UNDO tablespace Corruption

issue: database hang because unod tablespace is full. All sessions wait for undo segments.

Problem: rollbank segment was not released back because its status  become something other than online/offline.

Solution:
drop old undo tablespace and create new one.

1. find corrupted rollbank segment
  select segment_name from dba_rollback_segs where status not in ('ONLINE','OFFLINE');

2. startup database mount
alter system set undo_management='MANUAL' scope=spfile;
  alter system set _corrupted_rollback_segments='segment_name' scope=spfile;
alter system set _offline_rollback_segments='segment_name' scope=spfile;
alter system set undo_tablespace='newone';
startup;
drop undo tablespace oldone;

reference:
SR 3-6031218201