PostgreSQL 8.0, the 2q memory manager
With the revolutionary PostgreSQL 8.0 were introduced a different memory manager, the two queues.
This algorithm uses three list of buffer page pointers called cache directory blocks (CDB). The lists T1,T2 are actually pointing buffered pages. B1 lists pages been recently in the shared buffer.
The list T1 is used as LRU for the pages loaded from disk. The list T2 is used as LRU list for pages already cached and evicted from the list T1.