host_cache 存储了主机名与IP之间的映射关系，以避免DNS的查询
系统表介绍
| 列名 | 含义 |
|---|---|
| IP | 客户端IP |
| HOST | 主机名 |
| HOST_VALIDATED | 是否主机名与地址解析成功执行 |
| SUM_CONNECT_ERRORS | 连接错误数 |
| COUNT_HOST_BLOCKED_ERRORS | 由于达到最大错误连接数被锁定后被阻塞的连接数 |
| COUNT_NAMEINFO_TRANSIENT_ERRORS | IP到主机名短时转换错误数量 |
| COUNT_NAMEINFO_PERMANENT_ERRORS | IP到主机名持续转换错误数量 |
| COUNT_FORMAT_ERRORS | 主机名格式错误 |
| COUNT_ADDRINFO_TRANSIENT_ERRORS | 主机名到IP转换短时错误数 |
| COUNT_ADDRINFO_PERMANENT_ERRORS | 主机名到IP转换持续错误数 |
| COUNT_FCRDNS_ERRORS | 被证实的DNS翻转错误,出现在IP到主机名时,找不到提供的IP地址 |
| COUNT_HOST_ACL_ERRORS | 由于没有被授权的登录用户引发的登录错误数 |
| COUNT_NO_AUTH_PLUGIN_ERRORS | 由于认证插件没有就绪引发的错误数量 |
| COUNT_AUTH_PLUGIN_ERRORS | 认证插件报告的错误数 |
| COUNT_HANDSHAKE_ERRORS | 在连接协议层呗发现的错误数量 |
| COUNT_PROXY_USER_ERRORS | 代理用户不存在引发的错误数量 |
| COUNT_PROXY_USER_ACL_ERRORS | 代理用户存在但缺乏代理权限引发的错误 |
| COUNT_AUTHENTICATION_ERRORS | 认证失败次数 |
| COUNT_SSL_ERRORS | SSL失败次数 |
| COUNT_MAX_USER_CONNECTIONS_ERRORS | 由单用户限流引发的错误 |
| COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS | 由单位时间内限流引发的错误 |
| COUNT_DEFAULT_DATABASE_ERRORS | 用户无权访问默认数据库或访问的数据库不存在引发的错误 |
| COUNT_INIT_CONNECT_ERRORS | 连接时调用初始化脚本引发的错误数 |
| COUNT_LOCAL_ERRORS | 本地报错数量 |
| COUNT_UNKNOWN_ERRORS | 未知错误数量 |
| FIRST_SEEN | 首次尝试连接时间 |
| LAST_SEEN | 最后尝试连接时间 |
| FIRST_ERROR_SEEN | 首次报错时间 |
| LAST_ERROR_SEEN | 最后报错时间 |
实例
mysql> select * from host_cache \G;
*************************** 1. row ***************************
IP: 192.168.2.1
HOST: NULL
HOST_VALIDATED: YES
SUM_CONNECT_ERRORS: 0
COUNT_HOST_BLOCKED_ERRORS: 0
COUNT_NAMEINFO_TRANSIENT_ERRORS: 0
COUNT_NAMEINFO_PERMANENT_ERRORS: 1
COUNT_FORMAT_ERRORS: 0
COUNT_ADDRINFO_TRANSIENT_ERRORS: 0
COUNT_ADDRINFO_PERMANENT_ERRORS: 0
COUNT_FCRDNS_ERRORS: 0
COUNT_HOST_ACL_ERRORS: 4
COUNT_NO_AUTH_PLUGIN_ERRORS: 0
COUNT_AUTH_PLUGIN_ERRORS: 0
COUNT_HANDSHAKE_ERRORS: 0
COUNT_PROXY_USER_ERRORS: 0
COUNT_PROXY_USER_ACL_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 3
COUNT_SSL_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0
COUNT_DEFAULT_DATABASE_ERRORS: 0
COUNT_INIT_CONNECT_ERRORS: 0
COUNT_LOCAL_ERRORS: 0
COUNT_UNKNOWN_ERRORS: 0
FIRST_SEEN: 2021-03-15 06:01:51
LAST_SEEN: 2021-08-09 10:14:18
FIRST_ERROR_SEEN: 2021-03-15 06:01:51
LAST_ERROR_SEEN: 2021-03-20 17:50:23
*************************** 2. row ***************************
IP: 192.168.2.62
HOST: NULL
HOST_VALIDATED: YES
SUM_CONNECT_ERRORS: 0
COUNT_HOST_BLOCKED_ERRORS: 0
COUNT_NAMEINFO_TRANSIENT_ERRORS: 0
COUNT_NAMEINFO_PERMANENT_ERRORS: 1
COUNT_FORMAT_ERRORS: 0
COUNT_ADDRINFO_TRANSIENT_ERRORS: 0
COUNT_ADDRINFO_PERMANENT_ERRORS: 0
COUNT_FCRDNS_ERRORS: 0
COUNT_HOST_ACL_ERRORS: 0
COUNT_NO_AUTH_PLUGIN_ERRORS: 0
COUNT_AUTH_PLUGIN_ERRORS: 0
COUNT_HANDSHAKE_ERRORS: 0
COUNT_PROXY_USER_ERRORS: 0
COUNT_PROXY_USER_ACL_ERRORS: 0
COUNT_AUTHENTICATION_ERRORS: 0
COUNT_SSL_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_ERRORS: 0
COUNT_MAX_USER_CONNECTIONS_PER_HOUR_ERRORS: 0
COUNT_DEFAULT_DATABASE_ERRORS: 0
COUNT_INIT_CONNECT_ERRORS: 0
COUNT_LOCAL_ERRORS: 0
COUNT_UNKNOWN_ERRORS: 0
FIRST_SEEN: 2021-08-07 17:06:35
LAST_SEEN: 2021-08-07 17:15:07
FIRST_ERROR_SEEN: 2021-08-07 17:06:35
LAST_ERROR_SEEN: 2021-08-07 17:06:35