Re: stress test for parallel workers

Thomas Munro <thomas(dot)munro(at)gmail(dot)com> writes:
> *I suspect that the only thing implicating parallelism in this failure
> is that parallel leaders happen to print out that message if the
> postmaster dies while they are waiting for workers; most other places
> (probably every other backend in your cluster) just quietly exit.
> That tells us something about what's happening, but on its own doesn't
> tell us that parallelism plays an important role in the failure mode.

I agree that there's little evidence implicating parallelism directly.
The reason I'm suspicious about a possible OOM kill is that parallel
queries would appear to the OOM killer to be eating more resources
than the same workload non-parallel, so that we might be at more
hazard of getting OOM'd just because of that.

A different theory is that there's some hard-to-hit bug in the
postmaster's processing of parallel workers that doesn't apply to
regular backends. I've looked for one in a desultory way but not
really focused on it.

In any case, the evidence from the buildfarm is pretty clear that
there is *some* connection. We've seen a lot of recent failures
involving "postmaster exited during a parallel transaction", while
the number of postmaster failures not involving that is epsilon.

regards, tom lane