To check High redo generation sessions .....

set lines 132
set pages 100
set time on
set timing on
col username format a20
col program format a30
spool redo_vol
--1) Query V$SESS_IO. This view contains the column BLOCK_CHANGES which indicates
--   how much blocks have been changed by the session. High values indicate a
--   session generating lots of redo.
--   The query you can use is:
       SELECT s.sid, s.serial#, s.username, s.program, i.block_changes
         FROM v$session s, v$sess_io i
        WHERE s.sid = i.sid
          AND i.block_changes > 200
        ORDER BY 5 desc, 1, 2, 3, 4;
--   Run the query multiple times and examine the delta between each occurrence
--   of BLOCK_CHANGES. Large deltas indicate high redo generation by the session.
--2) Query V$TRANSACTION. This view contains information about the amount of
--   undo blocks and undo records accessed by the transaction (as found in the
--   USED_UBLK and USED_UREC columns).

--  The query you can use is:
      SELECT s.sid, s.serial#, s.username, s.program, t.used_ublk, t.used_urec
        FROM v$session s, v$transaction t
       WHERE s.taddr = t.addr
         AND t.used_ublk > 200
       ORDER BY 5 desc, 6 desc, 1, 2, 3, 4;
--   Run the query multiple times and examine the delta between each occurrence
--   of USED_UBLK and USED_UREC. Large deltas indicate high redo generation by
--   the session.
spool off