Proper Sizing of Shared Buffer Cache

Ideally, the POSTGRESQL shared buffer cache will be:

• Large enough to hold most commonly-accessed tables
• Small enough to avoid swap pagein activity

Keep in mind that the postmaster allocates all shared memory when it starts. This area stays the same size even if no one is accessing the database. Some operating systems pageout unreferenced shared memory, while others lock shared memory into RAM. Locked shared memory is preferred. The POSTGRESQL administrators guide has information about kernel configuration for various operating systems, http://developer.postgresql.org/docs/postgres/kernel-resources.html