Re: shm_mq_set_sender() crash

On Thu, Sep 15, 2016 at 06:21:30PM -0400, Robert Haas wrote:
> On Thu, Sep 15, 2016 at 5:22 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> wrote:
> > Robert Haas <robertmhaas(at)gmail(dot)com> writes:
> >> Of course, it's also possible that the ParallelWorkerNumber code is
> >> entirely correct and something overwrote the null bytes that were
> >> supposed to be found at that location. It would be very useful to see
> >> (a) the value of ParallelWorkerNumber and (b) the contents of
> >> vmq->mq_sender, and in particular whether that's actually a valid
> >> pointer to a PGPROC in the ProcArray. But unless we can reproduce
> >> this I don't see how to manage that.
> >
> > Is it worth replacing that Assert with a test-and-elog that would
> > print those values?
> >
> > Given that we've seen only one such instance in the buildfarm, this
> > might've been just a cosmic ray bit-flip. So one part of me says
> > not to worry too much until we see it again. OTOH, if it is real
> > but rare, missing an opportunity to diagnose would be bad.
>
> I wonder if we could persuade somebody to run pgbench on a Windows
> machine with a similar environment, at least some concurrency, and
> force_parallel_mode=on. Assuming this is a generic
> initialize-the-parallel-stuff bug and not something specific to a
> particular query, that might well trigger it a lot quicker than
> waiting for it to recur in the BF.

For the sake of this thread in the archives, the cause was almost surely a
Cygwin signal handling bug:

https://postgr.es/m/20170803034740.GA2641942@rfd.leadboat.com
https://marc.info/?t=150183296400001
https://marc.info/?t=150291861700011