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

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.

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