Cookbook recipe

Manage WAL archive disk usage

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

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Estimated investigation4 min

Scenario

The pg_wal directory keeps growing and threatens to fill the disk — a classic cause of an outage. Find why WAL is being retained. Diagnose it Check what holds WAL back: SELECT slot_name, active, pg_size_pretty(pg_wal_lsn_diff(pg_current_wal_lsn(), restart_lsn))…

Investigation Path

The pg_wal directory keeps growing and threatens to fill the disk — a classic cause of an outage. Find why WAL is being retained.

Diagnose it

Check what holds WAL back:

SELECT slot_name, active,
  pg_size_pretty(pg_wal_lsn_diff(pg_current_wal_lsn(), restart_lsn)) AS retained
FROM pg_replication_slots ORDER BY retained DESC;

Why it happens

WAL is retained until it is archived and no longer needed by checkpoints or replication slots. An inactive replication slot or a failing archive_command pins WAL forever, filling the disk.

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Concepts on this page

Replication
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