Re: Synchronizing slots from primary to standby

On Mon, Jun 26, 2023 at 11:15 AM Drouvot, Bertrand
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> On 6/20/23 12:22 PM, Amit Kapila wrote:
> > On Mon, Jun 19, 2023 at 9:56 PM Drouvot, Bertrand
> > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> >> In such a case (slot valid on the primary but invalidated on the standby) then I think we
> >> could drop and recreate the invalidated slot on the standby.
> >>
> >
> > Will it be safe? Because after recreating the slot, it will reserve
> > the new WAL location and build the snapshot based on that which might
> > miss some important information in the snapshot. For example, to
> > update the slot's position with new information from the primary, the
> > patch uses pg_logical_replication_slot_advance() which means it will
> > process all records and update the snapshot via
> > DecodeCommit->SnapBuildCommitTxn().
>
> Your concern is that the slot could have been consumed on the standby?
>
> I mean, if we suppose the "synchronized" slot can't be consumed on the standby then
> drop/recreate such an invalidated slot would be ok?
>

That also may not be sufficient because as soon as the slot is
invalidated/dropped, the required WAL could be removed on standby.

--
With Regards,
Amit Kapila.