Re: Fix a test case in 035_standby_logical_decoding.pl

Hi,

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.

>> 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.

> 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.

Regards,

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