Comment by skunkworker

After working with the Postgres WAL through logical replication in the last few months on a work project. My largest gripe is that some specific behaviors (like how a WAL receiver process should respond to a fast-shutdown on the database backend), aren't well documented outside of asking questions on the postgres discord.

Specifically: If the server requests a reply on a heartbeat, the status update should include the heartbeat's LSN on the next loop. But a standby status update includes the LSN values + 1.

I was able to get it working and properly disconnecting to a fast shutdown, but when you get into the internals of the logical WAL receiver loop, it can get nuanced.

And my largest compliment is that the Postgres discord is filled with some extremely knowledgeable and helpful people. I was able to figure out some really specific and nuanced behavior around the different status messages being sent to the primary server, thanks to the in-depth responses there.