【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 |