code: func NewQueryFeedback(physicalID int64, hist *Histogram, expected int64, desc bool) *QueryFeedback {
  	if hist != nil && hist.Len() == 0 {
  		hist = nil
  	}
  	tp := PkType
  	if hist != nil && hist.IsIndexHist() {
  		tp = IndexType
  	}
  	return &QueryFeedback{
  		PhysicalID: physicalID,
  		Valid:      true,
  		Tp:         tp,
  		Hist:       hist,
  		Expected:   expected,
  		desc:       desc,
  	}
  }
docs: // NewQueryFeedback returns a new query feedback.