log to-backup-directory
     rm hostname-old.log

Update logging is smart because it logs only statements that really
update data. So an `UPDATE' or a `DELETE' with a `WHERE' that finds no
rows is not written to the log. It even skips `UPDATE' statements that
set a column to the value it already has.

The update logging is done immediately after a query completes but
before any locks are released or any commit is done. This ensures that
the log will be logged in the execution order.

If you want to update a database from update log files, you could do the
following (assuming your update logs have names of the form
`file_name.###'):

     shell> ls -1 -t -r file_name.[0-9]* | xargs cat | mysql

`ls' is used to get all the log files in the right order.

This can be useful if you have to revert to backup files after a crash
and you want to redo the updates that occurred between the time of the
backup and the crash.

The Binary Update Log
---------------------

The intention is that the binary log should replace the update log, so
we recommend you to switch to this log format as soon as possible!

The binary log contains all information that is available in the update
log in a more efficient format. It also contains information about how
long each query took that updated the database.  It doesn't contain
queries that don't modify any data.  If you want to log all queries
(for example to find a problem query) you should use the general query
log. *Note Query log::.

The binary log is also used when you are replicating a slave from a
master.  *Note Replication::.

When started with the `--log-bin[=file_name]' option, `mysqld' writes a
log file containing all SQL commands that update data. If no file name
is given, it defaults to the name of the host machine followed by
`-bin'. If file name is given, but it doesn't contain a path, the file
is written in the data directory.

If you supply an extension to `--log-bin=filename.extension', the
extension will be silenty removed.

To the binary log filename `mysqld' will append an extension that is a
number that is incremented each time you execute `mysqladmin refresh',
execute `mysqladmin flush-logs', execute the `FLUSH LOGS' statement or
restart the server. A new binary log will also automatically be created
when it reaches `max_binlog_size'. You can delete all not active binary
log files with the `RESET MASTER' command. *Note RESET::.

You can use the following options to `mysqld' to affect what is logged
to the binary log:

*Option*                    *Description*
`binlog-do-db=database_name' Tells the master it should log updates for
                            the specified database, and exclude all
                            others not explicitly mentioned.  (Example:
                            `binlog-do-db=some_database')
`binlog-ignore-db=database_name' Tells the master that updates to the given
                            database should not be logged to the binary
                            log (Example:
                            `binlog-ignore-db=some_database')

To be able to know which different binary log files have been used,
`mysqld' will also create a binary log index file that contains the
name of all used binary log files. By default this has the same name as
the binary log file, with the extension `'.index''.  You can change the
name of the binary log index file with the `--log-bin-index=[filename]'
option.

If you are using replication, you should not delete old binary log
files until you are sure that no slave will ever need to use them.  One
way to do this is to do `mysqladmin flush-logs' once a day and then
remove any logs that are more than 3 days old.

You can examine the binary log file with the `mysqlbinlog' command.
For example, you can update a MySQL server from the binary log as
follows:

     shell> mysqlbinlog log-file | mysql -h server_name

You can also use the `mysqlbinlog' program to read the binary log
directly from a remote MySQL server!

`mysqlbinlog --help' will give you more information of how to use this
program!

If you are using `BEGIN [WORK]' or `SET AUTOCOMMIT=0', you must use the
MySQL binary log for backups instead of the old update log.

The binary logging is done immediately after a query completes but
before any locks are released or any commit is done. This ensures that
the log will be logged in the execution order.

Updates to non-transactional tables are stored in the binary log
immediately after execution.  For transactional tables such as `BDB' or
`InnoDB' tables, all updates (`UPDATE', `DELETE' or `INSERT') that
change tables are cached until a `COMMIT' command is sent to the
server. At this point `mysqld' writes the whole transaction to the
binary log before the `COMMIT' is executed.  very thread will, on
start, allocate a buffer of `binlog_cache_size' to buffer queries.  If
a query is bigger than this, the thread will open a temporary file to
store the transaction.  The temporary file will be deleted when the
thread ends.

The `max_binlog_cache_size' (default 4G) can be used to restrict the
total size used to cache a multi-query transaction.  If a transaction is
bigger than this it will fail and roll back.

If you are using the update or binary log, concurrent inserts will be
converted to normal inserts when using `CREATE ... SELECT' or `INSERT
... SELECT'.  This is to ensure that you can recreate an exact copy of
your tables by applying the log on a backup.

The Slow Query Log
------------------

When started with the `--log-slow-queries[=file_name]' option, `mysqld'
writes a log file containing all SQL commands that took more than
`long_query_time' to execute. The time to get the initial table locks
are not counted as execution time.

The slow query log is logged after the query is executed and after all
locks has been released. This may be different from the order in which
the statements are executed.

If no file name is given, it defaults to the name of the host machine
suffixed with `-slow.log'. If a filename is given, but doesn't contain
a path, the file is written in the data directory.

The slow query log can be used to find queries that take a long time to
execute and are thus candidates for optimisation. With a large log, that
can become a difficult task. You can pipe the slow query log through the
`mysqldumpslow' command to get a summary of the queries which appear in
the log.

You are using `--log-long-format' then also queries that are not using
indexes are printed. *Note Command-line options::.

Log File Maintenance
--------------------

The MySQL Server can create a number of different log files, which make
it easy to see what is going on. *Note Log Files::. One must however
regularly clean up these files, to ensure that the logs don't take up
too much disk space.

When using MySQL with log files, you will, from time to time, want to
remove/backup old log files and tell MySQL to start logging on new
files.  *Note Backup::.

On a Linux (`Redhat') installation, you can use the `mysql-log-rotate'
script for this. If you installed MySQL from an RPM distribution, the
script should have been installed automatically.  Note that you should
be careful with this if you are using the log for replication!

On other systems you must install a short script yourself that you
start from `cron' to handle log files.

You can force MySQL to start using new log files by using `mysqladmin
flush-logs' or by using the SQL command `FLUSH LOGS'.  If you are using
MySQL Version 3.21 you must use `mysqladmin refresh'.

The above command does the following:

   * If standard logging (`--log') or slow query logging
     (`--log-slow-queries') is used, closes and reopens the log file
     (`mysql.log' and ``hostname`-slow.log' as default).

   * If update logging (`--log-update') is used, closes the update log
     and opens a new log file with a higher sequence number.

If you are using only an update log, you only have to flush the logs
and then move away the old update log files to a backup.  If you are
using the normal logging, you can do something like:

     shell> cd mysql-data-directory
     shell> mv mysql.log mysql.old
     shell> mysqladmin flush-logs

and then take a backup and remove `mysql.old'.

Replication in MySQL
====================

This section describes the various replication features in MySQL.  It
serves as a reference to the options available with replication.  You
will be introduced to replication and learn how to implement it.
Toward the end, there are some frequently asked questions and
descriptions of problems and how to solve them.

We suggest that you visit our website at `http://www.mysql.com/' often
and read updates to this section. Replication is constantly being
improved, and we update the manual frequently with the most current
information.

Introduction
------------

One way replication can be used is to increase both robustness and
speed. For robustness you can have two systems and can switch to the
backup if you have problems with the master. The extra speed is
achieved by sending a part of the non-updating queries to the replica
server. Of course this only works if non-updating queries dominate, but
that is the normal case.

Starting in Version 3.23.15, MySQL supports one-way replication
internally. One server acts as the master, while the other acts as the
slave. Note that one server could play the roles of master in one pair
and slave in the other. The master server keeps a binary log of updates
(*note Binary log::) and an index file to binary logs to keep track of
log rotation.  The slave, upon connecting, informs the master where it
left off since the last successfully propagated update, catches up on
the updates, and then blocks and waits for the master to notify it of
the new updates.

Note that if you are replicating a database, all updates to this
database should be done through the master!

Another benefit of using replication is that one can get live backups of
the system by doing a backup on a slave instead of doing it on the
master. *Note Backup::.

Replication Implementation Overview
-----------------------------------

MySQL replication is based on the server keeping track of all changes
to your database (updates, deletes, etc) in the binary log (*note
Binary log::) and the slave server(s) reading the saved queries from
the master server's binary log so that the slave can execute the same
queries on its copy of the data.

It is *very important* to realise that the binary log is simply a
record starting from a fixed point in time (the moment you enable binary
logging). Any slaves which you set up will need copies of all the data
from your master as it existed the moment that you enabled binary
logging on the master. If you start your slaves with data that doesn't
agree with what was on the master *when the binary log was started*,
your slaves may fail.

Please see the following table for an indication of master-slave
compatibility between different versions. With regard to version 4.0,
we recommend using same version on both sides.

                    *Master*    *Master**Master**Master*
                    *3.23.33    *4.0.0* *4.0.1* *4.0.3 and
                    and up*                     up*
*Slave* *3.23.33    yes         no      no      no
        and up*
*Slave* *4.0.0*     no          yes     no      no
*Slave* *4.0.1*     yes         no      yes     no
*Slave* *4.0.3 and  yes         no      no      yes
        up*

*Note*: MySQL Version 4.0.2 is not recommended for replication.

Starting from 4.0.0, one can use `LOAD DATA FROM MASTER' to set up a
slave. Be aware that `LOAD DATA FROM MASTER' currently works only if
all the tables on the master are `MyISAM' type, and will acquire a
global read lock, so no writes are possible while the tables are being
transferred from the master. This limitation is of a temporary nature,
and is due to the fact that we have not yet implemented hot lock-free
table backup.  It will be removed in the future 4.0 branch versions
once we implement hot backup enabling `LOAD DATA FROM MASTER' to work
without blocking master updates.

Due to the above limitation, we recommend that at this point  you use
`LOAD DATA FROM MASTER' only if the dataset on the master is relatively
small, or if a prolonged read lock on the master is acceptable. While
the actual speed of `LOAD DATA FROM MASTER' may vary from system to
system, a good rule for a rough estimate of how long it is going to
take is 1 second per 1 MB of the datafile. You will get close to the
estimate if both master and slave are equivalent to 700 MHz Pentium,
are connected through 100 MBit/s network, and your index file is about
half the size of your data file. Of course, your mileage will vary from
system to system, the above rule just gives you a rough order of
magnitude estimate.

Once a slave is properly configured and running, it will simply connect
to the master and wait for updates to process. If the master goes away
or the slave loses connectivity with your master, it will keep trying to
connect every `master-connect-retry' seconds until it is able to
reconnect and resume listening for updates.

Each slave keeps track of where it left off. The master server has no
knowledge of how many slaves there are or which ones are up-to-date at
any given time.

The next section explains the master/slave setup process in more detail.

How To Set Up Replication
-------------------------

Here is a quick description of how to set up complete replication on
your current MySQL server. It assumes you want to replicate all your
databases and have not configured replication before. You will need to
shutdown your master server briefly to complete the steps outlined here.

While this method is the most straightforward way to set up a slave, it
is not the only one. For example, if you already have a snapshot of the
master, and the master already has server id set and binary logging
enabled, you can set up a slave without shutting the master down or
even blocking the updates.  For more details, please see *Note
Replication FAQ::.

If you want to become a real MySQL replication guru, we suggest that you
begin by studying, pondering, and trying all commands mentioned in
*Note Replication SQL::. You should also familiarise yourself with
replication startup options in `my.cnf' in *Note Replication Options::.

  1. Make sure you have a recent version of MySQL installed on the
     master and slave(s).

     Use Version 3.23.29 or higher. Previous releases used a different
     binary log format and had bugs which have been fixed in newer
     releases. Please, do not report bugs until you have verified that
     the problem is present in the latest release.

  2. Set up special a replication user on the master with the `FILE'
     (in MySQL versions older than 4.0.2) or `REPLICATION SLAVE'
     privilege in newer MySQL versions.  You must also have given
     permission to connect from all the slaves. If the user is only
     doing replication (which is recommended), you don't need to grant
     any additional privileges.

     For example, to create a user named `repl' which can access your
     master from any host, you might use this command:

          mysql> GRANT FILE ON *.* TO repl@"%" IDENTIFIED BY '<password>';

  3. If you are using MyISAM tables, flush all the tables and block
     write queries by executing `FLUSH TABLES WITH READ LOCK' command.

          mysql> FLUSH TABLES WITH READ LOCK;

     and then take a snapshot of the data on your master server.

     The easiest way to do this (on Unix) is to simply use *tar* to
     produce an archive of your entire data directory. The exact data
     directory location depends on your installation.

          tar -cvf /tmp/mysql-snapshot.tar /path/to/data-dir

     Windows users can use `WinZIP' or similar software to create an
     archive of the data directory.

     After or during the process of taking a snapshot, read the value
     of the current binary log name and the offset on the master:

          mysql > SHOW MASTER STATUS;
          +---------------+----------+--------------+-------------------------------+
          | File          | Position | Binlog_do_db | Binlog_ignore_db              |
          +---------------+----------+--------------+-------------------------------+
          | mysql-bin.003 | 73       | test,bar     | foo,manual,sasha_likes_to_run |
          +---------------+----------+--------------+-------------------------------+
          1 row in set (0.06 sec)

     The `File' column shows the name of the log,  while `Position'
     shows the offset. n the above example, the binary log value is
     `mysql-bin.003' and the offset is 73. Record the values - you will
     need to use them later when you are setting up the slave.

     Once you have taken the snapshot and recorded the log name and
     offset, you can re-enable write activity on the master:

          mysql> UNLOCK TABLES;

     If you are using InnoDB tables, ideally you should use the InnoDB
     Hot Backup tool that is available to those who purchase MySQL
     commercial licenses, support, or the backup tool itself. It will
     take a consistent snapshot without acquiring any locks on the
     master server, and record the log name and offset corresponding to
     the snapshot to be later used on the slave. More information about
     the tool is avaliable at `http://www.innodb.com/hotbackup.html'.

     Without the hot backup tool, the quickest way to take a snapshot
     of  InnoDB tables is to shut the master server down and copy the
     data files, the logs, and the table definition files (`.frm'). To
     record the current log file name and offset, you should do the
     following before you shut down the server:

          mysql> FLUSH TABLES WITH READ LOCK;
          mysql> SHOW MASTER STATUS;

     And then record the log name and the offset from the output of
     `SHOW MASTER STATUS' as was shown earlier. Once you have recorded
     the log name and the offset, shut the server down without
     unlocking the tables to make sure it goes down with the snapshot
     corresponding to the current log file and offset:

          shell> mysqladmin -uroot shutdown

     If the master has been previously running without `log-bin'
     enabled, the values of log name and position will be empty when
     you run `SHOW MASTER STATUS'. In that case, record empty string
     (") for the log name, and 4 for the offset.

  4. Make sure that `my.cnf' on the master has  `log-bin' if it is not
     there already and `server-id=unique number' in the `[mysqld]'
     section. If those options are not present, add them and restart
     the server.  It is very important that the id of the slave is
     different from the id of the master. Think of `server-id' as
     something similar to the IP address - it uniquely identifies the
     server instance in the community of replication partners.

          [mysqld]
          log-bin
          server-id=1

  5. Add the following to `my.cnf' on the slave(s):

          server-id=<some unique number between 1 and 2^32-1 that is different from
           that of the master>

     replacing the values in <> with what is relevant to your system.

     `server-id' must be different for each server participating in
     replication.  If you don't specify a server-id, it will be set to
     1 if you have not defined `master-host', else it will be set to 2.
     Note that in the case of `server-id' omission the master will
     refuse connections from all slaves, and the slave will refuse to
     connect to a master. Thus, omitting `server-id' is only good for
     backup with a binary log.

  6. While the slave is running, make it forget about the old
     replication configuration if it has been replicating previously:

          mysql> RESET SLAVE;

  7. Copy the snapshot data into your data directory on your slave(s).
     Make sure that the privileges on the files and directories are
     correct. The user which MySQL runs as needs to be able to read and
     write to them, just as on the master.

  8. Restart the slave(s).

  9. Once the slave comes up, execute the following command:

          mysql> CHANGE MASTER TO MASTER_HOST='<master host name>',
           MASTER_USER='<replication user name>',
           MASTER_PASSWORD='<replication password>',
           MASTER_LOG_FILE='<recorded log file name>',
           MASTER_LOG_POS=<recorded log offset>;

     replacing the values in <> with the actual values relevant to your
     system.

 10. Start the slave thread:

          mysql> SLAVE START;


After you have done the above, the slave(s) should connect to the master
and catch up on any updates which happened since the snapshot was taken.

If you have forgotten to set `server-id' for the slave you will get the
following error in the error log file:

     Warning: one should set server_id to a non-0 value if master_host is set.
     The server will not act as a slave.

If you have forgotten to do this for the master, the slaves will not be
able to connect to the master.

If a slave is not able to replicate for any reason, you will find error
messages in the error log on the slave.

Once a slave is replicating, you will find a file called `master.info'
in the same directory as your error log. The `master.info' file is used
by the slave to keep track of how much of the master's binary log it
has processed. *Do not* remove or edit the file, unless you really know
what you are doing. Even in that case, it is preferred that you use
`CHANGE MASTER TO' command.

Now that you have a snapshot, you can use it to set up other slaves. To
do so, follow the slave portion of the procedure described above. You
do not need to take another snapshot of the master.

Replication Features and Known Problems
---------------------------------------

Here is an explanation of what is supported and what is not:

   * Replication will be done correctly with `AUTO_INCREMENT',
     `LAST_INSERT_ID()', and `TIMESTAMP' values.

   * `RAND()' in updates does not replicate properly. Use
     `RAND(some_non_rand_expr)' if you are replicating updates with
     `RAND()'. You can, for example, use `UNIX_TIMESTAMP()' for the
     argument to `RAND()'.

   * You have to use the same character set (`--default-character-set')
     on the master and the slave. If not, you may get duplicate key
     errors on the slave, because a key that is regarded as unique in
     the master character set may not be unique in the slave character
     set.

   * In 3.23, `LOAD DATA INFILE' will be handled properly as long as
     the file still resides on the master server at the time of update
     propagation. `LOAD LOCAL DATA INFILE' will be skipped. In 4.0, this
     limitation is not present - all forms of `LOAD DATA INFILE' are
     properly replicated.

   * Update queries that use user variables are not replication-safe
     (yet).

   * `FLUSH' commands are not stored in the binary log and are because
     of this not replicated to the slaves. This is not normally a
     problem as `FLUSH' doesn't change anything. This does however mean
     that if you update the MySQL privilege tables directly without
     using the `GRANT' statement and you replicate the `mysql' privilege
     database, you must do a `FLUSH PRIVILEGES' on your slaves to put
     the new privileges into effect.

   * Temporary tables starting in 3.23.29 are replicated properly with
     the exception of the case when you shut down slave server ( not
     just slave thread), you have some temporary tables open, and they
     are used in subsequent updates.  To deal with this problem
     shutting down the slave, do `SLAVE STOP', check
     `Slave_open_temp_tables' variable to see if it is 0, then issue
     `mysqladmin shutdown'. If the number is not 0, restart the slave
     thread with `SLAVE START' and see if you have better luck next
     time. There will be a cleaner solution, but it has to wait until
     version 4.0.  In earlier versions temporary tables are not
     replicated properly - we recommend that you either upgrade, or
     execute `SET SQL_LOG_BIN=0' on your clients before all queries
     with temp tables.

   * MySQL only supports one master and many slaves. In 4.x, we will
     add a voting algorithm to automatically change master if something
     goes wrong with the current master. We will also introduce 'agent'
     processes to help do load balancing by sending select queries to
     different slaves.

   * Starting in Version 3.23.26, it is safe to connect servers in a
     circular master-slave relationship with `log-slave-updates'
     enabled.  Note, however, that many queries will not work right in
     this kind of setup unless your client code is written to take care
     of the potential problems that can happen from updates that occur
     in different sequence on different servers.

     This means that you can do a setup like the following:

          A -> B -> C -> A

     This setup will only works if you only do non conflicting updates
     between the tables.  In other words, if you insert data in A and
     C, you should never insert a row in A that may have a conflicting
     key with a row insert in C.  You should also not update the sam
     rows on two servers if the order in which the updates are applied
     matters.

     Note that the log format has changed in Version 3.23.26 so that
     pre-3.23.26 slaves will not be able to read it.

   * If the query on the slave gets an error, the slave thread will
     terminate, and a message will appear in the `.err' file. You should
     then connect to the slave manually, fix the cause of the error (for
     example, non-existent table), and then run the `SLAVE START' SQL
     command (available starting in Version 3.23.16). In Version
     3.23.15, you will have to restart the server.

   * If connection to the master is lost, the slave will retry
     immediately, and then in case of failure every
     `master-connect-retry' (default 60) seconds. Because of this, it
     is safe to shut down the master, and then restart it after a
     while. The slave will also be able to deal with network
     connectivity outages.

   * Shutting down the slave (cleanly) is also safe, as it keeps track
     of where it left off.  Unclean shutdowns might produce problems,
     especially if disk cache was not synced before the system died.
     Your system fault tolerance will be greatly increased if you have
     a good UPS.

   * If the master is listening on a non-standard port, you will also
     need to specify this with `master-port' parameter in `my.cnf' .

   * In Version 3.23.15, all of the tables and databases will be
     replicated. Starting in Version 3.23.16, you can restrict
     replication to a set of databases with `replicate-do-db'
     directives in `my.cnf' or just exclude a set of databases with
     `replicate-ignore-db'. Note that up until Version 3.23.23, there
     was a bug that did not properly deal with `LOAD DATA INFILE' if
     you did it in a database that was excluded from replication.

   * Starting in Version 3.23.16, `SET SQL_LOG_BIN = 0' will turn off
     replication (binary) logging on the master, and `SET SQL_LOG_BIN =
     1' will turn it back on - you must have the `SUPER' (in MySQL
     4.0.2 and above) or `PROCESS' (in older MySQL versions) privilege
     to do this.

   * Starting in Version 3.23.19, you can clean up stale replication
     leftovers when something goes wrong and you want a clean start
     with `FLUSH MASTER' and `FLUSH SLAVE' commands. In Version 3.23.26
     we have renamed them to `RESET MASTER' and `RESET SLAVE'
     respectively to clarify what they do. The old `FLUSH' variants
     still work, though, for compatibility.

   * Starting in Version 3.23.23, you can change masters and adjust log
     position with `CHANGE MASTER TO'.

   * Starting in Version 3.23.23, you tell the master that updates in
     certain databases should not be logged to the binary log with
     `binlog-ignore-db'.

   * Starting in Version 3.23.26, you can use `replicate-rewrite-db' to
     tell the slave to apply updates from one database on the master to
     the one with a different name on the slave.

   * Starting in Version 3.23.28, you can use `PURGE MASTER LOGS TO
     'log-name'' to get rid of old logs while the slave is running.
     This will remove all old logs before, but not including
     `'log-name''.

   * Due to the non-transactional nature of MyISAM tables, it is
     possible to have a query that will only partially update a table
     and return an error code. This can happen, for example, on a
     multi-row insert that has one row violating a key constraint, or
     if a long update query is killed after updating some of the rows.
     If that happens on the master, the slave thread will exit and wait
     for the DBA to decide what to do about it unless the error code is
     legitimate and the query execution results in the same error code.
     If this error code validation behaviour is not desirable, some (
     or all) errors could be masked out with `slave-skip-errors' option
     starting in Version 3.23.47.

   * While individual tables can be excluded from replication with
     `replicate-do-table'/`replicate-ignore-table' or
     `replicate-wild-do-table'/`replicate-wild-ignore-table', there are
     currently some design deficiencies that in some rather rare cases
     produce unexpected results. The replication protocol does not
     inform the slave explicitly which tables are going to be modified
     by the query - so the slave has to parse the query to know this.
     To avoid redundant parsing for queries that will end up actually
     being executed, table exclusion is currently implemented by
     sending the query to the standard MySQL parser, which will
     short-circuit the query and report success if it detects that the
     table should be ignored. In addition to several inefficiencies,
     this approach is also more bug prone, and there are two known bugs
     as of Version 3.23.49 - because the parser automatically opens the
     table when parsing some queries the ignored table has to exist on
     the slave. The other bug is that if the ignored table gets
     partially updated, the slave thread will not notice that the table
     actually should have been ignored and will suspend the replication
     process. While the above bugs are conceptually very simple to fix,
     we have not yet found a way to do this without a significant code
     change that would compromise the stability status of 3.23 branch.
     There exists a workaround for both if in the rare case it happens
     to affect your application - use `slave-skip-errors'.

Replication Options in `my.cnf'
-------------------------------

If you are using replication, we recommend that you use MySQL Version
3.23.33 or later. Older versions work, but they do have some bugs and
are missing some features. Some of the options mentioned here may not
be available in your version if it is not the most recent one. For all
options specific to the 4.0 branch, there is a note indicating so.
Otherwise, if you discover that the option you are interested in is not
available in your 3.23 version, and you really need it, please upgrade
to the most recent 3.23 branch.

Please be aware that 4.0 branch is still in alpha, so some things may
not be working as smoothly as you would like. If you really would like
to try the new features of 4.0, we recommend you do it in such a way
that in case there is a problem  your mission critical applications
will not be disrupted.

On both master and slave you need to use the `server-id' option.  This
sets a unique replication id. You should pick a unique value in the
range between 1 to 2^32-1 for each master and slave.  Example:
`server-id=3'

The following table describes the options you can use for the `MASTER':

*Option*                    *Description*
`log-bin=filename'           Write to a binary update log to the
                            specified location. Note that if you give it
                            a parameter with an extension (for example,
                            `log-bin=/mysql/logs/replication.log' )
                            versions up to 3.23.24 will not work right
                            during replication if you do `FLUSH LOGS' .
                            The problem is fixed in Version 3.23.25. If
                            you are using this kind of log name, `FLUSH
                            LOGS' will be ignored on binlog. To clear
                            the log, run `FLUSH MASTER', and do not
                            forget to run `FLUSH SLAVE' on all slaves.
                            In Versions 3.23.26 and later, you should use
                            `RESET MASTER' and `RESET SLAVE'
`log-bin-index=filename'     Because the user could issue the `FLUSH
                            LOGS' command, we need to know which log is
                            currently active and which ones have been
                            rotated out and in what sequence. This
                            information is stored in the binary log
                            index file.  The default is
                            ``hostname`.index'. You should not need to
                            change this.

                            Example: `log-bin-index=db.index'
`sql-bin-update-same'        If set, setting `SQL_LOG_BIN' to a value
                            will automatically set `SQL_LOG_UPDATE' to
                            the same value and vice versa.
`binlog-do-db=database_name' Tells the master that it should log updates
                            to the binary log if the current database is
                            `database_name'. All other databases are
                            ignored.  Note that if you use this, you
                            should ensure that you do updates only in
                            the current database.

                            Example: `binlog-do-db=sales'
`binlog-ignore-db=database_name' Tells the master that updates where the
                            current database is `database_name' should
                            not be stored in the binary log.  Note that
                            if you use this, you should ensure that you
                            do updates only in the current database.

                            Example: `binlog-ignore-db=accounting'

The following table describes the options you can use for the `SLAVE':

*Option*                    *Description*
`master-host=host'           Master hostname or IP address for
                            replication. If not set, the slave thread
                            will not be started. Note that the setting
                            of `master-host' will be ignored if there
                            exists a valid `master.info' file. Probably a
                            better name for this options would have been
                            something like `bootstrap-master-host', but
                            it is too late to change now.

                            Example:
                            `master-host=db-master.mycompany.com'
`master-user=username'       The username the slave thread will use for
                            authentication when connecting to the
                            master. The user must have the `FILE'
                            privilege. If the master user is not set,
                            user `test' is assumed. The value in
                            `master.info' will take precedence if it can
                            be read.

                            Example: `master-user=scott'
`master-password=password'   The password the slave thread will
                            authenticate with when connecting to the
                            master. If not set, an empty password is
                            assumed.The value in `master.info' will take
                            precedence if it can be read.

                            Example: `master-password=tiger'
`master-port=portnumber'     The port the master is listening on. If not
                            set, the compiled setting of `MYSQL_PORT' is
                            assumed. If you have not tinkered with
                            `configure' options, this should be 3306.
                            The value in `master.info' will take
                            precedence if it can be read.

                            Example: `master-port=3306'
`master-connect-retry=seconds' The number of seconds the slave thread will
                            sleep before retrying to connect to the
                            master in case the master goes down or the
                            connection is lost.  Default is 60.

                            Example: `master-connect-retry=60'
`master-ssl'                 Available after 4.0.0. Turn SSL on for
                            replication. Be warned that is this is a
                            relatively new feature.

                            Example: `master-ssl'
`master-ssl-key'             Available after 4.0.0. Master SSL keyfile
                            name. Only applies if you have enabled
                            `master-ssl'.

                            Example: `master-ssl-key=SSL/master-key.pem'
`master-ssl-cert'            Available after 4.0.0. Master SSL
                            certificate file name. Only applies if you
                            have enabled `master-ssl'.

                            Example: `master-ssl-key=SSL/master-cert.pem'
`master-info-file=filename'  The location of the file that remembers
                            where we left off on the master during the
                            replication process. The default is
                            `master.info' in the data directory. You
                            should not need to change this.

                            Example: `master-info-file=master.info'
`report-host'                Available after 4.0.0. Hostname or IP of
                            the slave to be reported to the master
                            during slave registration. Will appear in
                            the output of `SHOW SLAVE HOSTS'. Leave
                            unset if you do not want the slave to
                            register itself with the master. Note that
                            it is not sufficient for the master to
                            simply read the IP of the slave off the
                            socket once the slave connects. Due to `NAT'
                            and other routing issues, that IP may not be
                            valid for connecting to the slave from the
                            master or other hosts.

                            Example: `report-host=slave1.mycompany.com'
`report-port'                Available after 4.0.0. Port for connecting
                            to slave reported to the master during slave
                            registration.  Set it only if the slave is
                            listening on a non-default port or if you
                            have a special tunnel from the master or
                            other clients to the slave. If not sure,
                            leave this option unset.
`replicate-do-table=db_name.table_name' Tells the slave thread to restrict
                            replication to the specified table.  To
                            specify more than one table, use the
                            directive multiple times, once for each
                            table.  This will work for cross-database
                            updates, in contrast to `replicate-do-db'.

                            Example:
                            `replicate-do-table=some_db.some_table'
`replicate-ignore-table=db_name.table_name' Tells the slave thread to not replicate any
                            command that updates the specified table
                            (even if any other tables may be update by
                            the same command). To specify more than one
                            table to ignore, use the directive multiple
                            times, once for each table. This will work
                            for cross-datbase updates, in contrast to
                            `replicate-ignore-db'.

                            Example:
                            `replicate-ignore-table=db_name.some_table'
`replicate-wild-do-table=db_name.table_name' Tells the slave thread to restrict
                            replication to queries where any of the
                            updated tables match the specified wildcard
                            pattern.  To specify more than one table,
                            use the directive multiple times, once for
                            each table.  This will work for
                            cross-database updates.

                            Example: `replicate-wild-do-table=foo%.bar%'
                            will replicate only updates that uses a
                            table in any databases that start with `foo'
                            and whose table names start with `bar'.
`replicate-wild-ignore-table=db_name.table_name' Tells the slave thread to not replicate a
                            query where any table matches the given
                            wildcard pattern. To specify more than one
                            table to ignore, use the directive multiple
                            times, once for each table. This will work
                            for cross-database updates.

                            Example:
                            `replicate-wild-ignore-table=foo%.bar%' will
                            not do updates to tables in databases that
                            start with `foo' and whose table names start
                            with `bar'.
`replicate-ignore-db=database_name' Tells the slave thread to not replicate any
                            command where the current database is
                            `database_name'. To specify more than one
                            database to ignore, use the directive
                            multiple times, once for each database.  You
                            should not use this directive if you are
                            using cross table updates and you don't want
                            these update to be replicated.

                            The main reason for this behaviour is that
                            it's hard from the command alone know if a
                            query should be replicated or not; For
                            example if you are using multi-table-delete
                            or multi-table-update commands in MySQL 4.x
                            that goes across multiple databases.  It's
                            also very fast to just check the current
                            database, as this only has to be done once
                            at connect time or when the database changes.

                            If you need cross database updates to work,
                            make sure you have 3.23.28 or later, and use
                            `replicate-wild-ignore-table=db_name.%'.

                            Example: `replicate-ignore-db=some_db'
`replicate-do-db=database_name' Tells the slave thread to restrict
                            replication to commands where the current
                            database is `database_name'.  To specify
                            more than one database, use the directive
                            multiple times, once for each database. Note
                            that this will not replicate cross-database
                            queries such as `UPDATE some_db.some_table
                            SET foo='bar'' while having selected a
                            different or no database. If you need cross
                            database updates to work, make sure you have
                            3.23.28 or later, and use
                            `replicate-wild-do-table=db_name.%'.

                            Example: `replicate-do-db=some_db'
`log-slave-updates'          Tells the slave to log the updates from the
                            slave thread to the binary log. Off by
                            default. You will need to turn it on if you
                            plan to daisy-chain the slaves.
`replicate-rewrite-db=from_name->to_name' Updates to a database with a different name
                            than the original.

                            Example:
                            `replicate-rewrite-db=master_db_name->slave_db_name'
`slave-skip-errors=          Available only in 3.23.47 and later. Tells
[err_code1,err_code2,... |  the slave thread to continue replication
all]'                       when a query returns an error from the
                            provided list. Normally, replication will
                            discontinue when an error is encountered,
                            giving the user a chance to resolve the
                            inconsistency in the data manually. Do not
                            use this option unless you fully understand
                            why you are getting the errors.  If there
                            are no bugs in your replication setup and
                            client programs, and no bugs in MySQL
                            itself, you should never get an abort with
                            error. Indiscriminate use of this option
                            will result in slaves being hopelessly out
                            of sync with the master and you having no
                            idea how the problem happened.

                            For error codes, you should use the numbers
                            provided by the error message in your slave
                            error log and in the output of `SHOW SLAVE
                            STATUS'. Full list of error messages can be
                            found in the source distribution in
                            `Docs/mysqld_error.txt'.

                            You can (but should not) also use a very
                            non-recommended value of `all' which will
                            ignore all error messages and keep barging
                            along regardless.  Needless to say, if you
                            use it, we make no promises regarding your
                            data integrity. Please do not complain if
                            your data on the slave is not anywhere close
                            to what it is on the master in this case -
                            you have been warned.

                            Example:

                            `slave-skip-errors=1062,1053' or
                            `slave-skip-errors=all'
`skip-slave-start'           Tells the slave server not to start the
                            slave on the startup.  The user can start it
                            later with `SLAVE START'.
`slave_compressed_protocol=#' If 1, then use compression on the
                            slave/client protocol if both slave and
                            master support this.
`slave_net_timeout=#'        Number of seconds to wait for more data
                            from the master before aborting the read.

SQL Commands Related to Replication
-----------------------------------

Replication can be controlled through the SQL interface. Here is the
summary of commands:

*Command*                        *Description*
`SLAVE START'                    Starts the slave thread.  As of MySQL
                                 4.0.2, you can add `IO_THREAD' or
                                 `SQL_THREAD' options to the statement
                                 to start the I/O thread or the SQL
                                 thread.  The I/O thread reads queries
                                 from the master server and stores them
                                 in the relay log.  The SQL thread reads
                                 the relay log and executes the queries.
                                 (Slave)
`SLAVE STOP'                     Stops the slave thread. Like `SLAVE
                                 START', this statement may be used with
                                 `IO_THREAD' and `SQL_THREAD' options.
                                 (Slave)
`SET SQL_LOG_BIN=0'              Disables update logging if the user has
                                 the `SUPER' privilege.   Ignored
                                 otherwise. (Master)
`SET SQL_LOG_BIN=1'              Re-enables update logging if the user
                                 has the `SUPER' privilege.   Ignored
                                 otherwise. (Master)
`SET GLOBAL                      Skip the next `n' events from the
SQL_SLAVE_SKIP_COUNTER=n'        master. Only valid when the slave
                                 thread is not running, otherwise, gives
                                 an error. Useful for recovering from
                                 replication glitches.
`RESET MASTER'                   Deletes all binary logs listed in the
                                 index file, resetting the binlog index
                                 file to be empty. In pre-3.23.26
                                 versions, use `FLUSH MASTER'.  (Master)
`RESET SLAVE'                    Makes the slave forget its replication
                                 position in the master logs. In pre
                                 3.23.26 versions the command was called
                                 `FLUSH SLAVE'. (Slave)
`LOAD TABLE tblname FROM MASTER' Downloads a copy of the table from
                                 master to the slave. Implemented
                                 mainly for debugging of `LOAD DATA FROM
                                 MASTER', but some "gourmet"  users
                                 might find it useful for other things.
                                 Do not use it if you consider  yourself
                                 the average "non-hacker" type user.
                                 (Slave)
`LOAD DATA FROM MASTER'           Available starting in 4.0.0. Takes a
                                 snapshot of the master and copies it to
                                 the slave. Updates the values of
                                 `MASTER_LOG_FILE' and `MASTER_LOG_POS'
                                 so that the slave will start
                                 replicating from the correct position.
                                 Will honor table and database exclusion
                                 rules specified with `replicate-*'
                                 options. So far works only with
                                 `MyISAM' tables and acquires a global
                                 read lock on the master while taking
                                 the snapshot. In the future it is
                                 planned to make it work with `InnoDB'
                                 tables and to remove the need for
                                 global read lock using the non-blocking
                                 online backup feature.

                                 Note that `LOAD DATA FROM MASTER' does
                                 *NOT* copy of any tables in the `mysql'
                                 database.  This is to make it easy to
                                 have different users and privileges on
                                 the master and the slave.
`CHANGE MASTER TO                Changes the master parameters to the
master_def_list'                 values specified in `master_def_list'
                                 and restarts the slave thread.
                                 `master_def_list' is a comma-separated
                                 list of `master_def' where `master_def'
                                 is one of the following: `MASTER_HOST',
                                 `MASTER_USER', `MASTER_PASSWORD',
                                 `MASTER_PORT', `MASTER_CONNECT_RETRY',
                                 `MASTER_LOG_FILE', `MASTER_LOG_POS'.
                                 For example:

                                      CHANGE MASTER TO
                                        MASTER_HOST='master2.mycompany.com',
                                        MASTER_USER='replication',
                                        MASTER_PASSWORD='bigs3cret',
                                        MASTER_PORT=3306,
                                        MASTER_LOG_FILE='master2-bin.001',
                                        MASTER_LOG_POS=4;
                                 You only need to specify the values
                                 that need to be changed. The values that
                                 you omit will stay the same with the
                                 exception of when you change the host or
                                 the port. In that case, the slave will
                                 assume that since you are connecting to
                                 a different host or a different port,
                                 the master is different. Therefore, the
                                 old values of log and position are not
                                 applicable anymore, and will
                                 automatically be reset to an empty
                                 string and 0, respectively (the start
                                 values). Note that if you restart the
                                 slave, it will remember its last master.
                                 If this is not desirable, you should
                                 delete the `master.info' file before
                                 restarting, and the slave will read its
                                 master from `my.cnf' or the
                                 command-line.

                                 This command is useful for setting up a
                                 slave when you have the snapshot of the
                                 master and have recorded the log and
                                 the offset on the master that the
                                 snapshot corresponds to. You can run
                                 `CHANGE MASTER TO
                                 MASTER_LOG_FILE='log_name_on_master',
                                 MASTER_LOG_POS=log_offset_on_master' on
                                 the slave after restoring the snapshot.
                                 (Slave)
`SHOW MASTER STATUS'             Provides status information on the
                                 binlog of the master. (Master)
`SHOW SLAVE HOSTS'               Available after 4.0.0. Gives a listing
                                 of slaves currently registered with the
                                 master. (Master)
`SHOW SLAVE STATUS'              Provides status information on
                                 essential parameters of the slave
                                 thread. (Slave)
`SHOW MASTER LOGS'               Only available starting in Version
                                 3.23.28. Lists the binary logs on the
                                 master. You should use this command
                                 prior to `PURGE MASTER LOGS TO' to find
                                 out how far you should go. (Master)
`SHOW BINLOG EVENTS [ IN          Shows the events in the binary update
'logname' ] [ FROM pos ]  [      log. Primarily used for
LIMIT [offset,] rows ] '         testing/debugging, but can also be used
                                 by regular clients that for some reason
                                 need to read the binary log contents.
                                 (Master)
`SHOW NEW MASTER FOR SLAVE WITH   This command is used when a slave of a
MASTER_LOG_FILE='logfile' AND    possibly dead/unavailable master needs
MASTER_LOG_POS=pos AND           to be switched to replicate off another
MASTER_LOG_SEQ=log_seq AND       slave that has been replicating the
MASTER_SERVER_ID=server_id'      same master. The command will return
                                 recalculated replication coordinates
                                 (the slave's current binary log file
                                 name and position within that file).
                                 The output can be used in a subsequent
                                 `CHANGE MASTER TO' command. Normal
                                 users should never need to run this
                                 command. It is primarily reserved for
                                 internal use by the fail-safe
                                 replication code. We may later change
                                 the syntax if we find a more intuitive
                                 way to describe this operation.
`PURGE MASTER LOGS TO 'logname'' Available starting in Version 3.23.28.
                                 Deletes all the replication logs that
                                 are listed in the log index as being
                                 prior to the specified log, and removes
                                 them from the log index, so that the
                                 given log now becomes the first.
                                 Example:

                                      PURGE MASTER LOGS TO 'mysql-bin.010'
                                 This command will do nothing and fail
                                 with an error if you have an active
                                 slave that is currently reading one of
                                 the logs you are trying to delete.
                                 However, if you have a dormant slave,
                                 and happen to purge one of the logs it
                                 wants to read, the slave will be unable
                                 to replicate once it comes up.  The
                                 command is safe to run while slaves are
                                 replicating - you do not need to stop
                                 them.

                                 You must first check all the slaves
                                 with `SHOW SLAVE STATUS' to see which
                                 log they are on, then do a listing of
                                 the logs on the master with `SHOW
                                 MASTER LOGS', find the earliest log
                                 among all the slaves (if all the slaves
                                 are up to date, this will be the last
                                 log on the list), backup all the logs
                                 you are about to delete (optional) and
                                 purge up to the target log.

Replication FAQ
---------------

*Q*: How do I configure a slave if the master is already running and I
do not want to stop it?

*A*: There are several options. If you have taken a backup of the
master at some point and recorded the binlog name and offset ( from the
output of `SHOW MASTER STATUS' ) corresponding to the snapshot, do the
following:

   * Make sure unique server id is assigned to the slave.

   * Execute `CHANGE MASTER TO MASTER_HOST='master-host-name',
     MASTER_USER='master-user-name', MASTER_PASSWORD='master-pass',
     MASTER_LOG_FILE='recorded-log-name',
     MASTER_LOG_POS=recorded_log_pos'

   * Execute `SLAVE START'

If you do not have a backup of the master already, here is a quick way
to do it consistently:

   * `FLUSH TABLES WITH READ LOCK'

   * `gtar zcf /tmp/backup.tar.gz /var/lib/mysql' ( or a variation of
     this)

   * `SHOW MASTER STATUS' - make sure to record the output - you will
     need it later

   * `UNLOCK TABLES'

Afterwards, follow the instructions for the case when you have a
snapshot and have recorded the log name and offset. You can use the
same snapshot to set up several slaves. As long as the binary logs of
the master are left intact, you can wait as long as several days or in
some cases maybe a month to set up a slave once you have the snapshot
of the master. In theory the waiting gap can be infinite. The two
practical limitations is the diskspace of the master getting filled
with old logs, and the amount of time it will take the slave to catch
up.

In version 4.0.0 and newer, you can also use `LOAD DATA FROM MASTER'.
This is a convenient command that will take a snapshot, restore it to
the slave, and adjust the log name and offset on the slave all at once.
In the future, `LOAD DATA FROM MASTER' will be the recommended way to
set up a slave.  Be warned, howerver, that the read lock may be held
for a long time if you use this command. It is not yet implemented as
efficiently as we would like to have it. If you have large tables, the
preferred method at this time is still with a local `tar' snapshot
after executing `FLUSH TABLES WITH READ LOCK'.

*Q*: Does the slave need to be connected to the master all the time?

*A*: No, it does not. You can have the slave go down or stay
disconnected for hours or even days, then reconnect, catch up on the
updates, and then disconnect or go down for a while again. So you can,
for example, use master-slave setup over a dial-up link that is up only
for short periods of time. The implications of that are that at any
given time the slave is not guaranteed to be in sync with the master
unless you take some special measures. In the future, we will have the
option to block the master until at least one slave is in sync.

*Q*: How do I force the master to block updates until the slave catches
up?

*A*: Execute the following commands:

   * Master: `FLUSH TABLES WITH READ LOCK'

   * Master: `SHOW MASTER STATUS' - record the log name and the offset

   * Slave: `SELECT MASTER_POS_WAIT('recorded_log_name',
     recorded_log_offset)' When the select returns, the slave is
     currently in sync with the master

   * Master: `UNLOCK TABLES' - now the master will continue updates.

*Q*: Why do I sometimes see more than one `Binlog_Dump' thread on the
master after I have restarted the slave?

*A*: `Binlog_Dump' is a continuous process that is handled by the
server in the following way:

   * Catch up on the updates.

   * Once there are no more updates left, go into `pthread_cond_wait()',
     from which we can be awakened either by an update or a kill.

   * On wake up, check the reason. If we are not supposed to die,
     continue the `Binlog_dump' loop.

   * If there is some fatal error, such as detecting a dead client,
     terminate the loop.

So if the slave thread stops on the slave, the corresponding
`Binlog_Dump' thread on the master will not notice it until after at
least one update to the master (or a kill), which is needed to wake it
up from `pthread_cond_wait()'.  In the meantime, the slave could have
opened another connection, which resulted in another `Binlog_Dump'
thread.

The above problem should not be present in Version 3.23.26 and later
versions.  In Version 3.23.26 we added `server-id' to each replication
server, and now all the old zombie threads are killed on the master
when a new replication thread connects from the same slave

*Q*: How do I rotate replication logs?

*A*: In Version 3.23.28 you should use `PURGE MASTER LOGS TO' command
after determining which logs can be deleted, and optionally backing
them up first. In earlier versions the process is much more painful,
and cannot be safely done without stopping all the slaves in the case
that you plan to re-use log names. You will need to stop the slave
threads, edit the binary log index file, delete all the old logs,
restart the master, start slave threads, and then remove the old log
files.

*Q*: How do I upgrade on a hot replication setup?

*A*: If you are upgrading  pre-3.23.26 versions, you should just lock
the master tables, let the slave catch up, then run `FLUSH MASTER' on
the master, and `FLUSH SLAVE' on the slave to reset the logs, then
restart new versions of the master and the slave. Note that the slave
can stay down for some time - since the master is logging all the
updates, the slave will be able to catch up once it is up and can
connect.

After 3.23.26, we have locked the replication protocol for
modifications, so you can upgrade masters and slave on the fly to a
newer 3.23 version and you can have different versions of MySQL running
on the slave and the master, as long as they are both newer than
3.23.26.

*Q*: What issues should I be aware of when setting up two-way
replication?

*A*: MySQL replication currently does not support any locking protocol
between master and slave to guarantee the atomicity of a distributed
(cross-server) update. In other words, it is possible for client A to
make an update to  co-master 1, and in the meantime, before it
propagates to co-master 2, client B could make an update to co-master 2
that will make the update of client A work differently than it did on
co-master 1. Thus when the update of client A will make it to co-master
2, it will produce  tables that will be different from what you have on
co-master 1, even after all the updates from co-master 2 have also
propagated. So you should not co-chain two servers in a two-way
replication relationship, unless you are sure that you updates can
safely happen in any order, or unless you take care of mis-ordered
updates somehow in the client code.

You must also realise that two-way replication actually does not improve
performance very much, if at all, as far as updates are concerned. Both
servers need to do the same amount of updates each, as you would have
one server do. The only difference is that there will be a little less
lock contention, because the updates originating on another server will
be serialised in one slave thread. This benefit, though, might be
offset by network delays.

*Q*: How can I use replication to improve performance of my system?

*A*: You should set up one server as the master, and direct all writes
to it, and configure as many slaves as you have the money and rackspace
for, distributing the reads among the master and the slaves.  You can
also start the slaves with `--skip-bdb', `--low-priority-updates' and
`--delay-key-write=ALL' to get speed improvements for the slave.  In
this case the slave will use non-transactional `MyISAM' tables instead
of `BDB' tables to get more speed.

*Q*: What should I do to prepare my client code to use
performance-enhancing replication?

*A*: If the part of your code that is responsible for database access
has been properly abstracted/modularised, converting it to run with the
replicated setup should be very smooth and easy - just change the
implementation of your database access to read from some slave or the
master, and to always write to the master. If your code does not have
this level of abstraction, setting up a replicated system will give you
an opportunity/motivation to it clean up.   You should start by
creating a wrapper library /module with the following functions:

   * `safe_writer_connect()'

   * `safe_reader_connect()'

   * `safe_reader_query()'

   * `safe_writer_query()'

`safe_' means that the function will take care of handling all the
error conditions.

You should then convert your client code to use the wrapper library.
It may be a painful and scary process at first, but it will pay off in
the long run. All applications that follow the above pattern will be
able to take advantage of one-master/many slaves solution.  The code
will be a lot easier to maintain, and adding troubleshooting options
will be trivial. You will just need to modify one or two functions, for
example, to log how long each query took, or which query, among your
many thousands, gave you an error. If you have written a lot of code
already, you may want to automate the conversion task by using Monty's
`replace' utility, which comes with the standard distribution of MySQL,
or just write your own Perl script.  Hopefully, your code follows some
recognisable pattern. If not, then you are probably better off
rewriting it anyway, or at least going through and manually beating it
into a pattern.

Note that, of course, you can use different names for the functions.
What is important is having unified interface for connecting for reads,
connecting for writes, doing a read, and doing a write.

*Q*: When and how much can MySQL replication improve the performance of
my system?

*A*: MySQL replication is most beneficial for a system with frequent
reads and not so frequent writes. In theory, by using a one master/many
slaves setup you can scale by adding more slaves until you either run
out of network bandwidth, or your update load grows to the point that
the master cannot handle it.

In order to determine how many slaves you can get before the added
benefits begin to level out, and how much you can improve performance
of your site, you need to know your query patterns, and empirically
(by benchmarking) determine the relationship between the throughput on
reads (reads per second, or `max_reads') and on writes `max_writes') on
a typical master and a typical slave. The example here will show you a
rather simplified calculation of what you can get with replication for
our imagined system.

Let's say our system load consists of 10% writes and 90% reads, and we
have determined that `max_reads' = 1200 - 2 * `max_writes', or in other
words, our system can do 1200 reads per second with no writes, our
average write is twice as slow as average read, and the relationship is
linear. Let us suppose that our master and slave are of the same
capacity, and we have N slaves and 1 master. Then we have for each
server (master or slave):

`reads = 1200 - 2 * writes' (from bencmarks)

`reads = 9* writes / (N + 1) ' (reads split, but writes go to all
servers)

`9*writes/(N+1) + 2 * writes = 1200'

`writes = 1200/(2 + 9/(N+1)'

So if N = 0, which means we have no replication, our system can handle
1200/11, about 109 writes per second (which means we will have 9 times
as many reads due to the nature of our application).

If N = 1, we can get up to 184 writes per second.

If N = 8, we get up to 400.

If N = 17, 480 writes.

Eventually as N approaches infinity (and our budget negative infinity),
we can get very close to 600 writes per second, increasing system
throughput about 5.5 times. However, with only 8 servers, we increased
it almost 4 times already.

Note that our computations assumed infinite network bandwidth, and
neglected several other factors that could turn out to be significant on
your system. In many cases, you may not be able to make a computation
similar to the one above that will accurately predict what will happen
on your system if you add N replication slaves. However, answering the
following questions should help you decided whether and how much, if at
all, the replication will improve the performance of your system:

   * What is the read/write ratio on your system?

   * How much more write load can one server handle if you reduce the
     reads?

   * How many slaves do you have bandwidth for on your network?

*Q*: How can I use replication to provide redundancy/high availability?

*A*: With the currently available features, you would have to set up a
master and a slave (or several slaves), and write a script that will
monitor the master to see if it is up, and instruct your applications
and the slaves of the master change in case of failure. Some
suggestions:

   * To tell a slave to change the master use the `CHANGE MASTER TO'
     command.

   * A good way to keep your applications informed as to the location
     of the master is by having a dynamic DNS entry for the master.
     With `bind' you can use `nsupdate' to dynamically update your DNS.

   * You should run your slaves with the `log-bin' option and without
     `log-slave-updates'. This way the slave will be ready to become a
     master as soon as you issue `STOP SLAVE'; `RESET MASTER', and
     `CHANGE MASTER TO' on the other slaves. It will also help you catch
     spurious updates that may happen because of misconfiguration of the
     slave (ideally, you want to configure access rights so that no
     client can update the slave, except for the slave thread) combined
     with the bugs in your client programs (they should never update
     the slave directly).


We are currently working on integrating an automatic master election
system into MySQL, but until it is ready, you will have to create your
own monitoring tools.

Troubleshooting Replication
---------------------------

If you have followed the instructions, and your replication setup is not
working, first eliminate the user error factor by checking the
following:

   * Is the master logging to the binary log? Check with `SHOW MASTER
     STATUS'.  If it is, `Position' will be non-zero. If not, verify
     that you have given the master `log-bin' option and have set
     `server-id'.

   * Is the slave running? Check with `SHOW SLAVE STATUS'. The answer
     is found in `Slave_running' column. If not, verify slave options
     and check the error log for messages.

   * If the slave is running, did it establish connection with the
     master? Do `SHOW PROCESSLIST', find the thread with `system user'
     value in `User' column and `none' in the `Host' column, and check
     the `State' column. If it says `connecting to master', verify the
     privileges for the replication user on the master, master host
     name, your DNS setup, whether the master is actually running,
     whether it is reachable from the slave, and if all that seems
     okay, read the error logs.

   * If the slave was running, but then stopped, look at SHOW SLAVE
     STATUS output and check the error logs. It usually happens when
     some query that succeeded on the master fails on the slave. This
     should never happen if you have taken a proper snapshot of the
     master, and never modify the data on the slave outside of the
     slave thread. If it does, it is a bug, read below on how to report
     it.

   * If a query on that succeeded on the master refuses to run on the
     slave, and a full database resync ( the proper thing to do ) does
     not seem feasible, try the following:
        - First see if there is some stray record in the way.
          Understand how it got there, then delete it and run `SLAVE
          START'

        - If the above does not work or does not apply, try to
          understand if it would be safe to make the update manually (
          if needed) and then ignore the next query from the master.

        - If you have decided you can skip the next query, do `SET
          GLOBAL SQL_SLAVE_SKIP_COUNTER=1; SLAVE START;' to skip a
          query that does not use `AUTO_INCREMENT' or
          `LAST_INSERT_ID()',  or `SET GLOBAL SQL_SLAVE_SKIP_COUNTER=2;
          SLAVE START;' otherwise. The reason queries that use
          `AUTO_INCREMENT' or `LAST_INSERT_ID()' are different is that
          they take two events in the binary log of the master.

        - If you are sure the slave started out perfectly in sync with
          the master, and no one has updated  the tables involved
          outside of slave thread, report the bug, so you will not have
          to do the above tricks again.

   * Make sure you are not running into an old bug by upgrading to the
     most recent version.

   * If all else fails, read the error logs. If they are big, `grep -i
     slave /path/to/your-log.err' on the slave. There is no generic
     pattern to search for on the master, as the only errors it logs
     are general system errors - if it can, it will send the error to
     the slave when things go wrong.

When you have determined that there is no user error involved, and
replication still either does not work at all or is unstable, it is
time to start working on a bug report. We need to get as much info as
possible from you to be able to track down the bug. Please do spend
some time and effort preparing a good bug report. Ideally, we would
like to have a test case in the format found in `mysql-test/t/rpl*'
directory of the source tree. If you submit a test case like that, you
can expect a patch within a day or two in most cases, although, of
course, you mileage may vary depending on a number of factors.

The second best option is to write a simple program with easily
configurable connection arguments for the master and the slave that
will demonstrate the problem on our systems. You can write one in Perl
or in C, depending on which language you know better.

If you have one of the above ways to demonstrate the bug, use
`mysqlbug' to prepare a bug report and send it to
<[e-mail]>. If you have a phantom - a problem that does
occur but you cannot duplicate "at will":

   * Verify that there is no user error involved. For example, if you
     update the slave outside of the slave thread, the data will be out
     of sync, and you can have unique key violations on updates, in
     which case the slave thread will stop and wait for you to clean up
     the tables manually to bring them in sync.

   * Run slave with `log-slave-updates' and `log-bin' - this will keep
     a log of all updates on the slave.

   * Save all evidence before resetting the replication. If we have no
     or only sketchy information, it would take us a while to track
     down the problem. The evidence you should collect is:
        - All binary logs on the master

        - All binary log on the slave

        - The output of `SHOW MASTER STATUS' on the master at the time
          you have discovered the problem

        - The output of `SHOW SLAVE STATUS' on the master at the time
          you have discovered the problem

        - Error logs on the master and on the slave

   * Use `mysqlbinlog' to examine the binary logs. The following should
     be helpful to find the trouble query, for example:
          mysqlbinlog -j pos_from_slave_status /path/to/log_from_slave_status | head

Once you have collected the evidence on the phantom problem, try hard to
isolate it into a separate test case first. Then report the problem to
<[e-mail]> with as much info as possible.

MySQL Optimisation
******************

Optimisation is a complicated task because it ultimately requires
understanding of the whole system. While it may be possible to do some
local optimisations with small knowledge of your system or application,
the more optimal you want your system to become the more you will have
to know about it.

This chapter will try to explain and give some examples of different
ways to optimise MySQL.  Remember, however, that there are always some
(increasingly harder) additional ways to make the system even faster.

Optimisation Overview
=====================

The most important part for getting a system fast is of course the basic
design. You also need to know what kinds of things your system will be
doing, and what your bottlenecks are.

The most common bottlenecks are:
   * Disk seeks.  It takes time for the disk to find a piece of data.
     With modern disks in 1999, the mean time for this is usually lower
     than 10ms, so we can in theory do about 100 seeks a second. This
     time improves slowly with new disks and is very hard to optimise
     for a single table. The way to optimise this is to spread the data
     on more than one disk.

   * Disk reading/writing.  When the disk is at the correct position we
     need to read the data. With modern disks in 1999, one disk
     delivers something like 10-20MB/s. This is easier to optimise than
     seeks because you can read in parallel from multiple disks.

   * CPU cycles.  When we have the data in main memory (or if it
     already were there) we need to process it to get to our result.
     Having small tables compared to the memory is the most common
     limiting factor. But then, with small tables speed is usually not
     the problem.

   * Memory bandwidth.  When the CPU needs more data than can fit in
     the CPU cache the main memory bandwidth becomes a bottleneck. This
     is an uncommon bottleneck for most systems, but one should be
     aware of it.

MySQL Design Limitations/Tradeoffs
----------------------------------

When using the MyISAM storage engine, MySQL uses extremely fast table
locking (multiple readers / single writers). The biggest problem with
this table type is a if you have a mix of a steady stream of updates and
slow selects on the same table.  If this is a problem with some tables,
you can use another table type for these. *Note Table types::.

MySQL can work with both transactional and not transactional tables.  To
be able to work smoothly with not transactional tables (which can't
rollback if something goes wrong), MySQL has the following rules:

   * All columns has default values.

   * If you insert a 'wrong' value in a column like a `NULL' in a `NOT
     NULL' column or a too big numerical value in a numerical column,
     MySQL will instead of giving an error instead set the column to
     the 'best possible value'.  For numerical values this is 0, the
     smallest possible values or the largest possible value. For
     strings this is either the empty string or the longest possible
     string that can be in the column.

   * All calculated expressions returns a value that can be used
     instead of signaling an error condition. For example 1/0 returns
     `NULL'

The reason for the above rules is that we can't check these conditions
before the query starts to execute.  If we encounter a problem after
updating a few rows, we can't just rollback as the table type may not
support this.  We can't stop because in that case the update would be
'half done' which is probably the worst possible scenario.  In this case
it's better to 'do the best you can' and then continue as if nothing
happened.

The above means that one should not use MySQL to check fields content,
but one should do this in the application.

Portability
-----------

Because all SQL servers implement different parts of SQL, it takes work
to write portable SQL applications. For very simple selects/inserts it
is very easy, but the more you need the harder it gets. If you want an
application that is fast with many databases it becomes even harder!

To make a complex application portable you need to choose a number of
SQL servers that it should work with.

You can use the MySQL `crash-me' program/web-page
`http://www.mysql.com/information/crash-me.php' to find functions,
types, and limits you can use with a selection of database servers.
Crash-me now tests far from everything possible, but it is still
comprehensive with about 450 things tested.

For example, you shouldn't have column names longer than 18 characters
if you want to be able to use Informix or DB2.

Both the MySQL benchmarks and `crash-me' programs are very
database-independent.  By taking a look at how we have handled this, you
can get a feeling for what you have to do to write your application
database-independent.  The benchmarks themselves can be found in the
`sql-bench' directory in the MySQL source distribution. They are
written in Perl with DBI database interface (which solves the access
part of the problem).

See `http://www.mysql.com/information/benchmarks.html' for the results
from this benchmark.

As you can see in these results, all databases have some weak points.
That is, they have different design compromises that lead to different
behaviour.

If you strive for database independence, you need to get a good feeling
for each SQL server's bottlenecks. MySQL is very fast in retrieving and
updating things, but will have a problem in mixing slow readers/writers
on the same table. Oracle, on the other hand, has a big problem when
you try to access rows that you have recently updated (until they are
flushed to disk). Transaction databases in general are not very good at
generating summary tables from log tables, as in this case row locking
is almost useless.

To get your application _really_ database-independent, you need to
define an easy extendable interface through which you manipulate your
data. As C++ is available on most systems, it makes sense to use a C++
classes interface to the databases.

If you use some specific feature for some database (like the `REPLACE'
command in MySQL), you should code a method for the other SQL servers
to implement the same feature (but slower).  With MySQL you can use the
`/*!  */' syntax to add MySQL-specific keywords to a query.  The code
inside `/**/' will be treated as a comment (ignored) by most other SQL
servers.

If high performance is more important than exactness, as in some web
applications, it is possibile to create an application layer that
caches all results to give you even higher performance. By letting old
results 'expire' after a while, you can keep the cache reasonably
fresh.  This provides a method to handle high load spikes, in which case
you can dynamically increase the cache and set the expire timeout higher
until things get back to normal.

In this case the table creation information should contain information
of the initial size of the cache and how often the table should normally
be refreshed.

What Have We Used MySQL For?
----------------------------

During MySQL initial development, the features of MySQL were made to
fit our largest customer. They handle data warehousing for a couple of
the biggest retailers in Sweden.

From all stores, we get weekly summaries of all bonus card transactions,
and we are expected to provide useful information for the store owners
to help them find how their advertisement campaigns are affecting their
customers.

The data is quite huge (about 7 million summary transactions per month),
and we have data for 4-10 years that we need to present to the users.
We got weekly requests from the customers that they want to get
'instant' access to new reports from this data.

We solved this by storing all information per month in compressed
'transaction' tables. We have a set of simple macros (script) that
generates summary tables grouped by different criteria (product group,
customer id, store ...) from the transaction tables.  The reports are
web pages that are dynamically generated by a small Perl script that
parses a web page, executes the SQL statements in it, and inserts the
results. We would have used PHP or mod_perl instead but they were not
available at that time.

For graphical data we wrote a simple tool in `C' that can produce GIFs
based on the result of a SQL query (with some processing of the
result). This is also dynamically executed from the Perl script that
parses the `HTML' files.

In most cases a new report can simply be done by copying an existing
script and modifying the SQL query in it.  In some cases, we will need
to add more fields to an existing summary table or generate a new one,
but this is also quite simple, as we keep all transactions tables on
disk.  (Currently we have at least 50G of transactions tables and 200G
of other customer data.)

We also let our customers access the summary tables directly with ODBC
so that the advanced users can themselves experiment with the data.

We haven't had any problems handling this with quite modest Sun Ultra
SPARCstation (2x200 Mhz). We recently upgraded one of our servers to a 2
CPU 400 Mhz UltraSPARC, and we are now planning to start handling
transactions on the product level, which would mean a ten-fold increase
of data. We think we can keep up with this by just adding more disk to
our systems.

We are also experimenting with Intel-Linux to be able to get more CPU
power cheaper. Now that we have the binary portable database format (new
in Version 3.23), we will start to use this for some parts of the
application.

Our initial feelings are that Linux will perform much better on
low-to-medium load and Solaris will perform better when you start to
get a high load because of extreme disk IO, but we don't yet have
anything conclusive about this. After some discussion with a Linux
Kernel developer, this might be a side effect of Linux giving so much
resources to the batch job that the interactive performance gets very
low. This makes the machine feel very slow and unresponsive while big
batches are going. Hopefully this will be better handled in future
Linux Kernels.

The MySQL Benchmark Suite
-------------------------

This should contain a technical description of the MySQL benchmark
suite (and `crash-me'), but that description is not written yet.
Currently, you can get a good idea of the benchmark by looking at the
code and results in the `sql-bench' directory in any MySQL source
distributions.

This benchmark suite is meant to be a benchmark that will tell any user
what things a given SQL implementation performs well or poorly at.

Note that this benchmark is single threaded, so it measures the minimum
time for the operations. We plan to in the future add a lot of
multi-threaded tests to the benchmark suite.

For example, (run on the same NT 4.0 machine):

*Reading 2000000 rows by  *Seconds**Seconds*
index*
mysql                     367     249
mysql_odbc                464
db2_odbc                  1206
informix_odbc             121126
ms-sql_odbc               1634
oracle_odbc               20800
solid_odbc                877
sybase_odbc               17614

*Inserting (350768)       *Seconds**Seconds*
rows*
mysql                     381     206
mysql_odbc                619
db2_odbc                  3460
informix_odbc             2692
ms-sql_odbc               4012
oracle_odbc               11291
solid_odbc                1801
sybase_odbc               4802

In the above test MySQL was run with a 8M index cache.

We have gathered some more benchmark results at
`http://www.mysql.com/information/benchmarks.html'.

Note that Oracle is not included because they asked to be removed. All
Oracle benchmarks have to be passed by Oracle! We believe that makes
Oracle benchmarks *very* biased because the above benchmarks are
supposed to show what a standard installation can do for a single
client.

To run the benchmark suite, you have to download a MySQL source
distribution, install the perl DBI driver, the perl DBD driver for the
database you want to test and then do:

     cd sql-bench
     perl run-all-tests --server=#

where # is one of supported servers. You can get a list of all options
and supported servers by doing `run-all-tests --help'.

`crash-me' tries to determine what features a database supports and
what its capabilities and limitations are by actually running queries.
For example, it determines:

   * What column types are supported

   * How many indexes are supported

   * What functions are supported

   * How big a query can be

   * How big a `VARCHAR' column can be

We can find the result from `crash-me' on a lot of different databases
at `http://www.mysql.com/information/crash-me.php'.

Using Your Own Benchmarks
-------------------------

You should definitely benchmark your application and database to find
out where the bottlenecks are.  By fixing it (or by replacing the
bottleneck with a 'dummy module') you can then easily identify the next
bottleneck (and so on).  Even if the overall performance for your
application is sufficient, you should at least make a plan for each
bottleneck, and decide how to solve it if someday you really need the
extra performance.

For an example of portable benchmark programs, look at the MySQL
benchmark suite. *Note MySQL Benchmarks: MySQL Benchmarks. You can take
any program from this suite and modify it for your needs. By doing
this, you can try different solutions to your problem and test which is
really the fastest solution for you.

It is very common that some problems only occur when the system is very
heavily loaded. We have had many customers who contact us when they
have a (tested) system in production and have encountered load
problems. In every one of these cases so far, it has been problems with
basic design (table scans are *not good* at high load) or OS/Library
issues. Most of this would be a *lot* easier to fix if the systems were
not already in production.

To avoid problems like this, you should put some effort into
benchmarking your whole application under the worst possible load!  You
can use Super Smack for this, and it is available at:
`http://www.mysql.com/Downloads/super-smack/super-smack-1.0.tar.gz'.
As the name suggests, it can bring your system down to its knees if you
ask it, so make sure to use it only on your development systems.

Optimising `SELECT's and Other Queries
======================================

First, one thing that affects all queries: The more complex permission
system setup you have, the more overhead you get.

If you do not have any `GRANT' statements done, MySQL will optimise the
permission checking somewhat. So if you have a very high volume it may
be worth the time to avoid grants. Otherwise, more permission check
results in a larger overhead.

If your problem is with some explicit MySQL function, you can always
time this in the MySQL client:

     mysql> SELECT BENCHMARK(1000000,1+1);
     +------------------------+
     | BENCHMARK(1000000,1+1) |
     +------------------------+
     |                      0 |
     +------------------------+
     1 row in set (0.32 sec)

The above shows that MySQL can execute 1,000,000 `+' expressions in
0.32 seconds on a `PentiumII 400MHz'.

All MySQL functions should be very optimised, but there may be some
exceptions, and the `BENCHMARK(loop_count,expression)' is a great tool
to find out if this is a problem with your query.

`EXPLAIN' Syntax (Get Information About a `SELECT')
---------------------------------------------------

         EXPLAIN tbl_name
     or  EXPLAIN SELECT select_options

`EXPLAIN tbl_name' is a synonym for `DESCRIBE tbl_name' or `SHOW
COLUMNS FROM tbl_name'.

When you precede a `SELECT' statement with the keyword `EXPLAIN', MySQL
explains how it would process the `SELECT', providing information about
how tables are joined and in which order.

With the help of `EXPLAIN', you can see when you must add indexes to
tables to get a faster `SELECT' that uses indexes to find the records.

You should frequently run `ANALYZE TABLE' to update table statistics
such as cardinality of keys which can affect the choices the optimiser
makes. *Note ANALYZE TABLE::.

You can also see if the optimiser joins the tables in an optimal order.
To force the optimiser to use a specific join order for a `SELECT'
statement, add a `STRAIGHT_JOIN' clause.

For non-simple joins, `EXPLAIN' returns a row of information for each
table used in the `SELECT' statement. The tables are listed in the order
they would be read.  MySQL resolves all joins using a single-sweep
multi-join method. This means that MySQL reads a row from the first
table, then finds a matching row in the second table, then in the third
table and so on. When all tables are processed, it outputs the selected
columns and backtracks through the table list until a table is found
for which there are more matching rows. The next row is read from this
table and the process continues with the next table.

In MySQL version 4.1 the `EXPLAIN' output was changed to work better
with constructs like `UNION's, subqueries and derived tables. Most
notable is the addition of two new columns: `id' and `select_type'.

Output from `EXPLAIN' consists of the following columns:

`id'
     `SELECT' identifier, the sequential number of this `SELECT' within
     the query.

`select_type'
     Type of `SELECT' clause, which can be any of the following:

    `SIMPLE'
          Simple `SELECT' (without `UNION's or subqueries).

    `PRIMARY'
          Outermost `SELECT'.

    `UNION'
          Second and further `UNION' `SELECT's.

    `DEPENDENT UNION'
          Second and further `UNION' `SELECTS's, dependent on outer
          subquery.

    `SUBSELECT'
          First `SELECT' in subquery.

    `DEPENDENT SUBSELECT'
          First `SELECT', dependent on outer subquery.

    `DERIVED'
          Derived table `SELECT'.

`table'
     The table to which the row of output refers.

`type'
     The join type. The different join types are listed here, ordered
     from best to worst type:

    `system'
          The table has only one row (= system table). This is a
          special case of the `const' join type.

    `const'
          The table has at most one matching row, which will be read at
          the start of the query. Because there is only one row, values
          from the column in this row can be regarded as constants by
          the rest of the optimiser. `const' tables are very fast as
          they are read only once!

    `eq_ref'
          One row will be read from this table for each combination of
          rows from the previous tables.  This is the best possible
          join type, other than the `const' types.  It is used when all
          parts of an index are used by the join and the index is
          `UNIQUE' or a `PRIMARY KEY'.

    `ref'
          All rows with matching index values will be read from this
          table for each combination of rows from the previous tables.
          `ref' is used if the join uses only a leftmost prefix of the
          key, or if the key is not `UNIQUE' or a `PRIMARY KEY' (in
          other words, if the join cannot select a single row based on
          the key value).  If the key that is used matches only a few
          rows, this join type is good.

    `range'
          Only rows that are in a given range will be retrieved, using
          an index to select the rows.  The `key' column indicates
          which index is used.  The `key_len' contains the longest key
          part that was used.  The `ref' column will be `NULL' for this
          type.

    `index'
          This is the same as `ALL', except that only the index tree is
          scanned.  This is usually faster than `ALL', as the index
          file is usually smaller than the datafile.

    `ALL'
          A full table scan will be done for each combination of rows
          from the previous tables.  This is normally not good if the
          table is the first table not marked `const', and usually
          *very* bad in all other cases. You normally can avoid `ALL'
          by adding more indexes, so that the row can be retrieved
          based on constant values or column values from earlier tables.

`possible_keys'
     The `possible_keys' column indicates which indexes MySQL could use
     to find the rows in this table. Note that this column is totally
     independent of the order of the tables. That means that some of
     the keys in possible_keys may not be usable in practice with the
     generated table order.

     If this column is empty, there are no relevant indexes. In this
     case, you may be able to improve the performance of your query by
     examining the `WHERE' clause to see if it refers to some column or
     columns that would be suitable for indexing.  If so, create an
     appropriate index and check the query with `EXPLAIN' again. *Note
     ALTER TABLE::.

     To see what indexes a table has, use `SHOW INDEX FROM tbl_name'.

`key'
     The `key' column indicates the key (index) that MySQL actually
     decided to use. The key is `NULL' if no index was chosen. To force
     MySQL to use an key listed in the `possible_keys' column, use `USE
     KEY/IGNORE KEY' in your query.  *Note SELECT::.

     Also, running `myisamchk --analyze' (*note myisamchk syntax::) or
     `ANALYZE TABLE' (*note ANALYZE TABLE::) on the table will help the
     optimiser choose better indexes.

`key_len'
     The `key_len' column indicates the length of the key that MySQL
     decided to use.  The length is `NULL' if the `key' is `NULL'. Note
     that this tells us how many parts of a multi-part key MySQL will
     actually use.

`ref'
     The `ref' column shows which columns or constants are used with the
     `key' to select rows from the table.

`rows'
     The `rows' column indicates the number of rows MySQL believes it
     must examine to execute the query.

`Extra'
     This column contains additional information of how MySQL will
     resolve the query. Here is an explanation of the different text
     strings that can be found in this column:

    `Distinct'
          MySQL will not continue searching for more rows for the
          current row combination after it has found the first matching
          row.

    `Not exists'
          MySQL was able to do a `LEFT JOIN' optimisation on the query
          and will not examine more rows in this table for the previous
          row combination after it finds one row that matches the `LEFT
          JOIN' criteria.

          Here is an example for this:

               SELECT * FROM t1 LEFT JOIN t2 ON t1.id=t2.id WHERE t2.id IS NULL;

          Assume that `t2.id' is defined with `NOT NULL'.  In this case
          MySQL will scan `t1' and look up the rows in `t2' through
          `t1.id'. If MySQL finds a matching row in `t2', it knows that
          `t2.id' can never be `NULL', and will not scan through the
          rest of the rows in `t2' that has the same `id'.  In other
          words, for each row in `t1', MySQL only needs to do a single
          lookup in `t2', independent of how many matching rows there
          are in `t2'.

    ``range checked for each record (index map: #)''
          MySQL didn't find a real good index to use. It will, instead,
          for each row combination in the preceding tables, do a check
          on which index to use (if any), and use this index to
          retrieve the rows from the table.  This isn't very fast but
          is faster than having to do a join without an index.

    `Using filesort'
          MySQL will need to do an extra pass to find out how to
          retrieve the rows in sorted order.  The sort is done by going
          through all rows according to the `join type' and storing the
          sort key + pointer to the row for all rows that match the
          `WHERE'. Then the keys are sorted. Finally the rows are
          retrieved in sorted order.

    `Using index'
          The column information is retrieved from the table using only
          information in the index tree without having to do an
          additional seek to read the actual row.  This can be done
          when all the used columns for the table are part of the same
          index.

    `Using temporary'
          To resolve the query MySQL will need to create a temporary
          table to hold the result.  This typically happens if you do an
          `ORDER BY' on a different column set than you did a `GROUP
          BY' on.

    `Using where'
          A `WHERE' clause will be used to restrict which rows will be
          matched against the next table or sent to the client.  If you
          don't have this information and the table is of type `ALL' or
          `index', you may have something wrong in your query (if you
          don't intend to fetch/examine all rows from the table).

     If you want to get your queries as fast as possible, you should
     look out for `Using filesort' and `Using temporary'.

You can get a good indication of how good a join is by multiplying all
values in the `rows' column of the `EXPLAIN' output. This should tell
you roughly how many rows MySQL must examine to execute the query. This
number is also used when you restrict queries with the `max_join_size'
variable.  *Note Server parameters::.

The following example shows how a `JOIN' can be optimised progressively
using the information provided by `EXPLAIN'.

Suppose you have the `SELECT' statement shown here, that you examine
using `EXPLAIN':

     EXPLAIN SELECT tt.TicketNumber, tt.TimeIn,
                 tt.ProjectReference, tt.EstimatedShipDate,
                 tt.ActualShipDate, tt.ClientID,
                 tt.ServiceCodes, tt.RepetitiveID,
                 tt.CurrentProcess, tt.CurrentDPPerson,
                 tt.RecordVolume, tt.DPPrinted, et.COUNTRY,
                 et_1.COUNTRY, do.CUSTNAME
             FROM tt, et, et AS et_1, do
             WHERE tt.SubmitTime IS NULL
                 AND tt.ActualPC = et.EMPLOYID
                 AND tt.AssignedPC = et_1.EMPLOYID
                 AND tt.ClientID = do.CUSTNMBR;

For this example, assume that:

   * The columns being compared have been declared as follows:

     *Table* *Column*   *Column
                        type*
     `tt'    `ActualPC' `CHAR(10)'
     `tt'    `AssignedPC'`CHAR(10)'
     `tt'    `ClientID' `CHAR(10)'
     `et'    `EMPLOYID' `CHAR(15)'
     `do'    `CUSTNMBR' `CHAR(15)'

   * The tables have the indexes shown here:

     *Table* *Index*
     `tt'    `ActualPC'
     `tt'    `AssignedPC'
     `tt'    `ClientID'
     `et'    `EMPLOYID' (primary
             key)
     `do'    `CUSTNMBR' (primary
             key)

   * The `tt.ActualPC' values aren't evenly distributed.

Initially, before any optimisations have been performed, the `EXPLAIN'
statement produces the following information:

     table type possible_keys                key  key_len ref  rows  Extra
     et    ALL  PRIMARY                      NULL NULL    NULL 74
     do    ALL  PRIMARY                      NULL NULL    NULL 2135
     et_1  ALL  PRIMARY                      NULL NULL    NULL 74
     tt    ALL  AssignedPC,ClientID,ActualPC NULL NULL    NULL 3872
           range checked for each record (key map: 35)

Because `type' is `ALL' for each table, this output indicates that
MySQL is doing a full join for all tables!  This will take quite a long
time, as the product of the number of rows in each table must be
examined!  For the case at hand, this is `74 * 2135 * 74 * 3872 =
45,268,558,720' rows.  If the tables were bigger, you can only imagine
how long it would take.

One problem here is that MySQL can't (yet) use indexes on columns
efficiently if they are declared differently.  In this context,
`VARCHAR' and `CHAR' are the same unless they are declared as different
lengths. Because `tt.ActualPC' is declared as `CHAR(10)' and
`et.EMPLOYID' is declared as `CHAR(15)', there is a length mismatch.

To fix this disparity between column lengths, use `ALTER TABLE' to
lengthen `ActualPC' from 10 characters to 15 characters:

     mysql> ALTER TABLE tt MODIFY ActualPC VARCHAR(15);

Now `tt.ActualPC' and `et.EMPLOYID' are both `VARCHAR(15)'.  Executing
the `EXPLAIN' statement again produces this result:

     table type   possible_keys   key     key_len ref         rows    Extra
     tt    ALL    AssignedPC,ClientID,ActualPC NULL NULL NULL 3872    Using where
     do    ALL    PRIMARY         NULL    NULL    NULL        2135
           range checked for each record (key map: 1)
     et_1  ALL    PRIMARY         NULL    NULL    NULL        74
           range checked for each record (key map: 1)
     et    eq_ref PRIMARY         PRIMARY 15      tt.ActualPC 1

This is not perfect, but is much better (the product of the `rows'
values is now less by a factor of 74). This version is executed in a
couple of seconds.

A second alteration can be made to eliminate the column length
mismatches for the `tt.AssignedPC = et_1.EMPLOYID' and `tt.ClientID =
do.CUSTNMBR' comparisons:

     mysql> ALTER TABLE tt MODIFY AssignedPC VARCHAR(15),
         ->                MODIFY ClientID   VARCHAR(15);

Now `EXPLAIN' produces the output shown here:

     table type   possible_keys   key      key_len ref           rows Extra
     et    ALL    PRIMARY         NULL     NULL    NULL          74
     tt    ref    AssignedPC,     ActualPC 15      et.EMPLOYID   52   where used
                  ClientID,
                  ActualPC
     et_1  eq_ref PRIMARY         PRIMARY  15      tt.AssignedPC 1
     do    eq_ref PRIMARY         PRIMARY  15      tt.ClientID   1

This is almost as good as it can get.

The remaining problem is that, by default, MySQL assumes that values in
the `tt.ActualPC' column are evenly distributed, and that isn't the
case for the `tt' table.  Fortunately, it is easy to tell MySQL about
this:

     shell> myisamchk --analyze PATH_TO_MYSQL_DATABASE/tt
     shell> mysqladmin refresh

Now the join is perfect, and `EXPLAIN' produces this result:

     table type   possible_keys key     key_len ref           rows Extra
     tt    ALL    AssignedPC    NULL    NULL    NULL          3872 where used
                  ClientID,
                  ActualPC
     et    eq_ref PRIMARY       PRIMARY 15      tt.ActualPC   1
     et_1  eq_ref PRIMARY       PRIMARY 15      tt.AssignedPC 1
     do    eq_ref PRIMARY       PRIMARY 15      tt.ClientID   1

Note that the `rows' column in the output from `EXPLAIN' is an educated
guess from the MySQL join optimiser. To optimise a query, you should
check if the numbers are even close to the truth.  If not, you may get
better performance by using `STRAIGHT_JOIN' in your `SELECT' statement
and trying to list the tables in a different order in the `FROM' clause.

Estimating Query Performance
----------------------------

In most cases you can estimate the performance by counting disk seeks.
For small tables, you can usually find the row in 1 disk seek (as the
index is probably cached).  For bigger tables, you can estimate that
(using B++ tree indexes) you will need: `log(row_count) /
log(index_block_length / 3 * 2 / (index_length + data_pointer_length)) +
1' seeks to find a row.

In MySQL an index block is usually 1024 bytes and the data pointer is
usually 4 bytes. A 500,000 row table with an index length of 3 (medium
integer) gives you: `log(500,000)/log(1024/3*2/(3+4)) + 1' = 4 seeks.

As the above index would require about 500,000 * 7 * 3/2 = 5.2M,
(assuming that the index buffers are filled to 2/3, which is typical)
you will probably have much of the index in memory and you will probably
only need 1-2 calls to read data from the OS to find the row.

For writes, however, you will need 4 seek requests (as above) to find
where to place the new index and normally 2 seeks to update the index
and write the row.

Note that the above doesn't mean that your application will slowly
degenerate by log N!  As long as everything is cached by the OS or SQL
server things will only go marginally slower while the table gets
bigger. After the data gets too big to be cached, things will start to
go much slower until your applications is only bound by disk-seeks
(which increase by log N). To avoid this, increase the index cache as
the data grows. *Note Server parameters::.

Speed of `SELECT' Queries
-------------------------

In general, when you want to make a slow `SELECT ... WHERE' faster, the
first thing to check is whether you can add an index. *Note MySQL
indexes: MySQL indexes. All references between different tables should
usually be done with indexes. You can use the `EXPLAIN' command to
determine which indexes are used for a `SELECT'.  *Note `EXPLAIN':
EXPLAIN.

Some general tips:

   * To help MySQL optimise queries better, run `myisamchk --analyze'
     on a table after it has been loaded with relevant data. This
     updates a value for each index part that indicates the average
     number of rows that have the same value.  (For unique indexes,
     this is always 1, of course.)  MySQL will use this to decide which
     index to choose when you connect two tables with 'a non-constant
     expression'.  You can check the result from the `analyze' run by
     doing `SHOW INDEX FROM table_name' and examining the `Cardinality'
     column.

   * To sort an index and data according to an index, use `myisamchk
     --sort-index --sort-records=1' (if you want to sort on index 1).
     If you have a unique index from which you want to read all records
     in order according to that index, this is a good way to make that
     faster.  Note, however, that this sorting isn't written optimally
     and will take a long time for a large table!

How MySQL Optimises `WHERE' Clauses
-----------------------------------

The `WHERE' optimisations are put in the `SELECT' part here because
they are mostly used with `SELECT', but the same optimisations apply for
`WHERE' in `DELETE' and `UPDATE' statements.

Also note that this section is incomplete. MySQL does many
optimisations, and we have not had time to document them all.

Some of the optimisations performed by MySQL are listed here:

   * Removal of unnecessary parentheses:
             ((a AND b) AND c OR (((a AND b) AND (c AND d))))
          -> (a AND b AND c) OR (a AND b AND c AND d)

   * Constant folding:
             (a<b AND b=c) AND a=5
          -> b>5 AND b=c AND a=5

   * Constant condition removal (needed because of constant folding):
             (B>=5 AND B=5) OR (B=6 AND 5=5) OR (B=7 AND 5=6)
          -> B=5 OR B=6

   * Constant expressions used by indexes are evaluated only once.

   * `COUNT(*)' on a single table without a `WHERE' is retrieved
     directly from the table information for `MyISAM' and `HEAP' tables.
     This is also done for any `NOT NULL' expression when used with
     only one table.

   * Early detection of invalid constant expressions. MySQL quickly
     detects that some `SELECT' statements are impossible and returns
     no rows.

   * `HAVING' is merged with `WHERE' if you don't use `GROUP BY' or
     group functions (`COUNT()', `MIN()'...).

   * For each sub-join, a simpler `WHERE' is constructed to get a fast
     `WHERE' evaluation for each sub-join and also to skip records as
     soon as possible.

   * All constant tables are read first, before any other tables in the
     query.  A constant table is:
        - An empty table or a table with 1 row.

        - A table that is used with a `WHERE' clause on a `UNIQUE'
          index, or a `PRIMARY KEY', where all index parts are used
          with constant expressions and the index parts are defined as
          `NOT NULL'.
     All the following tables are used as constant tables:
          mysql> SELECT * FROM t WHERE primary_key=1;
          mysql> SELECT * FROM t1,t2
              ->          WHERE t1.primary_key=1 AND t2.primary_key=t1.id;

   * The best join combination to join the tables is found by trying all
     possibilities. If all columns in `ORDER BY' and in `GROUP BY' come
     from the same table, then this table is preferred first when
     joining.

   * If there is an `ORDER BY' clause and a different `GROUP BY'
     clause, or if the `ORDER BY' or `GROUP BY' contains columns from
     tables other than the first table in the join queue, a temporary
     table is created.

   * If you use `SQL_SMALL_RESULT', MySQL will use an in-memory
     temporary table.

   * Each table index is queried, and the best index that spans fewer
     than 30% of the rows is used. If no such index can be found, a
     quick table scan is used.

   * In some cases, MySQL can read rows from the index without even
     consulting the datafile.  If all columns used from the index are
     numeric, then only the index tree is used to resolve the query.

   * Before each record is output, those that do not match the `HAVING'
     clause are skipped.

Some examples of queries that are very fast:

     mysql> SELECT COUNT(*) FROM tbl_name;
     mysql> SELECT MIN(key_part1),MAX(key_part1) FROM tbl_name;
     mysql> SELECT MAX(key_part2) FROM tbl_name
         ->        WHERE key_part_1=constant;
     mysql> SELECT ... FROM tbl_name
         ->        ORDER BY key_part1,key_part2,... LIMIT 10;
     mysql> SELECT ... FROM tbl_name
         ->        ORDER BY key_part1 DESC,key_part2 DESC,... LIMIT 10;

The following queries are resolved using only the index tree (assuming
the indexed columns are numeric):

     mysql> SELECT key_part1,key_part2 FROM tbl_name WHERE key_part1=val;
     mysql> SELECT COUNT(*) FROM tbl_name
         ->        WHERE key_part1=val1 AND key_part2=val2;
     mysql> SELECT key_part2 FROM tbl_name GROUP BY key_part1;

The following queries use indexing to retrieve the rows in sorted order
without a separate sorting pass:

     mysql> SELECT ... FROM tbl_name
         ->            ORDER BY key_part1,key_part2,... ;
     mysql> SELECT ... FROM tbl_name
         ->            ORDER BY key_part1 DESC,key_part2 DESC,... ;

How MySQL Optimises `DISTINCT'
------------------------------

`DISTINCT' is converted to a `GROUP BY' on all columns, `DISTINCT'
combined with `ORDER BY' will in many cases also need a temporary table.

When combining `LIMIT #' with `DISTINCT', MySQL will stop as soon as it
finds `#' unique rows.

If you don't use columns from all used tables, MySQL will stop the
scanning of the not used tables as soon as it has found the first match.

     SELECT DISTINCT t1.a FROM t1,t2 where t1.a=t2.a;

In the case, assuming `t1' is used before `t2' (check with `EXPLAIN'),
then MySQL will stop reading from `t2' (for that particular row in
`t1') when the first row in `t2' is found.

How MySQL Optimises `LEFT JOIN' and `RIGHT JOIN'
------------------------------------------------

`A LEFT JOIN B' in MySQL is implemented as follows:

   * The table `B' is set to be dependent on table `A' and all tables
     that `A' is dependent on.

   * The table `A' is set to be dependent on all tables (except `B')
     that are used in the `LEFT JOIN' condition.

   * All `LEFT JOIN' conditions are moved to the `WHERE' clause.

   * All standard join optimisations are done, with the exception that
     a table is always read after all tables it is dependent on.  If
     there is a circular dependence then MySQL will issue an error.

   * All standard `WHERE' optimisations are done.

   * If there is a row in `A' that matches the `WHERE' clause, but there
     wasn't any row in `B' that matched the `LEFT JOIN' condition, then
     an extra `B' row is generated with all columns set to `NULL'.

   * If you use `LEFT JOIN' to find rows that don't exist in some table
     and you have the following test: `column_name IS NULL' in the
     `WHERE' part, where column_name is a column that is declared as
     `NOT NULL', then MySQL will stop searching after more rows (for a
     particular key combination) after it has found one row that
     matches the `LEFT JOIN' condition.

`RIGHT JOIN' is implemented analogously as `LEFT JOIN'.

The table read order forced by `LEFT JOIN' and `STRAIGHT JOIN' will
help the join optimiser (which calculates in which order tables should
be joined) to do its work much more quickly, as there are fewer table
permutations to check.

Note that the above means that if you do a query of type:

     SELECT * FROM a,b LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key)
              WHERE b.key=d.key

MySQL will do a full scan on `b' as the `LEFT JOIN' will force it to be
read before `d'.

The fix in this case is to change the query to:

     SELECT * FROM b,a LEFT JOIN c ON (c.key=a.key) LEFT JOIN d (d.key=a.key)
              WHERE b.key=d.key

How MySQL Optimises `ORDER BY'
------------------------------

In some cases MySQL can uses index to satisfy an `ORDER BY' or `GROUP
BY' request without doing any extra sorting.

The index can also be used even if the `ORDER BY' doesn't match the
index exactly, as long as all the unused index parts and all the extra
are `ORDER BY' columns are constants in the `WHERE' clause. The
following queries will use the index to resolve the `ORDER BY' / `GROUP
BY' part:

     SELECT * FROM t1 ORDER BY key_part1,key_part2,...
     SELECT * FROM t1 WHERE key_part1=constant ORDER BY key_part2
     SELECT * FROM t1 WHERE key_part1=constant GROUP BY key_part2
     SELECT * FROM t1 ORDER BY key_part1 DESC,key_part2 DESC
     SELECT * FROM t1 WHERE key_part1=1 ORDER BY key_part1 DESC,key_part2 DESC

Some cases where MySQL can *not* use indexes to resolve the `ORDER BY':
(Note that MySQL will still use indexes to find the rows that matches
the `WHERE' clause):

   * You are doing an `ORDER BY' on different keys:

     `SELECT * FROM t1 ORDER BY key1,key2'

   * You are doing an `ORDER BY' using non-consecutive key parts.

     `SELECT * FROM t1 WHERE key2=constant ORDER BY key_part2'

   * You are mixing `ASC' and `DESC'.

     `SELECT * FROM t1 ORDER BY key_part1 DESC,key_part2 ASC'

   * The key used to fetch the rows are not the same one that is used to
     do the `ORDER BY':

     `SELECT * FROM t1 WHERE key2=constant ORDER BY key1'

   * You are joining many tables and the columns you are doing an `ORDER
     BY' on are not all from the first not-`const' table that is used to
     retrieve rows (This is the first table in the `EXPLAIN' output
     which doesn't use a `const' row fetch method).

   * You have different `ORDER BY' and `GROUP BY' expressions.

   * The used table index is an index type that doesn't store rows in
     order.  (Like the `HASH' index in `HEAP' tables).

   * The index colum may contain `NULL' values and one is using `ORDER
     BY ... DESC'.  This is because in SQL `NULL' values is always
     sorted before normal values, independent of you are using `DESC'
     or not.

In the cases where MySQL have to sort the result, it uses the following
algorithm:

   * Read all rows according to key or by table scanning.  Rows that
     don't match the `WHERE' clause are skipped.

   * Store the sort-key in a buffer (of size `sort_buffer').

   * When the buffer gets full, run a qsort on it and store the result
     in a temporary file.  Save a pointer to the sorted block.  (In the
     case where all rows fits into the sort buffer, no temporary file
     is created)

   * Repeat the above until all rows have been read.

   * Do a multi-merge of up to `MERGEBUFF' (7) regions to one block in
     another temporary file.  Repeat until all blocks from the first
     file are in the second file.

   * Repeat the following until there is less than `MERGEBUFF2' (15)
     blocks left.

   * On the last multi-merge, only the pointer to the row (last part of
     the sort-key) is written to a result file.

   * Now the code in `sql/records.cc' will be used to read through them
     in sorted order by using the row pointers in the result file.  To
     optimise this, we read in a big block of row pointers, sort these
     and then we read the rows in the sorted order into a row buffer
     (`record_rnd_buffer') .

You can with `EXPLAIN SELECT ... ORDER BY' check if MySQL can use
indexes to resolve the query.  If you get `Using filesort' in the
`extra' column, then MySQL can't use indexes to resolve the `ORDER BY'.
*Note EXPLAIN::.

If you want to have a higher `ORDER BY' speed, you should first see if
you can get MySQL to use indexes instead of having to do an extra
sorting phase. If this is not possible, then you can do:

   * Increase the size of the `sort_buffer' variable.

   * Increase the size of the `record_rnd_buffer' variable.

   * Change `tmpdir' to point to a dedicated disk with lots of empty
     space.

How MySQL Optimises `LIMIT'
---------------------------

In some cases MySQL will handle the query differently when you are
using `LIMIT #' and not using `HAVING':

   * If you are selecting only a few rows with `LIMIT', MySQL will use
     indexes in some cases when it normally would prefer to do a full
     table scan.

   * If you use `LIMIT #' with `ORDER BY', MySQL will end the sorting
     as soon as it has found the first `#' lines instead of sorting the
     whole table.

   * When combining `LIMIT #' with `DISTINCT', MySQL will stop as soon
     as it finds `#' unique rows.

   * In some cases a `GROUP BY' can be resolved by reading the key in
     order (or do a sort on the key) and then calculate summaries until
     the key value changes.  In this case `LIMIT #' will not calculate
     any unnecessary `GROUP BY's.

   * As soon as MySQL has sent the first `#' rows to the client, it
     will abort the query (if you are not using `SQL_CALC_FOUND_ROWS').

   * `LIMIT 0' will always quickly return an empty set.  This is useful
     to check the query and to get the column types of the result
     columns.

   * When the server uses temporary tables to resolve the query, the
     `LIMIT #' is used to calculate how much space is required.

Speed of `INSERT' Queries
-------------------------

The time to insert a record consists approximately of:

   * Connect:                 (3)

   * Sending query to server: (2)

   * Parsing query:           (2)

   * Inserting record:        (1 x size of record)

   * Inserting indexes:       (1 x number of indexes)

   * Close:                   (1)

where the numbers are somewhat proportional to the overall time. This
does not take into consideration the initial overhead to open tables
(which is done once for each concurrently running query).

The size of the table slows down the insertion of indexes by log N
(B-trees).

Some ways to speed up inserts:

   * If you are inserting many rows from the same client at the same
     time, use multiple value lists `INSERT' statements. This is much
     faster (many times in some cases) than using separate `INSERT'
     statements.  If you are adding data to non-empty table, you may
     tune up `bulk_insert_buffer_size'u`bulk_insert_buffer_size'
     variable to make it even faster.  *Note `bulk_insert_buffer_size':
     SHOW VARIABLES.

   * If you are inserting a lot of rows from different clients, you can
     get higher speed by using the `INSERT DELAYED' statement. *Note
     `INSERT': INSERT.

   * Note that with `MyISAM' tables you can insert rows at the same time
     `SELECT's are running if there are no deleted rows in the tables.

   * When loading a table from a text file, use `LOAD DATA INFILE'. This
     is usually 20 times faster than using a lot of `INSERT' statements.
     *Note `LOAD DATA': LOAD DATA.

   * It is possible with some extra work to make `LOAD DATA INFILE' run
     even faster when the table has many indexes. Use the following
     procedure:

       1. Optionally create the table with `CREATE TABLE'. For example,
          using `mysql' or Perl-DBI.

       2. Execute a `FLUSH TABLES' statement or the shell command
          `mysqladmin flush-tables'.

       3. Use `myisamchk --keys-used=0 -rq /path/to/db/tbl_name'. This
          will remove all usage of all indexes from the table.

       4. Insert data into the table with `LOAD DATA INFILE'. This will
          not update any indexes and will therefore be very fast.

       5. If you are going to only read the table in the future, run
          `myisampack' on it to make it smaller. *Note Compressed
          format::.

       6. Re-create the indexes with `myisamchk -r -q
          /path/to/db/tbl_name'. This will create the index tree in
          memory before writing it to disk, which is much faster
          because it avoids lots of disk seeks. The resulting index
          tree is also perfectly balanced.

       7. Execute a `FLUSH TABLES' statement or the shell command
          `mysqladmin flush-tables'.

     Note that `LOAD DATA INFILE' also does the above optimisation if
     you insert into an empty table; the main difference with the above
     procedure is that you can let `myisamchk' allocate much more
     temporary memory for the index creation that you may want MySQL to
     allocate for every index recreation.

     Since MySQL 4.0 you can also use `ALTER TABLE tbl_name DISABLE
     KEYS' instead of `myisamchk --keys-used=0 -rq
     /path/to/db/tbl_name' and `ALTER TABLE tbl_name ENABLE KEYS'
     instead of `myisamchk -r -q /path/to/db/tbl_name'. This way you
     can also skip `FLUSH TABLES' steps.

   * You can speed up insertions that is done over multiple statements
     by locking your tables:

          mysql> LOCK TABLES a WRITE;
          mysql> INSERT INTO a VALUES (1,23),(2,34),(4,33);
          mysql> INSERT INTO a VALUES (8,26),(6,29);
          mysql> UNLOCK TABLES;

     The main speed difference is that the index buffer is flushed to
     disk only once, after all `INSERT' statements have completed.
     Normally there would be as many index buffer flushes as there are
     different `INSERT' statements. Locking is not needed if you can
     insert all rows with a single statement.

     For transactional tables, you should use `BEGIN/COMMIT' instead of
     `LOCK TABLES' to get a speedup.

     Locking will also lower the total time of multi-connection tests,
     but the maximum wait time for some threads will go up (because
     they wait for locks).  For example:

          thread 1 does 1000 inserts
          thread 2, 3, and 4 does 1 insert
          thread 5 does 1000 inserts

     If you don't use locking, 2, 3, and 4 will finish before 1 and 5.
     If you use locking, 2, 3, and 4 probably will not finish before 1
     or 5, but the total time should be about 40% faster.

     As `INSERT', `UPDATE', and `DELETE' operations are very fast in
     MySQL, you will obtain better overall performance by adding locks
     around everything that does more than about 5 inserts or updates
     in a row.  If you do very many inserts in a row, you could do a
     `LOCK TABLES' followed by an `UNLOCK TABLES' once in a while
     (about each 1000 rows) to allow other threads access to the table.
     This would still result in a nice performance gain.

     Of course, `LOAD DATA INFILE' is much faster for loading data.

To get some more speed for both `LOAD DATA INFILE' and `INSERT',
enlarge the key buffer. *Note Server parameters::.

Speed of `UPDATE' Queries
-------------------------

Update queries are optimised as a `SELECT' query with the additional
overhead of a write. The speed of the write is dependent on the size of
the data that is being updated and the number of indexes that are
updated.  Indexes that are not changed will not be updated.

Also, another way to get fast updates is to delay updates and then do
many updates in a row later. Doing many updates in a row is much quicker
than doing one at a time if you lock the table.

Note that, with dynamic record format, updating a record to a longer
total length may split the record.  So if you do this often, it is very
important to `OPTIMIZE TABLE' sometimes.  *Note `OPTIMIZE TABLE':
OPTIMIZE TABLE.

Speed of `DELETE' Queries
-------------------------

If you want to delete all rows in the table, you should use `TRUNCATE
TABLE table_name'. *Note TRUNCATE::.

The time to delete a record is exactly proportional to the number of
indexes. To delete records more quickly, you can increase the size of
the index cache. *Note Server parameters::.

Other Optimisation Tips
-----------------------

Unsorted tips for faster systems:

   * Use persistent connections to the database to avoid the connection
     overhead. If you can't use persistent connections and you are
     doing a lot of new connections to the database, you may want to
     change the value of the `thread_cache_size' variable. *Note Server
     parameters::.

   * Always check that all your queries really use the indexes you have
     created in the tables. In MySQL you can do this with the `EXPLAIN'
     command. *Note Explain: (manual)EXPLAIN.

   * Try to avoid complex `SELECT' queries on `MyISAM' tables that are
     updated a lot. This is to avoid problems with table locking.

   * The new `MyISAM' tables can insert rows in a table without deleted
     rows at the same time another table is reading from it.  If this
     is important for you, you should consider methods where you don't
     have to delete rows or run `OPTIMIZE TABLE' after you have deleted
     a lot of rows.

   * Use `ALTER TABLE ... ORDER BY expr1,expr2...' if you mostly
     retrieve rows in `expr1,expr2...' order.  By using this option
     after big changes to the table, you may be able to get higher
     performance.

   * In some cases it may make sense to introduce a column that is
     'hashed' based on information from other columns. If this column
     is short and reasonably unique it may be much faster than a big
     index on many columns. In MySQL it's very easy to use this extra
     column: `SELECT * FROM table_name WHERE hash=MD5(CONCAT(col1,col2))
     AND col_1='constant' AND col_2='constant''

   * For tables that change a lot you should try to avoid all `VARCHAR'
     or `BLOB' columns. You will get dynamic row length as soon as you
     are using a single `VARCHAR' or `BLOB' column. *Note Table types::.

   * It's not normally useful to split a table into different tables
     just because the rows gets 'big'. To access a row, the biggest
     performance hit is the disk seek to find the first byte of the
     row. After finding the data most new disks can read the whole row
     fast enough for most applications. The only cases where it really
     matters to split up a table is if it's a dynamic row size table
     (see above) that you can change to a fixed row size, or if you
     very often need to scan the table and don't need most of the
     columns. *Note Table types::.

   * If you very often need to calculate things based on information
     from a lot of rows (like counts of things), it's probably much
     better to introduce a new table and update the counter in real
     time. An update of type `UPDATE table set count=count+1 where
     index_column=constant' is very fast!

     This is really important when you use MySQL table types like
     MyISAM and ISAM that only have table locking (multiple readers /
     single writers). This will also give better performance with most
     databases, as the row locking manager in this case will have less
     to do.

   * If you need to collect statistics from big log tables, use summary
     tables instead of scanning the whole table. Maintaining the
     summaries should be much faster than trying to do statistics
     'live'. It's much faster to regenerate new summary tables from the
     logs when things change (depending on business decisions) than to
     have to change the running application!

   * If possible, one should classify reports as 'live' or
     'statistical', where data needed for statistical reports are only
     generated based on summary tables that are generated from the
     actual data.

   * Take advantage of the fact that columns have default values. Insert
     values explicitly only when the value to be inserted differs from
     the default. This reduces the parsing that MySQL need to do and
     improves the insert speed.

   * In some cases it's convenient to pack and store data into a blob.
     In this case you have to add some extra code in your application
     to pack/unpack things in the blob, but this may save a lot of
     accesses at some stage.  This is practical when you have data that
     doesn't conform to a static table structure.

   * Normally you should try to keep all data non-redundant (what is
     called 3rd normal form in database theory), but you should not be
     afraid of duplicating things or creating summary tables if you
     need these to gain more speed.

   * Stored procedures or UDF (user-defined functions) may be a good
     way to get more performance.  In this case you should, however,
     always have a way to do this some other (slower) way if you use
     some database that doesn't support this.

   * You can always gain something by caching queries/answers in your
     application and trying to do many inserts/updates at the same
     time.  If your database supports lock tables (like MySQL and
     Oracle), this should help to ensure that the index cache is only
     flushed once after all updates.

   * Use `INSERT /*! DELAYED */' when you do not need to know when your
     data is written. This speeds things up because many records can be
     written with a single disk write.

   * Use `INSERT /*! LOW_PRIORITY */' when you want your selects to be
     more important.

   * Use `SELECT /*! HIGH_PRIORITY */' to get selects that jump the
     queue. That is, the select is done even if there is somebody
     waiting to do a write.

   * Use the multi-line `INSERT' statement to store many rows with one
     SQL command (many SQL servers supports this).

   * Use `LOAD DATA INFILE' to load bigger amounts of data. This is
     faster than normal inserts and will be even faster when `myisamchk'
     is integrated in `mysqld'.

   * Use `AUTO_INCREMENT' columns to make unique values.

   * Use `OPTIMIZE TABLE' once in a while to avoid fragmentation when
     using a dynamic table format. *Note `OPTIMIZE TABLE': OPTIMIZE
     TABLE.

   * Use `HEAP' tables to get more speed when possible. *Note Table
     types::.

   * When using a normal web server setup, images should be stored as
     files. That is, store only a file reference in the database.  The
     main reason for this is that a normal web server is much better at
     caching files than database contents. So it it's much easier to
     get a fast system if you are using files.

   * Use in memory tables for non-critical data that are accessed often
     (like information about the last shown banner for users that don't
     have cookies).

   * Columns with identical information in different tables should be
     declared identical and have identical names. Before Version 3.23
     you got slow joins otherwise.

     Try to keep the names simple (use `name' instead of
     `customer_name' in the customer table). To make your names portable
     to other SQL servers you should keep them shorter than 18
     characters.

   * If you need really high speed, you should take a look at the
     low-level interfaces for data storage that the different SQL
     servers support!  For example, by accessing the MySQL `MyISAM'
     directly, you could get a speed increase of 2-5 times compared to
     using the SQL interface.  To be able to do this the data must be
     on the same server as the application, and usually it should only
     be accessed by one process (because external file locking is
     really slow).  One could eliminate the above problems by
     introducing low-level `MyISAM' commands in the MySQL server (this
     could be one easy way to get more performance if needed).  By
     carefully designing the database interface, it should be quite
     easy to support this types of optimisation.

   * In many cases it's faster to access data from a database (using a
     live connection) than accessing a text file, just because the
     database is likely to be more compact than the text file (if you
     are using numerical data), and this will involve fewer disk
     accesses.  You will also save code because you don't have to parse
     your text files to find line and column boundaries.

   * You can also use replication to speed things up. *Note
     Replication::.

   * Declaring a table with `DELAY_KEY_WRITE=1' will make the updating
     of indexes faster, as these are not logged to disk until the file
     is closed.  The downside is that you should run `myisamchk' on
     these tables before you start `mysqld' to ensure that they are
     okay if something killed `mysqld' in the middle.  As the key
     information can always be generated from the data, you should not
     lose anything by using `DELAY_KEY_WRITE'.

Locking Issues
==============

How MySQL Locks Tables
----------------------

You can find a discussion about different locking methods in the
appendix.  *Note Locking methods::.

All locking in MySQL is deadlock-free, except for `InnoDB' and `BDB'
type tables.  This is managed by always requesting all needed locks at
once at the beginning of a query and always locking the tables in the
same order.

`InnoDB' type tables automatically acquire their row locks and `BDB'
type tables their page locks during the processing of SQL statements,
not at the start of the transaction.

The locking method MySQL uses for `WRITE' locks works as follows:

   * If there are no locks on the table, put a write lock on it.

   * Otherwise, put the lock request in the write lock queue.

The locking method MySQL uses for `READ' locks works as follows:

   * If there are no write locks on the table, put a read lock on it.

   * Otherwise, put the lock request in the read lock queue.

When a lock is released, the lock is made available to the threads in
the write lock queue, then to the threads in the read lock queue.

This means that if you have many updates on a table, `SELECT'
statements will wait until there are no more updates.

To work around this for the case where you want to do many `INSERT' and
`SELECT' operations on a table, you can insert rows in a temporary
table and update the real table with the records from the temporary
table once in a while.

This can be done with the following code:
     mysql> LOCK TABLES real_table WRITE, insert_table WRITE;
     mysql> INSERT INTO real_table SELECT * FROM insert_table;
     mysql> TRUNCATE TABLE insert_table;
     mysql> UNLOCK TABLES;

You can use the `LOW_PRIORITY' options with `INSERT', `UPDATE' or
`DELETE' or `HIGH_PRIORITY' with `SELECT' if you want to prioritise
retrieval in some specific cases.  You can also start `mysqld' with
`--low-priority-updates' to get the same behaveour.

Using `SQL_BUFFER_RESULT' can also help making table locks shorter.
*Note SELECT::.

You could also change the locking code in `mysys/thr_lock.c' to use a
single queue.  In this case, write locks and read locks would have the
same priority, which might help some applications.

Table Locking Issues
--------------------

The table locking code in MySQL is deadlock free.

MySQL uses table locking (instead of row locking or column locking) on
all table types, except `InnoDB' and `BDB' tables, to achieve a very
high lock speed.  For large tables, table locking is much better than
row locking for most applications, but there are, of course, some
pitfalls.

For `InnoDB' and `BDB' tables, MySQL only uses table locking if you
explicitly lock the table with `LOCK TABLES'.  For these table types we
recommend you to not use `LOCK TABLES' at all, because `InnoDB' uses
automatic row level locking and `BDB' uses page level locking to ensure
transaction isolation.

In MySQL Version 3.23.7 and above, you can insert rows into `MyISAM'
tables at the same time other threads are reading from the table.  Note
that currently this only works if there are no holes after deleted rows
in the table at the time the insert is made. When all holes has been
filled with new data, concurrent inserts will automatically be enabled
again.

Table locking enables many threads to read from a table at the same
time, but if a thread wants to write to a table, it must first get
exclusive access.  During the update, all other threads that want to
access this particular table will wait until the update is ready.

As updates on tables normally are considered to be more important than
`SELECT', all statements that update a table have higher priority than
statements that retrieve information from a table. This should ensure
that updates are not 'starved' because one issues a lot of heavy
queries against a specific table. (You can change this by using
`LOW_PRIORITY' with the statement that does the update or
`HIGH_PRIORITY' with the `SELECT' statement.)

Starting from MySQL Version 3.23.7 one can use the
`max_write_lock_count' variable to force MySQL to temporary give all
`SELECT' statements, that wait for a table, a higher priority after a
specific number of inserts on a table.

Table locking is, however, not very good under the following senario:

   * A client issues a `SELECT' that takes a long time to run.

   * Another client then issues an `UPDATE' on a used table. This client
     will wait until the `SELECT' is finished.

   * Another client issues another `SELECT' statement on the same
     table. As `UPDATE' has higher priority than `SELECT', this `SELECT'
     will wait for the `UPDATE' to finish.  It will also wait for the
     first `SELECT' to finish!

   * A thread is waiting for something like `full disk', in which case
     all threads that wants to access the problem table will also be
     put in a waiting state until more disk space is made available.

Some possible solutions to this problem are:

   * Try to get the `SELECT' statements to run faster. You may have to
     create some summary tables to do this.

   * Start `mysqld' with `--low-priority-updates'.  This will give all
     statements that update (modify) a table lower priority than a
     `SELECT' statement. In this case the last `SELECT' statement in
     the previous scenario would execute before the `INSERT' statement.

   * You can give a specific `INSERT', `UPDATE', or `DELETE' statement
     lower priority with the `LOW_PRIORITY' attribute.

   * Start `mysqld' with a low value for `max_write_lock_count' to give
     `READ' locks after a certain number of `WRITE' locks.

   * You can specify that all updates from a specific thread should be
     done with low priority by using the SQL command: `SET
     LOW_PRIORITY_UPDATES=1'.  *Note `SET': SET OPTION.

   * You can specify that a specific `SELECT' is very important with the
     `HIGH_PRIORITY' attribute. *Note `SELECT': SELECT.

   * If you have problems with `INSERT' combined with `SELECT', switch
     to use the new `MyISAM' tables as these support concurrent
     `SELECT's and `INSERT's.

   * If you mainly mix `INSERT' and `SELECT' statements, the `DELAYED'
     attribute to `INSERT' will probably solve your problems.  *Note
     `INSERT': INSERT.

   * If you have problems with `SELECT' and `DELETE', the `LIMIT'
     option to `DELETE' may help. *Note `DELETE': DELETE.

Optimising Database Structure
=============================

Design Choices
--------------

MySQL keeps row data and index data in separate files. Many (almost
all) other databases mix row and index data in the same file. We
believe that the MySQL choice is better for a very wide range of modern
systems.

Another way to store the row data is to keep the information for each
column in a separate area (examples are SDBM and Focus). This will
cause a performance hit for every query that accesses more than one
column. Because this degenerates so quickly when more than one column
is accessed, we believe that this model is not good for general purpose
databases.

The more common case is that the index and data are stored together
(like in Oracle/Sybase et al). In this case you will find the row
information at the leaf page of the index. The good thing with this
layout is that it, in many cases, depending on how well the index is
cached, saves a disk read.  The bad things with this layout are:

   * Table scanning is much slower because you have to read through the
     indexes to get at the data.

   * You can't use only the index table to retrieve data for a query.

   * You lose a lot of space, as you must duplicate indexes from the
     nodes (as you can't store the row in the nodes).

   * Deletes will degenerate the table over time (as indexes in nodes
     are usually not updated on delete).

   * It's harder to cache only the index data.

Get Your Data as Small as Possible
----------------------------------

One of the most basic optimisation is to get your data (and indexes) to
take as little space on the disk (and in memory) as possible. This can
give huge improvements because disk reads are faster and normally less
main memory will be used. Indexing also takes less resources if done on
smaller columns.

MySQL supports a lot of different table types and row formats.
Choosing the right table format may give you a big performance gain.
*Note Table types::.

You can get better performance on a table and minimise storage space
using the techniques listed here:

   * Use the most efficient (smallest) types possible. MySQL has many
     specialised types that save disk space and memory.

   * Use the smaller integer types if possible to get smaller tables.
     For example, `MEDIUMINT' is often better than `INT'.

   * Declare columns to be `NOT NULL' if possible. It makes everything
     faster and you save one bit per column. Note that if you really
     need `NULL' in your application you should definitely use it. Just
     avoid having it on all columns by default.

   * If you don't have any variable-length columns (`VARCHAR', `TEXT',
     or `BLOB' columns), a fixed-size record format is used. This is
     faster but unfortunately may waste some space.  *Note `MyISAM'
     table formats: MyISAM table formats.

   * The primary index of a table should be as short as possible. This
     makes identification of one row easy and efficient.

   * For each table, you have to decide which storage/index method to
     use. *Note Table types::.

   * Only create the indexes that you really need. Indexes are good for
     retrieval but bad when you need to store things fast. If you mostly
     access a table by searching on a combination of columns, make an
     index on them. The first index part should be the most used
     column. If you are *always* using many columns, you should use the
     column with more duplicates first to get better compression of the
     index.

   * If it's very likely that a column has a unique prefix on the first
     number of characters, it's better to only index this prefix. MySQL
     supports an index on a part of a character column. Shorter indexes
     are faster not only because they take less disk space but also
     because they will give you more hits in the index cache and thus
     fewer disk seeks. *Note Server parameters::.

   * In some circumstances it can be beneficial to split into two a
     table that is scanned very often. This is especially true if it is
     a dynamic format table and it is possible to use a smaller static
     format table that can be used to find the relevant rows when
     scanning the table.

How MySQL Uses Indexes
----------------------

Indexes are used to find rows with a specific value of one column fast.
Without an index MySQL has to start with the first record and then read
through the whole table until it finds the relevant rows. The bigger
the table, the more this costs. If the table has an index for the
columns in question, MySQL can quickly get a position to seek to in the
middle of the datafile without having to look at all the data. If a
table has 1000 rows, this is at least 100 times faster than reading
sequentially. Note that if you need to access almost all 1000 rows it
is faster to read sequentially because we then avoid disk seeks.

All MySQL indexes (`PRIMARY', `UNIQUE', and `INDEX') are stored in
B-trees. Strings are automatically prefix- and end-space compressed.
*Note `CREATE INDEX': CREATE INDEX.

Indexes are used to:
   * Quickly find the rows that match a `WHERE' clause.

   * Retrieve rows from other tables when performing joins.

   * Find the `MAX()' or `MIN()' value for a specific indexed column.
     This is optimised by a preprocessor that checks if you are using
     `WHERE' key_part_# = constant on all key parts < N.  In this case
     MySQL will do a single key lookup and replace the `MIN()'
     expression with a constant.  If all expressions are replaced with
     constants, the query will return at once:

          SELECT MIN(key_part2),MAX(key_part2) FROM table_name where key_part1=10

   * Sort or group a table if the sorting or grouping is done on a
     leftmost prefix of a usable key (for example, `ORDER BY
     key_part_1,key_part_2 '). The key is read in reverse order if all
     key parts are followed by `DESC'.  *Note ORDER BY optimisation::.

   * In some cases a query can be optimised to retrieve values without
     consulting the datafile. If all used columns for some table are
     numeric and form a leftmost prefix for some key, the values may be
     retrieved from the index tree for greater speed:

          SELECT key_part3 FROM table_name WHERE key_part1=1


Suppose you issue the following `SELECT' statement:

     mysql> SELECT * FROM tbl_name WHERE col1=val1 AND col2=val2;

If a multiple-column index exists on `col1' and `col2', the appropriate
rows can be fetched directly. If separate single-column indexes exist
on `col1' and `col2', the optimiser tries to find the most restrictive
index by deciding which index will find fewer rows and using that index
to fetch the rows.

If the table has a multiple-column index, any leftmost prefix of the
index can be used by the optimiser to find rows. For example, if you
have a three-column index on `(col1,col2,col3)', you have indexed
search capabilities on `(col1)', `(col1,col2)', and `(col1,col2,col3)'.

MySQL can't use a partial index if the columns don't form a leftmost
prefix of the index.  Suppose you have the `SELECT' statements shown
here:

     mysql> SELECT * FROM tbl_name WHERE col1=val1;
     mysql> SELECT * FROM tbl_name WHERE col2=val2;
     mysql> SELECT * FROM tbl_name WHERE col2=val2 AND col3=val3;

If an index exists on `(col1,col2,col3)', only the first query shown
above uses the index. The second and third queries do involve indexed
columns, but `(col2)' and `(col2,col3)' are not leftmost prefixes of
`(col1,col2,col3)'.

MySQL also uses indexes for `LIKE' comparisons if the argument to
`LIKE' is a constant string that doesn't start with a wildcard
character.  For example, the following `SELECT' statements use indexes:

     mysql> SELECT * FROM tbl_name WHERE key_col LIKE "Patrick%";
     mysql> SELECT * FROM tbl_name WHERE key_col LIKE "Pat%_ck%";

In the first statement, only rows with `"Patrick" <= key_col <
"Patricl"' are considered.  In the second statement, only rows with
`"Pat" <= key_col < "Pau"' are considered.

The following `SELECT' statements will not use indexes:
     mysql> SELECT * FROM tbl_name WHERE key_col LIKE "%Patrick%";
     mysql> SELECT * FROM tbl_name WHERE key_col LIKE other_col;

In the first statement, the `LIKE' value begins with a wildcard
character.  In the second statement, the `LIKE' value is not a constant.

MySQL 4.0 does another optimisation on `LIKE'.  If you use `... LIKE
"%string%"' and `string' is longer than 3 characters, MySQL will use
the `Turbo Boyer-Moore' algorithm to initialise the pattern for the
string and then use this pattern to perform the search quicker.

Searching using `column_name IS NULL' will use indexes if column_name
is an index.

MySQL normally uses the index that finds the least number of rows. An
index is used for columns that you compare with the following operators:
`=', `>', `>=', `<', `<=', `BETWEEN', and a `LIKE' with a non-wildcard
prefix like `'something%''.

Any index that doesn't span all `AND' levels in the `WHERE' clause is
not used to optimise the query. In other words:  To be able to use an
index, a prefix of the index must be used in every `AND' group.

The following `WHERE' clauses use indexes:
     ... WHERE index_part1=1 AND index_part2=2 AND other_column=3
     ... WHERE index=1 OR A=10 AND index=2      /* index = 1 OR index = 2 */
     ... WHERE index_part1='hello' AND index_part_3=5
               /* optimised like "index_part1='hello'" */
     ... WHERE index1=1 and index2=2 or index1=3 and index3=3;
               /* Can use index on index1 but not on index2 or index 3 */

These `WHERE' clauses do *NOT* use indexes:
     ... WHERE index_part2=1 AND index_part3=2  /* index_part_1 is not used */
     ... WHERE index=1 OR A=10                  /* Index is not used in
                                                             both AND parts */
     ... WHERE index_part1=1 OR index_part2=10  /* No index spans all rows  */

Note that in some cases MySQL will not use an index, even if one would
be available.  Some of the cases where this happens are:

   * If the use of the index would require MySQL to access more than
     30% of the rows in the table.  (In this case a table scan is
     probably much faster, as this will require us to do much fewer
     seeks.)  Note that if such a query uses `LIMIT' to only retrieve
     part of the rows, MySQL will use an index anyway, as it can much
     more quickly find the few rows to return in the result.

   * If the index range may contain `NULL' values and you are using
     `ORDER BY ... DESC'

Column Indexes
--------------

All MySQL column types can be indexed.  Use of indexes on the relevant
columns is the best way to improve the performance of `SELECT'
operations.

The maximum number of keys and the maximum index length is defined per
storage engine. *Note Table types::. You can with all storage engines
have at least 16 keys and a total index length of at least 256 bytes.

For `CHAR' and `VARCHAR' columns, you can index a prefix of a column.
This is much faster and requires less disk space than indexing the
whole column.  The syntax to use in the `CREATE TABLE' statement to
index a column prefix looks like this:

     KEY index_name (col_name(length))

The example here creates an index for the first 10 characters of the
`name' column:

     mysql> CREATE TABLE test (
         ->        name CHAR(200) NOT NULL,
         ->        KEY index_name (name(10)));

For `BLOB' and `TEXT' columns, you must index a prefix of the column.
You cannot index the entire column.

In MySQL Version 3.23.23 or later, you can also create special
`FULLTEXT' indexes. They are used for full-text search. Only the
`MyISAM' table type supports `FULLTEXT' indexes. They can be created
only from `CHAR', `VARCHAR', and `TEXT' columns.  Indexing always
happens over the entire column and partial indexing is not supported.
See *Note Fulltext Search:: for details.

Multiple-Column Indexes
-----------------------

MySQL can create indexes on multiple columns.  An index may consist of
up to 15 columns. (On `CHAR' and `VARCHAR' columns you can also use a
prefix of the column as a part of an index.)

A multiple-column index can be considered a sorted array containing
values that are created by concatenating the values of the indexed
columns.

MySQL uses multiple-column indexes in such a way that queries are fast
when you specify a known quantity for the first column of the index in a
`WHERE' clause, even if you don't specify values for the other columns.

Suppose a table is created using the following specification:

     mysql> CREATE TABLE test (
         ->       id INT NOT NULL,
         ->       last_name CHAR(30) NOT NULL,
         ->       first_name CHAR(30) NOT NULL,
         ->       PRIMARY KEY (id),
         ->       INDEX name (last_name,first_name));

Then the index `name' is an index over `last_name' and `first_name'.
The index will be used for queries that specify values in a known range
for `last_name', or for both `last_name' and `first_name'.  Therefore,
the `name' index will be used in the following queries:

     mysql> SELECT * FROM test WHERE last_name="Widenius";

     mysql> SELECT * FROM test WHERE last_name="Widenius"
         ->                    AND first_name="Michael";

     mysql> SELECT * FROM test WHERE last_name="Widenius"
         ->                    AND (first_name="Michael" OR first_name="Monty");

     mysql> SELECT * FROM test WHERE last_name="Widenius"
         ->                    AND first_name >="M" AND first_name < "N";

However, the `name' index will NOT be used in the following queries:

     mysql> SELECT * FROM test WHERE first_name="Michael";

     mysql> SELECT * FROM test WHERE last_name="Widenius"
         ->                    OR first_name="Michael";

For more information on the manner in which MySQL uses indexes to
improve query performance, see *Note MySQL indexes: MySQL indexes.

Why So Many Open tables?
------------------------

When you run `mysqladmin status', you'll see something like this:

     Uptime: 426 Running threads: 1 Questions: 11082 Reloads: 1 Open tables: 12

This can be somewhat perplexing if you only have 6 tables.

MySQL is multi-threaded, so it may have many queries on the same table
simultaneously. To minimise the problem with two threads having
different states on the same file, the table is opened independently by
each concurrent thread. This takes some memory but will normaly increase
performance.  Wth `ISAM' and `MyISAM' tables this also requires one
extra file descriptor for the datafile. With these table types the index
file descriptor is shared between all threads.

You can read more about this topic in the next section. *Note Table
cache::.

How MySQL Opens and Closes Tables
---------------------------------

`table_cache', `max_connections', and `max_tmp_tables' affect the
maximum number of files the server keeps open.  If you increase one or
both of these values, you may run up against a limit imposed by your
operating system on the per-process number of open file descriptors.
However, you can increase the limit on many systems.  Consult your OS
documentation to find out how to do this, because the method for
changing the limit varies widely from system to system.

`table_cache' is related to `max_connections'.  For example, for 200
concurrent running connections, you should have a table cache of at
least `200 * n', where `n' is the maximum number of tables in a join.
You also need to reserve some extra file descriptors for temporary
tables and files.

Make sure that your operating system can handle the number of open file
descriptors implied by the `table_cache' setting.  If `table_cache' is
set too high, MySQL may run out of file descriptors and refuse
connections, fail to perform queries, and be very unreliable.  You also
have to take into account that the `MyISAM' storage engine needs two
file descriptors for each unique open table. You can in increase the
number of file descriptors available for MySQL with the
`--open-files-limit=#' startup option. *Note Not enough file handles::.

The cache of open tables will be keept at a level of `table_cache'
entries (default 64; this can be changed with the `-O table_cache=#'
option to `mysqld').  Note that in MySQL may temporarly open even more
tables to be able to execute queries.

A not used table is closed and removed from the table cache under the
following circumstances:

   * When the cache is full and a thread tries to open a table that is
     not in the cache.

   * When the cache contains more than `table_cache' entries and a
     thread is no longer using a table.

   * When someone executes `mysqladmin refresh' or `mysqladmin
     flush-tables'.

   * When someone executes a `FLUSH TABLES' statement.

When the table cache fills up, the server uses the following procedure
to locate a cache entry to use:

   * Tables that are not currently in use are released, in
     least-recently-used order.

   * If the cache is full and no tables can be released, but a new
     table needs to be opened, the cache is temporarily extended as
     necessary.

   * If the cache is in a temporarily-extended state and a table goes
     from in-use to not-in-use state, the table is closed and released
     from the cache.

A table is opened for each concurrent access. This means that if you
have two threads accessing the same table or access the table twice in
the same query (with `AS') the table needs to be opened twice.  The
first open of any table takes two file descriptors; each additional use
of the table takes only one file descriptor.  The extra descriptor for
the first open is used for the index file; this descriptor is shared
among all threads.

If you are opening a table with the `HANDLER table_name OPEN'
statement, a dedicated table object is allocated for the thread.  This
table object is not shared by other threads an will not be closed until
the thread calls `HANDLER table_name CLOSE' or the thread dies.  *Note
`HANDLER': HANDLER.  When this happens, the table is put back in the
table cache (if it isn't full).

You can check if your table cache is too small by checking the `mysqld'
variable `Opened_tables'.  If this is quite big, even if you haven't
done a lot of `FLUSH TABLES', you should increase your table cache.
*Note `Opened_tables': SHOW STATUS.

Drawbacks to Creating Large Numbers of Tables in the Same Database
------------------------------------------------------------------

If you have many files in a directory, open, close, and create
operations will be slow.  If you execute `SELECT' statements on many
different tables, there will be a little overhead when the table cache
is full, because for every table that has to be opened, another must be
closed. You can reduce this overhead by making the table cache larger.

Optimising the MySQL Server
===========================

System/Compile Time and Startup Parameter Tuning
------------------------------------------------

We start with the system level things since some of these decisions have
to be made very early. In other cases a fast look at this part may
suffice because it not that important for the big gains. However, it is
always nice to have a feeling about how much one could gain by changing
things at this level.

The default OS to use is really important!  To get the most use of
multiple-CPU machines one should use Solaris (because the threads works
really nice) or Linux (because the 2.2 kernel has really good SMP
support). Also on 32-bit machines Linux has a 2G file-size limit by
default. Hopefully this will be fixed soon when new filesystems are
released (XFS/Reiserfs).  If you have a desperate need for files bigger
than 2G on Linux-intel 32 bit, you should get the LFS patch for the ext2
filesystem.

Because we have not run MySQL in production on that many platforms, we
advice you to test your intended platform before choosing it, if
possible.

Other tips:
   * If you have enough RAM, you could remove all swap devices. Some
     operating systems will use a swap device in some contexts even if
     you have free memory.

   * Use the `--skip-external-locking' MySQL option to avoid external
     locking. Note that this will not impact MySQL's functionality as
     long as you only run one server. Just remember to take down the
     server (or lock relevant parts) before you run `myisamchk'. On
     some system this switch is mandatory because the external locking
     does not work in any case.

     The `--skip-external-locking' option is on by default when
     compiling with MIT-pthreads, because `flock()' isn't fully
     supported by MIT-pthreads on all platforms.  It's also on default
     for Linux as Linux file locking are not yet safe.

     The only case when you can't use `--skip-external-locking' is if
     you run multiple MySQL _servers_ (not clients) on the same data,
     or run `myisamchk' on the table without first flushing and locking
     the `mysqld' server tables first.

     You can still use `LOCK TABLES'/`UNLOCK TABLES' even if you are
     using `--skip-external-locking'

Tuning Server Parameters
------------------------

You can get the default buffer sizes used by the `mysqld' server with
this command:

     shell> mysqld --help

This command produces a list of all `mysqld' options and configurable
variables. The output includes the default values and looks something
like this:

     Possible variables for option --set-variable (-O) are:
     back_log                 current value: 5
     bdb_cache_size           current value: 1048540
     binlog_cache_size        current value: 32768
     connect_timeout          current value: 5
     delayed_insert_timeout   current value: 300
     delayed_insert_limit     current value: 100
     delayed_queue_size       current value: 1000
     flush_time               current value: 0
     interactive_timeout      current value: 28800
     join_buffer_size         current value: 131072
     key_buffer_size          current value: 1048540
     lower_case_table_names   current value: 0
     long_query_time          current value: 10
     max_allowed_packet       current value: 1048576
     max_binlog_cache_size    current value: 4294967295
     max_connections          current value: 100
     max_connect_errors       current value: 10
     max_delayed_threads      current value: 20
     max_heap_table_size      current value: 16777216
     max_join_size            current value: 4294967295
     max_sort_length          current value: 1024
     max_tmp_tables           current value: 32
     max_write_lock_count     current value: 4294967295
     myisam_sort_buffer_size  current value: 8388608
     net_buffer_length        current value: 16384
     net_retry_count          current value: 10
     net_read_timeout         current value: 30
     net_write_timeout        current value: 60
     read_buffer_size         current value: 131072
     record_rnd_buffer_size   current value: 131072
     slow_launch_time         current value: 2
     sort_buffer              current value: 2097116
     table_cache              current value: 64
     thread_concurrency       current value: 10
     tmp_table_size           current value: 1048576
     thread_stack             current value: 131072
     wait_timeout             current value: 28800

Please note that `--set-variable' is deprecated since MySQL 4.0, just
use `--var=option' on its own.

If there is a `mysqld' server currently running, you can see what
values it actually is using for the variables by executing this command:

     shell> mysqladmin variables

You can find a full description for all variables in the `SHOW
VARIABLES' section in this manual. *Note SHOW VARIABLES::.

You can also see some statistics from a running server by issuing the
command `SHOW STATUS'. *Note SHOW STATUS::.

MySQL uses algorithms that are very scalable, so you can usually run
with very little memory. If you, however, give MySQL more memory, you
will normally also get better performance.

When tuning a MySQL server, the two most important variables to use are
`key_buffer_size' and `table_cache'.  You should first feel confident
that you have these right before trying to change any of the other
variables.

If you have much memory (>=256M) and many tables and want maximum
performance with a moderate number of clients, you should use something
like this:

     shell> safe_mysqld -O key_buffer=64M -O table_cache=256 \
                -O sort_buffer=4M -O read_buffer_size=1M &

If you have only 128M and only a few tables, but you still do a lot of
sorting, you can use something like:

     shell> safe_mysqld -O key_buffer=16M -O sort_buffer=1M

If you have little memory and lots of connections, use something like
this:

     shell> safe_mysqld -O key_buffer=512k -O sort_buffer=100k \
                -O read_buffer_size=100k &

or even:

     shell> safe_mysqld -O key_buffer=512k -O sort_buffer=16k \
                -O table_cache=32 -O read_buffer_size=8k -O net_buffer_length=1K &

If you are doing a `GROUP BY' or `ORDER BY' on files that are much
bigger than your available memory you should increase the value of
`record_rnd_buffer' to speed up the reading of rows after the sorting
is done.

When you have installed MySQL, the `support-files' directory will
contain some different `my.cnf' example files, `my-huge.cnf',
`my-large.cnf', `my-medium.cnf', and `my-small.cnf', you can use as a
base to optimise your system.

If there are very many connections, "swapping problems" may occur unless
`mysqld' has been configured to use very little memory for each
connection. `mysqld' performs better if you have enough memory for all
connections, of course.

Note that if you change an option to `mysqld', it remains in effect only
for that instance of the server.

To see the effects of a parameter change, do something like this:

     shell> mysqld -O key_buffer=32m --help

Make sure that the `--help' option is last; otherwise, the effect of any
options listed after it on the command-line will not be reflected in the
output.

How Compiling and Linking Affects the Speed of MySQL
----------------------------------------------------

Most of the following tests are done on Linux with the MySQL
benchmarks, but they should give some indication for other operating
systems and workloads.

You get the fastest executable when you link with `-static'.

On Linux, you will get the fastest code when compiling with `pgcc' and
`-O3'. To compile `sql_yacc.cc' with these options, you need about 200M
memory because `gcc/pgcc' needs a lot of memory to make all functions
inline. You should also set `CXX=gcc' when configuring MySQL to avoid
inclusion of the `libstdc++' library (it is not needed). Note that with
some versions of `pgcc', the resulting code will only run on true
Pentium processors, even if you use the compiler option that you want
the resulting code to be working on all x586 type processors (like AMD).

By just using a better compiler and/or better compiler options you can
get a 10-30% speed increase in your application.  This is particularly
important if you compile the SQL server yourself!

We have tested both the Cygnus CodeFusion and Fujitsu compilers, but
when we tested them, neither was sufficiently bug free to allow MySQL
to be compiled with optimisations on.

When you compile MySQL you should only include support for the
character sets that you are going to use. (Option `--with-charset=xxx'.)
The standard MySQL binary distributions are compiled with support for
all character sets.

Here is a list of some measurements that we have done:
   * If you use `pgcc' and compile everything with `-O6', the `mysqld'
     server is 1% faster than with `gcc' 2.95.2.

   * If you link dynamically (without `-static'), the result is 13%
     slower on Linux.  Note that you still can use a dynamic linked
     MySQL library. It is only the server that is critical for
     performance.

   * If you strip your `mysqld' binary with `strip libexec/mysqld', the
     resulting binary can be up to 4% faster.

   * If you connect using TCP/IP rather than Unix sockets, the result
     is 7.5% slower on the same computer. (If you are connection to
     `localhost', MySQL will, by default, use sockets.)

   * If you connect using TCP/IP from another computer over a 100M
     Ethernet, things will be 8-11% slower.

   * When running our benchmark tests using secure connections (all data
     encrypted with internal SSL support) things were 55% slower.

   * If you compile with `--with-debug=full', then you will lose 20%
     for most queries, but some queries may take substantially longer
     (The MySQL benchmarks ran 35% slower) If you use `--with-debug',
     then you will only lose 15%.  By starting a `mysqld' version
     compiled with `--with-debug=full' with `--skip-safemalloc' the end
     result should be close to when configuring with `--with-debug'.

   * On a Sun UltraSPARC-IIe, Forte 5.0 is 4% faster than `gcc' 3.2

   * On a Sun UltraSPARC-IIe, Forte 5.0 is 4% faster in 32 bit mode
     than in 64 bit mode.

   * Compiling with `gcc' 2.95.2 for UltraSPARC with the option
     `-mcpu=v8 -Wa,-xarch=v8plusa' gives 4% more performance.

   * On Solaris 2.5.1, MIT-pthreads is 8-12% slower than Solaris native
     threads on a single processor. With more load/CPUs the difference
     should get bigger.

   * Running with `--log-bin' makes mysqld 1% slower.

   * Compiling on Linux-x86 using gcc without frame pointers
     `-fomit-frame-pointer' or `-fomit-frame-pointer -ffixed-ebp' makes
     `mysqld' 1-4% faster.

The MySQL-Linux distribution provided by MySQL AB used to be compiled
with `pgcc', but we had to go back to regular gcc because of a bug in
`pgcc' that would generate the code that does not run on AMD. We will
continue using gcc until that bug is resolved.  In the meantime, if you
have a non-AMD machine, you can get a faster binary by compiling with
`pgcc'.  The standard MySQL Linux binary is linked statically to get it
faster and more portable.

How MySQL Uses Memory
---------------------

The following list indicates some of the ways that the `mysqld' server
uses memory.  Where applicable, the name of the server variable relevant
to the memory use is given:

   * The key buffer (variable `key_buffer_size') is shared by all
     threads; other buffers used by the server are allocated as needed.
     *Note Server parameters::.

   * Each connection uses some thread-specific space: A stack (default
     64K, variable `thread_stack'), a connection buffer (variable
     `net_buffer_length'), and a result buffer (variable
     `net_buffer_length'). The connection buffer and result buffer are
     dynamically enlarged up to `max_allowed_packet' when needed.  When
     a query is running, a copy of the current query string is also
     allocated.

   * All threads share the same base memory.

   * Only the compressed `ISAM' / `MyISAM' tables are memory mapped.
     This is because the 32-bit memory space of 4GB is not large enough
     for most big tables. When systems with a 64-bit address space
     become more common we may add general support for memory mapping.

   * Each request doing a sequential scan over a table allocates a read
     buffer (variable `record_buffer').

   * When reading rows in 'random' order (for example after a sort) a
     random-read buffer is allocated to avoid disk seeks.  (variable
     `record_rnd_buffer').

   * All joins are done in one pass, and most joins can be done without
     even using a temporary table. Most temporary tables are
     memory-based (`HEAP') tables.  Temporary tables with a big record
     length (calculated as the sum of all column lengths) or that
     contain `BLOB' columns are stored on disk.

     One problem in MySQL versions before Version 3.23.2 is that if a
     `HEAP' table exceeds the size of `tmp_table_size', you get the
     error `The table tbl_name is full'. In newer versions this is
     handled by automatically changing the in-memory (`HEAP') table to
     a disk-based (`MyISAM') table as necessary. To work around this
     problem, you can increase the temporary table size by setting the
     `tmp_table_size' option to `mysqld', or by setting the SQL option
     `BIG_TABLES' in the client program.  *Note `SET' Syntax: SET
     OPTION. In MySQL Version 3.20, the maximum size of the temporary
     table was `record_buffer*16', so if you are using this version,
     you have to increase the value of `record_buffer'. You can also
     start `mysqld' with the `--big-tables' option to always store
     temporary tables on disk. However, this will affect the speed of
     many complicated queries.

   * Most requests doing a sort allocates a sort buffer and 0-2
     temporary files depending on the result set size. *Note Temporary
     files::.

   * Almost all parsing and calculating is done in a local memory
     store. No memory overhead is needed for small items and the normal
     slow memory allocation and freeing is avoided. Memory is allocated
     only for unexpectedly large strings (this is done with `malloc()'
     and `free()').

   * Each index file is opened once and the datafile is opened once for
     each concurrently running thread. For each concurrent thread, a
     table structure, column structures for each column, and a buffer
     of size `3 * n' is allocated (where `n' is the maximum row length,
     not counting `BLOB' columns). A `BLOB' uses 5 to 8 bytes plus the
     length of the `BLOB' data. The `ISAM'/`MyISAM' storage engines
     will use one extra row buffer for internal usage.

   * For each table having `BLOB' columns, a buffer is enlarged
     dynamically to read in larger `BLOB' values. If you scan a table,
     a buffer as large as the largest `BLOB' value is allocated.

   * Storage engines for all in-use tables are saved in a cache and
     managed as a FIFO. Normally the cache has 64 entries. If a table
     has been used by two running threads at the same time, the cache
     contains two entries for the table. *Note Table cache::.

   * A `mysqladmin flush-tables' command closes all tables that are not
     in use and marks all in-use tables to be closed when the currently
     executing thread finishes. This will effectively free most in-use
     memory.

`ps' and other system status programs may report that `mysqld' uses a
lot of memory. This may be caused by thread-stacks on different memory
addresses. For example, the Solaris version of `ps' counts the unused
memory between stacks as used memory. You can verify this by checking
available swap with `swap -s'. We have tested `mysqld' with commercial
memory-leakage detectors, so there should be no memory leaks.

How MySQL uses DNS
------------------

When a new thread connects to `mysqld', `mysqld' will span a new thread
to handle the request.  This thread will first check if the hostname is
in the hostname cache. If not the thread will call `gethostbyaddr_r()'
and `gethostbyname_r()' to resolve the hostname.

If the operating system doesn't support the above thread-safe calls, the
thread will lock a mutex and call `gethostbyaddr()' and
`gethostbyname()' instead. Note that in this case no other thread can
resolve other hostnames that is not in the hostname cache until the
first thread is ready.

You can disable DNS host lookup by starting `mysqld' with
`--skip-name-resolve'.  In this case you can however only use IP names
in the MySQL privilege tables.

If you have a very slow DNS and many hosts, you can get more
performance by either disabling DNS lookop with `--skip-name-resolve'
or by increasing the `HOST_CACHE_SIZE' define (default: 128) and
recompile `mysqld'.

You can disable the hostname cache with `--skip-host-cache'. You can
clear the hostname cache with `FLUSH HOSTS' or `mysqladmin flush-hosts'.

If you don't want to allow connections over `TCP/IP', you can do this
by starting `mysqld' with `--skip-networking'.

`SET' Syntax
------------

     SET [GLOBAL | SESSION] sql_variable=expression, [[GLOBAL | SESSION] sql_variable=expression...]

`SET' sets various options that affect the operation of the server or
your client.

The following examples shows the different syntaxes one can use to set
variables:

In old MySQL versions we allowed the use of the `SET OPTION' syntax,
but this syntax is now deprecated.

In MySQL 4.0.3 we added the `GLOBAL' and `SESSION' options and access
to most important startup variables.

`LOCAL' can be used as a synonym for `SESSION'.

If you set several variables on the same command line, the last used
`GLOBAL | SESSION' mode is used.

     SET sort_buffer_size=10000;
     SET @@local.sort_buffer_size=10000;
     SET GLOBAL sort_buffer_size=1000000, SESSION sort_buffer_size=1000000;
     SET @@sort_buffer_size=1000000;
     SET @@global.sort_buffer_size=1000000, @@local.sort_buffer_size=1000000;

The `@@variable_name' syntax is supported to make MySQL syntax
compatible with some other databases.

The different system variables one can set are described in the system
variable section of this manual. *Note System Variables::.

If you are using `SESSION' (the default) the option you set remains in
effect until the current session ends, or until you set the option to a
different value. If you use `GLOBAL', which require the `SUPER'
privilege, the option is remembered and used for new connections until
the server restarts. If you want to make an option permanent, you
should set it in one of the MySQL option files. *Note Option files::.

To avoid wrong usage MySQL will give an error if you use `SET GLOBAL'
with a variable that can only be used with `SET SESSION' or if you are
not using `SET GLOBAL' with a global variable.

If you want to set a `SESSION' variable to the `GLOBAL' value or a
`GLOBAL' value to the MySQL default value, you can set it to `DEFAULT'.

     SET max_join_size=DEFAULT;

This is identical to:

     SET @@session.max_join_size=@@global.max_join_size;

If you want to restrict the maximum value a startup option can be set to
with the `SET' command, you can specify this by using the
`--maximum-variable-name' command line option. *Note Command-line
options::.

You can get a list of most variables with `SHOW VARIABLES'.  *Note SHOW
VARIABLES::.  You can get the value for a specific value with the
`@@[global.|local.]variable_name' syntax:
     SHOW VARIABLES like "max_join_size";
     SHOW GLOBAL VARIABLES like "max_join_size";
     SELECT @@max_join_size, @@global.max_join_size;

Here follows a description of the variables that uses a the variables
that uses a non-standard `SET' syntax and some of the other variables.
The other variable definitions can be found in the system variable
section, among the startup options or in the description of `SHOW
VARIABLES'. *Note System Variables::. *Note Command-line options::.
*Note SHOW VARIABLES::.

`CHARACTER SET character_set_name | DEFAULT'
     This maps all strings from and to the client with the given
     mapping.  Currently the only option for `character_set_name' is
     `cp1251_koi8', but you can easily add new mappings by editing the
     `sql/convert.cc' file in the MySQL source distribution.  The
     default mapping can be restored by using a `character_set_name'
     value of `DEFAULT'.

     Note that the syntax for setting the `CHARACTER SET' option differs
     from the syntax for setting the other options.

`PASSWORD = PASSWORD('some password')'
     Set the password for the current user. Any non-anonymous user can
     change his own password!

`PASSWORD FOR user = PASSWORD('some password')'
     Set the password for a specific user on the current server host.
     Only a user with access to the `mysql' database can do this.  The
     user should be given in `user@hostname' format, where `user' and
     `hostname' are exactly as they are listed in the `User' and `Host'
     columns of the `mysql.user' table entry.  For example, if you had
     an entry with `User' and `Host' fields of `'bob'' and
     `'%.loc.gov'', you would write:

          mysql> SET PASSWORD FOR bob@"%.loc.gov" = PASSWORD("newpass");

     Which is equivalent to:

          mysql> UPDATE mysql.user SET password=PASSWORD("newpass")
              ->                   WHERE user="bob' AND host="%.loc.gov";

`SQL_AUTO_IS_NULL = 0 | 1'
     If set to `1' (default) then one can find the last inserted row
     for a table with an `AUTO_INCREMENT' column with the following
     construct: `WHERE auto_increment_column IS NULL'.  This is used by
     some ODBC programs like Access.

`AUTOCOMMIT= 0 | 1'
     If set to `1' all changes to a table will be done at once. To start
     a multi-command transaction, you have to use the `BEGIN'
     statement. *Note COMMIT::. If set to `0' you have to use `COMMIT' /
     `ROLLBACK' to accept/revoke that transaction. *Note COMMIT::.  Note
     that when you change from not `AUTOCOMMIT' mode to `AUTOCOMMIT'
     mode, MySQL will do an automatic `COMMIT' on any open transactions.

`BIG_TABLES = 0 | 1'
     If set to `1', all temporary tables are stored on disk rather than
     in memory.  This will be a little slower, but you will not get the
     error `The table tbl_name is full' for big `SELECT' operations that
     require a large temporary table.  The default value for a new
     connection is `0' (that is, use in-memory temporary tables).  This
     option was before named `SQL_BIG_TABLES'.

`SQL_BIG_SELECTS = 0 | 1'
     If set to `0', MySQL will abort if a `SELECT' is attempted that
     probably will take a very long time. This is useful when an
     inadvisable `WHERE' statement has been issued. A big query is
     defined as a `SELECT' that probably will have to examine more than
     `max_join_size' rows.  The default value for a new connection is
     `1' (which will allow all `SELECT' statements).

`SQL_BUFFER_RESULT = 0 | 1'
     `SQL_BUFFER_RESULT' will force the result from `SELECT's to be put
     into a temporary table. This will help MySQL free the table locks
     early and will help in cases where it takes a long time to send
     the result set to the client.

`LOW_PRIORITY_UPDATES = 0 | 1'
     If set to `1', all `INSERT', `UPDATE', `DELETE', and `LOCK TABLE
     WRITE' statements wait until there is no pending `SELECT' or `LOCK
     TABLE READ' on the affected table.  This option was before named
     `SQL_LOW_PRIORITY_UPDATES'.

`MAX_JOIN_SIZE = value | DEFAULT'
     Don't allow `SELECT's that will probably need to examine more than
     `value' row combinations.  By setting this value, you can catch
     `SELECT's where keys are not used properly and that would probably
     take a long time. Setting this to a value other than `DEFAULT'
     will reset the `SQL_BIG_SELECTS' flag.  If you set the
     `SQL_BIG_SELECTS' flag again, the `SQL_MAX_JOIN_SIZE' variable
     will be ignored.  You can set a default value for this variable by
     starting `mysqld' with `-O max_join_size=#'.  This option was
     before named `SQL_MAX_JOIN_SIZE'.

     Note that if the result of the query is already in the query
     cache, the above check will not be made. Instead, MySQL will send
     the result to the client. Since the query result is already
     computed and it will not burden the server to send the result to
     the client.

`QUERY_CACHE_TYPE = OFF | ON | DEMAND'

`QUERY_CACHE_TYPE = 0   | 1  | 2'
     Set query cache setting for this thread.
     *Option*      *Description*
     0 or OFF      Don't cache or retrieve results.
     1 or ON       Cache all results except `SELECT SQL_NO_CACHE
                   ...' queries.
     2 or DEMAND   Cache only `SELECT SQL_CACHE ...' queries.

`SQL_SAFE_UPDATES = 0 | 1'
     If set to `1', MySQL will abort if an `UPDATE' or `DELETE' is
     attempted that doesn't use a key or `LIMIT' in the `WHERE' clause.
     This makes it possible to catch wrong updates when creating SQL
     commands by hand.

`SQL_SELECT_LIMIT = value | DEFAULT'
     The maximum number of records to return from `SELECT' statements.
     If a `SELECT' has a `LIMIT' clause, the `LIMIT' takes precedence
     over the value of `SQL_SELECT_LIMIT'.  The default value for a new
     connection is "unlimited." If you have changed the limit, the
     default value can be restored by using a `SQL_SELECT_LIMIT' value
     of `DEFAULT'.

`SQL_LOG_OFF = 0 | 1'
     If set to `1', no logging will be done to the standard log for this
     client, if the client has the `SUPER' privilege.  This does not
     affect the update log!

`SQL_LOG_UPDATE = 0 | 1'
     If set to `0', no logging will be done to the update log for the
     client, if the client has the `SUPER' privilege.  This does not
     affect the standard log!

`SQL_QUOTE_SHOW_CREATE = 0 | 1'
     If set to `1', `SHOW CREATE TABLE' will quote table and column
     names. This is *on* by default, for replication of tables with
     fancy column names to work.  *Note `SHOW CREATE TABLE': SHOW
     CREATE TABLE.

`TIMESTAMP = timestamp_value | DEFAULT'
     Set the time for this client.  This is used to get the original
     timestamp if you use the update log to restore rows.
     `timestamp_value' should be a Unix epoch timestamp, not a MySQL
     timestamp.

`LAST_INSERT_ID = #'
     Set the value to be returned from `LAST_INSERT_ID()'. This is
     stored in the update log when you use `LAST_INSERT_ID()' in a
     command that updates a table.

`INSERT_ID = #'
     Set the value to be used by the following `INSERT' or `ALTER TABLE'
     command when inserting an `AUTO_INCREMENT' value.  This is mainly
     used with the update log.

Disk Issues
===========

   * As mentioned before, disks seeks are a big performance bottleneck.
     This problems gets more and more apparent when the data starts to
     grow so large that effective caching becomes impossible. For large
     databases, where you access data more or less randomly, you can be
     sure that you will need at least one disk seek to read and a
     couple of disk seeks to write things. To minimise this problem,
     use disks with low seek times.

   * Increase the number of available disk spindles (and thereby reduce
     the seek overhead) by either symlink files to different disks or
     striping the disks.

    *Using symbolic links*
          This means that you symlink the index and/or datafile(s) from
          the normal data directory to another disk (that may also be
          striped). This makes both the seek and read times better (if
          the disks are not used for other things). *Note Symbolic
          links::.

    *Striping*
          Striping means that you have many disks and put the first
          block on the first disk, the second block on the second disk,
          and the Nth on the (N mod number_of_disks) disk, and so on.
          This means if your normal data size is less than the stripe
          size (or perfectly aligned) you will get much better
          performance. Note that striping is very dependent on the OS
          and stripe-size. So benchmark your application with different
          stripe-sizes. *Note Custom Benchmarks::.

          Note that the speed difference for striping is *very*
          dependent on the parameters. Depending on how you set the
          striping parameters and number of disks you may get a
          difference in orders of magnitude. Note that you have to
          choose to optimise for random or sequential access.

   * For reliability you may want to use RAID 0+1 (striping +
     mirroring), but in this case you will need 2*N drives to hold N
     drives of data. This is probably the best option if you have the
     money for it!  You may, however, also have to invest in some
     volume-management software to handle it efficiently.

   * A good option is to have semi-important data (that can be
     regenerated) on RAID 0 disk while storing really important data
     (like host information and logs) on a RAID 0+1 or RAID N disk.