UNDO 表空間重建（清理）

Oracle的AUM(Auto Undo Management)從出生以來就經常出現只擴展,不收縮(shrink)的情況(通常我們可以設置足夠的UNDO表空間大小,然後取消其自動擴展屬性).

查看錶空間使用情況

SELECT   a.tablespace_name,ROUND (a.total_size) "total_size(MB)",ROUND (a.total_size) - ROUND (b.free_size, 3) "used_size(MB)",ROUND (b.free_size, 3) "free_size(MB)",ROUND (b.free_size / total_size * 100, 2) || '%' free_rate  FROM   (  SELECT   tablespace_name, SUM (bytes) / 1024 / 1024 total_size FROM   dba_data_files GROUP BY   tablespace_name) a, (  SELECT   tablespace_name, SUM (bytes) / 1024 / 1024 free_size FROM   dba_free_space GROUP BY   tablespace_name) b WHERE   a.tablespace_name = b.tablespace_name(+);

現在我們可以採用如下步驟回收UNDO空間:
1.確認文件
select file_name,bytes/1024/1024 from dba_data_files where tablespace_name like 'UNDOTBS1';

2.檢查UNDO Segment狀態
select usn,xacts,rssize/1024/1024/1024,hwmsize/1024/1024/1024,shrinks from v$rollstat order by rssize;

3.創建新的UNDO表空間
SQL> create undo tablespace undotbs3 datafile '/u01/app/oradata/TJ/undotbs301.dbf' size 150M reuse AUTOEXTEND ON;

Tablespace created.
 

4.切換UNDO表空間爲新的UNDO表空間
SQL> alter system set undo_tablespace=undotbs3;

System altered.

 

5.等待原UNDO表空間所有UNDO SEGMENT OFFLINE 
  select usn,xacts,status,rssize/1024/1024/1024,hwmsize/1024/1024/1024,shrinks from v$rollstat order by rssize;
  
  6.刪除原UNDO表空間

 alter tablespace undotbs1 offline
 drop tablespace undotbs1 including contents and datafiles;

7.檢查空間情況

     日後增加數據文件方法

ALTER TABLESPACE undotbs3 ADD DATAFILE '/u01/app/oradata/TJ/undotbs303.dbf' size 150M reuse AUTOEXTEND ON;