max_wal_senders

max_wal_senders — Sets the maximum number of simultaneously running WAL sender processes. Observed in PG9.0–19 Beta 3; its last measured boot default is 10 in PG19 Beta 3, with postmaster context. This is a beta-snapshot fact and can change before PostgreSQL 19 GA.

Note

Fact — official short description: “Sets the maximum number of simultaneously running WAL sender processes.”

Identity

Type , Valueinteger: Upstream pg_settings type
Context , Valuepostmaster: Requires a server restart
Unit , Value—: Raw unit
Range , Value0 – 262143: Raw limits in the last observed version
Enum values , Value—: — for non-enum types
Category , ValueReplication / Sending Servers: Upstream classification
Latest boot value , Value10: 10

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	`0`	—	0
PG10–19 Beta 3	`10`	—	10

How it works

Sets the maximum number of simultaneously running WAL sender processes. The value is fixed when the server starts, so changing it requires a restart.

Each streaming standby, WAL-streaming base backup, or logical replication connection can occupy a WAL sender. Zero disables sending, disconnected clients may retain a slot until timeout, and a standby must reserve at least as many senders as its primary to accept hot-standby queries safely.

Monitor and change max_wal_senders together with wal_level, max_replication_slots, archive_mode. Validate on the relevant server role and real workload, then use its postmaster 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_wal_senders 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	`50`	different	`50`
OLAP	`50`	different	`50`
CRIT	`50`	different	`50`
TINY	`50`	different	`50`

Caution

Advice — pending human review. Fact from the current Pigsty template projection: OLTP: PG9.0–19 Beta 3 = 50 (dcs); OLAP: PG9.0–19 Beta 3 = 50 (dcs); CRIT: PG9.0–19 Beta 3 = 50 (dcs); TINY: PG9.0–19 Beta 3 = 50 (dcs). Advice, pending human review — Editorial interpretation, pending human maintainer review: the override appears intended to reserve connection headroom for replicas, backups, and logical clients; 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.

wal_level · max_replication_slots · archive_mode · wal_log_hints · output_plugin_libraries · wal_sender_timeout