Michael Paquier <michael@paquier.xyz> writes:
> On Fri, Aug 30, 2024 at 08:47:46PM +0000, Tom Lane wrote:
>> Make postgres_fdw's query_cancel test less flaky.
> Based on this recent report from the buildfarm, there is still
> something happening here:
> https://buildfarm.postgresql.org/cgi-bin/show_log.pl?nm=drongo&dt=2025-03-07%2004%3A31%3A37
> In details:
> -- This would take very long if not canceled:
> SELECT count(*) FROM ft1 a CROSS JOIN ft1 b CROSS JOIN ft1 c CROSS JOIN ft1 d;
> ERROR: canceling statement due to statement timeout
> +WARNING: could not send cancel request: cancel request timed out
> COMMIT;
I only promised to make it less flaky, not zero flaky ;-).
But this is an interesting failure, because it's different from
the previous symptoms. Before we were getting
>> +WARNING: could not get result of cancel request due to timeout
but here it's failing to send the cancel request in the first place.
Grepping the buildfarm logs finds one prior occurrence of this in
the last three months, also on drongo:
sysname | branch | snapshot | stage |
l
---------+--------+---------------------+-----------------------------------------------------+----------------------------------------------------------------------
drongo | HEAD | 2025-02-01 13:35:14 | postgres_fdwInstallCheck-C | +WARNING: could not
sendcancel request: cancel request timed out\r
drongo | HEAD | 2025-03-07 04:31:37 | postgres_fdwInstallCheck-English_United-States.1252 | +WARNING: could not
sendcancel request: cancel request timed out\r
(2 rows)
Looking at the code, we must have gotten past PQcancelStart, and
then we're waiting vainly for PQcancelPoll to report success.
The timeout for that is 30 seconds, so it's hard to credit that
we didn't wait long enough. Something must have gone wrong that
we couldn't detect.
It would be interesting to know what conn->status was, so that
we'd have some clue how far the cancel request got; though I have
relatively little hope that that would actually yield a fix.
Do you think it'd be reasonable to add PQcancelStatus() to the
"timed out" message? It looks like we don't have any infrastructure
for printing ConnStatusType, so we'd have to just print it as an
integer; but since this ought to be a can't-happen case I think
that'd be all right.
regards, tom lane
