On Mon, Aug 07, 2023 at 09:24:02AM +0530, Amit Kapila wrote: > > I think autovacuum is not enabled during the upgrade. See comment "Use > -b to disable autovacuum." in start_postmaster(). However, I am not > sure if there can't be any additional WAL from checkpointer or > bgwriter. Checkpointer has a code that ensures that if there is no > important WAL activity then it would be skipped. Similarly, bgwriter > also doesn't LOG xl_running_xacts unless there is an important > activity. I feel if there is a chance of any WAL activity during the > upgrade, we need to either change the check to ensure such WAL records > are expected or document the same in some way.
Unless I'm missing something I don't see what prevents something to connect using the replication protocol and issue any query or even create new replication slots? Note also that as complained a few years ago nothing prevents a bgworker from spawning up during pg_upgrade and possibly corrupt the upgraded cluster if multixid are assigned. If publications are preserved wouldn't it mean that such bgworkers could also lead to data loss?
