Re: Do I really need more than 1 rollback segment?

1)

It may be the inserts are not through a single transaction. Different transactions can use same rollback segment and even can exist in the same extent of a particular segment.Generally each transaction can fit into a single extent but it rarely happens. In your case, when the sessions starts query v$transaction for used_ublk by

 SQL> select r.name "Rollback segment"
 , substr( t.start_time, 10, 5) "Start" , t.used_ublk * p.value /  (1024*1024) undo_mb , t.used_ublk undo_blks from v$transaction t ,  v$rollname r , v$session s , v$parameter p where t.addr = s.taddr and  t.xidusn = r.usn and p.name = 'db_block_size' AND s.sid = &1 /

v$resource_limit is available from ORacle 8 onwards.

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