A stored outline is the stored data that pertains to an execution plan for a given SQL statement. It enables the optimizer to repeatedly re-create execution plans that are equivalent to the plan originally generated along with the outline. The data stored in an outline consists, in part, of a set of hints that are used to achieve plan stability.

DBMS_OUTLN consists of procedures like CLEAR_USED, CREATE_OUTLINE, DROP_BY_CAT, DROP_UNUSED etc. DBMS_OUTLN contains management procedures that should be available to privileged users only.

DBMS_OUTLN.CLEAR_USED

This procedure clears the outline 'used' flag.
Syntax: DBMS_OUTLN.CLEAR_USED ( name    IN    VARCHAR2);

DBMS_OUTLN.CREATE_OUTLINE

This procedure generates an outline from the shared cursor identified by hash value and child number.
Syntax:  DBMS_OUTLN.CREATE_OUTLINE ( hash_value    IN NUMBER, child_number  IN NUMBER, category  IN VARCHAR2 DEFAULT 'DEFAULT');

DBMS_OUTLN.DROP_BY_CAT

This procedure drops outlines that belong to a particular category. While outlines are put into the DEFAULT category unless otherwise specified, users have the option of grouping their outlines into groups called categories.
Syntax: DBMS_OUTLN.DROP_BY_CAT ( cat VARCHAR2);

DBMS_OUTLN.DROP_UNUSED

This procedure drops outlines that have never been applied in the compilation of a SQL statement.
Syntax:  DBMS_OUTLN.DROP_UNUSED;

DBMS_OUTLN.EXACT_TEXT_SIGNATURE

This procedure updates outline signatures to those that compute based on exact text matching.
Syntax:  DBMS.OUTLN.EXACT_TEXT_SIGNATURES;

DBMS_OUTLN.UPDATE_BY_CAT

This procedure changes the category of all outlines in one category to a new category.
Syntax: DBMS.OUTLN.UPDATE_BY_CAT ( oldcat    VARCHAR2 default 'DEFAULT', newcat    VARCHAR2 default 'DEFAULT');

DBMS_OUTLN.UPDATE_SIGNATURE

This procedure updates outline signatures to the current version's signature.
Syntax: DBMS.OUTLN.UPDATE_SIGNATURES;