1. 查看当前正在只用的undo段
select s.sid, s.serial#, s.username, r.name, t.STATUS, t.START_TIME, t.USED_UBLK, t.cr_get, t.phy_io, t.used_ublk, t.noundo ,s.program
from v$rollname r, v$transaction t, v$session s
where t.addr=s.taddr and t.xidusn=r.usn
order by t.cr_get,phy_io;
2. 查看回滚段争用,ratio大于2表示该回滚段争用
select a.name, b.gets, b.waits, (b.waits/b.gets)*100 ratio
from v$rollname a, v$rollstat b
where a.usn=b.usn;