Oracle optimizer version:
select * from v$version;
show parameter optimizer
OPTIMIZER_FEATURES_ENABLE
Parameter type: String
Parameter class: Static
Default value: 8.1.6
Range of values: 8.0.0, 8.0.3, 8.0.4, 8.0.5, 8.0.6, 8.1.0, 8.1.3, 8.1.4, 8.1.5, 8.1.6, 8.1.7
OPTIMIZER_FEATURES_ENABLE lets you change the behavior. of the Oracle optimizer based on a release number. For example, if you migrate your database from 8.0.5 to 8.1.5, but you want to keep the 8.0.5 optimizer behavior, you can do so by setting this parameter to 8.0.5. At another time, you can try the new enhancements introduced up to release 8.1.5 by setting the parameter to 8.1.5.
The oracle optimizer
The optimizer is influenced by its decision by the following factors:
OPTIMIZER_MODE in the initialization file
statistics in the data dictionary
OPTIMIZER_GOAL parameter of the ALTER SESSION statement
CHOOSE
ALL_ROWS
FIRST_ROWS
RULE
hints
select value from v$parameter where name='optimizer_mode'
alter session set optimizer_mode='rule';
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