Horton

Re: why not parallel seq scan for slow functions

Jeff Janes <jeff.janes@gmail.com>

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From: Jeff Janes <jeff.janes@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-07-24T15:51:46Z
Lists: pgsql-hackers 
On Sat, Jul 22, 2017 at 8:53 PM, Amit Kapila <amit.kapila16@gmail.com>
wrote:

> On Thu, Jul 13, 2017 at 7:38 AM, Amit Kapila <amit.kapila16@gmail.com>
> wrote:
> > On Wed, Jul 12, 2017 at 11:20 PM, Jeff Janes <jeff.janes@gmail.com>
> wrote:
> >>
> >>
> >>
> >> Setting parallel_workers to 8 changes the threshold for the parallel to
> even
> >> be considered from parellel_tuple_cost <= 0.0049 to <= 0.0076.  So it is
> >> going in the correct direction, but not by enough to matter.
> >>
> >
> > You might want to play with cpu_tuple_cost and or seq_page_cost.
> >
>
> I don't know whether the patch will completely solve your problem, but
> this seems to be the right thing to do.  Do you think we should stick
> this for next CF?
>

It doesn't solve the problem for me, but I agree it is an improvement we
should commit.

Cheers,

Jeff

Commits

  1. Rewrite the code that applies scan/join targets to paths.

  2. Teach create_projection_plan to omit projection where possible.

  3. Make the upper part of the planner work by generating and comparing Paths.