Re: pgsql: Implement pg_wal_replay_wait() stored procedure

On Mon, Nov 4, 2024 at 4:19 PM Alvaro Herrera <alvherre(at)alvh(dot)no-ip(dot)org> wrote:
> On 2024-Nov-04, Alexander Korotkov wrote:
>
> > On Mon, Nov 4, 2024 at 8:04 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
>
> > > Using output parameters in a procedure is something I did not recall.
> > > Based on your point about not using a function due your argument based
> > > on the snapshots, let's just use that and forget about the status
> > > function entirely (please?).
> >
> > Please, check [1]. Usage of output parameters is a bit awkward too,
> > because you need to pass some value in there. And more importantly,
> > usage of output parameters also causes snapshot problem, as it causes
> > another snapshot to be held.
>
> I wonder if it would be better to go back to the original idea of using
> special DDL syntax rather than a procedure. It seems we've been piling
> up hacks to get around the behavior of procedures, and we seem to have
> grown one more to handle repeatable read transactions.
>
> It's looking to me like there's just too much cruft in the quest to
> avoid having to reach consensus on new syntax. This might be a mistake.
> Is it possible to backtrack on that decision?

Before committing pg_wal_replay_wait() I was under impression that
stored procedure would require the same amount of efforts than utility
statement to make backend "snapshot-less". However, it appears that
if we have implicit REPEATABLE READ transaction, stored procedure
needs more efforts. That makes the whole decision, at least,
questionable.

------
Regards,
Alexander Korotkov
Supabase