UNDO 表空间重建（清理）

Oracle的AUM(Auto Undo Management)从出生以来就经常出现只扩展,不收缩(shrink)的情况(通常我们可以设置足够的UNDO表空间大小,然后取消其自动扩展属性).

查看表空间使用情况

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(+);

现在我们可以采用如下步骤回收UNDO空间:
1.确认文件
select file_name,bytes/1024/1024 from dba_data_files where tablespace_name like 'UNDOTBS1';

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

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

Tablespace created.
 

4.切换UNDO表空间为新的UNDO表空间
SQL> alter system set undo_tablespace=undotbs3;

System altered.

 

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

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

7.检查空间情况

     日后增加数据文件方法

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