Re: pgsql: Track last_inactive_time in pg_replication_slots.

On Mon, Mar 25, 2024 at 8:46 PM Bertrand Drouvot
<bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
>
> On Mon, Mar 25, 2024 at 08:38:16PM +0530, Amit Kapila wrote:
> > On Mon, Mar 25, 2024 at 7:51 PM Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
> > >
> > > On Mon, Mar 25, 2024 at 10:02 AM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > > > We considered the other two names as last_inactive_at and
> > > > last_active_time. For the first (last_inactive_at), there was an
> > > > argument that most other fields that display time ends with _time. For
> > > > the second (last_active_time), there was an argument that it could be
> > > > misleading as one could think that it should be updated each time WAL
> > > > record decoding is happening [1]. The other possibility is to name it
> > > > last_used_time but I think it won't be much different from
> > > > last_active_time.
> > >
> > > I don't understand the bit about updating it each time WAL record
> > > decoding is happening. If it's the last active time, and the slot is
> > > currently active, then the answer is either "right now" or "currently
> > > undefined." I'd expect to see NULL in the system view in such a case.
> > > And if that's so, then there's nothing to update each time a record is
> > > decoded, because it's just still going to show NULL.
> > >
> >
> > IIUC, Bertrand's point was that users can interpret last_active_time
> > as a value that gets updated each time they decode a change which is
> > not what we are doing. So, this can confuse users. Your expectation of
> > answer (NULL) when the slot is active is correct and that is what will
> > happen.
>
> Yeah, and so would be the confusion: why is last_active_time NULL while one is
> using the slot?
>

It is because we set it to zero when we acquire the slot and that
value will remain the same till the slot is active. I am not sure if I
understood your question so what I am saying might not make sense.

--
With Regards,
Amit Kapila.