From: Amit Kapila <amit.kapila@huawei.com>
To: 'Ghislain ROUVIGNAC' <ghr@sylob.com>
To: pgsql-performance@postgresql.org
Subject: Re: Not same plan between static and prepared query
Date: Thu, 6 Jun 2013 16:10:58 +0530
Message-ID: <007201ce62a2$56c35930$044a0b90$@kapila@huawei.com> (raw)
In-Reply-To: <CAH12p1AvzORBOBhpCOYc7NHpRrYdpLei3SX4oiCn3pw+LgT4xQ@mail.gmail.com>
References: <CAH12p1AvzORBOBhpCOYc7NHpRrYdpLei3SX4oiCn3pw+LgT4xQ@mail.gmail.com>
List-Unsubscribe: <mailto:majordomo@postgresql.org?body=unsub%20pgsql-performance>
On Thursday, June 06, 2013 1:56 PM Ghislain ROUVIGNAC wrote:
> Hello,
> We have a strange issue related to a prepared statement.
> We have two equals queries where the sole difference is in the limit.
> - The first is hard coded with limit 500.
> - The second is prepared with limit $1 ($1 is bound to 500).
> PostgreSQL give us two different plans with a huge execution time for the
prepared query:
It can generate different plan for prepared query, because optimizer uses
default selectivity in case of bound parameters (in your case limit $1).
> We met the same behaviour with both :
> - PostgreSQL 8.4.8 on Windows 2008 (Prod)
> - PostgreSQL 8.4.8 and 8.4.17 on Windows 7 (Dev)
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Reply to all the recipients using the --to and --cc options:
reply via email
To: pgsql-performance@postgresql.org
Cc: amit.kapila@huawei.com, ghr@sylob.com
Subject: Re: Not same plan between static and prepared query
In-Reply-To: <007201ce62a2$56c35930$044a0b90$@kapila@huawei.com>
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
This inbox is served by DDX for PostgreSQL; see mirroring instructions
for how to clone and mirror all data and code used for this inbox