mysql主从架构中其实就一个主在工作，而从就相当于一个备份机器，从通过日志监测的方式来备份主库上的数据而保证主库的数据安全。在这种架构中如果从上的数据做了改变，主数据是不会用任何变化的。因为mysql主从架构主要是mysql从监控mysql主的日志变化来实现同步，相反的在这个架构中主并没有监控从的日志变化。所以，mysql从数据反生变化，主也就没有什么变化了。
通过上述描述，可以看到如果想实现主主复制，无非就是在mysql主从架构上让mysql主实现监测从的日志变化，从而实现两台机器相互同步。(主从的架构前面有博文 http://www.linuxidc.com/Linux/2013-10/91682.htm )
实验环境：两台服务器：
主机名：HA1,HA2(呵呵,这个主机名是英文缩写High availability，高可用的意思)
ip:

192.168.1.231

192.168.1.232

主机系统：CentOS6.4
mysql版本5.5.22
首先，看下HA1（192.168.1.231）的mysql配置文件
vim /etc/my.cnf 
# Example MySQL config file for very large systems. 
# 
# This is for a large system with memory of 1G-2G where the system runs mainly 
# MySQL. 
# 
# MySQL programs look for option files in a set of 
# locations which depend on the deployment platform. 
# You can copy this option file to one of those 
# locations. For information about these locations, see: 
# http://dev.mysql.com/doc/mysql/en/option-files.html 
# 
# In this file, you can use all long options that a program supports. 
# If you want to know which options a program supports, run the program 
# with the "--help" option. 
# The following options will be passed to all MySQL clients 
[client] 
#password      = your_password 
port            = 3306
socket          = /usr/local/mysql/tmp/mysql.sock 
# Here follows entries for some specific programs 
# The MySQL server 
[mysqld] 
port            = 3306
socket          = /usr/local/mysql/tmp/mysql.sock 
skip-external-locking 
key_buffer_size = 384M
max_allowed_packet = 1M
table_open_cache = 512
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size = 8
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency 
thread_concurrency = 8
# Don't listen on a TCP/IP port at all. This can be a security enhancement, 
# if all processes that need to connect to mysqld run on the same host. 
# All interaction with mysqld must be made via Unix sockets or named pipes. 
# Note that using this option without enabling named pipes on Windows 
# (via the "enable-named-pipe" option) will render mysqld useless! 
# 
#skip-networking 
# Replication Master Server (default) 
# binary logging is required for replication 
log-bin=mysql-bin
log-slave-updates 
# required unique id between 1 and 2^32 - 1 
# defaults to 1 if master-host is not set 
# but will not function as a master if omitted 
server-id      = 1

在这个配置文件中，需要特别注意的三处地方：
log-bin=mysql-bin：这个选项基本默认都是开着的，如果没有打开，可以手动打开。
log-slave-updates：这个选项特别的重要它是为了让slave也能充当master，同时也为了更好的服务于 m-m + s 的环境，保证slave挂在任何一台master上都会接收到另一个master的写入信息。当然不局限于这个架构，级联复制的架构同样也需要log-slave-updates的支持。
server-id = 1：这个ID为服务器ID如果配置一样会出现冲突，而不能复制
接着再看下HA2（192.168.1.232）的mysql配置文件
vim /etc/my.cnf 
# Example MySQL config file for very large systems. 
# 
# This is for a large system with memory of 1G-2G where the system runs mainly 
# MySQL. 
# 
# MySQL programs look for option files in a set of 
# locations which depend on the deployment platform. 
# You can copy this option file to one of those 
# locations. For information about these locations, see: 
# http://dev.mysql.com/doc/mysql/en/option-files.html 
# 
# In this file, you can use all long options that a program supports. 
# If you want to know which options a program supports, run the program 
# with the "--help" option. 
# The following options will be passed to all MySQL clients 
[client] 
#password      = your_password 
port            = 3306
socket          = /usr/local/mysql/tmp/mysql.sock 
# Here follows entries for some specific programs 
# The MySQL server 
[mysqld] 
port            = 3306
socket          = /usr/local/mysql/tmp/mysql.sock 
skip-external-locking 
key_buffer_size = 384M
max_allowed_packet = 1M
table_open_cache = 512
sort_buffer_size = 2M
read_buffer_size = 2M
read_rnd_buffer_size = 8M
myisam_sort_buffer_size = 64M
thread_cache_size = 8
query_cache_size = 32M
# Try number of CPU's*2 for thread_concurrency 
thread_concurrency = 8
# Don't listen on a TCP/IP port at all. This can be a security enhancement, 
# if all processes that need to connect to mysqld run on the same host. 
# All interaction with mysqld must be made via Unix sockets or named pipes. 
# Note that using this option without enabling named pipes on Windows 
# (via the "enable-named-pipe" option) will render mysqld useless! 
# 
#skip-networking 
# Replication Master Server (default) 
# binary logging is required for replication 
log-bin=mysql-bin
log-slave-updates 
# required unique id between 1 and 2^32 - 1 
# defaults to 1 if master-host is not set 
# but will not function as a master if omitted 
server-id      = 10
# Replication Slave (comment out master section to use this)

在HA2的mysql配置文件中，除了server-id不一样，其他几乎一模一样。配置文件写好后，我们把两台服务器上的mysql服务器启动起来。

首先，登录HA2（192.168.1.232）的mysql中，查看master状态
mysql> show master status; 
+------------------+----------+--------------+------------------+
| File            | Position | Binlog_Do_DB | Binlog_Ignore_DB | 
+------------------+----------+--------------+------------------+
| mysql-bin.000016 |      615 |              |                  | 
+------------------+----------+--------------+------------------+
1 row in set (0.00 sec) 
mysql>

然后，登录HA1（192.168.1.231）的msyql中，把HA2配置成自己的主，

在做这个之前先在两台机器的mysql中建立一个可以复制用的帐号：
mysql>grant all on *.* to duyunlong@'192.168.1.%' identified by '123456'; 
Query OK, 0 rows affected (0.01 sec) 
mysql>change master to master_host='192.168.1.232',master_user='duyunlong',master_password='123456',master_log_file='mysql-bin.000016',master_log_pos=615;

同上，查看HA1(192.168.1.231)master，然后登录HA2(192.168.1.232),把HA1(192.168.1.231)，配置成自己的主，然后分别在两台机器的mysql中，启动slave
启动后HA1状态
mysql> show slave status \G; 
*************************** 1. row ***************************
              Slave_IO_State: Waiting for master to send event 
                  Master_Host: 192.168.1.232
                  Master_User: duyunlong 
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000016
          Read_Master_Log_Pos: 615
              Relay_Log_File: HA1-relay-bin.000002
                Relay_Log_Pos: 346
        Relay_Master_Log_File: mysql-bin.000016
            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: 615
              Relay_Log_Space: 500
              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: 10
1 row in set (0.00 sec) 
ERROR: 
No query specified

可以看到 Slave_IO_Running: Yes
Slave_SQL_Running: Yes
然后在看HA2的状态：
mysql> show slave status \G; 
*************************** 1. row ***************************
              Slave_IO_State: Waiting for master to send event 
                  Master_Host: 192.168.1.231
                  Master_User: duyunlong 
                  Master_Port: 3306
                Connect_Retry: 60
              Master_Log_File: mysql-bin.000018
          Read_Master_Log_Pos: 552
              Relay_Log_File: HA2-relay-bin.000002
                Relay_Log_Pos: 441
        Relay_Master_Log_File: mysql-bin.000018
            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: 552
              Relay_Log_Space: 595
              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: 1
1 row in set (0.00 sec) 
ERROR: 
No query specified

可以看到Slave_IO_Running: Yes
Slave_SQL_Running: Yes
接下来，我们要测试，是不是已经可以主主复制了呢，首先登录HA1(192.168.1.231)的mysql中，建立一数据库，当然在测试前我们先看下，两台服务器中的mysql中有哪些数据
首先看下HA1(192.168.1.231)
[root@HA1 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.231 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+
[root@HA1 ~]#

再看下HA2（192.168.1.232）
[root@HA2 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.232 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+
[root@HA2 ~]#

可以看到，现在两台服务器上的mysql中数据是一样的，接下来在HA中建立一数据库“a”,再看结果
[root@HA1 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.231 -e 'create database a;' 
[root@HA1 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.231 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| a                  | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+
[root@HA1 ~]#

然后看下HA2（192.168.1.232）是不是会把刚建立的数据库“a”复制过来
[root@HA2 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.232 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| a                  | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+

可以看到，数据库“a”已经成功复制过来了，反过来我们在HA2（192.168.1.232）上建立一数据库“b”看是否HA1也可以复制过去
[root@HA2 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.232 -e 'create database b;' 
[root@HA2 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.232 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| a                  | 
| b                  | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+
[root@HA2 ~]#

然后登录HA1（192.168.1.231），查看是否复制成功
[root@HA1 ~]# mysql mysql -uduyunlong -p123456 -h192.168.1.231 -e 'show databases;' 
+--------------------+
| Database          | 
+--------------------+
| information_schema | 
| a                  | 
| b                  | 
| mysql              | 
| performance_schema | 
| test              | 
| wanghaipeng        | 
+--------------------+
[root@HA1 ~]#

在HA1（192.168.1.231）可以看到数据库“b”已经复制过来了。
那么到此，主主复制架构已经陈功！

本文转自 chengxuyonghu 51CTO博客，原文链接：http://blog.51cto.com/6226001001/1736944，如需转载请自行联系原作者