OPTIMIZER_FEATURES_ENABLE

Parameter type	String
Syntax	OPTIMIZER_FEATURES_ENABLE = release_number
Default value	9.0.0
Parameter class	Static
Range of values	8.0.0, 8.0.3, 8.0.4, 8.0.5, 8.0.6, 8.1.0, 8.1.3, 8.1.4, 8.1.5, 8.1.6, 8.1.7,9.0.0

OPTIMIZER_FEATURES_ENABLE lets you change the behavior of the Oracle optimizer based on a release number. For example, if you upgrade your database from release 8.0.5 to release 8.1.5, but you want to keep the release 8.0.5 optimizer behavior, you can do so by setting this parameter to 8.0.5. At another time, you can try the new enhancements introduced up to release 8.1.5 by setting the parameter to 8.1.5.

Table 1-5 lists some optimizer features and indicates which release settings enable those features. The features listed in Table 1-5 are described in the documents indicated.

Table 1-5  Enabling Optimizer Features Based on Release Number

Features	Release
	8.0.0	8.0.3	8.0.4	8.0.5	8.0.6	8.1.0	8.1.3	8.1.4	8.1.5	8.1.6	8.1.7
Use of index fast full scans (Oracle9i Database Performance Guide and Reference, Oracle9i Database Concepts)			X	X	X	X	X	X	X	X
Consideration of bitmap access paths for tables with only B-tree indexes			X	X	X
Complex view merging (Oracle9i Database Concepts)			X	X	X
Push-join predicate feature (Oracle9i Database Performance Guide and Reference)			X	X	X
Subquery unnesting (Oracle9i SQL Reference)											X
Common subexpression elimination											X
Index joins (Oracle9i Database Performance Guide and Reference, Oracle9i Database Concepts)											X