Horton

Re: why not parallel seq scan for slow functions

Amit Kapila <amit.kapila16@gmail.com>

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From: Amit Kapila <amit.kapila16@gmail.com>
To: Jeff Janes <jeff.janes@gmail.com>
Cc: Dilip Kumar <dilipbalaut@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-07-23T03:53:52Z
Lists: pgsql-hackers 
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?


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

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.