Horton

Re: [HACKERS] postgres_fdw bug in 9.6

Robert Haas <robertmhaas@gmail.com>

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From: Robert Haas <robertmhaas@gmail.com>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Ashutosh Bapat <ashutosh.bapat@enterprisedb.com>, Etsuro Fujita <fujita.etsuro@lab.ntt.co.jp>, Jeff Janes <jeff.janes@gmail.com>, David Steele <david@pgmasters.net>, pgsql-hackers <pgsql-hackers@postgresql.org>
Date: 2018-01-15T19:10:36Z
Lists: pgsql-hackers 
On Mon, Jan 15, 2018 at 12:31 PM, Tom Lane <tgl@sss.pgh.pa.us> wrote:

>> After some thought, it seems that there's a much simpler way that we
>> could fix the problem you identified in that original email: if the
>> EPQ path isn't properly sorted, have postgres_fdw's
>> add_paths_with_pathkeys_for_rel stick a Sort node on top of it.  I
>> tried this and it does indeed fix Jeff Janes' initial test case.
>
> Hm.  Simple is certainly good, but if there's multiple rows coming
> back during an EPQ recheck then I think we have a performance problem.

You are correct ... I was wrong about that part, and said so in an
email on this thread sent about 45 minutes before yours.  However, I
still think the patch is a good fix for the immediate issue, unless
you see some problem with it.  It's simple and back-patchable and does
not preclude further work anybody, including you, might want to do in
the future.

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

Commits

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

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

  3. postgres_fdw: Consider foreign joining and foreign sorting together.

  4. Allow foreign and custom joins to handle EvalPlanQual rechecks.

  5. Allow FDWs to push down quals without breaking EvalPlanQual rechecks.