wal_sender_delay

Definition PG 9.1 manual

Specifies the delay between activity rounds for WAL sender processes. In each round the WAL sender sends any WAL accumulated since the last round to the standby server. It then sleeps for wal_sender_delay milliseconds, and repeats. The sleep is interrupted by transaction commit, so the effects of a committed transaction are sent to standby servers as soon as the commit happens, regardless of this setting. The default value is one second (1s). Note that on many systems, the effective resolution of sleep delays is 10 milliseconds; setting wal_sender_delay to a value that is not a multiple of 10 might have the same results as setting it to the next higher multiple of 10. This parameter can only be set in the postgresql.conf file or on the server command line.

How it works

PostgreSQL describes wal_sender_delay as follows: “WAL sender sleep time between WAL replications.” A configuration reload applies the value to the server without a full restart. The atlas measures it in PG9.0–9.1; boot_val is the compiled or initialized baseline, not proof of a running cluster's effective setting.

Early WAL senders slept for this interval between attempts to ship more WAL. It disappeared after PostgreSQL 9.1 as sender wakeup and streaming behavior evolved; modern latency and liveness controls are wal_sender_timeout, wal_receiver_status_interval, and wal_receiver_timeout, not a polling delay.

Read it together with wal_sender_timeout, wal_receiver_status_interval, wal_receiver_timeout, max_wal_senders. Check SHOW and pg_settings on the target server, verify the source and pending_restart fields, and compare workload, logs, and resource metrics before and after any change.

Operational considerations

Treating the measured boot_val for wal_sender_delay as proof of the effective value on an initialized or managed cluster.

Applying a change as though it were immediate while pg_settings reports sighup context.

Changing this setting in isolation without checking the linked limits, observability, and rollback path.

Copying the removed name into a modern postgresql.conf instead of migrating to its documented successor.

Workload guidance

OLAP: For an upgrade or analytical estate, inventory every generated configuration before cutover. Map the old control to its successor and compare plans, throughput, WAL, or logging behavior rather than assuming the old numeric value is portable.

OLTP: Do not add this retired name to a current OLTP configuration. Translate its intent to the documented successor, test the migration under connection and write concurrency, and remove stale automation that still emits it.

SMALL: Delete the obsolete override after recording why it existed. On a small node, prefer the successor's default until measurements justify a new value; an unknown startup parameter can otherwise stop the server.