max_sync_workers_per_subscription

max_sync_workers_per_subscription — Maximum number of workers per subscription for synchronizing tables and sequences. Observed in PG10–19 Beta 3; its last measured boot default is 2 in PG19 Beta 3, with sighup context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Maximum number of workers per subscription for synchronizing tables and sequences.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuesighup: Takes effect after configuration reload
Unit , Value—: Raw unit
Range , Value0 – 262143: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueReplication / Subscribers: Upstream classification
Latest boot value , Value2: 2

Lifecycle

Fact	Value
First observed	PG10
Present in	PG10–19 Beta 3
Removed in	No
Introduction commit	`7c4f52409a8c` — Logical replication support for initial data copy
Commit date	2017-03-23
Discussion	—

Default history

Measured PG9.0–19 Beta 3 boot defaults
Versions	Raw `boot_val`	Unit	Human value
PG10–19 Beta 3	`2`	—	2

How it works

Maximum number of table synchronization workers per subscription. A configuration reload applies a new value; existing work already in flight is not retroactively changed.

Initial table copies use synchronization workers up to this per-subscription ceiling. They share max_logical_replication_workers and max_worker_processes with apply workers, so the configured number is not a guaranteed concurrency level.

Monitor and change max_sync_workers_per_subscription together with max_logical_replication_workers, max_parallel_apply_workers_per_subscription, max_worker_processes. Validate on the relevant server role and real workload, then use its sighup context to choose session change, reload, or restart; a historical boot default is not the current effective value.

Tuning advice

Tip

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

Workload	Guidance
OLTP	Size max_sync_workers_per_subscription from topology, failover roles, slot/subscription count, and reconnect headroom. Test worst-case primary latency, standby replay, and disk retention before production.
OLAP	Read standbys and logical subscribers often see long queries or large transactions. Put explicit bounds on replay/apply and monitor lag, worker saturation, slot restart_lsn, and conflict cancellations.
Small nodes	Configure only replication capacity that is actually used. Even a small topology needs bounded timeouts and slot lifecycle; unlimited retention is not reliability.

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	`6`	different	`6`
OLAP	`6`	different	`6`
CRIT	`6`	different	`6`
TINY	`6`	different	`6`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG10–19 Beta 3 = 6 (dcs); OLAP: PG10–19 Beta 3 = 6 (dcs); CRIT: PG10–19 Beta 3 = 6 (dcs); TINY: PG10–19 Beta 3 = 6 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to accelerate initial logical-replication table copies within the global worker budget; confirm it against the current Pigsty templates, hardware fixture, and operational guarantees before publication.

Common pitfalls

Changing it on the wrong primary, standby, sender, or subscriber role.
Watching only configured bytes/time instead of actual lag, slot position, and worker state.
Failing over to a node that lacks the old primary’s capacity or prerequisites.
Using infinite waits or WAL retention to hide a failed consumer.

max_logical_replication_workers · max_parallel_apply_workers_per_subscription · max_worker_processes · max_replication_slots · max_active_replication_origins · hot_standby