| From: | Robert Haas <robertmhaas(at)gmail(dot)com> |
|---|---|
| To: | Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)us> |
| Cc: | Ashutosh Bapat <ashutosh(dot)bapat(at)enterprisedb(dot)com>, Etsuro Fujita <fujita(dot)etsuro(at)lab(dot)ntt(dot)co(dot)jp>, Jeff Janes <jeff(dot)janes(at)gmail(dot)com>, David Steele <david(at)pgmasters(dot)net>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: [HACKERS] postgres_fdw bug in 9.6 |
| Date: | 2018-01-15 19:10:36 |
| Message-ID: | CA+TgmoY-jd1yXdQ6i7sX4GV0RTvETo+D4kGRPD7XVWvvqq_58w@mail.gmail.com |
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| Lists: | pgsql-hackers |
On Mon, Jan 15, 2018 at 12:31 PM, Tom Lane <tgl(at)sss(dot)pgh(dot)pa(dot)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
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