OPTIMIZER_FEATURES_ENABLE

Sometimes it's necessary to downgrade features for Oracle DB:

NOTE: Modifying the OPTIMIZER_FEATURES_ENABLE parameter generally is strongly discouraged and should only be used as a short term measure at the suggestion of Oracle Global Support.

The parameter can be set from the system or session level:

alter system set optimizer_features_enable='10.2.0.4' scope=spfile;

alter session set optimizer_features_enable='10.2.0.4';

It can also be set by adding a hint:

SELECT /*+ optimizer_features_enable('10.2.0.4') */ ENAME FROM EMP;

When setting this parameter, remember that all optimizer parameter settings will revert back to the older version. Thus, any 'new' optimizer features will not be used and other queries may be detrimentally affected