【MySQL】MySQL一主二从复制环境切换主从库

假设有一个一主二从的环境，当主库M出现故障时，需要将其中一个从库S1切换为主库，同时将S2指向新的主库S1，如果可能，需要将故障的主库M修复并重置为新的从库。

搭建一主二从复制环境可参考：MySQL搭建主从复制环境。

下面将演示一主二从复制环境主从库的切换，具体如下：

1、环境信息；

Mater：192.168.1.110
Slave1：192.168.1.111
Slave2：192.168.1.112

2、查看主备库状态；

Master库：

mysql> show processlist;
+----+------+---------------------+------+-------------+------+---------------------------------------------------------------+------------------+
| Id | User | Host                | db   | Command     | Time | State                                                         | Info             |
+----+------+---------------------+------+-------------+------+---------------------------------------------------------------+------------------+
|  2 | root | localhost           | NULL | Query       |    0 | starting                                                      | show processlist |
|  3 | repl | 192.168.1.112:49819 | NULL | Binlog Dump |  207 | Master has sent all binlog to slave; waiting for more updates | NULL             |
|  4 | repl | 192.168.1.111:53017 | NULL | Binlog Dump |  165 | Master has sent all binlog to slave; waiting for more updates | NULL             |
+----+------+---------------------+------+-------------+------+---------------------------------------------------------------+------------------+
3 rows in set (0.00 sec)

mysql> use test;
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> select *from t_repl;
+------+-------+---------------------+
| id   | name  | cdate               |
+------+-------+---------------------+
|    1 | Alen  | 2018-03-04 17:56:57 |
|    2 | Repl  | 2018-03-04 20:10:45 |
|    3 | USA   | 2018-03-04 22:19:48 |
|    4 | China | 2018-03-04 22:19:48 |
|    5 | Japan | 2018-03-04 22:23:28 |
|    6 | UK    | 2018-03-04 22:23:28 |
+------+-------+---------------------+
6 rows in set (0.00 sec)

mysql> insert into t_repl(id,name) values(7,'Jacky'),(8,'Tom');
Query OK, 2 rows affected (0.03 sec)
Records: 2  Duplicates: 0  Warnings: 0

mysql> 

Slave1库：

mysql> show processlist;
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
| Id | User        | Host      | db   | Command | Time | State                                                  | Info             |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
|  1 | system user |           | NULL | Connect |  299 | Waiting for master to send event                       | NULL             |
|  2 | system user |           | NULL | Connect |  173 | Slave has read all relay log; waiting for more updates | NULL             |
|  4 | root        | localhost | NULL | Query   |    0 | starting                                               | show processlist |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
3 rows in set (0.00 sec)

mysql> use test;
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> select *from t_repl;
+------+-------+---------------------+
| id   | name  | cdate               |
+------+-------+---------------------+
|    1 | Alen  | 2018-03-04 17:56:57 |
|    2 | Repl  | 2018-03-04 20:10:45 |
|    3 | USA   | 2018-03-04 22:19:48 |
|    4 | China | 2018-03-04 22:19:48 |
|    5 | Japan | 2018-03-04 22:23:28 |
|    6 | UK    | 2018-03-04 22:23:28 |
|    7 | Jacky | 2018-03-05 18:55:32 |
|    8 | Tom   | 2018-03-05 18:55:32 |
+------+-------+---------------------+
8 rows in set (0.00 sec)

mysql> 

Slave2库：

mysql> show processlist;
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
| Id | User        | Host      | db   | Command | Time | State                                                  | Info             |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
|  1 | system user |           | NULL | Connect |  356 | Waiting for master to send event                       | NULL             |
|  2 | system user |           | NULL | Connect |  291 | Slave has read all relay log; waiting for more updates | NULL             |
|  4 | root        | localhost | test | Query   |    0 | starting                                               | show processlist |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
3 rows in set (0.00 sec)

mysql> select *from t_repl;
+------+-------+---------------------+
| id   | name  | cdate               |
+------+-------+---------------------+
|    1 | Alen  | 2018-03-04 17:56:57 |
|    2 | Repl  | 2018-03-04 20:10:45 |
|    3 | USA   | 2018-03-04 22:19:48 |
|    4 | China | 2018-03-04 22:19:48 |
|    5 | Japan | 2018-03-04 22:23:28 |
|    6 | UK    | 2018-03-04 22:23:28 |
|    7 | Jacky | 2018-03-05 18:55:32 |
|    8 | Tom   | 2018-03-05 18:55:32 |
+------+-------+---------------------+
8 rows in set (0.00 sec)

mysql> 

3、模拟主库Master宕机；

mysql> shutdown;
Query OK, 0 rows affected (0.01 sec)

mysql> system service mysql.server status;
 ERROR! MySQL is not running, but lock file (/var/lock/subsys/mysql) exists
mysql> 

4、确保从库都执行了relay log的全部更新，在每个从库上执行stop slave io_thread，然后检查show processlist的输出，状态是Slave has read all relay log; waiting for more updates，表示更新都执行完毕；

mysql> stop slave io_thread;
Query OK, 0 rows affected (0.01 sec)

mysql> show processlist;
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
| Id | User        | Host      | db   | Command | Time | State                                                  | Info             |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
|  2 | system user |           | NULL | Connect | 7500 | Slave has read all relay log; waiting for more updates | NULL             |
|  4 | root        | localhost | test | Query   |    0 | starting                                               | show processlist |
+----+-------------+-----------+------+---------+------+--------------------------------------------------------+------------------+
2 rows in set (0.00 sec)

5、在从库Slave1上，执行stop slave来停止从服务，然后执行reset master重置成主库；

mysql> show master status;
Empty set (0.00 sec)

mysql> stop slave;
Query OK, 0 rows affected (0.00 sec)

mysql> reset master;
Query OK, 0 rows affected (0.00 sec)

6、检查从库Slave1的log-bin是否打开，没打开则打开；

7、删除从库Slave1上的master.info和relay-log.info，否则下次重启则按照从库启动；

8、在Slave2上，执行stop slave停止从库服务，然后执行change master to重新指向主库slave1，再执行start slave启动从库；

mysql> stop slave;
Query OK, 0 rows affected (0.01 sec)

mysql> change master to 
    -> master_host='192.168.1.111';
Query OK, 0 rows affected (0.02 sec)

mysql> start slave;
Query OK, 0 rows affected (0.02 sec)

mysql> 

9、检查Slave2的状态，发现已经指向新的主库Slave1；

mysql> show slave statusG;
*************************** 1. row ***************************
               Slave_IO_State: Waiting for master to send event
                  Master_Host: 192.168.1.111
                  Master_User: repl
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql111-bin.000002
          Read_Master_Log_Pos: 154
               Relay_Log_File: mysql-relay-bin.000003
                Relay_Log_Pos: 373
        Relay_Master_Log_File: mysql111-bin.000002
             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: 154
              Relay_Log_Space: 799
              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: 111
                  Master_UUID: c8368e4a-1fa4-11e8-aa25-000c299f40a9
             Master_Info_File: /usr/local/mysql-5.7.21-linux-glibc2.12-x86_64/data/master.info
                    SQL_Delay: 0
          SQL_Remaining_Delay: NULL
      Slave_SQL_Running_State: Slave has read all relay log; waiting for more updates
           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
         Replicate_Rewrite_DB: 
                 Channel_Name: 
           Master_TLS_Version: 
1 row in set (0.00 sec)

ERROR: 
No query specified

10、将应用程序指向新的主库Slave1，这样Slave1的所有更新写入到Slave1的Binlog中，从而同步到新的从库Slave2中；

新的主库Slave1：

mysql> use test;
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> select *from t_repl;
+------+-------+---------------------+
| id   | name  | cdate               |
+------+-------+---------------------+
|    1 | Alen  | 2018-03-04 17:56:57 |
|    2 | Repl  | 2018-03-04 20:10:45 |
|    3 | USA   | 2018-03-04 22:19:48 |
|    4 | China | 2018-03-04 22:19:48 |
|    5 | Japan | 2018-03-04 22:23:28 |
|    6 | UK    | 2018-03-04 22:23:28 |
|    7 | Jacky | 2018-03-05 18:55:32 |
|    8 | Tom   | 2018-03-05 18:55:32 |
+------+-------+---------------------+
8 rows in set (0.00 sec)

mysql> insert into t_repl(id,name) values(9,'Slave1-->Master');
Query OK, 1 row affected (0.01 sec)

mysql> 

新的从库Slave2：

mysql> use test ;
Database changed
mysql> select *from t_repl;
+------+-----------------+---------------------+
| id   | name            | cdate               |
+------+-----------------+---------------------+
|    1 | Alen            | 2018-03-04 17:56:57 |
|    2 | Repl            | 2018-03-04 20:10:45 |
|    3 | USA             | 2018-03-04 22:19:48 |
|    4 | China           | 2018-03-04 22:19:48 |
|    5 | Japan           | 2018-03-04 22:23:28 |
|    6 | UK              | 2018-03-04 22:23:28 |
|    7 | Jacky           | 2018-03-05 18:55:32 |
|    8 | Tom             | 2018-03-05 18:55:32 |
|    9 | Slave1-->Master | 2018-03-05 21:28:54 |
+------+-----------------+---------------------+
9 rows in set (0.00 sec)

11、最后，如果主库Master修复，则将其重新配置成Slave1的从库；