Retrieve locks from a Postgres DB

sys_get_locks

SELECT pg_stat_activity.pid,
    pg_stat_activity.usename,
    pg_blocking_pids(pg_stat_activity.pid) AS blocked_by,
    pg_stat_activity.query AS blocked_query
   FROM pg_stat_activity
  WHERE cardinality(pg_blocking_pids(pg_stat_activity.pid)) > 0;