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:
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.
Determine the relation in the current database with the most ungranted locks (which might be a source of contention among database clients).
Determine the effect of lock contention on overall database performance, as well as the extent to which contention varies with overall database traffic.