'Updates a tracker information.
:param tracker_url: The given tracker_url.
:param is_successful: If the check was successful.'

def update_tracker_info(self, tracker_url, is_successful):

    if (tracker_url not in self._tracker_dict):
        self._logger.error('Trying    to    update    the    tracker    info    of    an    unknown    tracker    URL')
        return
    tracker_info = self._tracker_dict[tracker_url]
    current_time = int(time.time())
    failures = (0 if is_successful else (tracker_info[u'failures'] + 1))
    is_alive = (tracker_info[u'failures'] < self._max_tracker_failures)
    tracker_info[u'last_check'] = current_time
    tracker_info[u'failures'] = failures
    tracker_info[u'is_alive'] = is_alive
    sql_stmt = u'UPDATE    TrackerInfo    SET    last_check    =    ?,    failures    =    ?,    is_alive    =    ?    WHERE    tracker_id    =    ?'
    value_tuple = (tracker_info[u'last_check'], tracker_info[u'failures'], tracker_info[u'is_alive'], tracker_info[u'id'])
    self._session.sqlite_db.execute(sql_stmt, value_tuple)
