在学习和使用的过程中，经常会出现一些简单的概念，了解了，也就不深究了。
但是在很多时候，忽然发现，并不能完全深入的理解其含义和功能。
近日使用到maxsize参数，突然不确定它最终限制的是什么，所以做了一个实验，测试其真正的功能和含义。
下面就是我的测试步骤和最后的总结：
1. 创建一个500k的自动扩展10m最大100M的表空间
sys@R11203> CREATE TABLESPACE tbs_02_test DATAFILE '/opt/oracle/oradata/R11203/tbs_f5_test.dbf' SIZE 500K REUSE AUTOEXTEND ON NEXT 10m MAXSIZE 100M;
Tablespace created.
2. 可以通过下面名称查询这个数据文件的属性
sys@R11203> select FILE_NAME,TABLESPACE_NAME,MAXBYTES,MAXBLOCKS,USER_BYTES from dba_data_files where TABLESPACE_NAME='TBS_02_TEST';
FILE_NAME TABLESPACE_NAME MAXBYTES MAXBLOCKS USER_BYTES
-------------------------------------------------- ------------------------------ ---------- ---------- ----------
/opt/oracle/oradata/R11203/tbs_f5_test.dbf TBS_02_TEST 104857600 12800 458752
3. 创建test表到这个表空间中
sys@R11203> CREATE TABLE test TABLESPACE TBS_02_TEST AS (SELECT * FROM dba_objects);
Table created.
4. 连续插入数据，来填满表空间
sys@R11203> insert into test select * from test;
83710 rows created.
sys@R11203> commit；
5. 查询该表大小，单位M
sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME USED_SIZE
--------------------------------------------------------------------------------- ----------
TEST 20
6. 再次插入
sys@R11203> insert into test select * from test;
commit;
167420 rows created.
sys@R11203>
Commit complete.
7. 目前该表大小达到39M
sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME USED_SIZE
--------------------------------------------------------------------------------- ----------
TEST 39
8. 当前表空间已经使用42M
sys@R11203> select FILE_NAME,TABLESPACE_NAME,MAXBYTES,MAXBLOCKS,USER_BYTES from dba_data_files where TABLESPACE_NAME='TBS_02_TEST';
FILE_NAME TABLESPACE_NAME MAXBYTES MAXBLOCKS USER_BYTES
-------------------------------------------------- ------------------------------ ---------- ---------- ----------
/opt/oracle/oradata/R11203/tbs_f5_test.dbf TBS_02_TEST 104857600 12800 42401792
9. 继续插入
sys@R11203> insert into test select * from test;
commit;
10. 查询，达到79.5M
sys@R11203> sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME USED_SIZE
--------------------------------------------------------------------------------- ----------
TEST 79.5
11. 表空间达到84M
sys@R11203> select FILE_NAME,TABLESPACE_NAME,MAXBYTES,MAXBLOCKS,USER_BYTES from dba_data_files where TABLESPACE_NAME='TBS_02_TEST';
FILE_NAME TABLESPACE_NAME MAXBYTES MAXBLOCKS USER_BYTES
-------------------------------------------------- ------------------------------ ---------- ---------- ----------
/opt/oracle/oradata/R11203/tbs_f5_test.dbf TBS_02_TEST 104857600 12800 84344832
12. 再次插入，失败，无法扩展表空间
sys@R11203> insert into test select * from test;
commit;
insert into test select * from test;
commit;
insert into test select * from test
*
ERROR at line 1:
ORA-01653: unable to extend table SYS.TEST by 1024 in tablespace TBS_02_TEST
sys@R11203>
Commit complete.
sys@R11203> insert into test select * from test
*
ERROR at line 1:
ORA-01653: unable to extend table SYS.TEST by 1024 in tablespace TBS_02_TEST
13. 查询表空间，已经到达maxsize的值
sys@R11203> select FILE_NAME,TABLESPACE_NAME,MAXBYTES,MAXBLOCKS,USER_BYTES from dba_data_files where TABLESPACE_NAME='TBS_02_TEST';
FILE_NAME TABLESPACE_NAME MAXBYTES MAXBLOCKS USER_BYTES
-------------------------------------------------- ------------------------------ ---------- ---------- ----------
/opt/oracle/oradata/R11203/tbs_f5_test.dbf TBS_02_TEST 104857600 12800 104792064
14. 当前表95.5M
sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME USED_SIZE
--------------------------------------------------------------------------------- ----------
TEST 95.5
15. 在不能自动扩展的情况下，如果手动介入呢，是否可以继续扩展表空间的数据文件大小呢？
测试结果是，可以继续手工扩展表空间
sys@R11203> alter database datafile '/opt/oracle/oradata/R11203/tbs_f5_test.dbf' resize 300m;
Database altered.
16. 当前表空间大小为300M
sys@R11203> select FILE_NAME,TABLESPACE_NAME,MAXBYTES,MAXBLOCKS,USER_BYTES from dba_data_files where TABLESPACE_NAME='TBS_02_TEST';
FILE_NAME TABLESPACE_NAME MAXBYTES MAXBLOCKS USER_BYTES
-------------------------------------------------- ------------------------------ ---------- ---------- ----------
/opt/oracle/oradata/R11203/tbs_f5_test.dbf TBS_02_TEST 104857600 12800 314507264
sys@R11203>
17. 可以继续向test表插入数据
sys@R11203> insert into test select * from test;
commit;
669680 rows created.
sys@R11203>
Commit complete.
18. 目前表已经达到159.5M
sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME USED_SIZE
--------------------------------------------------------------------------------- ----------
TEST 159.5
19. 再次插入数据，目前表大小达到295.5M，
sys@R11203> select segment_name, bytes/1024/1024 used_size from user_segments where segment_name = 'TEST';
SEGMENT_NAME
--------------------------------------------------------------------------------
USED_SIZE
----------
TEST
295.5
20. 表空间已经不能自动扩展，只有手工介入来增加表空间大小：
sys@R11203> insert into test select * from test;
insert into test select * from test
*
ERROR at line 1:
ORA-01653: unable to extend table SYS.TEST by 1024 in tablespace TBS_02_TEST
总结：
maxsize值只是限制auto extend的，在到达之前设定的maxsize大小之后，就不能自动扩展了，但是并不是说这样，表空间就不能扩展了，可以继续手动扩展数据文件大小。
同时，我们也可以通过增加数据文件来达到扩展表空间的目的。