Re: REL_13_STABLE Windows 10 Regression Failures

Heath Lord <heath(dot)lord(at)crunchydata(dot)com> writes:
> When building from source on a Windows 10 VM using MinGW (8.1.0), I
> get a random number of regression failures off the REL_13_STABLE
> branch. I debugged this a little bit and found out that the "random"
> number of failures is fully dependent on the machine and if I disable
> the "stats_ext.sql" regression test; all other tests pass without
> issue. When the "stats_ext.sql" regression test runs, it causes a
> database exception and PostgreSQL crashes.

Hmph ... it's weird that we have not seen this in the buildfarm.
Have you tried to extract any info from the crash, like a stack trace?

> I did some digging and determined that on the REL_13_STABLE branch
> this instability was introduced with this commit
> "b380484a850b6bf7d9fc0d85c555a2366e38451f"[1]. This corresponds to
> commit "19f5a37b9fc48a12c77edafb732543875da2f4a3"[1] on master. I
> worked backwards from there to determine when the regressions stopped
> failing and determined that with commit
> "be0a6666656ec3f68eb7d8e7abab5139fcd47012"[2] the regression tests are
> no longer failing.

I'm having a hard time believing that b380484a8 would have introduced
a portability problem, and an even harder time believing that be0a66666
would have resolved it if so. What seems more likely is that there's
some underlying issue such as a memory stomp, that the first commit
accidentally exposed and the second one accidentally hid again.
So, even if back-patching be0a66666 seemed feasible from a stability
standpoint (which I don't think it is), I fear it'd just mask a problem
that would eventually bite us again.

So I think we need to dig down and try to identify the root cause,
without any preconceptions about how to fix it. Again, a stack trace
would be pretty useful. Or at least some info about which step of
stats_ext.sql is crashing.

regards, tom lane