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

Hi,

On Tue, Apr 02, 2024 at 12:41:35PM +0530, Bharath Rupireddy wrote:
> On Tue, Apr 2, 2024 at 11:58 AM Bertrand Drouvot
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >
> > > Or a simple solution is that the slotsync worker updates
> > > inactive_since as it does for non-synced slots, and disables
> > > timeout-based slot invalidation for synced slots.
> >
> > Yeah, I think the main question to help us decide is: do we want to invalidate
> > "inactive" synced slots locally (in addition to synchronizing the invalidation
> > from the primary)?
>
> I think this approach looks way simpler than the other one. The other
> approach of linking inactive_since on the standby for synced slots to
> the actual LSNs (or other slot parameters) being updated or not looks
> more complicated, and might not go well with the end user. However,
> we need to be able to say why we don't invalidate synced slots due to
> inactive timeout unlike the wal_removed invalidation that can happen
> right now on the standby for synced slots. This leads us to define
> actually what a slot being active means. Is syncing the data from the
> remote slot considered as the slot being active?
>
> On the other hand, it may not sound great if we don't invalidate
> synced slots due to inactive timeout even though they hold resources
> such as WAL and XIDs.

Right and the "only" benefit then would be to give an idea as to when the last
sync did occur on the local slot.

Regards,

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