Manual:$wgMainCacheType

Details
Object cache setting. Replaces $wgUseMemCached.

Here are the available CACHE constants, as defined in Defines.php


 * CACHE_ANYTHING - Use anything, as long as it works
 * CACHE_NONE - Do not cache
 * CACHE_DB - Store cache objects in the DB
 * CACHE_MEMCACHED - memcached, must specify servers in $wgMemCachedServers
 * CACHE_ACCEL - eAccelerator, mmTurck, APC or XCache, whichever is available


 * CACHE_DBA - Use PHP's DBA extension to store in a DBM-style database


 * Roan Kattouw has stated that CACHE_MEMCACHED directive will provide the most significant performance improvements in the case where you have memcached and an opcode cache installed. APC still caches ( others may as well,) though I am unsure it is used in the final transaction with the client.
 * Squid or Varnish HTML caching is not considered with this setting., but is also greatly helpful in Round Trip Time reduction. --Teststudent (talk) 03:13, 17 April 2012 (UTC)