Oracle中truncate删除的数据还能找到？

Oracle的truncate删除数据操作，不会写日志，不产生回滚段，因此执行速度快，相当于Windows的shift+del，不经回收站直接删除。

如果想找回truncate删除的数据，常规的可以采用这几种方案，

（1）使用数据泵导入。操作简单，但是前提必须要有备份可用，并且会有数据的丢失。（2）使用RMAN进行不完全恢复。前提是开启备份，可将数据库恢复到truncate之前的时刻，但是恢复时间较长。

还可以采用非常规的方案，例如通过odu、prm-dul、GDUL等收费软件进行恢复，还可以使用fy_recover_data包。

FY_Recover_Data是国内曾经的Oracle ACE大佬黄玮（个人网站：http://www.hellodba.com）开发的一个package，该脚本专门用于对truncate的表进行恢复。

作者讲述这个包的原理：如果我们已经有一套元数据及数据块，然后将被TRUNCATE的用户数据块的内容取代其用户数据块的内容，是否可以"骗"过Oracle，让它读出这些数据呢？

回顾一下表扫描的过程，这个方法应该是可行的。我们只要想办法构造出一个结构相同、且具有完整元数据信息和格式化了的用户数据块的傀儡表对象，然后将被truncate的用户数据块找出，再将其数据内容部分嫁接到傀儡对象的用户数据块，让Oracle认为这是傀儡对象的数据，就能让Oracle扫描并读出数据内容。

其原理用图示描述如下，

                                               +-------------------------+  
| Copy Of Dummy Data File |
| (With Formmated Blocks)|
+-------------------------+
||
/
(Blcok Header, Block Tail)
||
/
+-------------------+ +----------------+ Table Scan +---------------+
| Source Data File | => (Data Block Content) => | Dummy Table | ============> | Restore Table |
|(Without Meta Data)| |(With Meta Data)| +---------------+
+-------------------+ +----------------+

FY_Recover_Data对于表恢复的支持性如下，

通过使用FY_Recover_Data对truncate几种情况进行恢复测试，以验证fy_recover_data的恢复能力。

（1）使用fy_recover_data包执行truncate恢复，truncate后未有新数据进入表。

STEP1：创建测试表，并执行truncate

SQL> create table test01 as select * from dba_objects;


SQL> select count(*) from test01;
  COUNT(*)
----------
86968


SQL> truncate table test01;
Table truncated


SQL> select count(*) from test01;
  COUNT(*)
----------
0

STEP2：导入FY_Recover_Data.pck包

[oracle@source-node ~]$ sqlplus as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Tue Apr 21 10:50:17 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> @/home/oracle/FY_Recover_Data.pck -- 第一次执行发现第30行存在“&”符号，删除该符号


Enter value for files:
old 30: -- 1. Temp Restore and Recover tablespace & files ---
new 30: -- 1. Temp Restore and Recover tablespace ---


Package created.


Warning: Package Body created with compilation errors.


SQL> @/home/oracle/FY_Recover_Data.pck -- 删除“&”符号后导入成功


Package created.


Package body created.

STEP3：开始执行恢复，只需要两个参数：schema和table_name，

[oracle@source-node ~]$ sqlplus as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Tue Apr 21 11:11:20 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> set time on
11:11:43 SQL> set serveroutput on
11:11:54 SQL> exec fy_recover_data.recover_truncated_table('TEST','TEST01');
11:12:01: Use existing Directory Name: FY_DATA_DIR
11:12:02: Recover Table: TEST.TEST01$
11:12:02: Restore Table: TEST.TEST01$$
11:12:09: Copy file of Recover Tablespace: FY_REC_DATA_COPY.DAT1
11:12:09: begin to recover table TEST.TEST01
11:12:09: Use existing Directory Name: TMP_HF_DIR
11:12:09: Recovering data in datafile
/u01/app/oracle/oradata/testdb1/users01.dbf
11:12:09: Use existing Directory Name: TMP_HF_DIR
11:12:39: 1242 truncated data blocks found.
11:12:39: 86968 records recovered in backup table TEST.TEST01$$
11:12:39: Total: 1242 truncated data blocks found.
11:12:39: Total: 86968 records recovered in backup table TEST.TEST01$$
11:12:39: Recovery completed.
11:12:39: Data has been recovered to TEST.TEST01$$


PL/SQL procedure successfully completed.

STEP4：根据恢复日志，会创建临时中转表test01$和test01$$，恢复的数据保存在test01$$中，

SQL> show user
User is "TEST"


SQL> select count(*) from test01$$;
  COUNT(*)
----------
86968


--将数据还原到test01表中
SQL> insert into test01 select * from test01$$;


--确认数据已经还原回来
SQL> select count(*) from test01;


COUNT(*)
----------
86968

经过测试，如果表被truncate后，未执行其它操作，数据可以使用fy_recover_data恢复回来。

（2）使用fy_recover_data包执行truncate恢复，truncate后有新数据进入表（新插入的数据比truncate之前多）

STEP1：创建测试表、序列、存储过程

SQL> create table test01
2 (
3 col1 number,
4 col2 number,
5 col3 date,
6 col4 varchar2(30),
7 col5 varchar2(100)
  8  );
Table created


SQL> --创建自增序列
SQL> CREATE SEQUENCE seq01
2 START WITH 1
3 MAXVALUE 99999999
4 MINVALUE 0
5 CYCLE
6 CACHE 10
  7    ORDER;
Sequence created

SQL> --创建随机数据插入存储过程,其中col1列单调递增
create or replace procedure p_insert_test01 IS
v_col1 NUMBER;
BEGIN
FOR i IN 1..10000 LOOP
select seq01.nextval INTO v_col1 from dual;
insert into test01(col1,col2,col3,col4,col5)
values
(v_col1,
(select round(dbms_random.value(10000, 100000000)) from dual),
sysdate,
(select dbms_random.string('a', 25) from dual),
(select dbms_random.string('a', 85) from dual));
END LOOP;
commit;
end p_insert_test01;

STEP2：测试表插入10000条数据，col1列的值从1到10000，

SQL> exec p_insert_test01;
PL/SQL procedure successfully completed




SQL> select count(*) from test01;
COUNT(*)
----------
10000



SQL> SELECT MIN(col1),MAX(col1) FROM test01;
MIN(COL1) MAX(COL1)
---------- ----------
1 10000

STEP3：执行truncate操作，

SQL> truncate table test01;
Table truncated

STEP4：接着往表里插入20000条数据，

SQL> exec p_insert_test01;
PL/SQL procedure successfully completed


SQL> exec p_insert_test01;
PL/SQL procedure successfully completed




SQL> select count(*) from test01;
  COUNT(*)
----------
20000



SQL> SELECT MIN(col1),MAX(col1) FROM test01;
MIN(COL1)  MAX(COL1)
---------- ----------
10001 30000

STEP5：执行恢复操作，

[oracle@source-node ~]$ sqlplus as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Tue Apr 21 14:00:57 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> set serveroutput on
SQL> set time on


14:01:09 SQL> exec fy_recover_data.recover_truncated_table('TEST','TEST01');
14:01:13: Use existing Directory Name: FY_DATA_DIR
14:01:13: Recover Table: TEST.TEST01$
14:01:14: Restore Table: TEST.TEST01$$
14:01:18: Copy file of Recover Tablespace: FY_REC_DATA_COPY.DAT1
14:01:18: begin to recover table TEST.TEST01
14:01:18: Use existing Directory Name: TMP_HF_DIR
14:01:18: Recovering data in datafile
/u01/app/oracle/oradata/testdb1/users01.dbf
14:01:18: Use existing Directory Name: TMP_HF_DIR
14:01:32: 402 truncated data blocks found.
14:01:32: 20000 records recovered in backup table TEST.TEST01$$
14:01:32: Total: 402 truncated data blocks found.
14:01:32: Total: 20000 records recovered in backup table TEST.TEST01$$
14:01:32: Recovery completed.
14:01:32: Data has been recovered to TEST.TEST01$$
PL/SQL procedure successfully completed.

STEP6：通过对test01$$表进行确认，发现返回的数据是truncate之后插入的数据，不符合要求。

SQL> select count(*) from test01;


COUNT(*)
----------
20000
SQL> select count(*) from test01$$;


COUNT(*)
----------
20000


SQL> SELECT MIN(col1),MAX(col1) FROM test01;


MIN(COL1) MAX(COL1)
---------- ----------
10001 30000


SQL> SELECT MIN(col1),MAX(col1) FROM test01$$;


MIN(COL1) MAX(COL1)
---------- ----------
10001 30000

（3）使用fy_recover_data包执行truncate恢复，truncate后有新数据进入表（新插入的数据比truncate之前少）。

STEP1：创建测试表、序列、存储过程，

SQL> DROP TABLE  test01 PURGE;
Table dropped


SQL> create table test01
2 (
3 col1 number,
4 col2 number,
5 col3 date,
6 col4 varchar2(30),
7 col5 varchar2(100)
8 );
Table created


SQL> DROP SEQUENCE seq01;
Sequence dropped


SQL> --创建自增序列
SQL> CREATE SEQUENCE seq01
2 START WITH 1
3 MAXVALUE 99999999
4 MINVALUE 0
5 CYCLE
6 CACHE 10
7 ORDER;
Sequence created


SQL> --创建随机数据插入存储过程,其中col1列单调递增
SQL> create or replace procedure p_insert_test01 IS
2 v_col1 NUMBER;
3 BEGIN
4 FOR i IN 1..10000 LOOP
5 select seq01.nextval INTO v_col1 from dual;
6 insert into test01(col1,col2,col3,col4,col5)
7 values
8 (v_col1,
9 (select round(dbms_random.value(10000, 100000000)) from dual),
10 sysdate,
11 (select dbms_random.string('a', 25) from dual),
12 (select dbms_random.string('a', 85) from dual));
13 END LOOP;
14 commit;
15 end p_insert_test01;
16  /


Procedure created

STEP2：测试表插入10000条数据，col1列的值从1到10000，

SQL> exec p_insert_test01;
PL/SQL procedure successfully completed




SQL> select count(*) from test01;
  COUNT(*)
----------
10000



SQL> SELECT MIN(col1),MAX(col1) FROM test01;
MIN(COL1)  MAX(COL1)
---------- ----------
1 10000

STEP3：执行truncate操作，

SQL> truncate table test01;
Table truncated

STEP4：修改存储过程，酶促插入100条数据，

SQL> --创建随机数据插入存储过程,其中col1列单调递增
SQL> create or replace procedure p_insert_test01 IS
2 v_col1 NUMBER;
3 BEGIN
4 FOR i IN 1..100 LOOP
5 select seq01.nextval INTO v_col1 from dual;
6 insert into test01(col1,col2,col3,col4,col5)
7 values
8 (v_col1,
9 (select round(dbms_random.value(10000, 100000000)) from dual),
10 sysdate,
11 (select dbms_random.string('a', 25) from dual),
12 (select dbms_random.string('a', 85) from dual));
13 END LOOP;
14 commit;
15 end p_insert_test01;
16 /


Procedure created


-- 测试表插入100条数据
SQL> exec p_insert_test01;
PL/SQL procedure successfully completed

STEP5：执行恢复操作，

[oracle@source-node ~]$ sqlplus as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Tue Apr 21 14:22:34 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> set time on
14:22:39 SQL> set serveroutput on
14:22:44 SQL> exec fy_recover_data.recover_truncated_table('TEST','TEST01');
14:22:52: Use existing Directory Name: FY_DATA_DIR
14:22:52: Recover Table: TEST.TEST01$
14:22:52: Restore Table: TEST.TEST01$$
14:22:57: Copy file of Recover Tablespace: FY_REC_DATA_COPY.DAT1
14:22:57: begin to recover table TEST.TEST01
14:22:57: Use existing Directory Name: TMP_HF_DIR
14:22:57: Recovering data in datafile
/u01/app/oracle/oradata/testdb1/users01.dbf
14:22:57: Use existing Directory Name: TMP_HF_DIR
14:23:06: 5 truncated data blocks found.
14:23:06: 100 records recovered in backup table TEST.TEST01$$
14:23:06: Total: 5 truncated data blocks found.
14:23:06: Total: 100 records recovered in backup table TEST.TEST01$$
14:23:06: Recovery completed.
14:23:06: Data has been recovered to TEST.TEST01$$


PL/SQL procedure successfully completed.

STEP6：通过对test01$$表进行确认，发现返回的数据是truncate之后插入的数据，不符合要求。

SQL> select count(*) from test01;
  COUNT(*)
----------
100


SQL> SELECT MIN(col1),MAX(col1) FROM test01;
MIN(COL1)  MAX(COL1)
---------- ----------
10001 10100


SQL> select count(*) from test01$$;
  COUNT(*)
----------
100


SQL> SELECT MIN(col1),MAX(col1) FROM test01$$;
MIN(COL1)  MAX(COL1)
---------- ----------
10001 10100

（4）测试数据文件被覆盖是否影响恢复。

STEP1：创建测试表，

SQL> create table test01
2 (
3 col1 number,
4 col2 number,
5 col3 date,
6 col4 varchar2(30),
7 col5 varchar2(100)
8 ) TABLESPACE USERS;
Table created

STEP2：初始时候，表空间总共20MB，剩余15.94MB，

SQL> SELECT SUBSTR(a.TABLESPACE_NAME,1,30) TablespaceName,
2 round(SUM(a.bytes/1024/1024),2) AS "Totle_size(MB)",
3 round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Free_space(MB)",
4 round(SUM(a.bytes/1024/1024),2)-round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Used_space(MB)",
5 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0))) *100/SUM(a.bytes/1024/1024),2) AS "Used_percent%",
6 round(SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_size(MB)",
7 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0)))*100/SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_percent%"
8 FROM dba_data_files a,
9 (SELECT SUM(NVL(bytes,0)) free_space1,
10 file_id
11 FROM dba_free_space
12 GROUP BY file_id
13 ) b
14 WHERE a.file_id = b.file_id(+)
15 AND a.TABLESPACE_NAME = 'USERS'
16 GROUP BY a.TABLESPACE_NAME;


TABLESPACENAME     Totle_size(MB) Free_space(MB) Used_space(MB) Used_percent% Max_size(MB) Max_percent%
------------------ -------------- -------------- -------------- ------------- ------------ ------------
USERS               20             15.94          4.06           20.31         20         20.31

STEP3：test01表插入大量数据，

SQL> exec p_insert_test01;
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL>
PL/SQL procedure successfully completed


SQL> /
PL/SQL procedure successfully completed


SQL> /
begin p_insert_test01; end;


ORA-01653: unable to extend table TEST.TEST01 by 128 in tablespace USERS
ORA-06512: at "TEST.P_INSERT_TEST01", line 6
ORA-06512: at line 1

STEP4：此时，表空间总共20MB，剩余0.94MB，

SQL> SELECT SUBSTR(a.TABLESPACE_NAME,1,30) TablespaceName,
2 round(SUM(a.bytes/1024/1024),2) AS "Totle_size(MB)",
3 round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Free_space(MB)",
4 round(SUM(a.bytes/1024/1024),2)-round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Used_space(MB)",
5 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0))) *100/SUM(a.bytes/1024/1024),2) AS "Used_percent%",
6 round(SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_size(MB)",
7 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0)))*100/SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_percent%"
8 FROM dba_data_files a,
9 (SELECT SUM(NVL(bytes,0)) free_space1,
10 file_id
11 FROM dba_free_space
12 GROUP BY file_id
13 ) b
14 WHERE a.file_id = b.file_id(+)
15 AND a.TABLESPACE_NAME = 'USERS'
16 GROUP BY a.TABLESPACE_NAME;


TABLESPACENAME    Totle_size(MB) Free_space(MB) Used_space(MB) Used_percent% Max_size(MB) Max_percent%
----------------- -------------- -------------- -------------- ------------- ------------ ------------
USERS              20             0.94           19.06          95.31         20         95.31

STEP5：此时test01表有90000行数据，

SQL> select count(*) from test01;
  COUNT(*)
----------
90000


SQL> SELECT MIN(col1),MAX(col1) FROM test01;
MIN(COL1)  MAX(COL1)
---------- ----------
109751 199750

STEP6：对test01执行truncate，

SQL> truncate table test01;
Table truncated

STEP7：执行truncate后，空间已经释放，

SQL> SELECT SUBSTR(a.TABLESPACE_NAME,1,30) TablespaceName,
2 round(SUM(a.bytes/1024/1024),2) AS "Totle_size(MB)",
3 round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Free_space(MB)",
4 round(SUM(a.bytes/1024/1024),2)-round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Used_space(MB)",
5 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0))) *100/SUM(a.bytes/1024/1024),2) AS "Used_percent%",
6 round(SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_size(MB)",
7 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0)))*100/SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_percent%"
8 FROM dba_data_files a,
9 (SELECT SUM(NVL(bytes,0)) free_space1,
10 file_id
11 FROM dba_free_space
12 GROUP BY file_id
13 ) b
14 WHERE a.file_id = b.file_id(+)
15 AND a.TABLESPACE_NAME = 'USERS'
16 GROUP BY a.TABLESPACE_NAME;


TABLESPACENAME    Totle_size(MB) Free_space(MB) Used_space(MB) Used_percent% Max_size(MB) Max_percent%
----------------- -------------- -------------- -------------- ------------- ------------ ------------
USERS              20             15.88          4.12           20.63         20         20.63

STEP8：创建表test02，用来覆盖test01释放的空间，

SQL> create table test02 as select * from dba_objects;
Table created

STEP9：test02表创建之后，剩余空间为5.88MB，可以说明：test02表的数据占用了test01表释放出来的空间，即test01表的部分数据已经被覆盖。

SQL> SELECT SUBSTR(a.TABLESPACE_NAME,1,30) TablespaceName,
2 round(SUM(a.bytes/1024/1024),2) AS "Totle_size(MB)",
3 round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Free_space(MB)",
4 round(SUM(a.bytes/1024/1024),2)-round(SUM(NVL(b.free_space1/1024/1024,0)),2) AS "Used_space(MB)",
5 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0))) *100/SUM(a.bytes/1024/1024),2) AS "Used_percent%",
6 round(SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_size(MB)",
7 ROUND((SUM(a.bytes/1024/1024)-SUM(NVL(b.free_space1/1024/1024,0)))*100/SUM((case when a.MAXBYTES = 0 then a.bytes else a.MAXBYTES end)/1024/1024),2) AS "Max_percent%"
8 FROM dba_data_files a,
9 (SELECT SUM(NVL(bytes,0)) free_space1,
10 file_id
11 FROM dba_free_space
12 GROUP BY file_id
13 ) b
14 WHERE a.file_id = b.file_id(+)
15 AND a.TABLESPACE_NAME = 'USERS'
16 GROUP BY a.TABLESPACE_NAME;


TABLESPACENAME   Totle_size(MB) Free_space(MB) Used_space(MB) Used_percent% Max_size(MB) Max_percent%
---------------- -------------- -------------- -------------- ------------- ------------ ------------
USERS             20             5.88           14.12          70.63         20         70.63

STEP10：执行恢复操作，

[oracle@source-node ~]$ sqlplus / as sysdba
SQL*Plus: Release 11.2.0.4.0 Production on Tue Apr 21 15:09:58 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.
Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options


SQL> set time on
15:10:05 SQL> set serveroutput on
15:10:10 SQL> exec fy_recover_data.recover_truncated_table('LIJIAMAN','TEST01');
15:10:17: Use existing Directory Name: FY_DATA_DIR
15:10:17: Recover Table: LIJIAMAN.TEST01$
15:10:17: Restore Table: LIJIAMAN.TEST01$$
15:10:22: Copy file of Recover Tablespace: FY_REC_DATA_COPY.DAT1
15:10:22: begin to recover table LIJIAMAN.TEST01
15:10:22: Use existing Directory Name: TMP_HF_DIR
15:10:22: Recovering data in datafile
/u01/app/oracle/oradata/testdb1/users01.dbf
15:10:22: Use existing Directory Name: TMP_HF_DIR
15:10:31: 645 truncated data blocks found.
15:10:31: 24439 records recovered in backup table LIJIAMAN.TEST01$$
15:10:31: Total: 645 truncated data blocks found.
15:10:31: Total: 24439 records recovered in backup table LIJIAMAN.TEST01$$
15:10:31: Recovery completed.
15:10:31: Data has been recovered to LIJIAMAN.TEST01$$


PL/SQL procedure successfully completed.

STEP11：发现只恢复了部分数据，不符合要求，

-- truncate之前test01表有90000行数据，恢复了24339行数据
SQL> select count(*) from test01$$;
  COUNT(*)
----------
24439


SQL> SELECT MIN(col1),MAX(col1) FROM test01$$;
MIN(COL1)  MAX(COL1)
---------- ----------
109751 199750

因此，使用工具fy_recover_data进行数据恢复，需要确认，

（1）truncate之后，需要保证没有新的数据进入表中，否则无法还原；

（2）存放该表的数据文件块不能被覆盖，否则无法完整还原数据。

在发生故障后，可以迅速使用，

SQL> alter tablespace users read only;
SQL> alter tablespace users read write;

来关闭/开启表空间的写功能，这样可以保证数据文件不会被覆写。

参考，https://www.modb.pro/db/32403?utm_source=index_aihttps://www.cnblogs.com/lijiaman/p/12747658.html

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