Hi,
On Tue, Apr 16, 2024 at 08:21:04AM +0530, Amit Kapila wrote:
> On Mon, Apr 15, 2024 at 7:47 PM Bertrand Drouvot
> <bertranddrouvot.pg@gmail.com> wrote:
> >
> > 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.
> >
>
> I think if the slotsync worker is available, it can do that as well.
Right, but one has no control as to when the sync is triggered.
> There is no clear use case for allowing them in parallel and I feel it
> would add more confusion when it can work sometimes but not other
> times. However, if we receive some report from the field where there
> is a real demand for such a thing, it should be easy to achieve. For
> example, I can imagine that we can have sync_state that has values
> 'started', 'in_progress' , and 'finished'. This should allow us to
> achieve what the current proposed patch is doing along with allowing
> the API to work in parallel when the sync_state is not 'in_progress'.
>
> I think for now let's restrict their usage in parallel and make the
> promotion behavior consistent both for worker and API.
Okay, let's do it that way. Is it worth to add a few words in the doc related to
pg_sync_replication_slots() though? (to mention it can not be used if the sync
slot worker is running).
Regards,
--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com
