log_disconnections

log_disconnections is the PostgreSQL setting that controls whether PostgreSQL logs end of a session, including duration.

Note

Fact — official short description: “Logs end of a session, including duration.”

Identity

Type , Valuebool: Upstream pg_settings type
Context , Valuesuperuser-backend: Fixed when a superuser backend starts
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 , Valueoff: off

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	`off`	—	off

How it works

log_disconnections logs end of a session, including duration. The record is emitted at session end and includes session duration, pairing naturally with connection-start identity but not proving that every abrupt failure reached the logger.

log_disconnections has SUPERUSER_BACKEND context: configuration changes apply when a new backend session starts and require superuser-level authority; established sessions keep their startup 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_disconnections 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_disconnections telemetry, but account for long statements, large bind values, and bursty completion patterns in the log pipeline.
Small nodes	Keep log_disconnections 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	`on`	different	`'on'`
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 = on (dcs); TINY: PG9.0–19 Beta 3 unmodified. Advice, pending human review — Editorial inference: CRIT records session endings and durations to complete its connection audit trail, accepting additional volume only in that profile.

Common pitfalls

Expecting existing sessions to inherit a new log_disconnections value even though it is fixed when each backend starts.
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.
Changing log_disconnections globally without a rollback plan and a client or operational compatibility test.

log_statement · log_duration · log_connections · log_parameter_max_length · log_parameter_max_length_on_error