bgwriter_delay

bgwriter_delay — Background writer sleep time between rounds. Observed in PG9.0–19 Beta 3; its last measured boot default is 200 ms in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Background writer sleep time between rounds.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Valuems: Raw unit
Range , Value10 – 10000: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueResource Usage / Background Writer: Upstream classification
Latest boot value , Value200: 200 ms

Lifecycle

Fact	Value
First observed	PG9.0 (research boundary)
Present in	PG9.0–19 Beta 3
Removed in	No
Introduction commit	Not asserted: predates the PG9.0 research boundary
Commit date	—
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG9.0–19 Beta 3	`200`	`ms`	200 ms

How it works

The background writer performs a round, writes selected dirty shared buffers, then sleeps for bgwriter_delay. When no dirty buffers are found it can enter a longer sleep regardless of this value.

A shorter interval reacts sooner to buffer demand but wakes the process more often. Effective timer granularity can be about 10 ms on some systems, so smaller or non-multiple values may round up in practice.

The number of pages considered per round is derived from recent buffer allocation demand, bgwriter_lru_multiplier, and bgwriter_lru_maxpages; checkpoints are handled separately. Its SIGHUP context allows configuration reload without a server restart.

Tuning advice

Tip

Advice. These are workload-specific starting points and must be validated with measurements.

Workload	Guidance
OLTP	Tune bgwriter_delay only with bgwriter and checkpoint metrics. The goal is fewer backend writes and smoother latency without excessive repeated writes; change one dimension at a time.
OLAP	Bulk writes can reach bgwriter_delay limits continuously. Measure total bytes written, checkpoints, and storage queueing, not just foreground query latency.
Small nodes	A small host usually needs conservative write smoothing. Aggressive bgwriter_delay can consume I/O needed by foreground work, so retain the default unless backend writes are a measured problem.

Pigsty

Values use the fixed 8-vCPU, 32-GiB, 100-GiB SSD fixture and render the current Pigsty templates for PG19 Beta 3; this does not assert current Pigsty support for that historical or beta release.

Template	Effective value	Versus upstream boot	Source expression
OLTP	`10ms`	different	`10ms`
OLAP	`10ms`	different	`10ms`
CRIT	`10ms`	different	`10ms`
TINY	`10ms`	different	`10ms`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 10ms (dcs); OLAP: PG9.0–19 Beta 3 = 10ms (dcs); CRIT: PG9.0–19 Beta 3 = 10ms (dcs); TINY: PG9.0–19 Beta 3 = 10ms (dcs). Advice, pending human review — Editorial inference, pending maintainer review: The 10ms interval is intended to make the background writer inspect dirty-buffer demand much more frequently than PostgreSQL’s boot default.

Common pitfalls

Changing bgwriter_delay without applying its documented unit and configuration context.
Optimizing an isolated benchmark while ignoring concurrent aggregate resource use.
Assuming a configured value guarantees operating-system or storage behavior.
Failing to retest startup, failover, and workload latency after the change.

bgwriter_lru_maxpages · bgwriter_lru_multiplier · bgwriter_flush_after · shared_buffers · checkpoint_completion_target