最近一MySQL服务器,由于一些特殊因素遇到“ERROR 1129 (00000): Host 'xxx' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'”,在问题解决后,在详细了解参数max_connect_errors的过程中,有些不同网络资料的矛盾描述确实让我有点迷惑和混淆(关于这个错误,本质原因是因为同一个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),下面介绍我的探索问题、分析问题、释疑的一个过程。 首先,我在网上搜索了一些资料,不少资料信誓旦旦的介绍,密码输入错误的尝试次数超过max_connect_errors变量,MySQL就会阻塞这个客户端登录,然后我找到了官方资料关于max_connect_errors的介绍,如下所示,MySQL 5.6/5.7的介绍一致 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. 如上所示,翻译出来的话,大致如下: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。网上搜索到这么一个资料: 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. 好吧,那么我们自己动手实验验证一下,就能弄明白到底那个是正确的。在MySQL数据库里面创建一个test账号,然后我们将max_connect_errors变量设置为3. 然后我们在另外一台测试机器,以错误的密码去连接这个MySQL数据库,如下所示,即使前面输入了三次错误密码,第四次输入是也没有碰到上面错误。那么可以排除这个变量与密码错误输入有关系。 [root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES) [root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES) [root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES) [root@mytestlnx02 tmp]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 1045 (28000): Access denied for user 'test'@'mytestlnx02' (using password: YES) [root@mytestlnx02 tmp]# 其实,关于某个IP输入了错误密码,MySQL会在performance_schema数据库下的host_cache表中记录。它会累计记录在COUNT_AUTHENTICATION_ERRORS字段,如下所示:
官方资料介绍,host_cache的字段是统计被视为“阻塞”的连接错误的数量(根据max_connect_errors系统变量进行评估)。 只计算协议握手错误,并且仅用于通过验证的主机(HOST_VALIDATED = YES)。 SUM_CONNECT_ERRORS The number of connection errors that are deemed “blocking” (assessed against the max_connect_errors system variable). Only protocol handshake errors are counted, and only for hosts that passed validation (HOST_VALIDATED = YES). MySQL客户端与数据库建立连接需要发起三次握手协议,正常情况下,这个时间非常短,但是一旦网络异常,网络超时等因素出现,就会导致这个握手协议无法完成,MySQL有个参数connect_timeout,它是MySQL服务端进程mysqld等待连接建立完成的时间,单位为秒。如果超过connect_timeout时间范围内,仍然无法完成协议握手话,MySQL客户端会收到异常,异常消息类似于: Lost connection to MySQL server at 'XXX', system error: errno,该变量默认是10秒:
那么我们就构造一个网络超时引起的数据库连接被中断案例吧,我们用Linux下的netem与tc命令模拟构造出复杂环境下的网络传输延时案例,如下设置后,此时从测试服务器去访问MySQL服务器,都会出现延时11秒: [root@gettestlnx02 ~]# ping 10.20.57.24 PING 10.20.57.24 (10.20.57.24) 56(84) bytes of data. 64 bytes from 10.20.57.24: icmp_seq=1 ttl=62 time=0.251 ms 64 bytes from 10.20.57.24: icmp_seq=2 ttl=62 time=0.330 ms 64 bytes from 10.20.57.24: icmp_seq=3 ttl=62 time=0.362 ms 64 bytes from 10.20.57.24: icmp_seq=4 ttl=62 time=0.316 ms 64 bytes from 10.20.57.24: icmp_seq=5 ttl=62 time=0.281 ms 64 bytes from 10.20.57.24: icmp_seq=6 ttl=62 time=0.377 ms ^C --- 10.20.57.24 ping statistics --- 6 packets transmitted, 6 received, 0% packet loss, time 5716ms rtt min/avg/max/mdev = 0.251/0.319/0.377/0.047 ms [root@gettestlnx02 ~]# tc qdisc add dev eth0 root netem delay 11000ms [root@gettestlnx02 ~]# ping 10.20.57.24 PING 10.20.57.24 (10.20.57.24) 56(84) bytes of data. 64 bytes from 10.20.57.24: icmp_seq=1 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=2 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=3 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=4 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=5 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=6 ttl=62 time=11000 ms 64 bytes from 10.20.57.24: icmp_seq=7 ttl=62 time=11000 ms
我们在测试服务器gettestlnx02连接MySQL数据库,如下所示(注意,如果你是在通过ssh连接这台服务器的话,此时在gettestlnx02上操作会相当慢。当然你也可以在MySQL服务器模拟网络延时,或者你将connect_timeout和网络延时都设小一点) [root@gettestlnx02 ~]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 2013 (HY000): Lost connection to MySQL server at 'reading authorization packet', system error: 0 [root@gettestlnx02 ~]# 如上所示,由于网络延时超过10秒,导致连接MySQL失败,此时,你在MySQL服务器上查询host_cache表时,那么你就会看到SUM_CONNECT_ERRORS变成1了,COUNT_HANDSHAKE_ERRORS也变成了1.
那么我们反复这样折腾三次,那么你会看到SUM_CONNECT_ERRORS变成3了,COUNT_HANDSHAKE_ERRORS也变成了3了. 然后我们用netem与tc 命令在测试服务器上取消网络延迟模拟,然后去测试连接MySQL数据库,如下测试所示: [root@gettestlnx02 ~]# tc qdisc del dev eth0 root netem delay 11000ms [root@gettestlnx02 ~]# mysql -h10.20.57.24 -utest -p Enter password: ERROR 1129 (HY000): Host '192.168.27.180' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts' [root@gettestlnx02 ~]#
此时就能构造出“ERROR 1129 (HY000): Host '192.168.27.180' is blocked because of many connection errors; unblock with 'mysqladmin flush-hosts'”错误了。 解决方案 解决ERROR 1129 (00000): Host 'xxx' is blocked because of many connection errors. Unblock with 'mysqladmin flush-hosts'这个错误的方法比较多,不过有些方案都是临时方案。临时方案是指标不治本。关键还是需要解决网络错误(这个往往需要求助网络管理人员或系统管理员) 解决方法: 1、将变量max_connection_errors的值设置为一个更大的值
这个临时方案只是延迟触发IP被禁止访问的条件而已,而且在复杂情况或高并发的情况下,需要设置一个很大的值,否则很容易就会再次被触发。另外,变量只对当前环境生效,如果重启就会失效,如果需要永久有效,可以在my.cnf配置文件里面配置。 2:使用flush hosts mysql> flush hosts; Query OK, 0 rows affected (0.00 sec) mysql> select * from performance_schema.host_cache; Empty set (0.00 sec) mysql> 当然你也可以mysqladmin flush-hosts 命令清理一下hosts cache信息 [root@DB-Server ~]# mysqladmin --port=3306 -uroot -p flush-host Enter password: 那么host cache是什么呢? 官方介绍如下: The MySQL server maintains a host cache in memory that contains information about clients: IP address, host name, and error information. The server uses this cache for nonlocal TCP connections. It does not use the cache for TCP connections established using a loopback interface address (127.0.0.1 or ::1), or for connections established using a Unix socket file, named pipe, or shared memory. 简单来说,就是MySQL服务器在内存中维护一个包含客户端信息的缓存:IP地址,主机名和错误信息等。 服务器会将非本地TCP连接信息缓存起来。它不会缓存使用环回接口地址(127.0.0.1或者:: 1)建立的TCP连接,或者使用Unix套接字文件,命名管道或共享内存建立的连接。host cache信息可以通过performance_schema数据库下的host_cache表查询。 3:将变量host_cache_size设置为0 其实我想说这是一个最不靠谱的解决方法,只是让MySQL服务器不记录host cache信息而已。完全可以忽略这个方法。
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