PL/SQL Packages DBMS_SESSION

Set session preferences and security levels.
Equivalent to ALTER SESSION and SET ROLE statements.

Subprocedures:

SET_IDENTIFIER  Set the indentifier. 

SET_CONTEXT     Set the context. 

CLEAR_CONTEXT   Clear the context. 

CLEAR_IDENTIFIER  Clear the identifier. 

SET_ROLE        Set role. 

SET_SQL_TRACE   Turn tracing on or off. 

SET_NLS         Set national language support (NLS). 

CLOSE_DATABASE_LINK Close database link. 

RESET_PACKAGE   Deinstantiates all packages in the session. 

UNIQUE_SESSION_ID Function
                Returns an identifier that is unique for all sessions
                currently connected to this database. 

IS_ROLE_ENABLED Function
                Determines if the named role is enabled for the session. 

IS_SESSION_ALIVE Function
                Determine if the specified session is alive. 

SET_CLOSE_CACHED_OPEN_CURSORS
                Turn close_cached_open_cursors on or off. 

FREE_UNUSED_USER_MEMORY
                Reclaim unused memory - use after performing an operation
                that required a large amount of memory. 

SET_CONTEXT     Set or resets the value of a context attribute. 

LIST_CONTEXT    Returns a list of active namespace and context for the current session. 

SWITCH_CURRENT_CONSUMER_GROUP
                Change the current resource consumer group of
                a user's current session.  

For full documentation of the packaged procedures above see the Oracle Manual:
"Oracle9i Supplied PL/SQL Packages and Types Reference"
or the book Oracle Built in Packages by Steven Feuerstein et al

Related:

V$SESSION