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1.版本
1)操作系统
cat /etc/issue
Red Hat Enterprise Linux Server release 5.5 (Tikanga)
Kernel \r on an \m
cat /proc/version
Linux version 2.6.32-504.el6.x86_64 (mockbuild@c6b9.bsys.dev.centos.org) (gcc version 4.4.7 20120313 (Red Hat 4.4.7-11) (GCC) ) #1 SMP Wed Oct 15 04:27:16 UTC 2014
2)mysql数据库版本
mysql --version
mysql Ver 14.14 Distrib 5.6.26, for linux-glibc2.5 (x86_64) using EditLine wrapper
2.问题描述
2.1 发现问题
今天应用反应发现某个应用第一次响应很慢，当第一次响应成功后，后面所做的处理速度就正常了。我看了一下mysql的errorlog，发现有如warning：
2016-02-24 09:16:05 19114 [Warning] IP address '172.172.200.86' could not be resolved: Temporary failure in name resolution
2016-02-24 09:16:10 19114 [Warning] IP address '172.172.200.88' could not be resolved: Temporary failure in name resolution
2016-02-24 09:16:15 19114 [Warning] IP address '172.172.200.86' could not be resolved: Temporary failure in name resolution我们查看mysql的 performance_schema.host_cache表中可以发现如下信息：
<span style="color:#333333;">*************************** 1. row ***************************IP: 172.172.200.86HOST: NULLHOST_VALIDATED: NO >>>注意此处标识为NO，这时从88过来的登录请求就不会使用host_cache缓存，需要重新解析SUM_CONNECT_ERRORS: 0COUNT_HOST_BLOCKED_ERRORS: 0COUNT_NAMEINFO_TRANSIENT_ERRORS: 163COUNT_NAMEINFO_PERMANENT_ERRORS: 0COUNT_FORMAT_ERRORS: 0COUNT_ADDRINFO_TRANSIENT_ERRORS: 0COUNT_ADDRINFO_PERMANENT_ERRORS: 0COUNT_FCRDNS_ERRORS: 0COUNT_HOST_ACL_ERRORS: 0COUNT_NO_AUTH_PLUGIN_ERRORS: 0COUNT_AUTH_PLUGIN_ERRORS: 0COUNT_HANDSHAKE_ERRORS: 0COUNT_PROXY_USER_ERRORS: 0COUNT_PROXY_USER_ACL_ERRORS: 0COUNT_AUTHENTICATION_ERRORS: 0COUNT_SSL_ERRORS: 0COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0COUNT_DEFAULT_DATABASE_ERRORS: 0COUNT_INIT_CONNECT_ERRORS: 0COUNT_LOCAL_ERRORS: 0COUNT_UNKNOWN_ERRORS: 0FIRST_SEEN: 2016-02-13 08:03:54LAST_SEEN: 2016-02-21 09:16:55FIRST_ERROR_SEEN: 2016-02-13 08:03:54LAST_ERROR_SEEN: 2016-02-21 09:16:55
*************************** 2. row ***************************IP: 172.172.200.88HOST: NULLHOST_VALIDATED: NO >>>注意此处标识为NO，这时从88过来的登录请求就不会使用host_cache缓存，需要重新解析SUM_CONNECT_ERRORS: 0COUNT_HOST_BLOCKED_ERRORS: 0COUNT_NAMEINFO_TRANSIENT_ERRORS: 139COUNT_NAMEINFO_PERMANENT_ERRORS: 0COUNT_FORMAT_ERRORS: 0COUNT_ADDRINFO_TRANSIENT_ERRORS: 0COUNT_ADDRINFO_PERMANENT_ERRORS: 0COUNT_FCRDNS_ERRORS: 0COUNT_HOST_ACL_ERRORS: 0COUNT_NO_AUTH_PLUGIN_ERRORS: 0COUNT_AUTH_PLUGIN_ERRORS: 0COUNT_HANDSHAKE_ERRORS: 0COUNT_PROXY_USER_ERRORS: 0COUNT_PROXY_USER_ACL_ERRORS: 0COUNT_AUTHENTICATION_ERRORS: 0COUNT_SSL_ERRORS: 0COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0COUNT_DEFAULT_DATABASE_ERRORS: 0COUNT_INIT_CONNECT_ERRORS: 0COUNT_LOCAL_ERRORS: 0COUNT_UNKNOWN_ERRORS: 0FIRST_SEEN: 2016-02-13 08:00:30LAST_SEEN: 2016-02-21 09:16:11FIRST_ERROR_SEEN: 2016-02-13 08:00:30LAST_ERROR_SEEN: 2016-02-21 09:16:11
2.2 问题分析
请见官方文档中 8.12.6.2 DNS Lookup Optimization and the Host Cache，或者我的博客
http://blog.csdn.net/shaochenshuo/article/details/50727975
2.3 问题解决
2.3.1 方法1
为了彻底解决该问题，我们可以在mysql 的cnf文件中加入如下参数skip_name_resolve = 1，因为该参数为非动态参数，需要重启实例才能生效。（建议在安装mysql的时候就加上该参数）
2.3.2 方法2
1)利用/etc/host 进行解析
当然生成数据库可能并不能轻易重启，那么我们可以临时在/etc/hosts文件中写入有问题的ip地址，等mysql解析成功后(此时会被记录在host_cache中)，再注释掉。如下是我在商用环境/etc/hosts中加入内容：
172.172.200.86 test1
172.172.200.88 test2
2)从86和88重新发起数据库连接请求
此时连接会很快，并且我们查询performance_schema.host_cache会发现：
<span style="color:#333333;">*************************** 1. row ***************************IP: 172.172.200.86HOST: test1 >>注意ip成功被解析为域名HOST_VALIDATED: YES >>此处被标记为YESSUM_CONNECT_ERRORS: 0COUNT_HOST_BLOCKED_ERRORS: 0COUNT_NAMEINFO_TRANSIENT_ERRORS: 163COUNT_NAMEINFO_PERMANENT_ERRORS: 0COUNT_FORMAT_ERRORS: 0COUNT_ADDRINFO_TRANSIENT_ERRORS: 0COUNT_ADDRINFO_PERMANENT_ERRORS: 0COUNT_FCRDNS_ERRORS: 0COUNT_HOST_ACL_ERRORS: 0COUNT_NO_AUTH_PLUGIN_ERRORS: 0COUNT_AUTH_PLUGIN_ERRORS: 0COUNT_HANDSHAKE_ERRORS: 0COUNT_PROXY_USER_ERRORS: 0COUNT_PROXY_USER_ACL_ERRORS: 0COUNT_AUTHENTICATION_ERRORS: 0COUNT_SSL_ERRORS: 0COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0COUNT_DEFAULT_DATABASE_ERRORS: 0COUNT_INIT_CONNECT_ERRORS: 0COUNT_LOCAL_ERRORS: 0COUNT_UNKNOWN_ERRORS: 0FIRST_SEEN: 2016-02-13 08:03:54LAST_SEEN: 2016-02-21 09:30:55FIRST_ERROR_SEEN: 2016-02-13 08:03:54LAST_ERROR_SEEN: 2016-02-21 09:16:55
*************************** 2. row ***************************IP: 172.172.200.88HOST: TEST2HOST_VALIDATED: YESSUM_CONNECT_ERRORS: 0COUNT_HOST_BLOCKED_ERRORS: 0COUNT_NAMEINFO_TRANSIENT_ERRORS: 139COUNT_NAMEINFO_PERMANENT_ERRORS: 0COUNT_FORMAT_ERRORS: 0COUNT_ADDRINFO_TRANSIENT_ERRORS: 0COUNT_ADDRINFO_PERMANENT_ERRORS: 0COUNT_FCRDNS_ERRORS: 0COUNT_HOST_ACL_ERRORS: 0COUNT_NO_AUTH_PLUGIN_ERRORS: 0COUNT_AUTH_PLUGIN_ERRORS: 0COUNT_HANDSHAKE_ERRORS: 0COUNT_PROXY_USER_ERRORS: 0COUNT_PROXY_USER_ACL_ERRORS: 0COUNT_AUTHENTICATION_ERRORS: 0COUNT_SSL_ERRORS: 0COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0COUNT_DEFAULT_DATABASE_ERRORS: 0COUNT_INIT_CONNECT_ERRORS: 0COUNT_LOCAL_ERRORS: 0COUNT_UNKNOWN_ERRORS: 0FIRST_SEEN: 2016-02-13 08:00:30LAST_SEEN: 2016-02-21 09:30:11FIRST_ERROR_SEEN: 2016-02-13 08:00:30LAST_ERROR_SEEN: 2016-02-21 09:16:11
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