Check replication lag postgres
Replication state and byte lag per replica
psql -U postgres -c "SELECT client_addr, state, sent_lsn, replay_lsn, (sent_lsn - replay_lsn) AS lag_bytes FROM pg_stat_replication;"
more postgres
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Show locks
psql -U postgres -d mydb -c "SELECT pid, relation::regclass, mode, granted, left(query,60) FROM pg_locks l JOIN pg_stat_activity a USING(pid) WHERE relation IS NOT NULL ORDER BY granted;"
Find long-running queries
SELECT pid, now()-query_start AS dur, state, query FROM pg_stat_activity WHERE state='active' AND now()-query_start > interval '5 min' ORDER BY dur DESC;
Kill a stuck backend
SELECT pg_terminate_backend(<pid>); -- graceful first: SELECT pg_cancel_backend(<pid>);
Top queries by total time
SELECT query, calls, total_exec_time, mean_exec_time, rows FROM pg_stat_statements ORDER BY total_exec_time DESC LIMIT 20;
EXPLAIN with buffers
EXPLAIN (ANALYZE, BUFFERS, VERBOSE) SELECT ... ; -- shared hit/read shows cache vs disk I/O