Apache: The Definitive Guide, Second Edition

9.2. Caching

Another reason for using a proxy server is to cache data from the Web to save the bandwidth of the world's sadly overloaded telephone systems and therefore to improve access time on our server.

The directive CacheRoot, cunningly inserted in the Config file shown earlier, and the provision of a properly permissioned cache directory allow us to show this happening. We start by providing the directory ... / site.proxy/cache, and Apache then improves on it with some sort of directory structure like ... /site.proxy/cache/d/o/j/gfqbZ@49rZiy6LOCw.

The file gfqbZ@49rZiy6LOCw contains the following:

320994B6 32098D95 3209956C 00000000 0000001E
X-URL: http://192.168.124.1/message
HTTP/1.0 200 OK
Date: Thu, 08 Aug 1996 07:18:14 GMT
Server: Apache/1.1.1
Content-length: 30
Last-modified Thu, 08 Aug 1996 06:47:49 GMT

I am a web site far out there

Next time someone wants to access http://192.168.124.1/message, the proxy server does not have to lug bytes over the Web; it can just go and look it up.

There are a number of housekeeping directives that help with caching.

9.2.1. CacheRoot

               CacheRoot directory
Default: none
Server config, virtual host

Sets the directory to contain cache files—must be writable by Apache.

9.2.2. CacheSize

               
               CacheSize size_in_kilobytes
Default: 5
Server config, virtual host

This directive sets the size of the cache area in kilobytes. More may be stored, but garbage collection reduces it to less than the set number.

9.2.3. CacheGcInterval

CacheGcInterval ...