Re: xid_wraparound tests intermittent failure.

On Thu, Jul 25, 2024 at 6:52 PM Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
>
>
> On 2024-07-25 Th 3:40 PM, Masahiko Sawada wrote:
>
> On Thu, Jul 25, 2024 at 11:06 AM Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com> wrote:
>
> On Thu, Jul 25, 2024 at 10:56 AM Andrew Dunstan <andrew(at)dunslane(dot)net> wrote:
>
> On 2024-07-23 Tu 6:59 PM, Masahiko Sawada wrote:
>
> See <https://bitbucket.org/adunstan/rotfang-fdw/downloads/xid-wraparound-result.tar.bz2>
>
>
> The failure logs are from a run where both tests 1 and 2 failed.
>
> Thank you for sharing the logs.
>
> I think that the problem seems to match what Alexander Lakhin
> mentioned[1]. Probably we can fix such a race condition somehow but
> I'm not sure it's worth it as setting autovacuum = off and
> autovacuum_max_workers = 1 (or a low number) is an extremely rare
> case. I think it would be better to stabilize these tests. One idea is
> to turn the autovacuum GUC parameter on while setting
> autovacuum_enabled = off for each table. That way, we can ensure that
> autovacuum workers are launched. And I think it seems to align real
> use cases.
>
> Regards,
>
> [1] https://www.postgresql.org/message-id/02373ec3-50c6-df5a-0d65-5b9b1c0c86d6%40gmail.com
>
>
> OK, do you want to propose a patch?
>
> Yes, I'll prepare and share it soon.
>
> I've attached the patch. Could you please test if the patch fixes the
> instability you observed?
>
> Since we turn off autovacuum on all three tests and we wait for
> autovacuum to complete processing databases, these tests potentially
> have a similar (but lower) risk. So I modified these tests to turn it
> on so we can ensure the autovacuum runs periodically.
>
>
> I assume you actually meant to remove the "autovacuum = off" in 003_wraparound.pl. With that change in your patch I retried my test, but on iteration 100 out of 100 it failed on test 002_limits.pl.
>

I think we need to remove the "autovacuum = off' also in 002_limits.pl
as it waits for autovacuum to process both template0 and template1
databases. Just to be clear, the failure happened even without
"autovacuum = off"?

Regards,

--
Masahiko Sawada
Amazon Web Services: https://aws.amazon.com