Managing logical slot synchronization for RDS for PostgreSQL - Amazon Relational Database Service

Managing logical slot synchronization for RDS for PostgreSQL

Starting in community PostgreSQL 17, a new feature to automatically synchronize logical replication slots from primary to standby servers has been introduced through the parameter sync_replication_slots or the related function pg_sync_replication_slots(), which manually synchronizes slots on execution.

These features are available starting with RDS for PostgreSQL 17. A typical setup will have a primary instance and its read replica, as well as a logical replication subscriber to the primary.

Ensure the subscription is created with the failover option set to true:

CREATE SUBSCRIPTION subname CONNECTION 'host=...' PUBLICATION pubname WITH (failover = true);

This creates a logical slot on the publisher with failover enabled.

postgres=> SELECT slot_name, slot_type, failover FROM pg_catalog.pg_replication_slots;
 slot_name | slot_type | failover 
-----------+-----------+----------
 subname   | logical   | t
(1 row)

By enabling slot synchronization, all of the failover logical replication slots on the primary are automatically created on the physical standbys and are synced periodically. Ensure the following values have been set through parameter groups:

  • rds.logical_replication must be 1 to enable logical replication

  • hot_standby_feedback must be 1 on the standby

  • rds.logical_slot_sync_dbname on the standby must be set to a valid database name

    The parameter's default value is postgres. If the logical publishing instance has the postgres database, the default parameter does not need to be changed.

  • synchronized_standby_slots on the primary must be set to the physical replication slot of the standby intended to be in-sync

  • sync_replication_slots must be 1 to enable automatic synchronization

With a failover-enabled subscription slot and the above parameter values, when a standby is promoted, the subscriber can alter its subscription to this newly promoted instance and continue logical replication seamlessly.