mysql只读模式的设置方法与实验_查看mysql当前是否只读

      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=1;
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=0;


      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=1;


     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=0;


     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。

       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             |
+------------------+
3 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   |
+------------------+-------+
3 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=3;
<span style="color:#ff0000;">ERROR 1290 (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+30 where id1=3;
ERROR 1290 (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(9,9,9);
ERROR 1290 (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   |
+-----+------+------+
|   1 |    1 |    1 |
|   2 |    2 |    2 |
|   4 |    4 |    4 |
|   5 |    5 |    5 |
|   6 |    6 |    6 |
+-----+------+------+
5 rows in set (0.00 sec)
 
(test01@172.32.1.200) [data03]> 

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 -A
 
Database changed
mysql> show tables;
+------------------+
| Tables_in_data03 |
+------------------+
| t01              |
| t02              |
| user             |
+------------------+
3 rows in set (0.00 sec)
 
mysql> select * from t01;
+-----+------+------+
| id1 | a1   | b1   |
+-----+------+------+
|   1 |    1 |    1 |
|   2 |    2 |    2 |
|   4 |    4 |    4 |
|   5 |    5 |    5 |
|   6 |    6 |    6 |
+-----+------+------+
5 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   |
+------------------+-------+
3 rows in set (0.00 sec)
 
mysql> 
mysql> 
mysql> insert into t01(id1,a1,b1) values(8,8,8);       
Query OK, 1 row affected (0.00 sec)
 
mysql> update t01 set a1=a1+10 where id1=2;
Query OK, 1 row affected (0.00 sec)
Rows matched: 1  Changed: 1  Warnings: 0
 
mysql> delete from t01 where id1=4;
Query OK, 1 row affected (0.00 sec)
 
mysql> select * from t01;
+-----+------+------+
| id1 | a1   | b1   |
+-----+------+------+
|   1 |    1 |    1 |
|   2 |   12 |    2 |
|   5 |    5 |    5 |
|   6 |    6 |    6 |
|   8 |    8 |    8 |
+-----+------+------+
5 rows in set (0.00 sec)
 
mysql> 
mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)
 
mysql> 
mysql> insert into t01(id1,a1,b1) values(9,9,9);
<span style="color:#ff0000;">ERROR 1223 (HY000): Can't execute the query because you have a conflicting read lock</span>
mysql> 
mysql> update t01 set a1=a1+10 where id1=5;
ERROR 1223 (HY000): Can't execute the query because you have a conflicting read lock
mysql> 
mysql> delete from t01 where id1=5;
ERROR 1223 (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             |
+--------------------+
10 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   |
+------------------+-------+
3 rows in set (0.00 sec)
 
mysql> 
mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 172.32.1.200
                  Master_User: repl
                  Master_Port: 3307
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000009
          Read_Master_Log_Pos: 5853
               Relay_Log_File: huobiDBtest-relay-bin.000002
                Relay_Log_Pos: 6016
        Relay_Master_Log_File: mysql-bin.000009
             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: 0
                   Last_Error: 
                 Skip_Counter: 0
          Exec_Master_Log_Pos: 5853
              Relay_Log_Space: 6195
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 2003307
                  Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
             Master_Info_File: /data/mysqldata/3308/data/master.info
                    SQL_Delay: 0
          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: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
1 row in set (0.00 sec)
 
mysql> 
mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 172.32.1.200
                  Master_User: repl
                  Master_Port: 3307
                Connect_Retry: 60
       <span style="color:#ff0000;">       Master_Log_File: mysql-bin.000009
          Read_Master_Log_Pos: 6531</span>
               Relay_Log_File: huobiDBtest-relay-bin.000002
                Relay_Log_Pos: 6016
        Relay_Master_Log_File: mysql-bin.000009
             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: 0
                   Last_Error: 
                 Skip_Counter: 0
        <span style="color:#ff0000;">  Exec_Master_Log_Pos: 5853</span>
              Relay_Log_Space: 6873
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 120
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 2003307
                  Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
             Master_Info_File: /data/mysqldata/3308/data/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Waiting for global read lock
           Master_Retry_Count: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
1 row in set (0.00 sec)
 
mysql> 
mysql> 
mysql> select * from data03.t01;
+-----+------+------+
| id1 | a1   | b1   |
+-----+------+------+
|   1 |    1 |    1 |
|   2 |    2 |    2 |
|   4 |    4 |    4 |
|   5 |    5 |    5 |
|   6 |    6 |    6 |
+-----+------+------+
5 rows in set (0.00 sec)
 
mysql> 
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)
 
mysql> show slave status\G
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 172.32.1.200
                  Master_User: repl
                  Master_Port: 3307
                Connect_Retry: 60
<span style="color:#ff0000;">              Master_Log_File: mysql-bin.000009
          Read_Master_Log_Pos: 6531</span>
               Relay_Log_File: huobiDBtest-relay-bin.000002
                Relay_Log_Pos: 6694
        Relay_Master_Log_File: mysql-bin.000009
             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: 0
                   Last_Error: 
                 Skip_Counter: 0
         <span style="color:#ff0000;"> Exec_Master_Log_Pos: 6531</span>
              Relay_Log_Space: 6873
              Until_Condition: None
               Until_Log_File: 
                Until_Log_Pos: 0
           Master_SSL_Allowed: No
           Master_SSL_CA_File: 
           Master_SSL_CA_Path: 
              Master_SSL_Cert: 
            Master_SSL_Cipher: 
               Master_SSL_Key: 
        Seconds_Behind_Master: 0
Master_SSL_Verify_Server_Cert: No
                Last_IO_Errno: 0
                Last_IO_Error: 
               Last_SQL_Errno: 0
               Last_SQL_Error: 
  Replicate_Ignore_Server_Ids: 
             Master_Server_Id: 2003307
                  Master_UUID: 6f68eea7-76e9-11e4-8f99-00221904cd5d
             Master_Info_File: /data/mysqldata/3308/data/master.info
                    SQL_Delay: 0
          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: 86400
                  Master_Bind: 
      Last_IO_Error_Timestamp: 
     Last_SQL_Error_Timestamp: 
               Master_SSL_Crl: 
           Master_SSL_Crlpath: 
           Retrieved_Gtid_Set: 
            Executed_Gtid_Set: 
                Auto_Position: 0
1 row in set (0.00 sec)
 
mysql> select * from data03.t01;
+-----+------+------+
| id1 | a1   | b1   |
+-----+------+------+
|   1 |    1 |    1 |
|   2 |   12 |    2 |
|   5 |    5 |    5 |
|   6 |    6 |    6 |
|   8 |    8 |    8 |
+-----+------+------+
5 rows in set (0.00 sec)