undo表空间中常用的操作：
（1）查看undo表空间undotbs1的属性：
SQL> select b.tablespace_name,AUTOEXTENSIBLE,RETENTION from dba_tablespaces a,dba_data_files b
where a.TABLESPACE_NAME=b.TABLESPACE_NAME and b.TABLESPACE_NAME='UNDOTBS1';
TABLESPACE_NAME AUT RETENTION
---------------------- --- ----------------
UNDOTBS1 NO NOGUARANTEE
（2）查看各个回退段的使用信息：
select a.name,b.extents,b.rssize,b.writes,b.xacts,b.wraps
from v$rollname a,v$rollstat b where a.usn=b.usn;
（3）确定哪些用户正在使用undo段：
SQL> select a.username,b.name,c.used_ublk from v$session a,v$rollname b,v$transaction c
where a.saddr=c.ses_addr and b.usn=c.xidusn;
USERNAME NAME USED_UBLK
---------- ----------------------- ----------
NDMC _SYSSMU1_1255220753$ 1
NDMC _SYSSMU5_1255220754$ 1
（4）每秒生成的UNDO量，可以通过如下SQL得出:
SQL> SELECT (SUM(undoblks))/ SUM((end_time - begin_time) * 86400) FROM v$undostat;
(SUM(UNDOBLKS))/SUM((END_TIME-BEGIN_TIME)*86400)
--------------------------------------------------------------
7.97590055
或者可以看下AWR报告中的Undo Statistics部分。
（5）当前undo表空间使用状态:
SQL> SELECT DISTINCT STATUS,SUM(BYTES),COUNT(*) FROM DBA_UNDO_EXTENTS GROUP BY STATUS;
STATUS SUM(BYTES) COUNT(*)
--------- ---------------- ----------
UNEXPIRED 3225157632 5667
EXPIRED 1063518208 1588
ACTIVE 1048576 1
（6）查看活动事务v$transaction
SQL> SELECT A.SID, A.USERNAME, B.XIDUSN, B.USED_UREC, B.USED_UBLK
FROM V$SESSION A, V$TRANSACTION B WHERE A.SADDR=B.SES_ADDR;
SID USERNAME XIDUSN USED_UREC USED_UBLK
---------- ------------ ---------- ---------- ----------
407 NDMC 15 3 1
SQL> SELECT XID AS "txn_id", XIDUSN AS "undo_seg", USED_UBLK "used_undo_blocks",
XIDSLOT AS "slot", XIDSQN AS "seq", STATUS AS "txn_status"
FROM V$TRANSACTION;
txn_id undo_seg used_undo_blocks slot seq txn_status
---------------- ---------- ---------------- ---------- --------- -------------
14001600733A0C00 20 1 22 801395 ACTIVE