Question

How can I improve a WAL Replication Slot?

Environment

Connector: PostgreSQL using Logical Replication (WAL)

Answer

Parameters are set per database cluster and hence tuning this to support consistent and reliable WAL replication.

Recommended values:

• max_wal_size: Default is set to 1 Gb. Set max_wal_size to high enough to be rarely reached.
• checkpoint_timeout: Default is set to 5 minutes. Set checkpoint_timeout to 30mins.
• max_wal_sender: Default is set to 10. Ideally set max_wal_sender to 3 * Numbers of WAL connectors.
• wal_buffer : Default is set to 16MB. Ideally set wal_buffer to 64MB - higher value is recommended when there are many concurrent connection to the database.

Cause

• Replication Slot struggle with processing logs either inflated or logs not being cleared.
• WAL Stuck.
• WAL Performance is low.