实现原理

主主复制即在两台MySQL主机内都可以变更数据，而且另外一台主机也会做出相应的变更。就是将两个主从复制有机合并起来就好了。只不过在配置的时候我们需要注意一些问题，例如，主键重复，server-id不能重复等等。

安装环境

server-1 IP：192.168.4.58
server-2 IP：192.168.4.88
操作系统CentOS6.8 应用程序MySQL 5.6.40

MySQL安装步骤

详细步骤请参考：
[MySQL5.6安装步骤]
(https://blog.51cto.com/437549/2114513)

配置步骤

1、修改配置文件
server-1（IP：192.168.4.58）
log-bin=mysql-bin #启用二进制日志
server-id=58 #任意自然是n，只要保证两台MySQl主机不重复就行
relay-log=relay-mysql #启用中继日志
relay-log-index=relay-mysql.index
auto-increment-increment=2 #步进值auto_imcrement 一般有n台主MySQL就填n
auto-increment-offset=1 #起始值。一般填第n台主MySQL。此时为第一台主MySQL

server-2（IP：192.168.4.88）
server-id=88
log-bin=mysql-bin
relay-log=relay-mysql
relay-log-index=relay-mysql.index
auto-increment-increment=2
auto-increment-offset=2

注：配置好后重启MySQL

2、在两台服务器上互相创建具有复制权限的用户
mysql> GRANT REPLICATION SLAVE ON . TO 'backup'@'192.168.4.88' IDENTIFIED BY '123456';
mysql> FLUSH PRIVILEGES;

3、如果此时两台服务器均为新建立，且无其它写入操作，各服务器只需记录当前自己二进制日志文件及事件位置，以之作为另外的服务器复制起始位置即可
查看server-1（192.168.4.58）二进制日志名和位置
mysql> show master status\G;
1. row
File: mysql-bin.000002
Position: 420
Binlog_Do_DB:
Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)

查看server-1（192.168.4.88）二进制日志名和位置
mysql> show master status\G;
1. row
File: mysql-bin.000002
Position: 420
Binlog_Do_DB:
Binlog_Ignore_DB:
Executed_Gtid_Set:
1 row in set (0.00 sec)

4、各服务器接下来指定对另一台服务器为自己的主服务器即可
告知二进制文件名及位置
服务器server-1（ 192.168.4.58）
mysql> change master to master_host='192.168.4.88',master_user='backup',master_password='123456',master_log_file='mysql-bin.000002',master_log_pos=420;
mysql> start slave; # 启动从服务器

服务器server-2（ 192.168.4.58）
mysql> change master to master_host='192.168.4.58',master_user='backup',master_password='123456',master_log_file='mysql-bin.000002',master_log_pos=420;
mysql> start slave; # 启动从服务器

5、查看主从复制是否成功：

服务器server-1（ 192.168.4.58）
mysql> show slave status\G;
1. row
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.4.88
Master_User: backup
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000002
Read_Master_Log_Pos: 420
Relay_Log_File: relay-mysql.000002
Relay_Log_Pos: 283
Relay_Master_Log_File: mysql-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: 420
Relay_Log_Space: 452
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: 88
Master_UUID: 7e7ddde3-4a3b-11e8-8195-000c29f5e0c1
Master_Info_File: /data/mysql/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

服务器server-2（ 192.168.4.58）
mysql> show slave status\G;
1. row
Slave_IO_State: Waiting for master to send event
Master_Host: 192.168.4.58
Master_User: backup
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000002
Read_Master_Log_Pos: 420
Relay_Log_File: relay-mysql.000002
Relay_Log_Pos: 283
Relay_Master_Log_File: mysql-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: 420
Relay_Log_Space: 452
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: 58
Master_UUID: 65930153-383f-11e8-8c4e-000c29138f00
Master_Info_File: /data/mysql/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
当看到Slave_IO_Running: YES；Slave_SQL_Running: YES才表明状态正常

测试结果

在server-1 192.168.4.58上创建
mysql> create database test_db;
mysql> use test_db;
mysql> CREATE TABLE test_tb(id INT UNSIGNED NOT NULL PRIMARY KEY AUTO_INCREMENT,name CHAR(30));

在server-2 192.168.4.58上查看结果：
mysql> show tables;
+-------------------+
| Tables_in_test_db |
+-------------------+
| test_tb |
+-------------------+
server-2 192.168.4.88 自动创建test_db数据库和 test_tb表，即主从复制成功。

再验证主主复制

在server-1 192.168.4.58插入数据：
mysql> INSERT INTO test_tb (name) VALUES ('11'),('22'),('33');
在server-2 192.168.4.88插入数据：
mysql> INSERT INTO test_tb (name) VALUES ('88'),('88'),('88');

分别查看两个服务器数据：
mysql> SELECT * FROM test_tb;
+----+------+
| id | name |
+----+------+
| 1 | 11 |
| 3 | 22 |
| 5 | 33 |
| 6 | 88 |
| 8 | 88 |
| 10 | 88 |
+----+------+