Apache Cookbook, 2nd Edition

Caching Dynamic Content

Problem

You want to cache dynamically generated documents that don’t actually change very often.

Solution

In Apache 2.2, use the following recipe:

CacheEnable disk / 
CacheRoot /var/www/cache
CacheIgnoreCacheControl On
CacheDefaultExpire 600

In 2.3 and later, you can use something like this:

CacheEnable disk / 
CacheRoot /var/www/cache
CacheDefaultExpire 600
CacheMinExpire 600

Discussion

Caching is usually explicitly disabled for dynamic content. Dynamic content, by definition, is content that is generated on demand—that is, created fresh each time it is requested. Thus, caching it is contrary to its very nature

However, it is often—even usually—the case that dynamically generated content doesn’t actually change very much from one minute to the next. This means that you end up wasting an awful lot of time generating content that hasn’t actually changed since the last time it was requested. If you’re doing this several times per second, you’re probably causing your server a great deal more work than is really necessary.

The recipes above solve this problem in two slightly different ways. The solution for 2.3 is better, but, as of this writing, 2.3 hasn’t been released yet, so it’s not a terribly practical solution yet.

The recipe for Apache 2.2 takes the approach of disabling cache control—that is, it tells Apache to ignore the request made by the dynamic content that it not be cached, and caches it anyway. Then, for good measure, a default cache expiration time of 5 minutes ...