RE: Explain plan accuracy and bind variables
- From: Wolfgang Breitling <breitliw@xxxxxxxxxxxxx>
- To: oracle-l@xxxxxxxxxxxxx
- Date: Fri, 06 Feb 2004 09:40:19 -0700
Oracle 8i Designing and Tuning For Performance page 5-23 "With bind
variables in general, the EXPLAIN PLAN output may not represent the real
execution plan."
On top of that, if you use explain plan in a development/test environment,
those results can easily be different from the plan used in production.
At 09:19 AM 2/6/2004, you wrote:
>Cary, et al:
>
>Is this documented somewhere? I run an SAP shop, and I have
>ABAP'ers who swear that the v9 CBO is buggy because a pre-execution
>plan and a post-execution plan don't necessarily match, and=20
>our performance-problem meetings are turning into shouting
>matches.
>
>Thanks,
>Mike
>
>
>-----Original Message-----
>From: Cary Millsap [mailto:cary.millsap@xxxxxxxxxx]
>Sent: Friday, February 06, 2004 7:32 AM
>To: oracle-l@xxxxxxxxxxxxx
>Subject: RE: Explain plan accuracy and bind variables
>
>
>It means "wrong plan." Different row source operations which aren't what
>Oracle would really do if you were to run the query.
>
>
>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 Khedr, Waleed
>Sent: Friday, February 06, 2004 9:18 AM
>To: 'oracle-l@xxxxxxxxxxxxx'
>Subject: RE: Explain plan accuracy and bind variables
>
>How do you define inaccurate?
>
>Waleed
>
>-----Original Message-----
>From: ryan.gaffuri@xxxxxxx [mailto:ryan.gaffuri@xxxxxxx]
>Sent: Friday, February 06, 2004 7:38 AM
>To: oracle-l@xxxxxxxxxxxxx
>Subject: Explain plan accuracy and bind variables
>
>
>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?=20
>
>Are explain plans more apt to be inaccurate with bind variables(I think
>I
>read that somewhere). If so, why?=20
>
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Wolfgang Breitling
Oracle7, 8, 8i, 9i OCP DBA
Centrex Consulting Corporation
http://www.centrexcc.com
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