最近MySQL经常报主从错误，如果是网络问题，应该是间断性的，但是今天早上一直在报错。上去看了一下log，发现一直在报这个错误：

 11:30:01 [Note] Slave I/O thread killed while connecting to master27 11:30:01 [Note] Slave I/O thread exiting, read up to log 'master-bin.000052', position 30867802727 11:30:01 [Note] Slave SQL thread initialized, starting replication in log 'master-bin.000052' at position 308678027, relay log './copyer1-relay-bin.002681' position: 538276627 11:30:02 [ERROR] Slave I/O: error connecting to master 'copyer@10.242.73.34:3306' - retry-time: 60  retries: 86400, Error_code: 1129

在命令行手动执行远程连接：

[xxx@xxx-xxx-xxx.xxx mysql-5.1.73-linux-x86_64-glibc23]$ bin/mysql -h10.242.73.34 -ucoyper -pEnter password:ERROR 1129 (HY000): Host 'xxxxx' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

这下子对1129错误码有了更明确的错误信息和指示。谷歌一下，根据官方文档 B.5.2.6 Host 'host_name' is blocked 进行相应的操作：

登陆到master，执行：

mysql> flush hosts;Query OK, 0 rows affected (0.00 sec)

slave立马就可以连接成功了。

再把允许的错误连接调大：

mysql> SET GLOBAL max_connect_errors=10000;Query OK, 0 rows affected (0.00 sec)

固化在配置文件中： [root@xxxx ~]# vim /etc/my.cnf max_connect_errors = 10000

但是正如官方文档所说的，这个错误一般是因为网络原因，但是如果是网络原因，调整这个参数其实对于主从同步没有什么帮助。。

If you get the Host 'host_name' is blocked error message for a given host, you should first verify that there is nothing wrong with TCP/IP connections from that host. If you are having network problems, it does you no good to increase the value of the max_connect_errors variable.

但是同步问题还是一直存在，统计了一下，发现主要是如下错误码

[xxx@xxx log]$ grep 'Error_code:' mysqld.log| awk '{print $NF}'|sort | uniq -c | sort -n 2003115911292013

对照官方错误码文档 Appendix B Errors, Error Codes, and Common Problems ，主要是如下错误：

Error: 1129 SQLSTATE: HY000 (ER_HOST_IS_BLOCKED) Message: Host '%s' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'

Error: 1159 SQLSTATE: 08S01 (ER_NET_READ_INTERRUPTED) Message: Got timeout reading communication packets

Error: 2003 (CR_CONN_HOST_ERROR) Message: Can't connect to MySQL server on '%s' (%d)

Error: 2013 (CR_SERVER_LOST) Message: Lost connection to MySQL server during query

一看很明显，都是网络问题，1129前面已经说过了。现在看报的最多的2013。同样在官方文档上也有相应的说明：

1. B.5.2.3 Lost connection to MySQL server

2. B.5.2.9 MySQL server has gone away

建议是调整timeout相关的参数看看 5.1.4 Server System Variables ：

• connect_timeout

• net_read_timeout

• net_write_timeout

• slave_net_timeout

• wait_timeout

使用 show variables; 可以看到现在的值：

• connect_timeout = 10

• interactive_timeout = 28800

• net_read_timeout = 30 |

• net_retry_count = 10

• net_write_timeout = 60

• slave_net_timeout = 3600

• wait_timeout = 28800

可以用 SET语句 进行动态修改：

mysql> SET GLOBAL net_read_timeout=60;mysql> SET GLOBAL net_write_timeout=120;

改了一下，貌似好一些，但是还是会不时报错。。网络问题，没有太好的办法:

原文地址：MySQL主从同步失败, 感谢原作者分享。