Another useful tool for monitoring database activity is the pg_locks system table. It allows the database administrator to view information about the outstanding locks in the lock manager. For example, this capability can be used to:
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View all the locks currently outstanding, all the locks on relations in a particular database, all the locks on a particular relation, or all the locks held by a particular PostgreSQL session.
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Determine the relation in the current database with the most ungranted locks (which might be a source of contention among database clients).
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Determine the effect of lock contention on overall database performance, as well as the extent to which contention varies with overall database traffic.
Details of the pg_locks view appear in Section 42.37. For more information on locking and managing concurrency with PostgreSQL, refer to Chapter 12.
