我们知道Oracle有DataGuard实时备份数据，可以做主备切换，而MySQL也有自己的一套备库方案，称之为主从复制。
搭建MySQL从库是为了实时同步主库数据，同时也可以分担主库的读压力，对数据库端做成读写分离结构。
搭建MySQL主从库注意点：
1.主库和从库的 server-id 一定不能相同。
2.在主库创建replication slave账户。
grant replication slave on *.* to ‘repl‘@‘192.168.0.232‘ identified ‘oracle‘;
3.查看主库master状态
mysql> show master status \G
*************************** 1. row ***************************
File: mysql-bin.000005
Position: 251651
Binlog_Do_DB:
Binlog_Ignore_DB:
1 row in set (0.00 sec)
4.配置从库
change master to
-> master_host=‘192.168.0.232‘,
-> master_user=‘repl‘,
-> master_password=‘oracle‘,
-> master_log_file=‘mysql-bin.000005‘,
-> master_log_pos=251651;
5. 启动从库
slave start
show slave status\G
*************************** 1. row ***************************
Slave_IO_State: Waiting for master to send event
Master_Host: ***********
Master_User: repl
Master_Port: 3306
Connect_Retry: 60
Master_Log_File: mysql-bin.000005
Read_Master_Log_Pos: 463725968
Relay_Log_File: mysql-relay-bin.000006
Relay_Log_Pos: 463726114
Relay_Master_Log_File: mysql-bin.000005
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: 463725968
Relay_Log_Space: 873569451
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: 100
注意：
如果从库Slave_IO_Running: No/ Slave_SQL_Running: No
关闭slave
设置set GLOBALSQL_SLAVE_SKIP_COUNTER=1;
在开启slave