Cookbook recipe

Diagnose wraparound-driven aggressive autovacuum

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

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Estimated investigation4 min

Scenario

Autovacuum suddenly scans huge old tables even though they barely changed, hammering I/O. This is anti-wraparound (aggressive) vacuum doing its job. Diagnose it See which tables are due for freezing: SELECT relname, age(relfrozenxid) AS xid_age FROM…

Investigation Path

Autovacuum suddenly scans huge old tables even though they barely changed, hammering I/O. This is anti-wraparound (aggressive) vacuum doing its job.

Diagnose it

See which tables are due for freezing:

SELECT relname, age(relfrozenxid) AS xid_age
FROM pg_class WHERE relkind='r'
ORDER BY xid_age DESC LIMIT 15;

Why it happens

When a table’s age(relfrozenxid) crosses autovacuum_freeze_max_age, PostgreSQL forces an aggressive vacuum that scans all unfrozen pages to freeze old XIDs — preventing wraparound. It cannot be skipped and ignores the cost-delay nap as needed.

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Related & next steps

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Concepts on this page

Transaction ID wraparound Autovacuum VACUUM
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