用Shrink Space收缩Oracle数据段

在oracle中可以使用alter table table_name shrink space收缩表,使用shrink有两个前提条件:

  1、表必须启用row movement
  2、表段所在表空间的段空间管理(segment space management)必须为auto

实验如下：

--建立一个segment space management auto表空间
SQL> create tablespace ts_auto datafile 'd:\oracle\product\10.2.0\oradata\orcl\ts_auto.dbf' size 100m
 extent management local segment space management auto;

表空间已创建。

--建议测试表
SQL> create table  tb_auto  as select * from dba_objects;

表已创建。

--查看shrink前的块数量
SQL> select blocks from dba_segments where segment_name='TB_AUTO';

    BLOCKS                                                                     
----------                                                                     
       768                                                                    

--delete数据后，空间占用没有变化
SQL> delete from tb_auto;

已删除50390行。

SQL> commit;

提交完成。

SQL> select blocks from dba_segments where segment_name='TB_AUTO';

    BLOCKS                                                                     
----------                                                                     
       768                                                                     

--直接收缩，提示必须启动row movement选项
SQL> alter table tb_auto shrink space;
alter table tb_auto shrink space
*
第 1 行出现错误:
ORA-10636: ROW MOVEMENT is not enabled

SQL> alter table tb_auto enable row movement;

表已更改。

--收缩成功，空间已经释放
SQL> alter table tb_auto shrink space;

表已更改。

SQL> select blocks from dba_segments where segment_name='TB_AUTO';

    BLOCKS                                                                     
----------                                                                     
         8                                                                     

--shrink不能在segment space management manaual的表空间的段上执行
SQL> create tablespace ts_manual datafile 'd:\oracle\product\10.2.0\oradata\orcl\ts_mannel.dbf' size 100m
 extent management local segment space management manual;

表空间已创建。

SQL> select tablespace_name,segment_space_management from dba_tablespaces;

TABLESPACE_NAME                SEGMEN                                          
------------------------------ ------                                          
SYSTEM                         MANUAL                                          
UNDOTBS1                       MANUAL                                          
SYSAUX