Oracle Optimizer: Migrate to the cost-based optimizer ---- Series 1.4
3.2.3 Minimum requirements
The minimum requirement with CBO is to set the optimizer mode to find_rows or all_rows (or choose) and generate statistics for the object. However, this does not guarantee your system to work best. Refer to the information of the first part (initialization parameter) involves the initialization parameter.
No matter whether it is set to set an optimizer mode. If there is one of the following cases, CBO will automatically call:
1. Use a prompt. 2. Use the partition table. 3. Set parallel
3.2.4 Why is the RBO to remove?
Oracle 9i Second Edition will be the last version that officially supports CBO. Oracle recommends all partners and customers to verify applications using CBO, although RBO is still available in Oracle10i (now Oracle10g), but is not supported. As in each released Oracle note, the presence of RBO hinders the key enhancement of Oralce for the query processing engine. Its removal will allow Oracle to improve the performance and reliability of the database engine query processing component. Currently, Oracle's support for RBO is only used to fix a limited incorrect correction and Oracle does not add new features to RBO.
3.2.5 Why is Move to CBO?
CBO is mainly beneficial to:
1. After the Oracle stops the development of the RBO environment.
2. The subsequent Oracle database will remove RBO
3. Compared with CBO, RBO's access method is limited.
4. All new features are based on CBO, most new features are important for settings, etc. Cluster index, bitmap index, function-based index, reverse index, hash connection, materialized view, index table, and parallel query, star connection, etc.
5. Media link support.
6. Once RBO is not supported, Oracle support is not available.
7.CBO is already mature
In the previous Oracle7, RBO is over some scenes CBO, and even CBO is not a good idea, and often chooses a bad implementation plan. In the subsequent release version, the CBO function has improved, and now for new features, it provides better interactivity to considering income.
8. Distributed and remote queries are more reliable
In RBO, database links are quite difficult to adjust from local to remote databases than one table. The same work, CBO is better than RBO. The local optimizer knows the current statistics of the remote table and makes better decisions for the execution plan. RBO may consider the index of the remote database, but CBO has the right to statistically the remote database index information and make a decision on the query plan.
