session1占用的undo blocks计算出session1修改的数据量

session1 blocker session2 ,此SQL可查出session1占用的undo blocks，从而计算出session1修改的数据量 

select s.sid,s.USERNAME,r.name "rvs name", t.START_TIME, t.USED_UBLK "undo blocks", t.UBAREC "undo recs", lo.OBJECT_ID "object id" from v$session s,v$transaction t, v$rollname r, v$locked_object lo where t.addr=s.TADDR and r.usn=t.XIDUSN and t.XIDUSN=lo.XIDUSN and t.XIDSLOT=lo.XIDSLOT and t.XIDSQN=lo.XIDSQN;