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   Oracle Tips by Burleson

Oracle10g Optimizer Mode

CHOOSE and RULE are no longer supported as optimizer_mode initialization parameter values. If you set up any of these parameters, a warning is displayed in the alert log. The functionalities of those parameter values still exist but will be removed in a future release. Now, for 10g, all_rows is the default value for the optimizer_mode initialization parameter.

Moving from RBO to the Cost-Based Optimizer

The RBO was in use for many years, and lots of applications were developed using the rule-based optimizer. SQL statements were tuned manually and optimized. Now, when you want to move the database environment over to CBO, it is natural to want to preserve the optimization work you have done.

By creating outlines for an application before switching to CBO, the plans generated by the RBO can be used. This section shows the methodology of creating the plan outlines and using them in the new environment.

Grant CREATE ANY OUTLINE privilege to the schema in which the outlines will be created

For example, from SYS:

  1. GRANT CREATE ANY OUTLINE TO user-name
  2. Execute syntax similar to the following to designate, for example, the RBGROUP outline category.

    ALTER SESSION SET CREATE_STORED_OUTLINES = RBGROUP;
     
  3. Run the application long enough to capture stored outlines for all the important SQL statements.
  4. Suspend outline generation by statement:

    ALTER SESSION SET CREATE_STORED_OUTLINES = FALSE;
     
  5. Gather statistics with the dbms_stats package.
  6. Change the initialization parameter optimizer_mode to CHOOSE.
  7. Execute the following statement to make Oracle use the outlines in category RBGROUP:

    ALTER SESSION SET USE_STORED_OUTLINES = RBGROUP;

Then run the application. With this procedure for plan stability, access paths of the SQL statements can be used.
 


Get the complete Oracle10g story:

The above text is an excerpt from "Oracle Database 10g New Features: Oracle10g Reference for Advanced Tuning and Administration", by Rampant TechPress.  Written by top Oracle experts, this book has a complete online code deport with ready to use scripts. 

To get the code instantly, click here:

http://www.rampant-books.com/book_2003_2_oracle10g.htm


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