Re: [HACKERS] parallel.c oblivion of worker-startup failures

On Wed, Jan 24, 2018 at 5:43 PM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
>> Hmm. Yeah. I can't seem to reach a stuck case and was probably just
>> confused and managed to confuse Robert too. If you make
>> fork_process() fail randomly (see attached), I see that there are a
>> couple of easily reachable failure modes (example session at bottom of
>> message):
>>
>
> In short, we are good with committed code. Right?

Yep. Sorry for the noise.

> Yes, this is what I am trying to explain on parallel create index
> thread. I think there we need to either use
> WaitForParallelWorkersToFinish or WaitForParallelWorkersToAttach (a
> new API as proposed in that thread) if we don't want to use barriers.
> I see a minor disadvantage in using WaitForParallelWorkersToFinish
> which I will say on that thread.

Ah, I see. So if you wait for them to attach you can detect
unexpected dead workers (via shm_mq_receive), at the cost of having
the leader wasting time waiting around for forked processes to say
hello when it could instead be sorting tuples.

--
Thomas Munro
http://www.enterprisedb.com