PG>9.2
postgres=# SELECT blocked_locks.pid AS blocked_pid,
postgres-# blocked_activity.usename AS blocked_user,
postgres-# blocking_locks.pid AS blocking_pid,
postgres-# blocking_activity.usename AS blocking_user,
postgres-# blocked_activity.query AS blocked_statement,
postgres-# blocking_activity.query AS current_statement_in_blocking_process
postgres-# FROM pg_catalog.pg_locks blocked_locks
postgres-# JOIN pg_catalog.pg_stat_activity blocked_activity ON blocked_activity.pid = blocked_locks.pid
postgres-# JOIN pg_catalog.pg_locks blocking_locks
postgres-# ON blocking_locks.locktype = blocked_locks.locktype
postgres-# AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
postgres-# AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
postgres-# AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
postgres-# AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
postgres-# AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
postgres-# AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
postgres-# AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
postgres-# AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
postgres-# AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
postgres-# AND blocking_locks.pid != blocked_locks.pid
postgres-#
postgres-# JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
postgres-# WHERE NOT blocked_locks.GRANTED;
blocked_pid | blocked_user | blocking_pid | blocking_user | blocked_statement | current_statement_in_blocking_process
-------------+--------------+--------------+---------------+-------------------+---------------------------------------
(0 rows)
PG< 9.2:
SELECT bl.pid AS blocked_pid,
a.usename AS blocked_user,
kl.pid AS blocking_pid,
ka.usename AS blocking_user,
a.current_query AS blocked_statement
FROM pg_catalog.pg_locks bl
JOIN pg_catalog.pg_stat_activity a ON a.procpid = bl.pid
JOIN pg_catalog.pg_locks kl ON kl.transactionid = bl.transactionid AND kl.pid != bl.pid
JOIN pg_catalog.pg_stat_activity ka ON ka.procpid = kl.pid
WHERE NOT bl.GRANTED;https://wiki.postgresql.org/wiki/Lock_Monitoring