Oracle Drop Table 释放空间测试

　　Drop Table会释放所占segment的空间，而数据文件占用OS空间不变

一.创建表空间，表，插入300条数据

 1 SQL> create tablespace tbs datafile '/opt/oracle/oradata/nwom/TEST_TBS.dbf' size 1m autoextend off;

 2 

 3 Tablespace created.

 4 

 5 SQL> create table t1 (a char(2000)) tablespace tbs;

 6 

 7 Table created.

 8 

 9 --插入300条数据

10 SQL> begin

11   2     for i in 1..300 loop

12   3             insert into t1 values('a');

13   4     end loop;

14   5  end;

15   6  /

16 

17 PL/SQL procedure successfully completed.

18 

19 SQL> commit;

20 

21 Commit complete.

22 

23 SQL> select count(*) from t1;

24 

25   COUNT(*)

26 ----------

27        300

二.查看表所占用的segment

 1 --300条数据占用段0.9375M

 2 SQL> col SEGMENT_NAME format a10;

 3 SQL> col SEGMENT_TYPE format a20

 4 SQL> col TABLESPACE_NAME format a20

 5 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)"

 6   2  from user_segments where segment_name='T1';

 7 

 8 SEGMENT_NA SEGMENT_TYPE         TABLESPACE_NAME         SIZE(M)

 9 ---------- -------------------- -------------------- ----------

10 T1         TABLE                TBS                       .9375

11 

12 SQL> 

三.Drop Table

1 SQL> drop table t1;

2 

3 Table dropped.

四.Drop Table后，查看表所占用的segment

1 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)"

2   2  from user_segments where segment_name='T1';

3 

4 no rows selected

五.重新建表t1，插入数据100条

 1 SQL> create table t1 (a char(2000)) tablespace tbs;

 2 

 3 Table created.

 4 

 5 --插入100条数据

 6 SQL> begin

 7   2     for i in 1..100 loop

 8   3             insert into t1 values('a');

 9   4     end loop;

10   5  end;

11   6  /

12 

13 PL/SQL procedure successfully completed.

14 

15 SQL> commit;

16 

17 Commit complete.

18 

19 

20 SQL> select count(*) from t1;

21 

22   COUNT(*)

23 ----------

24        100

六.查看表t1所占用segment

1 SQL> select segment_name, segment_type, tablespace_name, bytes/1024/1024 "SIZE(M)"

2   2  from user_segments where segment_name='T1';

3 

4 SEGMENT_NA SEGMENT_TYPE         TABLESPACE_NAME         SIZE(M)

5 ---------- -------------------- -------------------- ----------

6 T1         TABLE                TBS                       .3125

7 

8 SQL>

结论：对比二与六的size(M)，可知Drop Table会释放表占用的segment。