为什么，会有mysql的主主复制。因为在一些高可用的环境中，mysql的主从不能满足现实中的一些实际需求。比如，一些流量大的网站数据库访问有了瓶颈，需要负载均衡的时候就用两个或者多个的mysql服务器，而这些mysql服务器的数据库数据必须要保持一致，那么就会用到主主复制。
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://duyunlong.blog.51cto.com/1054716/1102237)
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！
