Oracle Groundbreakers EMEA 2021 
Michigan Oracle Users Summit 2021 

Would you please download and install the one-off patch for your database version and OS for bugs not included in RU yet? If you do not find a patch for your specific version and OS from MOS, please open a Service Request with details on the patch needed. In addition, please include a list of patches already applied (opatch lsinventory -detail) and any other patches you intend to apply.

Some of the Optimizer bug fixes (not all) are controlled by the “_FIX_CONTROL” setting and are DISABLED by default in 19c when installed either through one-off backport or through RUs. Please refer to the corresponding Patch Readme carefully for one-off patches and enable the fixed control to activate the fix.

Example:

SQL> alter system set “_FIX_CONTROL”=”29302565:1”;

Oracle CBO performs transitivity as the first step in optimization. Transitivity means generating additional predicates based on existing predicates. The main advantage is the inclusion of extra access methods. Transitivity is not done for join predicates.

Assume A, B, and C are columns. If A=5 and A=B, you can conclude that B=5. This can be applied to queries as shown on the following page. Note that A=5 contains a constant.
However, in terms of joins, if A=B and B=C, it is not concluded that A=C; in other words, the Oracle server does not generate transitive closures for join predicates.
For more details about transitivity, see Doc ID 68979.1