一、问题引入
1.1、报错
最近一台mysql服务器报错：ERROR 1129 (00000): Host 'xxx' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'。
1.2、本质原因
因为同一个IP在短时间内产生太多中断的数据库连接（超过max_connect_errors的最大值）而导致的
If more than this many successive connection requests from a host are interrupted without a successful connection, the server blocks that host from further connections. You can unblock blocked hosts by flushing the host cache. To do so, issue a FLUSH HOSTS statement or execute a mysqladmin flush-hosts command. If a connection is established successfully within fewer than max_connect_errors attempts after a previous connection was interrupted, the error count for the host is cleared to zero. However, once a host is blocked, flushing the host cache is the only way to unblock it. The default is 100.
翻译：如果MySQL服务器连续接收到了来自于同一个主机的请求，而且这些连续的请求全部都没有成功的建立连接就被中断了，当这些连续的请求的累计值大于max_connect_errors的设定值时，MySQL服务器就会阻止这台主机后续的所有请求。相信一开始你看到这些资料，也会被“many successive connection requests from a host are interrupted without a successful connection”给弄懵，其实这个就是因为由于网络异常而中止数据库连接
There seems to be confusion around that variable. It does not really block hosts for repeated invalid passwords but for aborted connections due to network errors.