V$SYS_OPTIMIZER_ENV displays the contents of the optimizer environment for the instance. The optimizer environment stores the value of the main parameters used by the Oracle optimizer when building the execution plan of a SQL statement. Hence, modifying the value of one or more of these parameters (for example, by issuing an ALTER SYSTEM statement) could lead to plan changes.

The parameters displayed by this view are either regular initialization parameters (such as OPTIMIZER_FEATURES_ENABLE) or pseudo parameters (such as ACTIVE_INSTANCE_COUNT).

Column Datatype Description
ID NUMBER Unique identifier of the parameter in the optimizer environment
NAME VARCHAR2(40) Name of the parameter
SQL_FEATURE VARCHAR2(64) Associated feature control ID
ISDEFAULT VARCHAR2(3) Indicates whether the parameter is set to the default value (YES) or not (NO)
VALUE VARCHAR2(25) Value of the parameter
DEFAULT_VALUE VARCHAR2(25) Default value of the parameter