2Q cache is variant of multi-level LRU cache. Original paper http://www.vldb.org/conf/1994/P439.PDF It is adaptive, scan-resistant and can give more hits than plain LRU.
This cache consists from three parts (In, Out and Main) where 'In' receive all new elements, 'Out' receives all overflows from 'In', and 'Main' is LRU cache which hold all long-lived data.
CacheLRU contains maximum size items