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Note: XCONLY: The following description applies only to Postgres-XC.
Please note that this section describes the task of individual Coordinator and Datanode.
Note: The following description applies both to Postgres-XC and PostgreSQL if not described explicitly. You can read PostgreSQL as Postgres-XC except for version number, which is specific to each product.
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.
Details of the pg_locks view appear in Section 47.62. For more information on locking and managing concurrency with PostgreSQL, refer to Chapter 13.