|PostgreSQL 8.2.23 Documentation|
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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.
select pg_stat_activity.datname,pg_class.relname,pg_locks.transaction, pg_locks.mode, pg_locks.granted,pg_stat_activity.usename,substr(pg_stat_activity.current_query,1,30), pg_stat_activity.query_start, age(now(),pg_stat_activity.query_start) as "age", pg_stat_activity.procpid from pg_stat_activity,pg_locks left outer join pg_class on (pg_locks.relation = pg_class.oid) where pg_locks.pid=pg_stat_activity.procpid order by query_start;