Re: pgsql: Implement pg_wal_replay_wait() stored procedure

On Thu, Sep 26, 2024 at 11:19 AM Michael Paquier <michael(at)paquier(dot)xyz> wrote:
> On Fri, Aug 02, 2024 at 06:22:21PM +0000, Alexander Korotkov wrote:
> > Implement pg_wal_replay_wait() stored procedure
> >
> > pg_wal_replay_wait() is to be used on standby and specifies waiting for
> > the specific WAL location to be replayed. This option is useful when
> > the user makes some data changes on primary and needs a guarantee to see
> > these changes are on standby.
> >
> > The queue of waiters is stored in the shared memory as an LSN-ordered pairing
> > heap, where the waiter with the nearest LSN stays on the top. During
> > the replay of WAL, waiters whose LSNs have already been replayed are deleted
> > from the shared memory pairing heap and woken up by setting their latches.
> >
> > pg_wal_replay_wait() needs to wait without any snapshot held. Otherwise,
> > the snapshot could prevent the replay of WAL records, implying a kind of
> > self-deadlock. This is why it is only possible to implement
> > pg_wal_replay_wait() as a procedure working without an active snapshot,
> > not a function.
> >
> > Catversion is bumped.
>
> I've spotted that this patch uses an OID that should not be used
> during the development cycle:
> +{ oid => '111',
> + descr => 'wait for the target LSN to be replayed on standby with an optional timeout',
>
> Please use something in the 8000-9999 range, as required by
> 98eab30b93d5.

Fixed, sorry for messing this up.
I would appreciate if you have time to look at [0] to check if it
meets your expectations.

Links.
1. https://www.postgresql.org/message-id/CAPpHfdsw9oq62Fvt65JApHJf1auUirdGJV7%3DnRyVnDL3M8z5xA%40mail.gmail.com

------
Regards,
Alexander Korotkov
Supabase