Configuring logical decoding on standby v15

Logical decoding on a standby server allows you to create a logical replication slot on a standby server that can respond to API operations such as get, peek, and advance.

For more information about logical decoding, refer to the PostgreSQL core documentation.

For a logical slot on a standby server to work, you must set the hot_standby_feedback parameter to ON on the standby. The hot_standby_feedback parameter prevents VACCUM from removing recently dead rows that are required by an existing logical replication slot on the standby server. If a slot conflict occurs on the standby, the slots are dropped.

For logical decoding on a standby to work, you must set wal_level to logical on both the primary and standby servers. If you set wal_level to a value other than logical, then slots aren't created. If you set wal_level to a value other than logical on primary, and if existing logical slots are on standby, such slots are dropped. You can't create new slots.

When transactions are written to the primary server, the activity triggers the creation of a logical slot on the standby server. If a primary server is idle, creating a logical slot on a standby server might take noticeable time.

For more information about functions that support replication, see the PostgreSQL documentation. See also this logical decoding example.