max_parallel_apply_workers_per_subscription — PostgreSQL configuration parameter

Maximum number of parallel apply workers per subscription.

At a glance

What it does

Maximum number of parallel apply workers per subscription. This parameter controls the amount of parallelism for streaming of in-progress transactions with subscription parameter streaming = parallel.

The parallel apply workers are taken from the pool defined by max_logical_replication_workers.

(Description quoted from the official PostgreSQL documentation.)

How to apply a change

Can be set per session with SET, per role/database with ALTER ROLE/DATABASE ... SET, or globally in postgresql.conf.

Inspect the current value and source with SHOW max_parallel_apply_workers_per_subscription; or SELECT name, setting, unit, context, source FROM pg_settings WHERE name = 'max_parallel_apply_workers_per_subscription';.

Tuning guidance

Raise it to apply large streamed transactions in parallel on the subscriber, reducing apply lag; it costs worker slots and only helps when transactions are big enough to stream.

Reference

PostgreSQL documentation — max_parallel_apply_workers_per_subscription.