Commit log (CLOG)

A log which maintains the states of all transactions

The commit log (CLOG) maintains the states of all transactions, and is part of the concurrency control mechanism. The commit log is allocated to shared memory and used throughout transaction processing. Files associated with the commit log are located in the data directory in the pg_xact subdirectory. Specifically, pg_xact contains records of the commit status for each transaction that has been assigned an XID.

Until PostgreSQL 7.1, transaction logs were maintained in a system catalogue table (pg_log, not to be confused with the former data directory subdirectory pg_log). See commit 2589735d for details of the change.


PostgreSQL internals, Storage, Transactions

See also