from metalink on RBO
desupport.
http://metalink.oracle.com/metalink/plsql/ml2_documents.showDocument?p_id=189702.1&p_database_id=NOT
"The RBO will still exist in Oracle10i, but will be an unsupported feature
and will be removed in a future release."
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 Oracle10i) 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 independant 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: http://otn.oracle.com/products/bi/pdf/o9i_optimization_twp.pdf What is being Desupported? The RBO is Oracle's legacy optimizer originating from Oracle Version 6 and earlier. The RBO is being desupported in Oracle10i. The RBO will still exist in Oracle10i, 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 The RBO was superseded in Oracle7 by the CBO and has continued to be available for backwards compatibility.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 Oracle10i 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 Oracle10i. The last release that supports the rule-based optimizer will be Oracle9i Release 2.
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