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