Re: Synchronizing slots from primary to standby

Hi,

On Mon, Apr 01, 2024 at 05:04:53PM +0530, Amit Kapila wrote:
> On Mon, Apr 1, 2024 at 2:51 PM Bertrand Drouvot
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > Then there is no need to call WaitForStandbyConfirmation() as it could go until
> > the RecoveryInProgress() in StandbySlotsHaveCaughtup() for nothing (as we already
> > know it).
> >
>
> Won't it will normally return from the first check in
> WaitForStandbyConfirmation() because standby_slot_names_config is not
> set on standby?

I think standby_slot_names can be set on a standby. One could want to set it in
a cascading standby env (though it won't have any real effects until the standby
is promoted).

>
> > 2 ===
> >
> > + {
> > + if (SnapBuildSnapshotExists(remote_slot->restart_lsn))
> > + {
> >
> > That could call SnapBuildSnapshotExists() multiple times for the same
> > "restart_lsn" (for example in case of multiple remote slots to sync).
> >
> > What if the sync worker records the last lsn it asks for serialization (and
> > serialized ? Then we could check that value first before deciding to call (or not)
> > SnapBuildSnapshotExists() on it?
> >
> > It's not ideal because it would record "only the last one" but that would be
> > simple enough for now (currently there is only one sync worker so that scenario
> > is likely to happen).
> >
>
> Yeah, we could do that but I am not sure how much it can help. I guess
> we could do some tests to see if it helps.

Yeah not sure either. I just think it can only help and shouldn't make things
worst (but could avoid extra SnapBuildSnapshotExists() calls).

Regards,

--
Bertrand Drouvot
PostgreSQL Contributors Team
RDS Open Source Databases
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