sync_replication_slots

sync_replication_slots enables a physical standby to synchronize logical failover replication slots from the primary server. It is a sighup setting present in PG17–18; the latest recorded boot default is off.

Note

Fact — official short description: “Enables a physical standby to synchronize logical failover replication slots from the primary server.”

Identity

Type , Valuebool: 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 , ValueReplication / Standby Servers: Upstream classification
Latest boot value , Valueoff: off

Lifecycle

Fact	Value
First observed	PG17
Present in	PG17–19 Beta 3
Removed in	No
Introduction commit	`93db6cbda037` — Add a new slot sync worker to synchronize logical slots.
Commit date	2024-02-22
Discussion	thread 1

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG17–19 Beta 3	`off`	—	off

How it works

Enables the slotsync worker on a physical standby to copy logical failover-slot state from its primary. A configuration reload applies a new value.

Synchronization requires a physical replication slot between primary and standby (primary_slot_name on the standby), hot_standby_feedback=on, and primary_conninfo containing a valid dbname. The logical source slots must have failover enabled.

Slot state is copied asynchronously. The primary should list the standby’s physical slot in synchronized_standby_slots so subscribers cannot outrun the failover standby, and operators must verify that every required slot is synchronized and ready before promotion.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Enable it only as part of a complete logical-failover design. Automate prerequisite checks and block planned promotion until all required failover slots report synchronized, non-conflicting state.
OLAP	Large transactions and delayed standbys can increase synchronization lag. Monitor subscriber confirmed positions, standby replay, physical-slot retention, and catalog horizon together.
Small nodes	Do not enable it merely because the switch is available. A small deployment still needs a permanent physical slot, hot_standby_feedback, dbname, retention limits, and a tested failover runbook.

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	`true`	different	`on`
OLAP	`true`	different	`on`
CRIT	`true`	different	`on`
TINY	`true`	different	`on`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG17–19 Beta 3 = True (dcs); OLAP: PG17–19 Beta 3 = True (dcs); CRIT: PG17–19 Beta 3 = True (dcs); TINY: PG17–19 Beta 3 = True (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to prepare logical failover slots on physical standbys for controlled failover; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

Enabling it without primary_slot_name and therefore without the mandatory physical slot.
Leaving hot_standby_feedback off, which prevents safe catalog-row retention for synchronized logical slots.
Omitting dbname from primary_conninfo.
Synchronizing ordinary logical slots that were not created with failover enabled and expecting them to appear.
Promoting before checking that every required slot is synchronized and not behind its subscriber.

primary_slot_name · hot_standby_feedback · primary_conninfo · synchronized_standby_slots · max_replication_slots · max_slot_wal_keep_size