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

Hi,

On Mon, Mar 25, 2024 at 12:59:52PM +0530, Amit Kapila wrote:
> On Mon, Mar 25, 2024 at 12:43 PM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> >
> > On Mon, Mar 25, 2024 at 11:53 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Mar 25, 2024 at 10:33 AM shveta malik <shveta(dot)malik(at)gmail(dot)com> wrote:
> > > >
> > > > On Sun, Mar 24, 2024 at 3:06 PM Bharath Rupireddy
> > > > <bharath(dot)rupireddyforpostgres(at)gmail(dot)com> wrote:
> > > > >
> > > > > I've attached the v18 patch set here.
> >
> > 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.

OTOH I think the timeout invalidation (if any) should be synced from primary.

Regards,

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