Caching has been rethought, and rewritten, a number of times in the last several versions of the Apache web server. This time, there are marked improvements over previous incarnations. There are a number of great new features and the caching modules seem to do what you expect, more of the time.

For the first time in what seems like forever, mod_cache and related modules, are no longer marked as experimental, as they have been for most of recent memory. This should encourage greater use by people who were concerned about using a module with that designation.

Of course, it’s more than just a designation. A lot of work has gone into this module and it shows. There’s a number of exciting new features, as well as some significant restructuring.

Caching Versus Proxying

You may recall that in Apache 1.3, caching was very tightly tied to proxying. They were implemented in the same module—mod_proxy—and there wasn’t really any way to use them independently of one another. Caching was, essentially, an optional feature of the proxying features of mod_proxy.

In Apache 2.0, mod_proxy was split from mod_cache. Some functionality of mod_cache was split out into submodules. Specifically, the storage mechanism was implemented in two modules. mod_disk_cache implemented a disk-based storage system, while mod_mem_cache implemented memory-based storage.

Unfortunately, since this functionality was somewhat poorly documented, and, more importantly, since the documentation stated that the module was experimental ...

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