Memcache
PHP Manual

Constantes pré-definidas

Memcache Constants
Name Description
MEMCACHE_COMPRESSED ( integer ) Used to turn on-the-fly data compression on with Memcache::set(), Memcache::add() e Memcache::replace().
MEMCACHE_HAVE_SESSION ( integer ) 1 if this Memcache session handler is available, 0 otherwise.

Memcache
PHP Manual