Oracle Database Tips by Donald Burleson

The only privilege needed to create outlines is the CREATE ANY OUTLINE privilege. However it is also useful to be able to select from DBA_OUTLINES

To force a session to either use or not create out lines you would issue the command:

 ALTER SESSION SET CREATE_STORED_OUTLINES = TRUE | FALSE | <category>

This command causes Oracle to automatically create outlines for all SQL statements issued during the session. If set to TRUE then the category name for the outlines is set to DEFAULT.

Note: Category should not be quoted contrary to documentation

To turn on or off the creation of stored outlines at the system level issue the command:

 ALTER SYSTEM SET CREATE_STORED_OUTLINES = TRUE | FALSE | <category> [NOOVERRIDE]  

This determines whether Oracle should automatically create and store an outline for each query submitted on the system.  These outlines are stored in the DEFAULT category. If a particular query already has an outline defined for it in the DEFAULT category, that outline will remain and a new outline will not be created.

The NOOVERRIDE option specifies that this system setting will not override the setting for any session in which this parameter was explicitly set.

It should be noted that outlines overide all other optimizer settings. They are only used if a session explicitly requests that they be used using the following command.

ALTER SESSION SET USE_STORED_OUTLINES = TRUE | FALSE | <category>

Note: As with the previous commands, category should not be quoted contrary to documentation

If USE_STORED_OUTLINES is set to TRUE then the DEFAULT category is used. If set to a category then TRUE is assumed and that category is used.

 When set Oracle checks for a known stored plan based on an address calculated from the SQL TEXT of the statement. If  a plan exists in the selected category then that plan will be used (provided it is valid).