Re: Introduce XID age and inactive timeout based replication slot invalidation

On Mon, Mar 25, 2024 at 1:37 PM Bertrand Drouvot
<bertranddrouvot.pg@gmail.com> wrote:
>
> > > I have one concern, for synced slots on standby, how do we disallow
> > > invalidation due to inactive-timeout immediately after promotion?
> > >
> > > For synced slots, last_inactive_time and inactive_timeout are both
> > > set.
>
> Yeah, and I can see last_inactive_time is moving on the standby (while not the
> case on the primary), probably due to the sync worker slot acquisition/release
> which does not seem right.
>
> > Let's say I bring down primary for promotion of standby and then
> > > promote standby, there are chances that it may end up invalidating
> > > synced slots (considering standby is not brought down during promotion
> > > and thus inactive_timeout may already be past 'last_inactive_time').
> > >
> >
> > This raises the question of whether we need to set
> > 'last_inactive_time' synced slots on the standby?
>
> Yeah, I think that last_inactive_time should stay at 0 on synced slots on the
> standby because such slots are not usable anyway (until the standby gets promoted).
>
> So, I think that last_inactive_time does not make sense if the slot never had
> the chance to be active.

Right. Done that way i.e. not setting the last_inactive_time for slots
both while releasing the slot and restoring from the disk.

Also, I've added a TAP function to check if the captured times are
sane per Bertrand's review comment.

Please see the attached v20 patch.

--
Bharath Rupireddy
PostgreSQL Contributors Team
RDS Open Source Databases
Amazon Web Services: https://aws.amazon.com