How to Find Sessions Generating Lots of Redo or Archive logs

To find sessions generating lots of redo, you can use either of the following
methods. Both methods examine the amount of undo generated. When a transaction
generates undo, it will automatically generate redo as well.

The methods are:
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:
       SQL> 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
           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:
      SQL> 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
          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.

You use the first query when you need to check for programs generating lots of
redo when these programs activate more than one transaction. The latter query
can be used to find out which particular transactions are generating redo.