Cookbook recipe

Watch wait events in pg_stat_activity

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

The database is busy but you cannot tell on what. Wait events show whether sessions wait on I/O, locks, or CPU. Diagnose it Aggregate current wait events: SELECT wait_event_type, wait_event, count(*) FROM pg_stat_activity WHERE state='active' GROUP…

Investigation Path

The database is busy but you cannot tell on what. Wait events show whether sessions wait on I/O, locks, or CPU.

Diagnose it

Aggregate current wait events:

SELECT wait_event_type, wait_event, count(*)
FROM pg_stat_activity
WHERE state='active'
GROUP BY 1,2 ORDER BY 3 DESC;

Why it happens

Each active backend reports what it is waiting on. A flood of IO/DataFileRead means disk-bound; Lock means contention; LWLock points at internal contention; mostly NULL means CPU-bound.

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Related & next steps

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Concepts on this page

Lock
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