[ELMA3] Поиск и прерывание блокирующих запросов в PostgreSQL

Поиск блокирующего запроса.

1. Выполняем запрос:

SELECT * FROM pg_stat_activity

Нас интересуют колонки waiting, state, query, xact_start, datname, pid (могут называться по-разному в разных версиях PgSQL)

Если state интересующего нас запроса = active, а waiting = ‘t’, скорее всего запрос заблокирован.

2. Для поиска блокирующего запроса выполняем

SELECT blocked_locks.pid     AS blocked_pid,
         blocked_activity.usename  AS blocked_user,
         blocking_locks.pid     AS blocking_pid,
         blocking_activity.usename AS blocking_user,
         blocked_activity.query    AS blocked_statement,
         blocking_activity.query   AS current_statement_in_blocking_process
   FROM  pg_catalog.pg_locks         blocked_locks
    JOIN pg_catalog.pg_stat_activity blocked_activity  ON blocked_activity.pid = blocked_locks.pid
    JOIN pg_catalog.pg_locks         blocking_locks 
        ON blocking_locks.locktype = blocked_locks.locktype
        AND blocking_locks.DATABASE IS NOT DISTINCT FROM blocked_locks.DATABASE
        AND blocking_locks.relation IS NOT DISTINCT FROM blocked_locks.relation
        AND blocking_locks.page IS NOT DISTINCT FROM blocked_locks.page
        AND blocking_locks.tuple IS NOT DISTINCT FROM blocked_locks.tuple
        AND blocking_locks.virtualxid IS NOT DISTINCT FROM blocked_locks.virtualxid
        AND blocking_locks.transactionid IS NOT DISTINCT FROM blocked_locks.transactionid
        AND blocking_locks.classid IS NOT DISTINCT FROM blocked_locks.classid
        AND blocking_locks.objid IS NOT DISTINCT FROM blocked_locks.objid
        AND blocking_locks.objsubid IS NOT DISTINCT FROM blocked_locks.objsubid
        AND blocking_locks.pid != blocked_locks.pid
 
    JOIN pg_catalog.pg_stat_activity blocking_activity ON blocking_activity.pid = blocking_locks.pid
   WHERE NOT blocked_locks.GRANTED;

Если в колонке blocked_statement есть интересующий нас запрос, смотрим на blocking_pid.

3. Сверяем по pid запрос из результатов п.1. Если то что там выполняется можно спокойно прервать, то прерываем.

Прерывание блокирующего запроса

1. Мягкое прерывание

SELECT pg_cancel_backend(PID);

2. Жесткое прерывание

SELECT pg_terminate_backend(PID);