Received: from malur.postgresql.org ([217.196.149.56])
	by arkaria.postgresql.org with esmtp (Exim 4.84_2)
	(envelope-from
 <pgsql-hackers-owner+M333284=pgsql-hackers-arkari@postgresql.org>)
	id 1dhggC-0002yV-43
	for pgsql-hackers@arkaria.postgresql.org; Tue, 15 Aug 2017 18:35:04 +0000
Received: from localhost ([127.0.0.1] helo=postgresql.org)
	by malur.postgresql.org with smtp (Exim 4.84_2)
	(envelope-from
 <pgsql-hackers-owner+M333284=pgsql-hackers-arkari@postgresql.org>)
	id 1dhggB-00031W-Jo
	for pgsql-hackers@arkaria.postgresql.org; Tue, 15 Aug 2017 18:35:03 +0000
Received: from makus.postgresql.org ([2001:4800:1501:1::229])
	by malur.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256)
	(Exim 4.84_2)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1dhggA-0002y5-Iq
	for pgsql-hackers@postgreSQL.org; Tue, 15 Aug 2017 18:35:02 +0000
Received: from sss.pgh.pa.us ([66.207.139.130])
	by makus.postgresql.org with esmtps (TLS1.2:ECDHE_RSA_AES_256_CBC_SHA384:256)
	(Exim 4.84_2)
	(envelope-from <tgl@sss.pgh.pa.us>)
	id 1dhgg7-0000Qa-TL
	for pgsql-hackers@postgreSQL.org; Tue, 15 Aug 2017 18:35:01 +0000
Received: from sss1.sss.pgh.pa.us (localhost [127.0.0.1])
	by sss.pgh.pa.us (8.14.4/8.14.4) with ESMTP id v7FIYwCN023426
	for <pgsql-hackers@postgreSQL.org>; Tue, 15 Aug 2017 14:34:58 -0400
From: Tom Lane <tgl@sss.pgh.pa.us>
To: pgsql-hackers@postgreSQL.org
Subject: Re: [COMMITTERS] pgsql: Simplify plpgsql's check for simple
 expressions.
In-reply-to: <E1dhehy-00034e-8N@gemulon.postgresql.org>
References: <E1dhehy-00034e-8N@gemulon.postgresql.org>
Comments: In-reply-to Tom Lane <tgl@sss.pgh.pa.us>
	message dated "Tue, 15 Aug 2017 16:28:46 -0000"
MIME-Version: 1.0
Content-Type: text/plain; charset="us-ascii"
Content-ID: <23424.1502822098.1@sss.pgh.pa.us>
Content-Transfer-Encoding: quoted-printable
Date: Tue, 15 Aug 2017 14:34:58 -0400
Message-ID: <23425.1502822098@sss.pgh.pa.us>
List-Archive: <http://archives.postgresql.org/pgsql-hackers>
List-Help: <mailto:majordomo@postgresql.org?body=help>
List-ID: <pgsql-hackers.postgresql.org>
List-Owner: <mailto:pgsql-hackers-owner@postgresql.org>
List-Post: <mailto:pgsql-hackers@postgresql.org>
List-Subscribe: <mailto:majordomo@postgresql.org?body=sub%20pgsql-hackers>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-hackers>
X-Mailing-List: pgsql-hackers
Precedence: bulk
Sender: pgsql-hackers-owner@postgresql.org

Tom Lane <tgl@sss.pgh.pa.us> writes:
> Simplify plpgsql's check for simple expressions.
> ...
> https://git.postgresql.org/pg/commitdiff/00418c61244138bd8ac2de58076a1d0d=
d4f539f3

The buildfarm members that are running force_parallel_mode =3D regress
are not happy with this.  Apparently, even a trivial SELECT <expression>
can be turned into a Gather plan if force_parallel_mode says so.

I assume (haven't looked) that I could hack the plpgsql code to prevent
generating a parallel plan when it's decided the command is a simple
SELECT.  But I wonder whether that's the right place to fix it.  Does
it ever make sense to parallelize a plan that can't possibly benefit?
IOW I am not sure that we should carry force_parallel_mode this far.

			regards, tom lane


--=20
Sent via pgsql-hackers mailing list (pgsql-hackers@postgresql.org)
To make changes to your subscription:
http://www.postgresql.org/mailpref/pgsql-hackers