PostgreSQL, Second Edition

The PostgreSQL BGWRITER Process

When a PostgreSQL server process reads data from disk, it first moves the page that contains the data into the shared buffer pool. The shared buffer pool is so named because it's a region of memory that's shared by all server processes that access a given cluster. Another way to look at it is that the shared buffer pool is shared by all processes spawned by a single postmaster. When the shared buffer pool fills, PostgreSQL starts pushing old pages out of the pool to make room for new ones. PostgreSQL uses the ARC algorithm, or, in older versions the LRU (least-recently-used) mechanism to select the page it evicts from the pool (see Chapter 4 for more information). If PostgreSQL chooses a page that has not been ...