undo表空間中常用的操作

undo表空間中常用的操作：

（1）檢視undo表空間undotbs1的屬性：
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）檢視各個回退段的使用資訊：
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）確定哪些使用者正在使用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，可以透過如下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報告中的Undo Statistics部分。

（5）當前undo表空間使用狀態:
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）檢視活動事務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