From: Bruce Momjian <bruce@momjian.us>
To: Tom Lane <tgl@sss.pgh.pa.us>
Cc: Pete Storer <Pete.Storer@sas.com>
Cc: pgsql-bugs@lists.postgresql.org <pgsql-bugs@lists.postgresql.org>
Subject: Re: FW: Query execution failure
Date: Wed, 27 Sep 2023 21:00:12 -0400
Message-ID: <ZRTQHKRhSLndfB5z@momjian.us> (raw)
In-Reply-To: <Y9fjfNpP7HZh1YX9@momjian.us>
References: <BL0PR05MB66282A9070EE621D031C27C7F3CE9@BL0PR05MB6628.namprd05.prod.outlook.com>
<BL0PR05MB66283C57D72E321591AE4EB1F3CE9@BL0PR05MB6628.namprd05.prod.outlook.com>
<2957101.1674746628@sss.pgh.pa.us>
<BL0PR05MB66282D22D96AB745FBBD521FF3CF9@BL0PR05MB6628.namprd05.prod.outlook.com>
<2961799.1674749201@sss.pgh.pa.us>
<Y9fjfNpP7HZh1YX9@momjian.us>
On Mon, Jan 30, 2023 at 10:34:20AM -0500, Bruce Momjian wrote:
> On Thu, Jan 26, 2023 at 11:06:41AM -0500, Tom Lane wrote:
> > I don't know anything about the mysql FDW, but another possible route
> > to fixing things is to get it to not believe that the remote's sort
> > ordering matches the local one. If the plan were relying on a local
> > sort instead of a remote sort then everything would be fine.
>
> When we implemented sort pushdown to FDWs I had not considered how hard
> it might be to match sort ordering, especially considering the problem
> we have in matching orderings from different operating system versions.
>
> Is this documented somewhere?
The attached patch documents this remote sort order requirement.
--
Bruce Momjian <bruce@momjian.us> https://momjian.us
EDB https://enterprisedb.com
Only you can decide what is important to you.
Attachments:fdw.diff (text/x-diff, 994B) downloaddiff --git a/doc/src/sgml/fdwhandler.sgml b/doc/src/sgml/fdwhandler.sgmlindex 25832d227f..17e17233fe 100644--- a/doc/src/sgml/fdwhandler.sgml+++ b/doc/src/sgml/fdwhandler.sgml@@ -415,7 +415,9 @@ GetForeignUpperPaths(PlannerInfo *root,
currently being considered. <literal>output_rel</literal> is the upper relation
that should receive paths representing computation of this step,
and <literal>input_rel</literal> is the relation representing the input to this
- step. The <literal>extra</literal> parameter provides additional details,+ step. Pushdown of sorts by <literal>UPPERREL_ORDERED</literal>+ should guarantee that remote sort ordering matches local ordering.+ The <literal>extra</literal> parameter provides additional details,
currently, it is set only for <literal>UPPERREL_PARTIAL_GROUP_AGG</literal>
or <literal>UPPERREL_GROUP_AGG</literal>, in which case it points to a
<literal>GroupPathExtraData</literal> structure;
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To: pgsql-bugs@postgresql.org
Cc: bruce@momjian.us, tgl@sss.pgh.pa.us, Pete.Storer@sas.com, pgsql-bugs@lists.postgresql.org
Subject: Re: FW: Query execution failure
In-Reply-To: <ZRTQHKRhSLndfB5z@momjian.us>
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