Manual:$wgUseEAccelShm

Details
(1.5) You can use this for persistent caching where your wiki runs on a single server. Enabled by default if eAccelerator is installed. Mutually exclusive with memcached and Turck MMCache, the preference order being memcached first, Turck MMCache second, and eAccelerator third. Most of the code to support this is directly copied from the Turck code.