show processlist 出现很多

unauthenticated user | connecting host | NULL | Connect | 179 | login

出现这种情况很大可能是因为DNS导致的，可以通过跳过dns解析skip-name-resolve来解决

进一步查看日志

也有可能是back_log值打满了。

back_log：如果MySql的连接数据达到max_connections时，新来的请求将会被存在堆栈中，以等待某一连接释放资源，该堆栈的数量即back_log，如果等待连接的数量超过back_log，将不被授予连接资源。将会报：unauthenticated user | xxx.xxx.xxx.xxx | NULL | Connect | NULL | login | NULL 的待连接进程时back_log值不能超过TCP/IP连接的侦听队列的大小。

查看错误日志

[ERROR] Threadpool could not create additional thread to handle queries, because the number of allowed threads was reached. Increasing 'thread_pool_max_threads' parameter can help in this situation.

线程池满了，连接池也打满。将unauthenticated user杀掉

for id in `mysqladmin -uroot -p"pass" processlist|grep -i "unauthenticated"|awk '{print $2}'`
do
        mysqladmin -uroot -p"pass" kill ${id}
done
或
mysql -uroot -p -S /tmp/mysql.sock -e "select * from information_schema.processlist where USER  in('unauthenticated user')  and command !='sleep' and time >100" | awk '{print "kill " $1 ";"}'>/tmp/a.txt
source  /tmp/a.txt;