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: Robert Haas <robertmhaas@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>, Thomas Munro <thomas.munro@enterprisedb.com>, Amit Khandekar <amitdkhan.pg@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-11-08T12:26:16Z
Lists: pgsql-hackers 
On Wed, Nov 8, 2017 at 4:34 PM, Robert Haas <robertmhaas@gmail.com> wrote:
> On Tue, Nov 7, 2017 at 9:41 PM, Amit Kapila <amit.kapila16@gmail.com> wrote:
>> This is required to prohibit generating gather path for top rel in
>> case of inheritence (Append node) at this place (we want to generate
>> it later when scan/join target is available).
>
> OK, but why don't we want to generate it later when there isn't
> inheritance involved?
>

We do want to generate it later when there isn't inheritance involved,
but only if there is a single rel involved (simple_rel_array_size
<=2).  The rule is something like this, we will generate the gather
paths at this stage only if there are more than two rels involved and
there isn't inheritance involved.


-- 
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.