---
title: "Configuration Settings"
id: logical-replication-config
pg_version: "20devel"
---

<a id="logical-replication-config"></a>

## 29.13. Configuration Settings

Logical replication requires several configuration options to be set. These options are relevant only on one side of the replication. 

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### 29.13.1. Publishers

[`wal_level`](runtime-config-wal.md#guc-wal-level) must be set to `replica` or `logical`. 

[`max_replication_slots`](runtime-config-replication.md#guc-max-replication-slots) must be set to at least the number of subscriptions expected to connect, plus some reserve for table synchronization. 

Logical replication slots are also affected by [`idle_replication_slot_timeout`](runtime-config-replication.md#guc-idle-replication-slot-timeout). 

[`max_wal_senders`](runtime-config-replication.md#guc-max-wal-senders) should be set to at least the same as `max_replication_slots`, plus the number of physical replicas that are connected at the same time. 

Logical replication walsender is also affected by [`wal_sender_timeout`](runtime-config-replication.md#guc-wal-sender-timeout). 

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### 29.13.2. Subscribers

[`max_active_replication_origins`](runtime-config-replication.md#guc-max-active-replication-origins) must be set to at least the number of subscriptions that will be added to the subscriber, plus some reserve for table synchronization. 

[`max_replication_slots`](runtime-config-replication.md#guc-max-replication-slots) must be set to at least 1 when [`retain_dead_tuples`](sql-createsubscription.md#sql-createsubscription-params-with-retain-dead-tuples) is enabled for any subscription. 

[`max_logical_replication_workers`](runtime-config-replication.md#guc-max-logical-replication-workers) must be set to at least the number of subscriptions (for leader apply workers), plus some reserve for the parallel apply workers, and table/sequence synchronization workers. 

[`max_worker_processes`](runtime-config-resource.md#guc-max-worker-processes) may need to be adjusted to accommodate for replication workers, at least ([`max_logical_replication_workers`](runtime-config-replication.md#guc-max-logical-replication-workers) + `1`). Note, some extensions and parallel queries also take worker slots from `max_worker_processes`. 

[`max_sync_workers_per_subscription`](runtime-config-replication.md#guc-max-sync-workers-per-subscription) controls how many tables can be synchronized in parallel during subscription initialization or when new tables are added. One additional worker is also needed for sequence synchronization. 

[`max_parallel_apply_workers_per_subscription`](runtime-config-replication.md#guc-max-parallel-apply-workers-per-subscription) controls the amount of parallelism for streaming of in-progress transactions with subscription parameter `streaming = parallel`. 

Logical replication workers are also affected by [`wal_receiver_timeout`](runtime-config-replication.md#guc-wal-receiver-timeout), [`wal_receiver_status_interval`](runtime-config-replication.md#guc-wal-receiver-status-interval) and [`wal_retrieve_retry_interval`](runtime-config-replication.md#guc-wal-retrieve-retry-interval).