Cookbook recipe

Flatten I/O spikes by tuning checkpoints

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

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Estimated investigation4 min

Scenario

Every few minutes write latency spikes. Checkpoints are flushing too much dirty data at once. Spreading them out smooths the I/O. Diagnose it Check checkpoint frequency and whether they are forced: SELECT * FROM pg_stat_bgwriter; --…

Investigation Path

Every few minutes write latency spikes. Checkpoints are flushing too much dirty data at once. Spreading them out smooths the I/O.

Diagnose it

Check checkpoint frequency and whether they are forced:

SELECT * FROM pg_stat_bgwriter;
-- checkpoints_timed vs checkpoints_req: many 'req' means too-small max_wal_size

Why it happens

A checkpoint writes all dirty buffers to disk. If checkpoints are forced by filling max_wal_size too often, they bunch up. A short checkpoint_completion_target compresses the write burst into a small window.

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Concepts on this page

Checkpoint
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