Cookbook recipe

Detect and resolve lock contention

Applies to PostgreSQL 13–17 Last reviewed May 2026 Grounded in source

What This Is

A production experience capsule based on real incident patterns.

Why It Matters

Builds production judgment under pressure.

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Estimated investigation4 min

Scenario

Queries hang waiting on locks. You need to see who blocks whom and break the jam. Diagnose it Show the blocking chain: SELECT blocked.pid AS blocked_pid, blocking.pid AS blocking_pid, left(blocked.query,50) AS blocked_q, left(blocking.query,50) AS blocking_q FROM…

Investigation Path

Queries hang waiting on locks. You need to see who blocks whom and break the jam.

Diagnose it

Show the blocking chain:

SELECT blocked.pid AS blocked_pid, blocking.pid AS blocking_pid,
  left(blocked.query,50) AS blocked_q, left(blocking.query,50) AS blocking_q
FROM pg_stat_activity blocked
JOIN pg_stat_activity blocking
  ON blocking.pid = ANY(pg_blocking_pids(blocked.pid));

Why it happens

A long transaction holds a lock that conflicts with what others want (e.g. an idle-in-transaction session holding a row lock, or DDL waiting behind a long SELECT). Everything downstream queues.

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Related & next steps

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Concepts on this page

Transaction pg_locks Deadlock Schema Bloat
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