How to Find Sessions Generating Lots of Redo or Archive logs

There  are  two methods   to  find  sessions generating lots of redo

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
   
   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;
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).
   
   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.

Note: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.