今早发现mysql日志中有很多如下的警告：

140724 18:41:25 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:25 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:26 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:26 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:27 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:28 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:28 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:28 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:41:28 [Warning] IP address ‘172.16.18.217‘ could not be resolved: Temporary failure in name resolution
140724 18:44:54 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:54 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:54 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:54 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:54 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:55 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:55 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:55 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution
140724 18:44:55 [Warning] IP address ‘61.143.209.110‘ could not be resolved: Temporary failure in name resolution

问题产生的原因：
出现错误的原因是MYSQL Server在本地内存中维护了一个非本地的Client TCP cache，这个cache中包含了远程Client的登录信息，比如IP地址，hostname等信息。
如果Client连接到服务器后，Mysql首先会在本地TCP池中根据IP地址解析客户端的hostname或者反解析，如果解析不到，就会去DNS中进行解析，如果还是解析失败
就是在error log中写入这样的警告信息。

解决的办法：
1.可以通过两个参数来disable这个功能，在MYSQL的配置文件中[mysqld]中加入下面的参数:
[mysqld]
--skip-host-cache
--skip-name-resolve

重新授权，将所有访问数据库服务器的授权方式都改成IP形式的。
grant all on *.* to ‘root’@’172.16.12.68’identified by ‘123456’;

2.添加授权。
将所有访问数据库服务器的授权方式都改成IP形式。
不同的用户用不同的用户名和密码。
grant all on *.* to ‘user_68’@’172.16.12.68’identified by ‘pwd_68’;
grant all on *.* to ‘user_67’@’172.16.12.67’identified by ‘pwd_67’;
....
然后去 mysql数据库下面的 user表  和db表 下面删除掉那些含有含有主机名字的权限记录。

总结：

1.要么加上
--skip-host-cache
--skip-name-resolve

使得MySQL将不再通过DNS解析地址。

2.要么在赋予权限的时候 直接用ip地址，去掉那些用主机名字的权限。