Manual:MemcachedSessions.php

Details
MemcachedSessions.php file gets included if sessions>Special:MyLanguage/Manual:$wgSessionsInMemcached|$wgSessionsInMemcached is set in the config. It redirects session handling functions to store their data in memcached instead of the local filesystem. Depending on circumstances, it may also be necessary to change the cookie settings to work across hostnames.