RE: Re: Explain plan accuracy and bind variables
- From: "Cary Millsap" <cary.millsap@xxxxxxxxxx>
- To: <oracle-l@xxxxxxxxxxxxx>
- Date: Fri, 6 Feb 2004 09:31:42 -0600
Nevermind; I've done it.
Cary Millsap
Hotsos Enterprises, Ltd.
http://www.hotsos.com
* Nullius in verba *
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-----Original Message-----
From: oracle-l-bounce@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of Cary Millsap
Sent: Friday, February 06, 2004 9:02 AM
To: oracle-l@xxxxxxxxxxxxx
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@xxxxxxxxxxxxx
[mailto:oracle-l-bounce@xxxxxxxxxxxxx] On Behalf Of ryan.gaffuri@xxxxxxx
Sent: Friday, February 06, 2004 7:37 AM
To: oracle-l@xxxxxxxxxxxxx
Subject: Re: Re: Explain plan accuracy and bind variables
what about autotrace? that occurs after the query is run? =
> =
> From: Connor McDonald <hamcdc@xxxxxxxxxxx>
> Date: 2004/02/06 Fri AM 08:18:49 EST
> To: oracle-l@xxxxxxxxxxxxx
> 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@xxxxxxx 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@xxxxxxxxx
> =
> "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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> =
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