Re: [PoC] pg_upgrade: allow to upgrade publisher node

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?