Received: from magus.postgresql.org ([2a02:c0:301:0:ffff::29]) by malur.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1TME2k-0003lO-8p for pgsql-performance@postgresql.org; Thu, 11 Oct 2012 08:22:58 +0000 Received: from smtp06.smtpout.orange.fr ([80.12.242.128] helo=smtp.smtpout.orange.fr) by magus.postgresql.org with esmtp (Exim 4.72) (envelope-from ) id 1TME2i-0003gG-A3 for pgsql-performance@postgresql.org; Thu, 11 Oct 2012 08:22:57 +0000 Received: from axege.com ([82.127.232.162]) by mwinf5d41 with ME id 9kNt1k00Y3WtTCJ03kNuqZ; Thu, 11 Oct 2012 10:22:54 +0200 Received: from localhost (localhost [127.0.0.1]) by axege.com (Postfix) with ESMTP id BE6CB43DE01 for ; Thu, 11 Oct 2012 10:22:53 +0200 (CEST) X-Virus-Scanned: Debian amavisd-new at myhostname="axege.com." Received: from axege.com ([127.0.0.1]) by localhost (axege.com [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id pjGHEwf8C2zW for ; Thu, 11 Oct 2012 10:22:53 +0200 (CEST) Received: from [10.0.0.78] (unknown [10.0.0.78]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) by axege.com (Postfix) with ESMTPSA id 34E384FFEB for ; Thu, 11 Oct 2012 10:22:53 +0200 (CEST) Message-ID: <507681DD.2000906@axege.com> Date: Thu, 11 Oct 2012 10:22:53 +0200 From: Franck Routier User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:16.0) Gecko/20121005 Thunderbird/16.0 MIME-Version: 1.0 To: pgsql-performance@postgresql.org Subject: Re: Drawbacks of create index where is not null ? References: <5075AB0F.5030005@axege.com> <5076586B.1000306@ringerc.id.au> In-Reply-To: <5076586B.1000306@ringerc.id.au> Content-Type: multipart/signed; protocol="application/pkcs7-signature"; micalg=sha1; boundary="------------ms040709040308050108050400" X-Pg-Spam-Score: -1.9 (-) X-Archive-Number: 201210/146 X-Sequence-Number: 48105 Ceci est un message signé cryptographiquement au format MIME. --------------ms040709040308050108050400 Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: quoted-printable Le 11/10/2012 07:26, Craig Ringer a =E9crit : > * The partial index will only be used for queries that use the=20 > condition "WHERE col IS NOT NULL" themselves. The planner isn't=20 > super-smart about how it matches index WHERE conditions to query WHERE = > conditions, so you'll want to use exactly the same condition text=20 > where possible. > From my experiments, the planner seems to be smart enougth to tell that = "where col =3D 'myvalue' " will match with partial index "where col is no= t=20 null". So it will use the index and not do a full tablescan. (this is on 8.4). This is also what Scott says in his reply. I'm not thinking of using more complex where predicat for my indexes,=20 just "is not null". So I think I should not be hit by this... 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