From: | Ghislain ROUVIGNAC <ghr(at)sylob(dot)com> |
---|---|
To: | Amit Kapila <amit(dot)kapila(at)huawei(dot)com> |
Cc: | pgsql-performance(at)postgresql(dot)org |
Subject: | Re: Not same plan between static and prepared query |
Date: | 2013-06-10 13:58:55 |
Message-ID: | CAH12p1DN5DouG5sMhmkmZeKE3mp7AF0UHZ1p96sykry21jxPGw@mail.gmail.com |
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Lists: | pgsql-performance |
Hello Amit,
Thank you for your help.
You are right, it work fine with PostgreSQL 9.2.
*Ghislain ROUVIGNAC*
2013/6/6 Amit Kapila <amit(dot)kapila(at)huawei(dot)com>
>
> 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)
>
> From PostgreSQL 9.2, it generates plan for prepared query during execution
> (Execute command) as well.
> So I think you will not face this problem in PostgreSQL 9.2 and above.
>
> With Regards,
> Amit Kapila.
>
>
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