public function jobsPerSecond($conditions = [], $field = 'created', $time_range = '-1 hour')
 {
     $start_time = new Time($time_range);
     $current_time = new Time();
     $second_count = $current_time->diffInSeconds($start_time);
     $conditions[$this->aliasField($field) . ' > '] = $start_time;
     $count = $this->find()->where($conditions)->count();
     return $count / $second_count;
 }