oracle 回滚时间预估

每隔10s运行以下sql可以大概估算出回滚需要时间

select
      s.username,
      t.xidusn,
      t.xidslot,
      t.xidsqn,
      x.ktuxesiz
    from
      sys.x$ktuxe x,
      sys.v_$transaction t,
      sys.v_$session s
    where
      x.inst_id = userenv('Instance') and
      x.ktuxesta = 'ACTIVE' and 
      x.ktuxesiz > 1 and 
      t.xidusn = x.ktuxeusn and
      t.xidslot = x.ktuxeslt and
      t.xidsqn = x.ktuxesqn and
      s.saddr = t.ses_addr;