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: 2019-03-08T16:25:49Z
Lists: pgsql-hackers 
Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp> wrote:

> (2019/03/01 20:16), Antonin Houska wrote:
> > Etsuro Fujita<fujita.etsuro@lab.ntt.co.jp>  wrote:
> 
> >> Conversely, it appears that add_foreign_ordered_paths() added by the patchset
> >> would generate such pre-sorted paths *redundantly* when the input_rel is the
> >> final scan/join relation.  Will look into that.
> >
> > Currently I have no idea how to check the plan created by FDW at the
> > UPPERREL_ORDERED stage, except for removing the sort from the
> > UPPERREL_GROUP_AGG stage as I proposed here:
> >
> > https://www.postgresql.org/message-id/11807.1549564431%40localhost
> 
> I don't understand your words "how to check the plan created by FDW". Could
> you elaborate on that a bit more?

I meant that I don't know how to verify that the plan that sends the ORDER BY
clause to the remote server was created at the UPPERREL_ORDERED and not at
UPPERREL_GROUP_AGG. However if the ORDER BY clause really should not be added
at the UPPERREL_GROUP_AGG stage and if we ensure that it no longer happens,
then mere presence of ORDER BY in the (remote) plan means that the
UPPERREL_ORDERED stage works fine.

-- 
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.