Re: BUG #15594: Unstable tests in contrib/test_decoding/output_iso/

17.01.2019 20:39, Andres Freund wrote:
> On 2019-01-17 13:42:40 +0300, Alexander Lakhin wrote:
>> 17.01.2019 13:25, Petr Jelinek wrote:
>>> On 16/01/2019 20:09, Andres Freund wrote:
>>>> On 2019-01-16 14:56:34 +0000, PG Bug reporting form wrote:
>>>>> The following bug has been logged on the website:
>>>>>
>>>>> Bug reference:      15594
>>>>> Logged by:          Alexander Lakhin
>>>>> Email address:      exclusion@gmail.com
>>>>> PostgreSQL version: 11.1
>>>>> Operating system:   Ubuntu 18.04
>>>>> Description:        
>>>>>
>>>>> Some tests in contrib/test_decoding/output_iso/ occasionally fail.
>>>>> To reproduce it reliable you can do:
>>>>> # sed 's/ mxact / $(shell printf "mxact %.0s" `seq 1000` ) /' -i
>>>>> contrib/test_decoding/Makefile
>>>>> # make check -C contrib/test_decoding/
>>>>>
>>>>> ...
>>>>>
>>>>> I observe this issue with the tests: mxact, delayed_startup, and
>>>>> ondisk_startup.
>>>> Interesting - I've not seen that on the buildfarm before, or in local tests
>>>> with a lot of repetitions. I assume the problem vanishes if you add 'skip-empty-xacts', '1'
>>>> to the options of pg_logical_slot_get_changes()?
>>>>
>>> I bet those empty transactions are from autovacuum. The probability of
>>> hitting this could be exaggerated by the fact that the test is run
>>> within the same instance 1000x rather than running the make check 1000x
>>> so we produce plenty of catalog bloat for autovacuum to clean.
>>>
>> Yes, it's almost impossible to hit this with `make check`, but with
>> `make installcheck` the probability is much higher as we use an existing
>> instance.
>> I've reproduced it with `make check` just to make it simple.
> I'll apply the fix for this, but please note that installcheck
> *intentionally* is disabled for test_decoding.
Thanks, Andres! I see a comment in Makefile:
# Disabled because these tests require "wal_level=logical", which
# typical installcheck users do not have (e.g. buildfarm clients).

So if I use for the installcheck'ed instance a config with the required
wal_level, is it ok to perform `make installcheck-force -C
contrib/test_decoding`?
Or maybe there is some other difficulty with installcheck?

Best regards,
Alexander