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Don Burleson Blog 







  Rule-based SQL optimizer (RBO) de-supported in Oracle10g

Oracle Tips by Burleson Consulting


With nearly 50% of production systems using rule-based SQL optimization (RBO), this is big for Oracle.  As you migrate to Oracle10g, you may need to undertake a migration from RBO to CBO.  This may involved re-writing rule-based SQL, especially queries where you rely on the ordering of the table names in the FROM clause to determine the driving table.

Also, remember that you will be able to adjust the all-important parameter optimizer_index_cost_adj to a small number (< 10) to make the CBO simulate the behavior of the RBO.

Below is a short excerpt from the MOSC note:

Desupport of the Rule-Based Optimizer

The rule-based optimizer (RBO) will no longer be supported when Oracle9i is de-supported. The release after Oracle9i (referred to in this article as Oracle10g) will only support the cost-based optimizer (CBO). Hence Oracle9i Release 2 is the last release to support the RBO. Partners and customers should certify their applications with the CBO before that time. The CBO has been Oracle's primary optimization method for many years now, and most major independent software vendors use the CBO by choice. Our surveys indicate that over 80% of customers are using the CBO with Oracle8i, and this number is expected to increase with Oracle9i. For more information on the CBO
please refer to the Query Optimization in Oracle9i white paper which can be found at:

What is being Desupported?

The RBO is Oracle's legacy optimizer originating from Oracle Version 6 and earlier. The RBO is being desupported in Oracle10g. The RBO will still exist in Oracle10g, but will be an unsupported feature and will be removed in a future release. No code changes will be made to the RBO code and no bug fixes will be provided. The RBO was superseded in Oracle7 by the CBO and has continued to be available for backwards compatibility. Oracle Oracle10g will support only one optimizer, and all applications running on that release should use that optimizer.

Versions Affected

Support for the RBO will be removed in Oracle10g. The last release that supports the rule-based optimizer will be Oracle9i Release 2.

Why is the RBO being Desupported?

The existence of the RBO prevents Oracle from making key enhancements to its query-processing engine. The removal of the RBO will permit Oracle to improve performance and reliability of the query-processing components of the database engine. Furthermore, using the RBO prevents customers from
taking advantage of all the query-processing technologies introduced since Oracle 7.3. For example, the RBO cannot take advantage of partitioned tables, bitmap indexes, hash join, parallel query, index organized tables, function-based indexes, materialized views and many others. As a result, customers never realize the benefits and the superior performance gained by
these techniques.

If you like Oracle tuning, you may enjoy my new book "Oracle Tuning: The Definitive Reference", over 900 pages of BC's favorite tuning tips & scripts. 

You can buy it direct from the publisher for 30%-off and get instant access to the code depot of Oracle tuning scripts.



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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.

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