Long-term connection with Mysql
There are three cars on the same grid. One is Mysql, two others are a client. In the same customer car, the connection is set in the valley of a second, the second long connection is fast. Checking team: telnet database.server 3306
The difference between two customers is that one is Ubuntu 14.04 for another Ubuntu 16.04
Question of where to dig?
The problem is, for every client, MySQL makes DNS lookup, add the next line (skip-name-resolve) to mysqld and reboot the server.
In order to determine the reasons for such problems, study and use the tcpdump team, she'll tell you what stage the problem of the compound was.