Horton

Re: why not parallel seq scan for slow functions

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Amit Kapila <amit.kapila16@gmail.com>
Cc: Jeff Janes <jeff.janes@gmail.com>, Dilip Kumar <dilipbalaut@gmail.com>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2017-08-15T13:45:42Z
Lists: pgsql-hackers 
On Sat, Aug 12, 2017 at 9:18 AM, Amit Kapila <amit.kapila16@gmail.com> wrote:
> I think skipping a generation of gather paths for scan node or top
> level join node generated via standard_join_search seems straight
> forward, but skipping for paths generated via geqo seems to be tricky
> (See use of generate_gather_paths in merge_clump).  Assuming, we find
> some way to skip it for top level scan/join node, I don't think that
> will be sufficient, we have some special way to push target list below
> Gather node in apply_projection_to_path, we need to move that part as
> well in generate_gather_paths.

I don't think that can work, because at that point we don't know what
target list the upper node wants to impose.

-- 
Robert Haas
EnterpriseDB: http://www.enterprisedb.com
The Enterprise PostgreSQL Company

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.