Received: from maia.hub.org (unknown [200.46.204.183])
	by mail.postgresql.org (Postfix) with ESMTP id 06AB163381D
	for <pgsql-performance-postgresql.org@mail.postgresql.org>;
	Thu,  5 Nov 2009 01:47:37 -0400 (AST)
Received: from mail.postgresql.org ([200.46.204.86])
	by maia.hub.org (mx1.hub.org [200.46.204.183]) (amavisd-maia,
	port 10024) with ESMTP id 80050-07
	for <pgsql-performance-postgresql.org@mail.postgresql.org>;
	Thu,  5 Nov 2009 05:47:29 +0000 (UTC)
X-Greylist: from auto-whitelisted by SQLgrey-1.7.6
Received: from EXHUB018-3.exch018.msoutlookonline.net
	(exhub018-3.exch018.msoutlookonline.net [64.78.17.18])
	by mail.postgresql.org (Postfix) with ESMTP id 0DE4F6331C2
	for <pgsql-performance@postgresql.org>;
	Thu,  5 Nov 2009 01:47:28 -0400 (AST)
Received: from EXVMBX018-1.exch018.msoutlookonline.net ([64.78.17.47]) by
	EXHUB018-3.exch018.msoutlookonline.net ([64.78.17.18]) with mapi;
	Wed, 4 Nov 2009 21:47:26 -0800
From: Scott Carey <scott@richrelevance.com>
To: David Kerr <dmk@mr-paradox.net>, Chris <dmagick@gmail.com>
CC: Craig Ringer <craig@postnewspapers.com.au>,
	"pgsql-performance@postgresql.org" <pgsql-performance@postgresql.org>
Date: Wed, 4 Nov 2009 21:47:01 -0800
Subject: Re: Optimizer + bind variables
Thread-Topic: [PERFORM] Optimizer + bind variables
Thread-Index: Acpc5F+HMPmMNBq6QJeKF9FxyMxfmQA9wWi5
Message-ID: <C717A6D5.15F03%scott@richrelevance.com>
In-Reply-To: <20091104001825.GA79191@mr-paradox.net>
Accept-Language: en-US
Content-Language: en
X-MS-Has-Attach: 
X-MS-TNEF-Correlator: 
acceptlanguage: en-US
Content-Type: text/plain; charset="iso-8859-1"
Content-Transfer-Encoding: quoted-printable
MIME-Version: 1.0
X-Virus-Scanned: Maia Mailguard 1.0.1
X-Spam-Status: No, hits=-2.599 tagged_above=-10 required=5
	tests=BAYES_00=-2.599
X-Spam-Level: 
X-Archive-Number: 200911/58
X-Sequence-Number: 36226




On 11/3/09 4:18 PM, "David Kerr" <dmk@mr-paradox.net> wrote:

> On Wed, Nov 04, 2009 at 11:02:22AM +1100, Chris wrote:
> - David Kerr wrote:
> - >On Wed, Nov 04, 2009 at 07:43:16AM +0800, Craig Ringer wrote:
> - >- David Kerr wrote:
> - No.
> -
> - This is explained in the notes here:
> -
> - http://www.postgresql.org/docs/current/static/sql-prepare.html
>=20
> <sigh> and i've read that before too.
>=20
> On the upside, then it behaves like I would expect it to, which is
> good.
>=20
> Thanks
>=20
> Dave

Note that the query plan can often be the same for the example here.

It depends on whether the knowledge of the exact value makes a difference.

The most common case is an identifier column.
If the column is unique and indexed, and the parameter is an exact =3D matc=
h
in the where clause to that column, the plans won't differ.


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