def is_flapping(self, alert, window=1800, count=2):
        """
        Return true if alert severity has changed more than X times in Y seconds
        """
        select = """
            SELECT COUNT(*)
              FROM alerts, unnest(history) h
             WHERE environment=%(environment)s
               AND resource=%(resource)s
               AND h.event=%(event)s
               AND h.update_time > (NOW() at time zone 'utc' - INTERVAL '{window} seconds')
               AND h.type='severity'
               AND {customer}
        """.format(window=window, customer='customer=%(customer)s' if alert.customer else 'customer IS NULL')
        return self._fetchone(select, vars(alert)).count > count