Cookbook recipe

Size WAL: max_wal_size, min_wal_size, checkpoint_timeout

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

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Estimated investigation4 min

Scenario

WAL volume swings wildly and checkpoints fire unpredictably. Right-sizing the WAL settings stabilizes both. Diagnose it Observe checkpoint cause and WAL generation: SELECT checkpoints_timed, checkpoints_req FROM pg_stat_bgwriter; Why it happens WAL accumulates until a checkpoint frees…

Investigation Path

WAL volume swings wildly and checkpoints fire unpredictably. Right-sizing the WAL settings stabilizes both.

Diagnose it

Observe checkpoint cause and WAL generation:

SELECT checkpoints_timed, checkpoints_req FROM pg_stat_bgwriter;

Why it happens

WAL accumulates until a checkpoint frees it. If max_wal_size is too small for the write rate, checkpoints are forced early (checkpoints_req high). min_wal_size keeps recycled segments around to avoid churn.

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