Oracle Optimizer: Migrating to using the cost-based optimizer-----series 1.4

oracle| optimization
Oracle Optimizer: Migrating to using the cost-based optimizer-----series 1.4

3.2.3 Minimum Requirements

The minimum requirement for CBO is to set the optimizer mode to Frist_rows or all_rows (or choose) and generate statistics for the object. However, this does not guarantee that your system will work optimally. Reference to the second part (initialization parameters) involves initializing the parameter information.

Whether or not to set the optimizer mode. If one of the following conditions is true, the CBO will automatically invoke:

1. Use the hint.
2. Use the partition table.
3. Set the parallel table


3.2.4 Why do you want to remove Rbo?

Oracle 9i Second Edition will be the last official support for the CBO version. Oracle recommends that all partners and customers validate applications using the CBO, although Rbo is still available in oracle10i (now called oracle10g) but is not supported.
As with every published Oracle note, the presence of Rbo hinders the Oralce key enhancements to 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 limited to bug fixes and Oracle does not add new functionality to Rbo.

Why did 3.2.5 move to the CBO?

The CBO's main benefits are as follows:

1. Oracle stops RBO the development of the environment later.

2. The subsequent Oracle database will remove the RBO

3. Compared with the CBO, the Rbo access method is limited in number.

4. All new features are based on the CBO, and most of these new features are important for setup and so on. Clustered index Table, bitmap index, function based index, reverse index, hash join, materialized view, Index table, and parallel query, star connection etc.

5. Media Link support.

6. Oracle support is not available once RBO is not supported.

7.CBO is ripe

Earlier in the Oracle7, Rbo in some scenarios than the CBO, and even the CBO is not as good as imagined, and often choose a bad execution plan. In later releases, the CBO function was upgraded, and now it provides better interactivity for the benefits of the new functionality

8. Distributed and remote query more reliable

In Rbo, a database link, which is more difficult to adjust than a table from a local to a remote database. For the same job, the CBO is better than the Rbo. The local optimizer knows the current statistics for the remote table and can make better decisions about the execution plan. Rbo may consider the index of a remote database, but the CBO has the right to count the information of the remote database index and make a decision on the query plan.