Re: promotion related handling in pg_sync_replication_slots()

Hi,

On Mon, Apr 15, 2024 at 06:29:49PM +0530, Amit Kapila wrote:
> On Mon, Apr 15, 2024 at 6:21 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > On Mon, Apr 15, 2024 at 03:38:53PM +0530, shveta malik wrote:
> > > Now both worker and SQL
> > > function set 'syncing' when they start and reset it when they exit.
> >
> > It means that it's not possible anymore to trigger a manual sync if
> > sync_replication_slots is on. Indeed that would trigger:
> >
> > postgres=# select pg_sync_replication_slots();
> > ERROR:  cannot synchronize replication slots concurrently
> >
> > That looks like an issue to me, thoughts?
> >
> 
> This is intentional as of now for the sake of keeping
> implementation/code simple. It is not difficult to allow them but I am
> not sure whether we want to add another set of conditions allowing
> them in parallel.

I think that the ability to launch a manual sync before a switchover would be
missed. Except for this case I don't think that's an issue to prevent them to
run in parallel.

> And that too in an unpredictable way as the API will
> work only for the time slot sync worker is not performing the sync.

Yeah but then at least you would know that there is "really" a sync in progress
(which is not the case currently with v4, as the sync worker being started is
enough to prevent a manual sync even if a sync is not in progress).

Regards,

-- 
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com