Re: Failure of subscription tests with topminnow

On Wed, Aug 25, 2021 at 5:43 PM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
>
> On Wed, Aug 25, 2021 at 4:22 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> >
> > On Wed, Aug 25, 2021 at 8:00 AM Ajin Cherian <itsajin(at)gmail(dot)com> wrote:
> > >
> > > On Tue, Aug 24, 2021 at 11:12 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> > >
> > > > But will poll function still poll or exit? Have you tried that?
> > >
> > > I have forced that condition with a changed query and found that the
> > > poll will not exit in case of a NULL return.
> > >
> >
> > What if the query in a poll is fired just before we get an error
> > "tap_sub ERROR: replication slot "tap_sub" is active for PID 16336"?
> > Won't at that stage both old and new walsender's are present, so the
> > query might return true. You can check that via debugger by stopping
> > just before this error occurs and then check pg_stat_replication view.
>
> If this error happens then the PID is NOT updated as the pid in the
> Replication slot. I have checked this
> and explained this in my first email itself
>

Sorry about the above email, I misunderstood. I was looking at
pg_stat_replication_slot rather than pg_stat_replication hence the confusion.
Amit is correct, just prior to the walsender erroring out, it briefly
appears in the
pg_stat_replication, and that is why this error happens. Sorry for the
confusion.
I just confirmed it, got both the walsenders stopped in the debugger:

postgres=# select pid from pg_stat_replication where application_name = 'sub';
pid
------
7899
7993
(2 rows)

ajin 7896 3326 0 05:22 pts/2 00:00:00 psql -p 6972 postgres
ajin 7897 7882 0 05:22 ? 00:00:00 postgres: ajin
postgres [local] idle
ajin 7899 7882 0 05:22 ? 00:00:00 postgres: walsender
ajin ::1(37719) START_REPLICATION
ajin 7992 3647 0 05:24 ? 00:00:00 postgres: logical
replication worker for subscription 16426
ajin 7993 7882 0 05:24 ? 00:00:00 postgres: walsender
ajin ::1(37720) START_REPLICATION

regards,
Ajin Cherian
Fujitsu Australia