Tune PostgreSQL Background Writer with pg_stat_bgwriter

Thu, 21 May 2026 00:00:00 +0000

Tune PostgreSQL Background Writer with pg_stat_bgwriter

Where pg_stat_statements does query-level aggregation and pgBadger does after-the-fact log analysis, pg_stat_bgwriter operates at the buffer-cache layer — answering whether the bgwriter and checkpointer are keeping shared_buffers clean enough that foreground queries never have to pay for a write inline. On a healthy OLTP cluster the answer is almost always yes; on a struggling one the counters say which knob to turn first.

Purpose and Overview

When a PostgreSQL backend needs a clean buffer in shared_buffers and none is available, something has to flush a dirty page back to disk before the backend can continue. Three subsystems share that workload. The checkpointer flushes every dirty buffer at checkpoint time, spreading the writes over checkpoint_completion_target × checkpoint_timeout to avoid I/O spikes. The background writer ("bgwriter") runs continuously, sweeping a small window of the LRU list each bgwriter_delay and writing out dirty buffers to keep a runway of clean buffers available. And when neither of those has kept up, the user-facing backend writes the buffer itself — inline, on the critical path of the query.

Pg_stat_checkpointer on Postgres Scripts

Tune PostgreSQL Background Writer with pg_stat_bgwriter

Tune PostgreSQL Background Writer with pg_stat_bgwriter

Purpose and Overview