expriry: $wgRevisionCacheExpiry
Sessions:
- controlled by: $wgSessionsInMemcached
+ controlled by: $wgSessionsInObjectCache
key: $wgBDname:session:$id
ex: wikidb:session:38d7c5b8d3bfc51egf40c69bc40f8be3
stores: $SESSION, useful when using a multi-sever wiki