The latest version of this software can always be found at <http://www.clearway.com/cscm/>
This software is free. It may be redistributed unmodified, provided that this document is included.
THIS SOFTWARE IS PROVIDED AS-IS. CLEARWAY TECHNOLOGIES, INC. (CLEARWAY) MAKES NO CLAIMS AS TO THE SUITABILITY OF THIS SOFTWARE TO ANY TASK. BY USING THIS UNSUPPORTED SOFTWARE, YOU ASSUME FULL RESPONSIBILITY FOR ANY AND ALL INJURIES, DAMAGES, OR LOSSES RESULTING EITHER DIRECTLY OR INDIRECTLY FROM THE USE OF THIS SOFTWARE. IF YOU DO NOT UNDERSTAND OR ACCEPT THESE TERMS, OR IF THIS WAIVER OF LIABILITY IS NOT VALID OR CANNOT BE ENFORCED IN YOUR LOCATION, YOU MUST NOT USE THIS SOFTWARE. FOR MORE INFORMATION ON BECOMING A LAWYER, CONSULT THE AMERICAN BAR ASSOCIATION AT <HTTP://WWW.ABANET.ORG/>
What is ClearWay Simple Cache Manager?
ClearWay Simple Cache Manager (CSCM) is a W*API 1.1 plug-in for WebSTAR-compatible Web servers that will clear the Web server's RAM caches upon request and to a certain extent, "automatically." It allows Webmasters to take advantage of Web server RAM caching to boost performance, while still allowing users to update their Web pages remotely and see the changes immediately.
CSCM will clear the Web server caches according to rules you can configure. You can set CSCM to clear the caches when:
- a browser requests the URL "/.clear" from your Web server.
Any user can request this URL, or you may password-protect it through the usual password
mechanisms.
- a user running Netscape Navigator chooses "Reload" for a page on your server
This means that remote users updating their Web pages simply have to do a
Netscape "Reload" to see their changes; no special URL is needed.
- CSCM can (optionally) filter out most 'regular' Reloads, and clear the caches only
when a "Super Reload" is requested. (Netscape: Option key + View->Reload)
This means that the caches will only be cleared 'deliberately', not by casual visitors
- CSCM can set a minimum time to wait between cache clears (default is 20 seconds)
CSCM prints a message to the Web server window whenever the cache is cleared, showing the percentage of hits that have been passed to the cache. Typically this percentage is in the 95%-99% range, indicating a very high level of cache usage.
A Webmaster can now enable full RAM caching on the server to improve performance, and remote users updating their Web pages can see their changes immediately. Even with the occasional "cache clear", Web servers using caching will still see significant performance improvements over servers without any caching. Remote users will happy to have simple control over when to "reload" their pages.
ClearWay Technologies will NOT provide technical support for this free product.
System Requirements / Installation
In order to function properly, this extension needs:
- a W*API 1.1 -compatible Web server such as WebSTAR or Quid Pro Quo
- 16K of free RAM
Place this extension into your Web server's Plug-Ins folder and restart the Web server program.
To test this Web server plug-in, browse a few pages from your Web server using Netscape Navigator. While watching the Web server status window, hold down Option key and choose "Super Reload" from the Netscape View menu. The Web server should display a message indicating that ClearWay Simple Cache Manager has cleared the cache. The message also shows the percentage of hits that have been passed to the cache.
Next, browse a few more pages from your server. Now access the URL <http://your.server.name/.clear>. You will see a page in your browser indicating that the caches have been cleared (and a message will appear in the Web server window again). You can bookmark this page to clear the caches at any time.
Usage Notes
- Using RAM caches and CSCM together makes your server much faster than not using caches at all, and CSCM is far more flexible than 'scheduled' cache-clearing or simply never clearing the cache. While having the cache SOMETIMES cleared may result in lower performance than NEVER clearing the cache, never clearing the cache makes remote updating basically impossible. ClearWay Simple Cache Manager is intended to be a high-performance hassle-free way of using caching and allowing easy remote updating.
- CSCM will not clear the cache more often than you set. Here's why you want this: when a Web page is reloaded from Netscape, Netscape sends the "Pragma: no-cache" message once for the HTML page itself, and also once for each graphic on the page. Since this would result in a large number of near-simultaneous cache clears, CSCM has this built-in "damping limit" which prevents inefficient use of CPU power spent clearing the caches dozens of times in very rapid succession.
- Microsoft Internet Explorer does not currently send the Pragma: no-cache message, even when the user requests a full "reload". MSIE users must use the "/.clear" URL to clear the caches.
- Users can bookmark the "/.clear" page for easy access to the "cache clearing" function. The page is named "Clear Server Cache" so its function is clear in the Bookmark menu.
- This plug-in installs itself in the "FILTER" role, and peacefully co-exists with other plug-ins that use the Filter role, including FireSite and various other plug-ins.
- CSCM sends the "clear cache" message to the Web server, and the Web server forwards the message to all plug-ins. Some plug-ins (specifically, those built directly from the W*API sample code) print cryptic and/or misleading messages when they receive the "clear cache" message. You may you see "PLUGIN: received bad message (5)" or "PLUGIN: Server reports that settings have changed." messages in the Web server window; you can safely ignore these. (Wouldn't it be nice if all plug-in developers always included the NAME of their plug-in in their status messages, rather than just printing "PLUGIN:"?)
- When CSCM sends the "clear cache" message, all W*API-savvy caches are cleared. This includes WebSTAR's File Info and Data caches, and possibly the caches of other plug-ins such as NetCloak.
- While RAM caching can help reduce Web server latency, bandwidth is usually much more of a limiting factor on Web server performance, especially on the Internet (as opposed to an internal intranet). To overcome the bandwidth limitations of your server's Internet connection, check out FireSite <http://www.clearway.com/firesite/>, also from ClearWay Technologies.
- FireSite 2.0 sends the "Pragma: no-cache" message to remote replication servers when remote files are added, deleted, or changed. For FireSite users replicating to remote WebSTAR-compatible servers, installing CSCM and turning on RAM caching on the remote server can give an extra performance boost without having to worry about cache synchronization.
- When FireSite 2.0 receives the "clear cache" message, FireSite's internal File Info and Data caches are marked as "expired" and are re-checked as needed, but they are not cleared from memory unless an individual file has changed.
About ClearWay Technologies, Inc.
ClearWay Technologies, Inc. is a smart, friendly, helpful company that consitently delivers astoundingly useful Internet products and supports them with great customer service. ClearWay was founded in January 1996, is privately held, and currently employs five people building and marketing fantastic Internet software.
Check out our Top "Twenty" Tips for Mac Webmasters! <http://mac-web-tips.clearway.com/>
Credits
ClearWay Simple Cache Manager was written by Ben Wyckoff with help from Mark Kriegsman. Thanks to Susan Marlett for helping to extend the "ClearWay" brand in this new direction. This software is dedicated to all the faithful readers of WebSTAR-talk and WebSTAR-dev. For more information on joining these mailing lists, visit <http://www.starnine.com/>
