MYSQL主从复制排错案例一：
问题：主从无法同步
现象：MASTER: mysql> show master status;
Empty set (0.00 sec)
SLAVE: mysql> show slave status \G;
Slave_IO_Running: Connecting
Slave_SQL_Running: Yes
Seconds_Behind_Master: NULL
Last_IO_Errno: 1045
Last_IO_Error: error connecting to master ‘[email protected]:3306‘
- retry-time: 60 retries: 86400
问题排查过程：
一 、 MASTER :[[email protected] ~]# egrep "log-bin|server" /etc/my.cnf
# The MySQL server
server-id = 1
#log-bin=mysql-bin //没有开启
SLAVE: [[email protected] ~]# egrep "log-bin|server" /etc/my.cnf
# The MySQL server
server-id = 3
#log-bin=mysql-bin
二、.开启MASTART log-bin日志，重新启动mysql数据库
MASTER: mysql> show master status;
mysql> show master status;
+------------------+----------+--------------+------------------+
| File | Position | Binlog_Do_DB | Binlog_Ignore_DB |
+------------------+----------+--------------+------------------+
| mysql-bin.000001 | 107 | | |
+------------------+----------+--------------+------------------+
SLAVE: mysql> show slave status \G;
Slave_IO_Running: Connecting
Slave_SQL_Running: Yes
三、查看master.info 和relay-log.info信息
SLAVE: [[email protected] data]# cat master.info
18
mysql-bin.000001
348
192.168.254.253
rep
oldboy123
3306
60
0
[[email protected] data]# cat relay-log.info
./localhost-relay-bin.000005
4
mysql-bin.000001
348
8
MASTER上的log-bin的POS点107，SLAVE上的log-bin的POS点348,两边不一致。
四、. 在master.info中用户名为rep,在MASTER端没有找到该用户注册的信息。
mysql> select host,user from mysql.user;
五、.重新注册用于同步的用户
grant replication slave on *.* to ‘rep‘@‘192.168.254.250‘ identified by ‘oldboy123‘;
六、 在SLAVE重新注册CHANGE MASTER TO
mysql> CHANGE MASTER TO
-> MASTER_HOST=‘192.168.254.253‘,
-> MASTER_PORT=3306,
-> MASTER_USER=‘rep‘,
-> MASTER_PASSWORD=‘oldboy123‘,
-> MASTER_LOG_FILE=‘mysql-bin.000002‘,
-> MASTER_LOG_POS=107;
mysql> start slave;
七、.mysql> show slave status \G;
Slave_IO_Running: Yes
Slave_SQL_Running: Yes
八、.测试：MASTER: mysql> create database mama;
Query OK, 1 row affected (0.00 sec)
SLAVE: mysql> show databases;
mama
问题：由于虚拟机测试环境，没有把MASTER数据库变为只读，备份主库。直接同步到从库，这样后果丢失数据。在出现问题之前创建新的数据库没有同步过来。 生产环境下要先备份主库。