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Use Kahan summation for sum accumulator #628

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Merged
merged 1 commit into from
Sep 24, 2025
Merged

Use Kahan summation for sum accumulator #628

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14 changes: 8 additions & 6 deletions execution/aggregate/accumulator.go
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Original file line number Diff line number Diff line change
Expand Up @@ -39,9 +39,10 @@ type vectorAccumulator interface {
}

type sumAcc struct {
value float64
histSum *histogram.FloatHistogram
hasFloatVal bool
value float64
compensation float64
histSum *histogram.FloatHistogram
hasFloatVal bool
}

func newSumAcc() *sumAcc {
Expand All @@ -50,7 +51,7 @@ func newSumAcc() *sumAcc {

func (s *sumAcc) AddVector(ctx context.Context, float64s []float64, histograms []*histogram.FloatHistogram) error {
if len(float64s) > 0 {
s.value += SumCompensated(float64s)
s.value, s.compensation = KahanSumInc(SumCompensated(float64s), s.value, s.compensation)
s.hasFloatVal = true
}

Expand All @@ -64,7 +65,7 @@ func (s *sumAcc) AddVector(ctx context.Context, float64s []float64, histograms [
func (s *sumAcc) Add(ctx context.Context, v float64, h *histogram.FloatHistogram) error {
if h == nil {
s.hasFloatVal = true
s.value += v
s.value, s.compensation = KahanSumInc(v, s.value, s.compensation)
return nil
}
if s.histSum == nil {
Expand Down Expand Up @@ -108,7 +109,7 @@ func (s *sumAcc) Value() (float64, *histogram.FloatHistogram) {
if s.histSum != nil {
s.histSum.Compact(0)
}
return s.value, s.histSum
return s.value + s.compensation, s.histSum
}

func (s *sumAcc) ValueType() ValueType {
Expand All @@ -125,6 +126,7 @@ func (s *sumAcc) Reset(_ float64) {
s.histSum = nil
s.hasFloatVal = false
s.value = 0
s.compensation = 0
}

func newMaxAcc() *maxAcc {
Expand Down
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