从源码解析ERROR 1129 (HY000)(2)以及unauthenticated user

原创 水平有限，只为抛砖，有误请指出


这里主要找一下m_connect是什么，以及怎么增加的，因为前文我没有找到，再次用断点的方式
描述一下unauthenticated user

一、m_connect是什么怎么增加的
m_connect实际上就是m_handshake下面是


sql_authentication.cc:
acl_authenticate函数

聚合函数Hostname.cc





sql_authentication.cc:1900
do_auth_once函数调用


下面是错误的宏定义



也就是说每次由于mpvio->write_packet函数问题导致的握手失败都会触发他+1，其实这很可能是网络
问题，关于mpvio->write_packet的返回值感兴趣的可以继续跟中下去
下面是官方关于错误的解释
If the following error occurs, it means that mysqldhas received many connection requests from the given
host that were interrupted in the middle:
Host 'host_name' is blocked because of many connection errors.
Unblock with 'mysqladmin flush-hosts'
The value of the max_connect_errorssystem variable determines how many successive
interrupted connection requests are permitted. (See Section 6.1.4, “Server System Variables”.) After
max_connect_errorsfailed requests without a successful connection, mysqldassumes that something
is wrong (for example, that someone is trying to break in), and blocks the host from further connections
until you issue a FLUSH HOSTSstatement or execute a mysqladmin flush-hostscommand.
By default, mysqldblocks a host after 100 connection errors. You can adjust the value by setting
max_connect_errorsat server startup:
shell> mysqld_safe --max_connect_errors=10000 &
The value can also be set at runtime:
mysql> SET GLOBAL max_connect_errors=10000;
If you get the Host 'host_name' is blockederror 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_errorsvariable.

二、  unauthenticated user为什么和反解析有关






check_connection会调用ip_to_hostname和acl_authenticate进行解析和密码认证过程，但是
ip_to_hostname出现在sql_connect.cc:1166而acl_authenticate出现在sql_connect.cc:1243
可以看到ip_to_hostname确实在acl_authenticate函数前，也就是反解析在密码认证前，也是在MYSQL协议握手成功前。
这也说明什么了为什么解析慢会导致unauthenticated user的用户。
mysql> show processlist;
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
| Id | User                 | Host                 | db   | Command | Time | State    | Info             | Rows_sent | Rows_examined |
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
|  5 | unauthenticated user | 192.168.190.60:12770 | NULL | Connect |   35 | login    | NULL             |         0 |             0 |
|  6 | root                 | localhost            | NULL | Query   |    0 | starting | show processlist |         0 |             0 |
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+

 为了验证我在源码check_connection处增加了等待10秒并且打日志的来验证不然不好观察这个问题，确实如上所诉

mysql> show processlist;
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
| Id | User                 | Host                 | db   | Command | Time | State    | Info             | Rows_sent | Rows_examined |
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
|  4 | root                 | localhost            | NULL | Query   |    0 | starting | show processlist |         0 |             0 |
|  6 | unauthenticated user | 192.168.190.60:61688 | NULL | Connect |    8 | login    | NULL             |         0 |             0 |
+----+----------------------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
2 rows in set (0.00 sec)

mysql> show processlist;
+----+---------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
| Id | User    | Host                 | db   | Command | Time | State    | Info             | Rows_sent | Rows_examined |
+----+---------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
|  4 | root    | localhost            | NULL | Query   |    0 | starting | show processlist |         0 |             0 |
|  6 | testuuu | 192.168.190.60:61688 | NULL | Connect |   12 | login    | NULL             |         0 |             0 |
+----+---------+----------------------+------+---------+------+----------+------------------+-----------+---------------+
2 rows in set (0.00 sec)

日志输出：
2017-05-31T22:34:28.605325Z 10 [Note] Before acl_authenticate sleep(10) check unauthenticated user
2017-05-31T22:34:38.606414Z 10 [Note] After acl_authenticate sleep(10) check authenticated user
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