Q: With MySQL, after a long time of in-activity, I got
   java.sql.SQLException: Communication link failure: java.net.SocketException.

A: This happens because of a connection timeout on the MySQL side.
   You need add "autoReconnect=true" in the jdbc url. You may also want configure
   your mysql server and add an entry 

        set-variable = interactive_timeout=50000

   in the file my.cnf (the default is 28800, 8hr).

   Note that, in later Bugzero versions, this exception shall not cause any
   real harm. It will simply try re-connect. It is logged in the log file, but
   end-user does not see it.
   

   You may also see a similar java.sql.SQLException:
   Communication link failure: java.io.IOException.