Re: Parallel Seq Scan

On Fri, Mar 27, 2015 at 2:34 AM, Amit Kapila <amit(dot)kapila16(at)gmail(dot)com> wrote:
> The reason of this problem is that above tab-completion is executing
> query [1] which contains subplan for the funnel node and currently
> we don't have capability (enough infrastructure) to support execution
> of subplans by parallel workers. Here one might wonder why we
> have choosen Parallel Plan (Funnel node) for such a case and the
> reason for same is that subplans are attached after Plan generation
> (SS_finalize_plan()) and if want to discard such a plan, it will be
> much more costly, tedious and not worth the effort as we have to
> eventually make such a plan work.
>
> Here we have two choices to proceed, first one is to support execution
> of subplans by parallel workers and second is execute/scan locally for
> Funnel node having subplan (don't launch workers).

It looks to me like the is an InitPlan, not a subplan. There
shouldn't be any problem with a Funnel node having an InitPlan; it
looks to me like all of the InitPlan stuff is handled by common code
within the executor (grep for initPlan), so it ought to work here the
same as it does for anything else. What I suspect is failing
(although you aren't being very clear about it here) is the passing
down of the parameters set by the InitPlan to the workers. I think we
need to make that work; it's an integral piece of the executor
infrastructure and we shouldn't leave it out just because it requires
a bit more IPC.

--
Robert Haas
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