log_transaction_sample_rate

log_transaction_sample_rate is the PostgreSQL setting that defines the fraction of transactions from which to log all statements.

Note

Fact — official short description: “Sets the fraction of transactions from which to log all statements.”

Identity

Type , Valuereal: Upstream pg_settings type
Context , Valuesuperuser: Settable at runtime by a superuser
Unit , Value—: Raw unit
Range , Value0 – 1: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueReporting and Logging / When to Log: Upstream classification
Latest boot value , Value0: 0

Lifecycle

Fact	Value
First observed	PG12
Present in	PG12–19 Beta 3
Removed in	No
Introduction commit	`799e220346f1` — Log all statements from a sample of transactions
Commit date	2019-04-03
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG12–19 Beta 3	`0`	—	0

How it works

log_transaction_sample_rate sets the fraction of transactions from which to log all statements. Use a value between 0.0 (never log) and 1.0 (log all statements for all transactions). A sampled transaction logs every statement, preserving transaction context but potentially creating bursts from long or chatty transactions.

log_transaction_sample_rate is a SUPERUSER-context setting. Superuser or a role granted the appropriate SET privilege can change it for a session, while ALTER ROLE or ALTER DATABASE can establish a default for future sessions.

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_transaction_sample_rate 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_transaction_sample_rate telemetry, but account for long statements, large bind values, and bursty completion patterns in the log pipeline.
Small nodes	Keep log_transaction_sample_rate 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: PG12–19 Beta 3 unmodified; OLAP: PG12–19 Beta 3 unmodified; CRIT: PG12–19 Beta 3 unmodified; TINY: PG12–19 Beta 3 unmodified. No Pigsty-specific rationale is inferred from an absent override.

Common pitfalls

Changing log_transaction_sample_rate in one session and assuming role defaults, database defaults, or other pooled sessions changed with it.
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.
Underestimating bursts when one sampled, chatty transaction causes every statement to be logged.

log_min_messages · log_min_error_statement · log_min_duration_statement · log_min_duration_sample · log_statement_sample_rate