Memcached provides a custom session handler that can be used to store user sessions in memcache. A completely separate memcached instance is used for that internally, so you can a different server pool if necessary. The session keys are stored under the prefix memc.sess.lock_key., so be aware of this if you use the same server pool for sessions and generic caching.
Set to memcached to enable sessions support.
Defines a comma separated of hostname:port entries to use for session server pool, for example "sess1:11211, sess2:11211".