log_line_prefix

log_line_prefix is the PostgreSQL setting that controls information prefixed to each log line.

Note

Fact — official short description: “Controls information prefixed to each log line.”

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 / What to Log: Upstream classification
Latest boot value , Value%m [%p]: %m [%p]

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
PG9.0–9.6	`""`	—	empty string
PG10–19 Beta 3	`%m [%p]`	—	%m [%p]

How it works

log_line_prefix controls information prefixed to each log line. An empty string means no prefix. Percent escapes add session, user, database, process, application, and timing context; csvlog and jsonlog already carry structured fields separately.

log_line_prefix 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.

It changes emitted diagnostic data rather than query semantics, but volume, sensitive content, log_line_prefix, destinations, collector throughput, and retention determine operational cost and usefulness.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Tune log_line_prefix against an explicit observability question and a measured log-volume budget. Prefer selective thresholds, sampling, or role-level overrides over indiscriminate capture.
OLAP	Analytical jobs can justify richer log_line_prefix telemetry, but account for long statements, large bind values, and bursty completion patterns in the log pipeline.
Small nodes	Keep log_line_prefix useful but bounded: verify disk, collector, retention, and redaction capacity before increasing detail or frequency.

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	Unmodified	—	—
OLAP	Unmodified	—	—
CRIT	Unmodified	—	—
TINY	Unmodified	—	—

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 unmodified; OLAP: PG9.0–19 Beta 3 unmodified; CRIT: PG9.0–19 Beta 3 unmodified; TINY: PG9.0–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Editing log_line_prefix without reloading configuration and verifying the effective value and subsequent behavior.
Enabling richer logging without budgeting collector throughput, storage, retention, and downstream query cost.
Writing SQL text, bind values, identities, or host data without a redaction and access-control policy.
Omitting process, session, database, user, or application identity needed to correlate multiline text logs.

application_name · cluster_name · update_process_title · log_timezone · log_hostname