Re: Parallel Seq Scan

On Fri, Mar 13, 2015 at 7:15 PM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Fri, Mar 13, 2015 at 7:01 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
wrote:
> > I think this can happen if funnel->nextqueue is greater than
> > funnel->nqueues.
> > Please see if attached patch fixes the issue, else could you share the
> > scenario in more detail where you hit this issue.
>
> Speaking as the guy who wrote the first version of that code...
>
> I don't think this is the right fix; the point of that code is to
> remove a tuple queue from the funnel when it gets detached, which is a
> correct thing to want to do. funnel->nextqueue should always be less
> than funnel->nqueues; how is that failing to be the case here?
>

I could not reproduce the issue, neither the exact scenario is
mentioned in mail. However what I think can lead to funnel->nextqueue
greater than funnel->nqueues is something like below:

Assume 5 queues, so value of funnel->nqueues will be 5 and
assume value of funnel->nextqueue is 2, so now let us say 4 workers
got detached one-by-one, so for such a case it will always go in else loop
and will never change funnel->nextqueue whereas value of funnel->nqueues
will become 1.

Am I missing something?

With Regards,
Amit Kapila.
EnterpriseDB: http://www.enterprisedb.com