- backend: $wgMessageCacheType
- key: $wgDBname:messages, $wgDBname:messages-hash, $wgDBname:messages-status
- ex: wikidb:messages, wikidb:messages-hash, wikidb:messages-status
- stores: an array where the keys are DB keys and the values are messages
- set in: wfMessage(), Article::editUpdates() and Title::moveTo()
- expiry: $wgMsgCacheExpiry
- cleared by: nothing