RE: Re: Explain plan accuracy and bind variables

From: Cary Millsap <cary.millsap_at_hotsos.com>
Date: Fri, 6 Feb 2004 09:01:31 -0600
Message-ID: <007601c3ecc2$1dff0a50$6a01a8c0@CVMLAP02>

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
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-----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"
> =

> =

> ___________________________________________________________
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=A3=
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Received on Fri Feb 06 2004 - 09:01:31 CST