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Tracking undo generated by session

The following statement displays a record for all sessions that have generated undo. It shows both how many undo blocks and undo records a session made. 
select
   s.sid, 
   s.username,
   r.name       "RBS name", 
   t.start_time,
   t.used_ublk  "Undo blocks",
   t.used_urec  "Undo recs"
 from
   v$session s,
   v$transaction t,
   v$rollname r
 where
   t.addr = s.taddr and
   r.usn  = t.xidusn;