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

 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
 Oracle Support

 SQL Tuning

 Oracle UNIX
 Oracle Linux
 Remote s
 Remote plans
 Application Server

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

 Remote S


 Consulting Staff
 Consulting Prices
 Help Wanted!


 Oracle Posters
 Oracle Books

 Oracle Scripts

Don Burleson Blog 







optimizer_capture_sql_plan_baselines Tips

Oracle Database Tips by Donald BurlesonMay 3, 2015

Question:  What is the optimizer_capture_sql_plan_baselines procedure and how can optimizer_capture_sql_plan_baselines help me in a database migration?

Answer:  The optimizer_capture_sql_plan_baselines is part of the Oracle 11g SQL Plan Management (SPM) feature.  The default is false but if optimizer_capture_sql_plan_baselines is set to "true" then Oracle will create baselines for repeatable SQL (v$sql where executions > 1).  Also see dba_sql_plan_baselines tips.

This is a somewhat frightening new features of 11g because it says that for any given SQL statement, multiple execution plans may exist.  As we know, it is a rare occurrence that the values of host variables would have such a skew as to allow for multiple execution plans for a single SQL statement.   As a general rule, most SQL has one, and only one, optimal execution plan, and it's the job of the optimizer to find that plan and lock it down!

The whole point of adaptive SQL plan baselines for for repeatable SQL statements.  This approach does not make sense for one-off SQL's.

Let's take a closer look at how this works.  When the Oracle optimizer created a cost-based decision tree, he chooses the branch of the tree with the lowest estimated cost.  However, when SQL plan baselines are enabled, Oracle will compare the SQL baselines to the newly-optimized SQL:

- If the SQL plan matches the newly optimized SQL, the plan is marked as "accepted"

- If the SQL plan does not match the newly-optimized plan, Oracle will use the SQL plan and mark is as "accepted", leaving the optimizers new plan in the library cache un-used.  If the "new" plan has a lower cost, it will be used, but not until it has been verified emprarcally.

In a sense, grabbing a SQL baseline, "freezes" the execution plan and the SQL baselines is used unless the optimizer generates a "new" execution plan for a query.  At that point, the optimizer evaluates if the new plan is cheaper than the existing plan.  If so, Oracle will use this new plan.  This is an attempt to ensure that only the "best" execution plan is used by these "evolving" baselines. 

However, it is important to remember that for the vast majority of databases, there exists one, and only one optimal execution plan for any given query.

See here for my research into Oracle SQL Plan Management.

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.



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.



Oracle Training at Sea
oracle dba poster

Follow us on Twitter 
Oracle performance tuning software 
Oracle Linux poster