Horton

Re: Problems with plan estimates in postgres_fdw

Antonin Houska <ah@cybertec.at>

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From: Antonin Houska <ah@cybertec.at>
To: Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>
Cc: Tom Lane <tgl@sss.pgh.pa.us>, Andrew Gierth <andrew@tao11.riddles.org.uk>, pgsql-hackers@postgresql.org
Date: 2019-02-22T15:21:41Z
Lists: pgsql-hackers 
Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:

> (2019/02/08 21:35), Etsuro Fujita wrote:

> > (2019/02/08 2:04), Antonin Houska wrote:

> >> * regression tests: I think test(s) should be added for queries that have
> >> ORDER BY clause but do not have GROUP BY (and also no LIMIT / OFFSET)
> >> clause. I haven't noticed such tests.
> >
> > Will do.
> 
> I noticed that such queries would be processed by what we already have for
> sort pushdown (ie, add_paths_with_pathkeys_for_rel()).  I might be missing
> something, though.

What about an ORDER BY expression that contains multiple Var nodes? For
example

SELECT * FROM foo ORDER BY x + y;

I think the base relation should not be able to generate paths with the
corresponding pathkeys, since its target should (besides PlaceHolderVars,
which should not appear in the plan of this simple query at all) only emit
individual Vars.

-- 
Antonin Houska
https://www.cybertec-postgresql.com

Commits

  1. postgres_fdw: Perform the (FINAL, NULL) upperrel operations remotely.

  2. Refactor create_limit_path() to share cost adjustment code with FDWs.

  3. postgres_fdw: Modify regression tests for EPQ-related planning problems.

  4. postgres_fdw: Perform the (ORDERED, NULL) upperrel operations remotely.

  5. Save PathTargets for distinct/ordered relations in root->upper_targets[].

  6. Split create_foreignscan_path() into three functions.

  7. Fix test case for 'outer pathkeys do not match mergeclauses' fix.

  8. postgres_fdw: Avoid 'outer pathkeys do not match mergeclauses' error.