RE: Synchronizing slots from primary to standby

On Thursday, February 1, 2024 12:20 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Feb 1, 2024 at 8:15 AM Euler Taveira <euler(at)eulerto(dot)com> wrote:
> >
> > On Mon, Jan 29, 2024, at 10:17 AM, Zhijie Hou (Fujitsu) wrote:
> >
> > Attach the V72-0001 which addressed above comments, other patches will
> be
> > rebased and posted after pushing first patch. Thanks Shveta for helping
> address
> > the comments.
> >
> >
> > While working on another patch I noticed a new NOTICE message:
> >
> > NOTICE: changed the failover state of replication slot "foo" on publisher to
> false
> >
> > I wasn't paying much attention to this thread then I start reading the 2
> > patches that was recently committed. The message above surprises me
> because
> > pg_createsubscriber starts to emit this message. The reason is that it doesn't
> > create the replication slot during the CREATE SUBSCRIPTION. Instead, it
> creates
> > the replication slot with failover = false and no such option is informed
> > during CREATE SUBSCRIPTION which means it uses the default value (failover
> =
> > false). I expect that I don't see any message because it is *not* changing the
> > behavior. I was wrong. It doesn't check the failover state on publisher, it
> > just executes walrcv_alter_slot() and emits a message.
> >
> > IMO if we are changing an outstanding property on node A from node B,
> node B
> > already knows (or might know) about that behavior change (because it is
> sending
> > the command), however, node A doesn't (unless log_replication_commands
> = on --
> > it is not the default).
> >
> > Do we really need this message as NOTICE?
> >
>
> The reason for adding this NOTICE was to keep it similar to other
> Notice messages in these commands like create/drop slot. However, here
> the difference is we may not have altered the slot as the property is
> already the same as we want to set on the publisher. So, I am not sure
> whether we should follow the existing behavior or just get rid of it.
> And then do we remove similar NOTICE in AlterSubscription() as well?
> Normally, I think NOTICE intends to let users know if we did anything
> with slots while executing subscription commands. Does anyone else
> have an opinion on this point?
>
> A related point, I think we can avoid setting the 'failover' property
> in ReplicationSlotAlter() if it is not changed, the advantage is we
> will avoid saving slots. OTOH, this won't be a frequent operation so
> we can leave it as it is as well.

Here is a patch to remove the NOTICE and improve the ReplicationSlotAlter.
The patch also includes few cleanups based on Peter's feedback.

Best Regards,
Hou zj