Memcache is a High-performance, distributed object caching system.
WordPress is a great piece of blogging / CMS software. If you’re running a WordPress site and you’re having growing pains, you can combine the two to handle increased traffic and, more than likely, get pages to load faster for everyone.
WordPress has built-in support for extensible caching, but by default, it’s only valid for one session. While this helps speed up page loads / reduce server load for individual users, caching the objects in a non-session-exclusive (persistent) cache has much more potential for performance improvements and generally scales better. (You can read more about built-in WP_Cache mechanisms here: http://codex.wordpress.org/Function_Reference/WP_Cache)
We recommend and have successfully implemented the WordPress plugin “Memcached object cache” (http://wordpress.org/extend/plugins/memcached/), which is trivial to install / configure. By default, it assumes that you are running a single memcached server on the same server that PHP is running on (i.e. 127.0.0.1 or localhost). It also assumes the port is 11211, which is the “standard” memcached port.
You’ll need the PECL ‘memcached’ extension: http://pecl.php.net/package/memcached, as well as memcached actually installed, running and accepting connections on whatever you configure Memcached object cache to use (127.0.0.1:11211 is again, the default).
Installing the actual adapter that lets WP_Cache use memcached is just a matter of putting the ‘object-cache.php’ into your wp-content directory. If you’re set up using the defaults, it should just start working immediately. This, in combination with the fantastic WP-SuperCache-Plus plugin (http://wpscp.trac.armadillo.homeip.net/) will allow your site to handle much more traffic than would otherwise be possible.