mod_memcached_cache

This module allows an Apache 2.2.x instance to use one or more memcached instances for HTTP 1.1 document caching, in addition to/instead of the modules distributed with Apache for file and in-process memory caching.

Installation

See INSTALL for details.

Implementation

My guess is that mod_memcached_cache will be useful in conjunction with one or both of the bundled caching modules:

On the plus side, it allows more than one Apache server to serve the same cached data, so that, for example, a group of servers behind a reverse proxy can have a high cache hit rate for requests because once one server caches a document, its cached for them all. Similarly, that proxy server itself could potentially skip requests to those backend servers more often because they, too, are working to keep requests cached.

The downside is that each cache hit still requires two memcached requests, which won't be as fast as in process memory (with mod_mem_cache). I haven't benchmarked the difference between a mod_memcached_cache hit and a mod_disk_cache hit.