log_filename

log_filename is the PostgreSQL setting that defines the file name pattern for log files.

Note

Fact — official short description: “Sets the file name pattern for log files.”

Identity

Type , Valuestring: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value—: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueReporting and Logging / Where to Log: Upstream classification
Latest boot value , Valuepostgresql-%Y-%m-%d_%H%M%S.log: postgresql-%Y-%m-%d_%H%M%S.log

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	`postgresql-%Y-%m-%d_%H%M%S.log`	—	postgresql-%Y-%m-%d_%H%M%S.log

How it works

log_filename sets the file name pattern for log files. logging_collector expands strftime escapes using log_timezone whenever it opens a new file, so repeating names must be coordinated with rotation and truncation.

log_filename is a SIGHUP-context setting: a configuration reload activates the new server value without a restart; subsequent operations that consult it use the refreshed value.

The active path is composed from log_destination, logging_collector or syslog/eventlog, file naming and permissions, rotation triggers, and external shipping or retention.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Use a filename pattern whose uniqueness matches rotation policy. If names repeat, combine time-based rotation, log_truncate_on_rotation, and confirmed shipping so a reused name cannot mix periods or overwrite uncollected data.
OLAP	Choose a predictable period boundary for large analytical logs and ensure downstream ingestion closes the previous file before the pattern repeats; do not rely on size rotation with a non-unique name.
Small nodes	A bounded weekday or date pattern is reasonable only with matching retention and free-space monitoring. Keep enough time components to prevent accidental collisions after restart or manual rotation.

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	`postgresql-%a.log`	different	`'postgresql-%a.log'`
OLAP	`postgresql-%a.log`	different	`'postgresql-%a.log'`
CRIT	`postgresql-%a.log`	different	`'postgresql-%a.log'`
TINY	`postgresql-%a.log`	different	`'postgresql-%a.log'`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = postgresql-%a.log (dcs); OLAP: PG9.0–19 Beta 3 = postgresql-%a.log (dcs); CRIT: PG9.0–19 Beta 3 = postgresql-%a.log (dcs); TINY: PG9.0–19 Beta 3 = postgresql-%a.log (dcs). Advice, pending human review — Editorial inference: A weekday filename creates a predictable seven-name cycle intended to work with daily rotation and truncation.

Common pitfalls

Editing log_filename without reloading configuration and verifying the effective value and subsequent behavior.
Combining incompatible destination, collector, filename, and rotation assumptions and then losing or overwriting logs.
Failing to monitor a full or unwritable log target, which can block logging or database activity depending on the path.
Using a repeating strftime name without matching rotation and truncation policy, causing append growth or overwrite surprises.

logging_collector · log_destination · log_directory · log_rotation_age · log_rotation_size