以前抽空做的MYSQL 的主主同步。
不过心理做好准备，对性能会有一定的影响！
把步骤写下来，至于会出现的什么问题，以后随时更新。这里我同步的数据库是TEST
1、环境描述。
主机：192.168.0.231（A）
主机：192.168.0.232（B）
MYSQL 版本为5.1.21
2、授权用户。
A：
mysql> grant replication slave,file on *.* to 'repl1'@'192.168.0.232' identified
by '123456';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
B：
mysql> grant replication slave,file on *.* to 'repl2'@'192.168.0.231' identified
by '123456';
Query OK, 0 rows affected (0.00 sec)
mysql> flush privileges;
Query OK, 0 rows affected (0.00 sec)
然后都停止MYSQL 服务器。
3、配置文件。
在两个机器上的my.cnf里面都开启二进制日志 。
A：
user = mysql
log-bin=mysql-bin
server-id = 1
binlog-do-db=test
binlog-ignore-db=mysql
replicate-do-db=test
replicate-ignore-db=mysql
log-slave-updates
slave-skip-errors=all
sync_binlog=1
auto_increment_increment=2
auto_increment_offset=1
B：
user = mysql
log-bin=mysql-bin
server-id = 2
binlog-do-db=test
binlog-ignore-db=mysql
replicate-do-db=test
replicate-ignore-db=mysql
log-slave-updates
slave-skip-errors=all
sync_binlog=1
auto_increment_increment=2
auto_increment_offset=2
至于这些参数的说明具体看手册。
红色的部分非常重要，如果一个MASTER 挂掉的话，另外一个马上接管。
紫红色的部分指的是服务器频繁的刷新日志。这个保证了在其中一台挂掉的话，日志刷新到另外一台。从而保证了数据的同步 。
4、重新启动MYSQL服务器。
在A和B上执行相同的步骤
[root@localhost ~]# /usr/local/mysql/bin/mysqld_safe &
[1] 4264
[root@localhost ~]# 071213 14:53:20 mysqld_safe Logging to '/usr/local/mysql/data/localhost.localdomain.err'.
/usr/local/mysql/bin/mysqld_safe: line 366: [: -eq: unary operator expected
071213 14:53:20 mysqld_safe Starting mysqld daemon with databases from /usr/local/mysql/data
5、进入MYSQL的SHELL。
A：
mysql> flush tables with read lock/G
Query OK, 0 rows affected (0.00 sec)
mysql> show master status/G
*************************** 1. row ***************************
File: mysql-bin.000007
Position: 528
Binlog_Do_DB: test
Binlog_Ignore_DB: mysql
1 row in set (0.00 sec)
B：
mysql> flush tables with read lock;
Query OK, 0 rows affected (0.00 sec)
mysql> show master status/G
*************************** 1. row ***************************
File: mysql-bin.000004
Position: 595
Binlog_Do_DB: test
Binlog_Ignore_DB: mysql
1 row in set (0.00 sec)
然后备份自己的数据，保持两个机器的数据一致。
方法很多。完了后看下一步。
6、在各自机器上执行CHANGE MASTER TO命令。
A：
mysql> change master to
-> master_host='192.168.0.232',
-> master_user='repl2',
-> master_password='123456',
-> master_log_file='mysql-bin.000004',
-> master_log_pos=595;
Query OK, 0 rows affected (0.01 sec)
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
B：
mysql> change master to
-> master_host='192.168.0.231',
-> master_user='repl1',
-> master_password='123456',
-> master_log_file='mysql-bin.000007',
-> master_log_pos=528;
Query OK, 0 rows affected (0.01 sec)
mysql> start slave;
Query OK, 0 rows affected (0.00 sec)
7、查看各自机器上的IO进程和 SLAVE进程是否都开启。
A：
mysql> show processlist/G
*************************** 1. row ***************************
Id: 2
User: repl
Host: 192.168.0.232:54475
db: NULL
Command: Binlog Dump
Time: 1590
State: Has sent all binlog to slave; waiting for binlog to be updated
Info: NULL
*************************** 2. row ***************************
Id: 3
User: system user
Host:
db: NULL
Command: Connect
Time: 1350
State: Waiting for master to send event
Info: NULL
*************************** 3. row ***************************
Id: 4
User: system user
Host:
db: NULL
Command: Connect
Time: 1149
State: Has read all relay log; waiting for the slave I/O thread to update it
Info: NULL
*************************** 4. row ***************************
Id: 5
User: root
Host: localhost
db: test
Command: Query
Time: 0
State: NULL
Info: show processlist
4 rows in set (0.00 sec)
B：
mysql> show processlist/G
*************************** 1. row ***************************
Id: 1
User: system user
Host:
db: NULL
Command: Connect
Time: 2130
State: Waiting for master to send event
Info: NULL
*************************** 2. row ***************************
Id: 2
User: system user
Host:
db: NULL
Command: Connect
Time: 1223
State: Has read all relay log; waiting for the slave I/O thread to update it
Info: NULL
*************************** 3. row ***************************
Id: 4
User: root
Host: localhost
db: test
Command: Query
Time: 0
State: NULL
Info: show processlist
*************************** 4. row ***************************
Id: 5
User: repl2
Host: 192.168.0.231:50718
db: NULL
Command: Binlog Dump
Time: 1398
State: Has sent all binlog to slave; waiting for binlog to be updated
Info: NULL
4 rows in set (0.00 sec)
如果红色部分没有出现，检查DATA目录下的错误文件。
8、释放掉各自的锁，然后进行插数据测试。
mysql> unlock tables;
Query OK, 0 rows affected (0.00 sec)
插入之前两个机器表的对比：
A：
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t11_innodb |
| t22 |
+----------------+
B：
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t11_innodb |
| t22 |
+----------------+
从A机器上进行插入
A：
mysql> create table t11_replicas
-> (id int not null auto_increment primary key,
-> str varchar(255) not null) engine myisam;
Query OK, 0 rows affected (0.01 sec)
mysql> insert into t11_replicas(str) values
-> ('This is a master to master test table');
Query OK, 1 row affected (0.01 sec)
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t11_innodb |
| t11_replicas |
| t22 |
+----------------+
3 rows in set (0.00 sec)
mysql> select * from t11_replicas;
+----+---------------------------------------+
| id | str |
+----+---------------------------------------+
| 1 | This is a master to master test table |
+----+---------------------------------------+
1 row in set (0.00 sec)
现在来看B机器：
mysql> show tables;
+----------------+
| Tables_in_test |
+----------------+
| t11_innodb |
| t11_replicas |
| t22 |
+----------------+
3 rows in set (0.00 sec)
mysql> select * from t11_replicas;
+----+---------------------------------------+
| id | str |
+----+---------------------------------------+
| 1 | This is a master to master test table |
+----+---------------------------------------+
1 row in set (0.00 sec)
现在反过来从B机器上插入数据：
B：
mysql> insert into t11_replicas(str) values('This is a test 2');
Query OK, 1 row affected (0.00 sec)
mysql> select * from t11_replicas;
+----+---------------------------------------+
| id | str |
+----+---------------------------------------+
| 1 | This is a master to master test table |
| 2 | This is a test 2 |
+----+---------------------------------------+
2 rows in set (0.00 sec)
我们来看A
A：
mysql> select * from t11_replicas;
+----+---------------------------------------+
| id | str |
+----+---------------------------------------+
| 1 | This is a master to master test table |
| 2 | This is a test 2 |
+----+---------------------------------------+
2 rows in set (0.00 sec)
好了。现在两个表互相为MASTER。
多MASTER自增字段冲突的问题。
具体文章见：
http://dev.mysql.com/tech-resources/articles/advanced-mysql-replication.html
在邮件列表中看到有人讨论在线同步与忽略库与表的问题，具体看：
http://dev.mysql.com/doc/refman/5.1/en/replication-rules.html