RE: Fix a test case in 035_standby_logical_decoding.pl

On Thu, Apr 27, 2023 9:53 PM Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>
> On Thu, Apr 27, 2023 at 4:07 PM Drouvot, Bertrand
> <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> >
> > On 4/27/23 11:53 AM, Amit Kapila wrote:
> > > On Thu, Apr 27, 2023 at 2:16 PM Drouvot, Bertrand
> > > <bertranddrouvot(dot)pg(at)gmail(dot)com> wrote:
> > >>
> > >> On 4/27/23 10:11 AM, Yu Shi (Fujitsu) wrote:
> > >>> Hi hackers,
> > >>>
> > >>> In 035_standby_logical_decoding.pl, I think that the check in the following
> test
> > >>> case should be performed on the standby node, instead of the primary
> node, as
> > >>> the slot is created on the standby node.
> > >>
> > >> Oh right, the current test is not done on the right node, thanks!
> > >>
> > >>> The test currently passes because it
> > >>> only checks the return value of psql. It might be more appropriate to check
> the
> > >>> error message.
> > >>
> > >> Agree, and it's consistent with what is being done in
> 006_logical_decoding.pl.
> > >>
> > >>> Please see the attached patch.
> > >>>
> > >>
> > >> +
> > >> +($result, $stdout, $stderr) = $node_standby->psql(
> > >> 'otherdb',
> > >> "SELECT lsn FROM
> pg_logical_slot_peek_changes('behaves_ok_activeslot', NULL, NULL) ORDER BY
> lsn DESC LIMIT 1;"
> > >> - ),
> > >> - 3,
> > >> - 'replaying logical slot from another database fails');
> > >> + );
> > >> +ok( $stderr =~
> > >> + m/replication slot "behaves_ok_activeslot" was not created in this
> database/,
> > >> + "replaying logical slot from another database fails");
> > >>
> > >>
> > >> That does look good to me.
> > >>
> > >
> > > I agree that that the check should be done on standby but how does it
> > > make a difference to check the error message or return value? Won't it
> > > be the same for both primary and standby?
> > >
> >
> > Yes that would be the same. I think the original idea from Shi-san (please
> correct me If I'm wrong)
> > was "while at it" let's also make this test on the right node even better.
> >
>
> Fair enough. Let''s do it that way then.
>
> > >> Nit: I wonder if while at it (as it was already there) we could not remove the
> " ORDER BY lsn DESC LIMIT 1" part of it.
> > >> It does not change anything regarding the test but looks more appropriate
> to me.
> > >>
> > >
> > > It may not make a difference as this is anyway an error case but it
> > > looks more logical to LIMIT by 1 as you are fetching a single LSN
> > > value and it will be consistent with other tests in this file and the
> > > test case in the file 006_logical_decoding.pl.
> > >
> >
> > yeah I think it all depends how one see this test (sort of test a failure or try to
> get
> > a result and see if it fails). That was a Nit so I don't have a strong opinion on
> this one.
> >
>
> I feel let's be consistent here and keep it as it is.
>
> > > BTW, in the same test, I see it uses wait_for_catchup() in one place
> > > and wait_for_replay_catchup() in another place after Insert. Isn't it
> > > better to use wait_for_replay_catchup in both places?
> > >
> >
> > They are both using the 'replay' mode so both are perfectly correct but for
> consistency (and as
> > they don't use the same "target_lsn" ('write' vs 'flush')) I think that using
> wait_for_replay_catchup()
> > in both places (which is using the 'flush' target lsn) is a good idea.
> >
>
> Yeah, let's use wait_for_replay_catchup() at both places.
>

Thanks for your reply. Your suggestions make sense to me.
Please see the attached patch.

Regards,
Shi Yu