为何会出现大量unauthenticated user？

为何会出现大量unauthenticated user

[dba@localhost:mysql.sock] [(none)]> show full processlist;
+----+----------------------+-------------------+------+---------+------+----------+-----------------------+
| Id | User                 | Host              | db   | Command | Time | State    | Info                  |
+----+----------------------+-------------------+------+---------+------+----------+-----------------------+
|  2 | unauthenticated user | 85.93.20.88:37146 | NULL | Connect |   24 | login    | NULL                  |
|  3 | dba                  | localhost         | NULL | Query   |    0 | starting | show full processlist |
+----+----------------------+-------------------+------+---------+------+----------+-----------------------+
2 rows in set (0.00 sec)

看下手册中的解释是：
unauthenticated user refers to a thread that has become associated with a client connection but for which authentication of the client user has not yet been done。
意思是：有一个线程在处理客户端的连接，但是该客户端还没通过用户验证。
原因可能有：
1、服务器在做DNS反响解析。
    解决办法有2：
        (1).在/etc/hosts中添加客户端ip。
            10.0.0.11 db01
        (2).MySQL启动参数增加一个skip-name-resolve，即不启用DNS反响解析。
2、服务器的线程还处于排队状态，因此可以加大back_log。