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Put explicit bounds on replay/apply and monitor lag, worker saturation, slot restart_lsn, and conflict cancellations.","oltp":"Size max_parallel_apply_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.","small":"Configure only replication capacity that is actually used. Even a small topology needs bounded timeouts and slot lifecycle; unlimited retention is not reliability."},"mechanism":["Maximum number of parallel apply workers per subscription. A configuration reload applies a new value; existing work already in flight is not retroactively changed.","A subscription leader can use up to this many parallel workers to apply suitable in-progress transactions. More workers do not parallelize every transaction and consume the global logical-replication and background-worker pools.","Monitor and change max_parallel_apply_workers_per_subscription together with max_logical_replication_workers, max_sync_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."],"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."],"references":[{"title":"PostgreSQL 19 Beta 4: max_parallel_apply_workers_per_subscription","url":"https://www.postgresql.org/docs/19/runtime-config-replication.html#GUC-MAX-PARALLEL-APPLY-WORKERS-PER-SUBSCRIPTION"},{"title":"PostgreSQL 19 release notes","url":"https://www.postgresql.org/docs/19/release-19.html"}],"related":["max_logical_replication_workers","max_sync_workers_per_subscription","max_worker_processes","max_replication_slots","max_active_replication_origins","hot_standby"],"summary":"max_parallel_apply_workers_per_subscription sets the maximum number of parallel apply workers per subscription. 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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. The default value is 2. This parameter can only be set in the postgresql.conf file or on the server command line.","BodyHTML":"\u003cp\u003e\n        Maximum number of parallel apply workers per subscription. This\n        parameter controls the amount of parallelism for streaming of\n        in-progress transactions with subscription parameter\n        \u003ccode\u003estreaming = parallel\u003c/code\u003e.\n       \u003c/p\u003e\u003cp\u003e\n        The parallel apply workers are taken from the pool defined by\n        \u003ccode\u003emax_logical_replication_workers\u003c/code\u003e.\n       \u003c/p\u003e\u003cp\u003e\n        The default value is 2. 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