In this new post to his blog Paul Reinheimer looks at one of the more powerful tools at a PHP developer's disposal - memcache - and how you can use it to store sessions.
I’ve been using memcached to store session data for the past while, but we ran into a few problems at work that led me to dive in a bit deeper and see how PHP, Sessions, and memcached play along. [...] When you start up a session a new entry is created in memcache, the expiry is the same as session.gc_maxlifetime. Session data is retrieved each time a session is started (either with session_start(), or if you have session.auto_start enabled, etc).
In his "long version" he explains what's actually happening behind the scenes between PHP's session handler and the memcached server.