HashGrowBucketsElect

Mechanism

WAIT_EVENT_HASH_GROW_BUCKETS_ELECT at src/backend/executor/nodeHash.c:1669 is the grep-verified reporting path. The public identity/resource is mapped at src/backend/utils/activity/wait_event_names.txt:132. The instrumented operation is: Waiting to elect a Parallel Hash participant to allocate more buckets. The HashGrowBucketsElect path has reached a process-coordination point and sleeps until a peer, worker, barrier, queue, or replication phase signals progress.

Expected behavior

Brief rendezvous is normal when every participant continues to advance.

When to investigate

Investigate when the same phase persists across three samples, the expected peer is absent or blocked, or a queue and its dependants stop moving.

Diagnostic actions

• Identify the peer or phase named by the event.
• Inspect that participant's wait, error, and progress state.
• Repair the stalled participant or upstream dependency instead of treating the waiter as the root cause.

Diagnostic queries

Sessions waiting on IPC/HashGrowBucketsElect

SELECT pid, backend_type, usename, datname, application_name,
       state, now() - query_start AS query_age,
       now() - xact_start AS xact_age,
       wait_event_type, wait_event,
       pg_blocking_pids(pid) AS blocking_pids,
       left(query, 160) AS query
FROM pg_stat_activity
WHERE wait_event_type = 'IPC'
  AND wait_event = 'HashGrowBucketsElect'
ORDER BY query_age DESC NULLS LAST;

Current IPC cohort

SELECT wait_event, count(*) AS waiting_sessions,
       count(*) FILTER (WHERE state = 'active') AS active_waiters,
       max(now() - query_start) AS oldest_query
FROM pg_stat_activity
WHERE wait_event_type = 'IPC'
GROUP BY wait_event
ORDER BY waiting_sessions DESC, wait_event;

Lock and relation context for these sessions

SELECT a.pid, l.locktype, l.mode, l.granted, l.fastpath,
       d.datname, n.nspname, c.relname,
       l.page, l.tuple, l.virtualxid, l.transactionid,
       l.classid, l.objid, l.objsubid
FROM pg_stat_activity AS a
LEFT JOIN pg_locks AS l ON l.pid = a.pid
LEFT JOIN pg_database AS d ON d.oid = l.database
LEFT JOIN pg_class AS c
  ON c.oid = l.relation
 AND l.database = (
       SELECT oid FROM pg_database WHERE datname = current_database()
     )
LEFT JOIN pg_namespace AS n ON n.oid = c.relnamespace
WHERE a.wait_event_type = 'IPC'
  AND a.wait_event = 'HashGrowBucketsElect'
ORDER BY a.pid, l.granted, l.locktype, l.mode;