code: func (q *QueryFeedback) CollectFeedback(numOfRanges int) bool {
  	if q.Hist == nil || q.Hist.Len() == 0 {
  		return false
  	}
  	if numOfRanges > MaxNumberOfRanges || rand.Float64() > FeedbackProbability.Load() {
  		return false
  	}
  	return true
  }
docs: // CollectFeedback decides whether to collect the feedback. It returns false when:
  // 1: the histogram is nil or has no buckets;
  // 2: the number of scan ranges exceeds the limit because it may affect the performance;
  // 3: it does not pass the probabilistic sampler.