RE: Explain plan accuracy and bind variables

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Fri, 6 Feb 2004 10:21:55 -0600
Message-ID: <000001c3eccd$5b4623c0$6c01a8c0@CVMLAP02>

Okay. Jared, can I send .txt and .sql attachments to the list? Size of each is <10KB.

Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *

Upcoming events:

- Performance Diagnosis 101: 2/24 San Diego, 3/23 Park City, 4/6 Seattle
- SQL Optimization 101: 2/16 Dallas
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- Visit www.hotsos.com for schedule details...

-----Original Message-----
From: oracle-l-bounce_at_freelists.org
[mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Daniel Fink Sent: Friday, February 06, 2004 9:37 AM
To: oracle-l_at_freelists.org
Subject: Re: Explain plan accuracy and bind variables

Could we see it?

Cary Millsap wrote:

> Nevermind; I've done it.
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
> * Nullius in verba *
>
> Upcoming events:
> - Performance Diagnosis 101: 2/24 San Diego, 3/23 Park City, 4/6
Seattle
> - SQL Optimization 101: 2/16 Dallas
> - Hotsos Symposium 2004: March 7-10 Dallas
> - Visit www.hotsos.com for schedule details...
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of Cary Millsap
> Sent: Friday, February 06, 2004 9:02 AM
> To: oracle-l_at_freelists.org
> Subject: RE: Re: Explain plan accuracy and bind variables
>
> Can someone provide an example of a query that emits STAT lines that
> contradict the output of EXPLAIN PLAN because of the use of bind
> variables?
>
> Cary Millsap
> Hotsos Enterprises, Ltd.
> http://www.hotsos.com
> * Nullius in verba *
>
> Upcoming events:
> - Performance Diagnosis 101: 2/24 San Diego, 3/23 Park City, 4/6
Seattle
> - SQL Optimization 101: 2/16 Dallas
> - Hotsos Symposium 2004: March 7-10 Dallas
> - Visit www.hotsos.com for schedule details...
>
> -----Original Message-----
> From: oracle-l-bounce_at_freelists.org
> [mailto:oracle-l-bounce_at_freelists.org] On Behalf Of
ryan.gaffuri_at_cox.net
> Sent: Friday, February 06, 2004 7:37 AM
> To: oracle-l_at_freelists.org
> Subject: Re: Re: Explain plan accuracy and bind variables
>
> what about autotrace? that occurs after the query is run? =
>
> > =
>
> > From: Connor McDonald <hamcdc_at_yahoo.co.uk>
> > Date: 2004/02/06 Fri AM 08:18:49 EST
> > To: oracle-l_at_freelists.org
> > Subject: Re: Explain plan accuracy and bind variables
> > =
>
> > I think this comes the various methods people use to take an
existing
> S=
> QL and attempt to determine
> > an explain plan.
> > =
>
> > eg you might see in a trace file a slow query
> > =
>
> > select * from table where col =3D :b1
> > =
>
> > You run this through explain plan and voila! Looks great - no
problem.
> =
> But what really happened
> > on the live system was that 'col' was char, and :b1 was numeric, and
> th=
> us the index on 'col' was
> > not used. The execution plan in a trace file *will* be the one that
> wa=
> s used. This is quite
> > different to the plan you would see if you ran 'tkprod explain=3D..'
> > =
>
> > etc etc etc
> > =
>
> > hth
> > connor
> > =
>
> > --- ryan.gaffuri_at_cox.net wrote: > I read somewhere that explain
plans
> =
> are not always accurate.
> > Does this include autotrace? What
> > > about if I do a 10046 or just a sql_trace? =
>
> > > =
>
> > > Are explain plans more apt to be inaccurate with bind variables(I
> thi=
> nk I read that somewhere).
> > > If so, why? =
>
> > > =
>
> > > ----------------------------------------------------------------
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> > =
>
> > =3D=3D=3D=3D=3D
> > Connor McDonald
> > Co-author: "Mastering Oracle PL/SQL - Practical Solutions" -
available
> =
> now
> > web: http://www.oracledba.co.uk
> > web: http://www.oaktable.net
> > email: connor_mcdonald_at_yahoo.com
> > =
>
> > "GIVE a man a fish and he will eat for a day. But TEACH him how to
> fish=
> , and...he will sit in a boat and drink beer all day"
> > =
>
> > =
>
> > =
>
> > =
>
> > =
>
> > ___________________________________________________________
> > BT Yahoo! Broadband - Free modem offer, sign up online today and
save
> =A3=
> 80 http://btyahoo.yahoo.co.uk
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Received on Fri Feb 06 2004 - 10:21:55 CST