Re: Parallel Seq Scan

On Mon, Jan 12, 2015 at 3:27 AM, Robert Haas <robertmhaas(at)gmail(dot)com> wrote:
>
> On Sun, Jan 11, 2015 at 5:27 AM, Stephen Frost <sfrost(at)snowman(dot)net> wrote:
> > * Robert Haas (robertmhaas(at)gmail(dot)com) wrote:
> >> On Thu, Jan 8, 2015 at 2:46 PM, Stephen Frost <sfrost(at)snowman(dot)net>
wrote:
> >> > Yeah, if we come up with a plan for X workers and end up not being
able
> >> > to spawn that many then I could see that being worth a warning or
notice
> >> > or something. Not sure what EXPLAIN has to do anything with it..
> >>
> >> That seems mighty odd to me. If there are 8 background worker
> >> processes available, and you allow each session to use at most 4, then
> >> when there are >2 sessions trying to do parallelism at the same time,
> >> they might not all get their workers. Emitting a notice for that
> >> seems like it would be awfully chatty.
> >
> > Yeah, agreed, it could get quite noisy. Did you have another thought
> > for how to address the concern raised? Specifically, that you might not
> > get as many workers as you thought you would?
>
> I'm not sure why that's a condition in need of special reporting.
>

So what should happen if no workers are available?
I don't think we can change the plan to a non-parallel at that
stage.

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