4. Why is RBO being removed?
9i release 2 will be the last version that officially supports RBO. Oracle
recommends all partners and customers to certify their applications with CBO
before this version is no longer supported. Though RBO will be available in
Oracle 10i, it will no longer be supported.
per a published Oracle note, the existence of RBO prevents Oracle from making
key enhancements to its query-processing engine. Its removal will permit Oracle
to improve performance and reliability of the query-processing components of
the database engine.
Oracle support for RBO is limited to bug fixes only and no new functionality
will be added to RBO.
5. Why move to CBO?
benefits that come to mind:
Oracle stopped developing for RBO environment a long time back.
RBO will subsequently be removed from the Oracle database.
RBO has a limited number of access methods compared to CBO.
All the new features require CBO. CBO is enabled to identify these features,
and how to evaluate their cost. Most of these features will be of importance
for any setup; e.g. Index organized tables, bitmap indexes, Function-based
indexes, reverse-key indexes, Partitioning, Hash joins, Materialized views,
parallel query, star joins, etc.
RBO is no longer supported, Oracle support will not be available.
CBO has matured.
to Oracle 7, RBO could outperform CBO in some situations. Moreover, CBO would
not behave as expected and often choose bad execution plans. CBO has been
improved across releases and today it is a much better alternative considering
the benefits and advances towards new features.
7. Distributed and remote queries are more reliable.
RBO, it was difficult to fine tune queries that used database links and has tables from both local and remote database. CBO outperforms RBO in
this regard. In CBO, the local optimizer is aware of the statistics present in
the remote table and is able to make better decisions on execution plans. RBO
may not consider indexes on remote databases, but CBO has access to statistics
and information regarding indexes on a remote database and can decide on an
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