缩减Oracle的UNDOTBS01.DBF文件大小

UNDOTBS01.DBF是什么文件？

表空间文件，主要就是为了undo，即撤销、回滚，只要有DML操作等，就会产生undo数据，久而久之会变得非常大，占用大量磁盘空间。这里要说的是怎么消除这种占用。

查询undo表空间的使用

SELECT a.tablespace_name as tablespace_name,
       to_char(b.total/1024/1024,999999.99) as Total,
       to_char((b.total-a.free)/1024/1024,999999.99) as Used,
       to_char(a.free/1024/1024,999999.99) as Free,
       to_char(round((total-free)/total,4)*100,999.99) as Used_Rate
FROM (SELECT tablespace_name, sum(bytes) free FROM DBA_FREE_SPACE GROUP BY tablespace_name) a,
     (SELECT tablespace_name, sum(bytes) total FROM DBA_DATA_FILES GROUP BY tablespace_name ) b
WHERE a.tablespace_name=b.tablespace_name
  AND a.tablespace_name='UNDOTBS_NEW'
ORDER BY a.tablespace_name;

处理方式

处理方式1：扩大undo tablespace的大小

alter database datafile 'D:\app\Administrator\oradata\kisbidb\undotbs01.dbf' resize 10240M;

处理方式2：缩小undo tablespace

--（1）创建一个新的小空间的undo tablespace
create undo tablespace undotBS2 datafile 'D:\app\Administrator\oradata\kisbidb\undotbs02.dbf' size 5m;
--（2）设置新的表空间为系统undo_tablespace
alter system set undo_tablespace=undotBS2;
--（3）删除旧的表空间
drop tablespace undotbs1 including contents;

处理方式3：禁止undo tablespace自动增长

alter database datafile 'D:\app\Administrator\oradata\kisbidb\undotbs01.dbf' autoextend off;