Thanks for the deep dive on Postgres WAL.

I recently had the opportunity to play with PostgreSQL WAL in the scope of implementing opensearch cdc pipeline, and it was really exciting to see what is possible to achieve with it.

Be cautious with idle replica slots though, I got bitten by inactive slots filling up the production database storage.

PostgreSQL 18 introduces idle_replication_slot_timeout to mitigate this.

For those not on 18 yet, there's also max_slot_wal_keep_size, which invalidates slots based on the amount of WAL they retain rather than based on a period of inactivity. It's available since PG 13.