Which oracle session is generating a lot of redo logs?

A simple and fast query to run:

set line 200 pages 80

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;

By the way, the view v$sess_io is very useful, to identify the top I/O consumers also.