Call now: 252-767-6166  
Oracle Training Oracle Support Development Oracle Apps

 
 Home
 E-mail Us
 Oracle Articles
New Oracle Articles


 Oracle Training
 Oracle Tips

 Oracle Forum
 Class Catalog


 Remote DBA
 Oracle Tuning
 Emergency 911
 RAC Support
 Apps Support
 Analysis
 Design
 Implementation
 Oracle Support


 SQL Tuning
 Security

 Oracle UNIX
 Oracle Linux
 Monitoring
 Remote s
upport
 Remote plans
 Remote
services
 Application Server

 Applications
 Oracle Forms
 Oracle Portal
 App Upgrades
 SQL Server
 Oracle Concepts
 Software Support

 Remote S
upport  
 Development  

 Implementation


 Consulting Staff
 Consulting Prices
 Help Wanted!

 


 Oracle Posters
 Oracle Books

 Oracle Scripts
 Ion
 Excel-DB  

Don Burleson Blog 


 

 

 


 

 

 
 

Oracle SQL Plan Regression

Oracle Database Tips by Donald BurlesonJanuary 20,  2015

 

In traditional regression analysis, past points are used in a predictive model to forecast future performance.  In Oracle11g, SQL plan regression refers to the process of tracking changed to execution plans and ensuring that the SQL does not "regress" into a sub-optimal execution plan when changes are made to optimizer parameters of CBO statistics.

One perplexing issue with Oracle is the dynamic nature of Oracle SQL, and the optimizer's propensity to change execution plans whenever CBO statistics change.  This has been dubbed "Monday Morning Mayhem" because some SQL explain plans will change for the worst.

Inside Oracle SQL plan regression

The CBO group notes that SQL plan regression of the processes of "reverting" to a sub-optimal execution plan.

"this best-cost plan will not be used but instead added to the statement's plan history for later verification.

In other words, the optimizer will use a known plan from the SQL plan baseline instead of a new and hitherto unknown plan."

The SQL plan regression feature operates on the processes of historical testing of SQL execution plans.  For details see my notes on SQL history analysis in 11g.

When invoking dbms_xplan.display_cursor, you can tell when SQL plan regression is being used by this message:

- SQL plan baseline SYS_SQL_PLAN_fcc170b0a62d0f4d used for this statement

If you purchased the extra-cost AWR, you can use the dbms_xplan.display_awr procedure allows you to input only a SQL_ID, and Oracle will show you the of the explain plans for that SQL_ID. This simple query will show changes to SQL explain plan history, if you have purchased the extra-cost licenses for AWR.

  select * from TABLE(DBMS_XPLAN.DISPLAY_AWR('&sqlid'));

In sum, Oracle SQL plan regression is a method that uses real-world empirical data to ensure that the optimal SQL execution plan is always used.

 
Get the Complete
Oracle SQL Tuning Information 

The landmark book "Advanced Oracle SQL Tuning  The Definitive Reference"  is filled with valuable information on Oracle SQL Tuning. This book includes scripts and tools to hypercharge Oracle 11g performance and you can buy it for 30% off directly from the publisher.


 

 

��  
 
 
Oracle Training at Sea
 
 
 
 
oracle dba poster
 

 
Follow us on Twitter 
 
Oracle performance tuning software 
 
Oracle Linux poster
 
 
 

 

Burleson is the American Team

Note: This Oracle documentation was created as a support and Oracle training reference for use by our DBA performance tuning consulting professionals.  Feel free to ask questions on our Oracle forum.

Verify experience! Anyone considering using the services of an Oracle support expert should independently investigate their credentials and experience, and not rely on advertisements and self-proclaimed expertise. All legitimate Oracle experts publish their Oracle qualifications.

Errata?  Oracle technology is changing and we strive to update our BC Oracle support information.  If you find an error or have a suggestion for improving our content, we would appreciate your feedback.  Just  e-mail:  

and include the URL for the page.


                    









Burleson Consulting

The Oracle of Database Support

Oracle Performance Tuning

Remote DBA Services


 

Copyright © 1996 -  2020

All rights reserved by Burleson

Oracle ® is the registered trademark of Oracle Corporation.