About DATABASE

   PARAMETERS
     level - tablespace number+1. If the value is 2147483647 then
             temp segments in ALL tablespaces are dropped, otherwise, only
             segments in a tablespace whose number is equal to the LEVEL
             specification are dropped.

   NOTES
     This routine does what SMON does in the background, i.e. drops
     temporary segments. It is provided as a manual intervention tool which
     the user may invoke if SMON misses the post and does not get to
     clean the temp segments for another 2 hours. We do not know whether
     missed post is a real possibility or more theoretical situation, so
     we provide this event as an insurance against SMON misbehaviour.

     Under normal operation there is no need to use this event.

     It may be a good idea to
        alter tablespace <tablespace> coalesce;
     after dropping lots of extents to tidy things up.

 *SQL Session (if you can connect to the database):     
    alter session set events 'immediate trace name DROP_SEGMENTS level TS#+1';

     The TS# can be obtained from v$tablespace view:
     select ts# from v$tablespace where name = '<Tablespace name>';

     Or from SYS.TS$:

     select ts# from sys.ts$ where name = '<Tablespace name>' and online$ != 3;
    
     If ts# is 5, an example of dropping the temporary segments in that tablespace
     would be:

    alter session set events 'immediate trace name DROP_SEGMENTS level 6';