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mysql只读模式的设置方法与实验 – yumushui的专栏 – CSDN博客
http://blog.csdn.net/yumushui/article/details/41645469
在MySQL数据库中，在进行数据迁移和从库只读状态设置时，都会涉及到只读状态和Master-slave的设置和关系。
经过实际测试，对于mysql单实例数据库和master库，如果需要设置为只读状态，需要进行如下操作和设置：
将MySQL设置为只读状态的命令：
# mysql -uroot -p
mysql> show global variables like "%read_only%";
mysql> flush tables with read lock;
mysql> set global read_only=;
mysql> show global variables like "%read_only%";
将MySQL从只读设置为读写状态的命令：
mysql> unlock tables;
mysql> set global read_only=;
对于需要保证master-slave主从同步的salve库，如果要设置为只读状态，需要执行的命令为：
mysql> set global read_only=;
将salve库从只读状态变为读写状态，需要执行的命令是：
mysql> set global read_only=;
对于数据库读写状态，主要靠 “read_only”全局参数来设定；默认情况下，数据库是用于读写操作的，所以read_only参数也是0或faluse状态，这时候不论是本地用户还是远程访问数据库的用户，都可以进行读写操作；如需设置为只读状态，将该read_only参数设置为1或TRUE状态，但设置 read_only=1 状态有两个需要注意的地方：
1.read_only=1只读模式，不会影响slave同步复制的功能，所以在MySQL slave库中设定了read_only=1后，通过 show slave status\G 命令查看salve状态，可以看到salve仍然会读取master上的日志，并且在slave库中应用日志，保证主从数据库同步一致；
2.read_only=1只读模式，可以限定普通用户进行数据修改的操作，但不会限定具有super权限的用户的数据修改操作；在MySQL中设置read_only=1后，普通的应用用户进行insert、update、delete等会产生数据变化的DML操作时，都会报出数据库处于只读模式不能发生数据变化的错误，但具有super权限的用户，例如在本地或远程通过root用户登录到数据库，还是可以进行数据变化的DML操作；
为了确保所有用户，包括具有super权限的用户也不能进行读写操作，就需要执行给所有的表加读锁的命令 “flush tables with read lock;”，这样使用具有super权限的用户登录数据库，想要发生数据变化的操作时，也会提示表被锁定不能修改的报错。
这样通过 设置“read_only=1”和“flush tables with read lock;”两条命令，就可以确保数据库处于只读模式，不会发生任何数据改变，在MySQL进行数据库迁移时，限定master主库不能有任何数据变化，就可以通过这种方式来设定。
但同时由于加表锁的命令对数据库表限定非常严格，如果再slave从库上执行这个命令后，slave库可以从master读取binlog日志，但不能够应用日志，slave库不能发生数据改变，当然也不能够实现主从同步了，这时如果使用 “unlock tables;”解除全局的表读锁，slave就会应用从master读取到的binlog日志，继续保证主从库数据库一致同步。所以从库slave不要使用 “flush tables with read lock;” 否则无法写入数据同步。
为了保证主从同步可以一直进行，在slave库上要保证具有super权限的root等用户只能在本地登录，不会发生数据变化，其他远程连接的应用用户只按需分配为select,insert,update,delete等权限，保证没有super权限，则只需要将salve设定“read_only=1”模式，即可保证主从同步，又可以实现从库只读。
相对的，设定“read_only=1”只读模式开启的解锁命令为设定“read_only=0”;设定全局锁“flush tables with read lock;”，对应的解锁模式命令为：“unlock tables;”.
当然设定了read_only=1后，所有的select查询操作都是可以正常进行的。
实验一：设置了read_only=1后，远程业务用户进行数据库修改会提示ERROR 1290错误
(test01@172.32.1.200) [data03]> show tables;
+------------------+
| Tables_in_data03 |
+------------------+
| t01 |
| t02 |
| user |
+------------------+
rows in set (0.00 sec)(test01@172.32.1.200) [data03]>
(test01@172.32.1.200) [data03]>
(test01@172.32.1.200) [data03]> show global variables like "%read_only%";
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| innodb_read_only | OFF |
| read_only | ON |
| tx_read_only | OFF |
+------------------+-------+
rows in set (0.00 sec)(test01@172.32.1.200) [data03]>
(test01@172.32.1.200) [data03]>
(test01@172.32.1.200) [data03]> delete from t01 where id1=;
<span style="color:#ff0000;">ERROR (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement</span>
(test01@172.32.1.200) [data03]> update t01 set id1=id1+ where id1=;
ERROR (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement
(test01@172.32.1.200) [data03]> insert into t01(id1,a1,b1) values(,,);
ERROR (HY000): The MySQL server is running with the --read-only option so it cannot execute this statement
(test01@172.32.1.200) [data03]>
(test01@172.32.1.200) [data03]> select * from t01;
+-----+------+------+
| id1 | a1 | b1 |
+-----+------+------+
| | | |
| | | |
| | | |
| | | |
| | | |
+-----+------+------+
rows in set (0.00 sec)(test01@172.32.1.200) [data03]>
实验二：设定了全局读写后，具有super权限的用户进行数据修改后，也会提示错误ERROR 1223：
mysql> use data03;
Reading table information for completion of table and column names
You can turn off this feature to get a quicker startup with -ADatabase changed
mysql> show tables;
+------------------+
| Tables_in_data03 |
+------------------+
| t01 |
| t02 |
| user |
+------------------+
rows in set (0.00 sec)mysql> select * from t01;
+-----+------+------+
| id1 | a1 | b1 |
+-----+------+------+
| | | |
| | | |
| | | |
| | | |
| | | |
+-----+------+------+
rows in set (0.00 sec)mysql>
mysql> show global variables like "%read_only%";
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| innodb_read_only | OFF |
| read_only | ON |
| tx_read_only | OFF |
+------------------+-------+
rows in set (0.00 sec)mysql>
mysql>
mysql> insert into t01(id1,a1,b1) values(,,);
Query OK, row affected (0.00 sec)mysql> update t01 set a1=a1+ where id1=;
Query OK, row affected (0.00 sec)
Rows matched: Changed: Warnings: mysql> delete from t01 where id1=;
Query OK, row affected (0.00 sec)mysql> select * from t01;
+-----+------+------+
| id1 | a1 | b1 |
+-----+------+------+
| | | |
| | | |
| | | |
| | | |
| | | |
+-----+------+------+
rows in set (0.00 sec)mysql>
mysql> flush tables with read lock;
Query OK, rows affected (0.00 sec)mysql>
mysql> insert into t01(id1,a1,b1) values(,,);
<span style="color:#ff0000;">ERROR (HY000): Can't execute the query because you have a conflicting read lock</span>
mysql>
mysql> update t01 set a1=a1+ where id1=;
ERROR (HY000): Can't execute the query because you have a conflicting read lock
mysql>
mysql> delete from t01 where id1=;
ERROR (HY000): Can't execute the query because you have a conflicting read lock
mysql>
mysql>
实验三：MySQL从库设定read_only=1后主从同步正常，设定表读锁后，不能同步，解除读锁后，主从同步恢复。
mysql>
mysql> show databases;
+--------------------+
| Database |
+--------------------+
| information_schema |
| bitvc |
| data03 |
| ga |
| jiradb |
| meibi |
| meibi02 |
| mysql |
| performance_schema |
| sbtest |
+--------------------+
rows in set (0.00 sec)mysql>
mysql>
mysql>
mysql> show global variables like "%read_only%";
+------------------+-------+
| Variable_name | Value |
+------------------+-------+
| innodb_read_only | OFF |
| read_only | ON |
| tx_read_only | OFF |
+------------------+-------+
rows in set (0.00 sec)mysql>
mysql> show slave status\G
*************************** . row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.32.1.200
Master_User: repl
Master_Port:
Connect_Retry:
Master_Log_File: mysql-bin.
Read_Master_Log_Pos:
Relay_Log_File: huobiDBtest-relay-bin.
Relay_Log_Pos:
Relay_Master_Log_File: mysql-bin.
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno:
Last_Error:
Skip_Counter:
Exec_Master_Log_Pos:
Relay_Log_Space:
Until_Condition: None
Until_Log_File:
Until_Log_Pos:
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master:
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno:
Last_IO_Error:
Last_SQL_Errno:
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id:
Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
Master_Info_File: /data/mysqldata//data/master.info
SQL_Delay:
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
Master_Retry_Count:
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position:
row in set (0.00 sec)mysql>
mysql> flush tables with read lock;
Query OK, rows affected (0.00 sec)mysql> show slave status\G
*************************** . row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.32.1.200
Master_User: repl
Master_Port:
Connect_Retry:
<span style="color:#ff0000;"> Master_Log_File: mysql-bin.
Read_Master_Log_Pos: </span>
Relay_Log_File: huobiDBtest-relay-bin.
Relay_Log_Pos:
Relay_Master_Log_File: mysql-bin.
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno:
Last_Error:
Skip_Counter:
<span style="color:#ff0000;"> Exec_Master_Log_Pos: </span>
Relay_Log_Space:
Until_Condition: None
Until_Log_File:
Until_Log_Pos:
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master:
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno:
Last_IO_Error:
Last_SQL_Errno:
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id:
Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
Master_Info_File: /data/mysqldata//data/master.info
SQL_Delay:
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Waiting for global read lock
Master_Retry_Count:
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position:
row in set (0.00 sec)mysql>
mysql>
mysql> select * from data03.t01;
+-----+------+------+
| id1 | a1 | b1 |
+-----+------+------+
| | | |
| | | |
| | | |
| | | |
| | | |
+-----+------+------+
rows in set (0.00 sec)mysql>
mysql> unlock tables;
Query OK, rows affected (0.00 sec)mysql> show slave status\G
*************************** . row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: 172.32.1.200
Master_User: repl
Master_Port:
Connect_Retry:
<span style="color:#ff0000;"> Master_Log_File: mysql-bin.
Read_Master_Log_Pos: </span>
Relay_Log_File: huobiDBtest-relay-bin.
Relay_Log_Pos:
Relay_Master_Log_File: mysql-bin.
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
Replicate_Do_DB:
Replicate_Ignore_DB:
Replicate_Do_Table:
Replicate_Ignore_Table:
Replicate_Wild_Do_Table:
Replicate_Wild_Ignore_Table:
Last_Errno:
Last_Error:
Skip_Counter:
<span style="color:#ff0000;"> Exec_Master_Log_Pos: </span>
Relay_Log_Space:
Until_Condition: None
Until_Log_File:
Until_Log_Pos:
Master_SSL_Allowed: No
Master_SSL_CA_File:
Master_SSL_CA_Path:
Master_SSL_Cert:
Master_SSL_Cipher:
Master_SSL_Key:
Seconds_Behind_Master:
Master_SSL_Verify_Server_Cert: No
Last_IO_Errno:
Last_IO_Error:
Last_SQL_Errno:
Last_SQL_Error:
Replicate_Ignore_Server_Ids:
Master_Server_Id:
Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
Master_Info_File: /data/mysqldata//data/master.info
SQL_Delay:
SQL_Remaining_Delay: NULL
Slave_SQL_Running_State: Slave has read all relay log; waiting for the slave I/O thread to update it
Master_Retry_Count:
Master_Bind:
Last_IO_Error_Timestamp:
Last_SQL_Error_Timestamp:
Master_SSL_Crl:
Master_SSL_Crlpath:
Retrieved_Gtid_Set:
Executed_Gtid_Set:
Auto_Position:
row in set (0.00 sec)mysql> select * from data03.t01;
+-----+------+------+
| id1 | a1 | b1 |
+-----+------+------+
| | | |
| | | |
| | | |
| | | |
| | | |
+-----+------+------+
rows in set (0.00 sec)
