Node.js MySQL 接続が真夜中頃に切断され続けるのはなぜですか?

Error: Connection lost: The server closed the connection.
at Protocol.end (/opt/node-v0.10.20-linux-x64/IM/node_modules/mysql/lib/protocol/Protocol.js:73:13)
at Socket.onend (stream.js:79:10)
at Socket.EventEmitter.emit (events.js:117:20)
at _stream_readable.js:920:16
at process._tickCallback (node.js:415:13)

var db_config = {
  host: 'localhost',
  user: 'root',
  password: '',
  database: 'example'
};

var connection;

function handleDisconnect() {
  connection = mysql.createConnection(db_config); // Recreate the connection

  connection.connect(function(err) {              // Attempt to connect
    if(err) {
      console.log('error when connecting to db:', err);
      setTimeout(handleDisconnect, 2000); // Delay reconnection attempts
    }
  });

  connection.on('error', function(err) {
    console.log('db error', err);
    if(err.code === 'PROTOCOL_CONNECTION_LOST') { // Connection lost due to server restart or idle timeout
      handleDisconnect();
    } else {
      throw err;
    }
  });
}

handleDisconnect();