Re: Synchronizing slots from primary to standby

On Mon, Oct 2, 2023 at 11:39 AM Drouvot, Bertrand
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> On 9/29/23 1:33 PM, Amit Kapila wrote:
> > On Thu, Sep 28, 2023 at 6:31 PM Drouvot, Bertrand
> > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >>
> >
> >> - probably open corner cases like: what if a standby is down? would that mean
> >> that synchronize_slot_names not being send to the primary would allow the decoding
> >> on the primary to go ahead?
> >>
> >
> > Good question. BTW, irrespective of whether we have
> > 'standby_slot_names' parameters or not, how should we behave if
> > standby is down? Say, if 'synchronize_slot_names' is only specified on
> > standby then in such a situation primary won't be even aware that some
> > of the logical walsenders need to wait.
>
> Exactly, that's why I was thinking keeping standby_slot_names to address
> this scenario. In such a case one could simply decide to keep or remove
> the associated physical replication slot from standby_slot_names. Keep would
> mean "wait" and removing would mean allow to decode on the primary.
>
> > OTOH, one can say that users
> > should configure 'synchronize_slot_names' on both primary and standby
> > but note that this value could be different for different standby's,
> > so we can't configure it on primary.
> >
>
> Yeah, I think that's a good use case for standby_slot_names, what do you think?
>

But, even if we keep 'standby_slot_names' for this purpose, the
primary doesn't know the value of 'synchronize_slot_names' once the
standby is down and or the primary is restarted. So, how will we know
which logical WAL senders needs to wait for 'standby_slot_names'?

--
With Regards,
Amit Kapila.