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Merged
dashpole merged 2 commits into from
Dec 16, 2025
Merged

Exponential histogram: defer computing count until collect #7702

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ea81069
exphist: defer computing count until collect
dashpole Dec 12, 2025
483d022
Merge branch 'main' into exphist_count_at_export
dashpole Dec 16, 2025
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1 change: 1 addition & 0 deletions CHANGELOG.md
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Expand Up @@ -16,6 +16,7 @@ This project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.htm
- Add experimental observability metrics in `go.opentelemetry.io/otel/exporters/stdout/stdoutmetric`. (#7492)
- Improve the concurrent performance of `HistogramReservoir` in `go.opentelemetry.io/otel/sdk/metric/exemplar` by 4x. (#7443)
- Improve performance of concurrent synchronous gauge measurements in `go.opentelemetry.io/otel/sdk/metric`. (#7478)
- Improve performance of concurrent exponential histogram measurements in `go.opentelemetry.io/otel/sdk/metric`. (#7702)

<!-- Released section -->
<!-- Don't change this section unless doing release -->
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25 changes: 17 additions & 8 deletions sdk/metric/internal/aggregate/exponential_histogram.go
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Expand Up @@ -32,10 +32,9 @@ type expoHistogramDataPoint[N int64 | float64] struct {
attrs attribute.Set
res FilteredExemplarReservoir[N]

count uint64
min N
max N
sum N
min N
max N
sum N

maxSize int
noMinMax bool
Expand Down Expand Up @@ -74,8 +73,6 @@ func newExpoHistogramDataPoint[N int64 | float64](

// record adds a new measurement to the histogram. It will rescale the buckets if needed.
func (p *expoHistogramDataPoint[N]) record(v N) {
p.count++

if !p.noMinMax {
if v < p.min {
p.min = v
Expand Down Expand Up @@ -193,6 +190,10 @@ func (p *expoHistogramDataPoint[N]) scaleChange(bin, startBin int32, length int)
return count
}

func (p *expoHistogramDataPoint[N]) count() uint64 {
return p.posBuckets.count() + p.negBuckets.count() + p.zeroCount
}

// expoBuckets is a set of buckets in an exponential histogram.
type expoBuckets struct {
startBin int32
Expand Down Expand Up @@ -285,6 +286,14 @@ func (b *expoBuckets) downscale(delta int32) {
b.startBin >>= delta
}

func (b *expoBuckets) count() uint64 {
var total uint64
for _, count := range b.counts {
total += count
}
return total
}

// newExponentialHistogram returns an Aggregator that summarizes a set of
// measurements as an exponential histogram. Each histogram is scoped by attributes
// and the aggregation cycle the measurements were made in.
Expand Down Expand Up @@ -376,7 +385,7 @@ func (e *expoHistogram[N]) delta(
hDPts[i].Attributes = val.attrs
hDPts[i].StartTime = e.start
hDPts[i].Time = t
hDPts[i].Count = val.count
hDPts[i].Count = val.count()
hDPts[i].Scale = val.scale
hDPts[i].ZeroCount = val.zeroCount
hDPts[i].ZeroThreshold = 0.0
Expand Down Expand Up @@ -439,7 +448,7 @@ func (e *expoHistogram[N]) cumulative(
hDPts[i].Attributes = val.attrs
hDPts[i].StartTime = e.start
hDPts[i].Time = t
hDPts[i].Count = val.count
hDPts[i].Count = val.count()
hDPts[i].Scale = val.scale
hDPts[i].ZeroCount = val.zeroCount
hDPts[i].ZeroThreshold = 0.0
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1 change: 0 additions & 1 deletion sdk/metric/internal/aggregate/exponential_histogram_test.go
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Expand Up @@ -706,7 +706,6 @@ func TestSubNormal(t *testing.T) {
want := &expoHistogramDataPoint[float64]{
attrs: alice,
maxSize: 4,
count: 3,
min: math.SmallestNonzeroFloat64,
max: math.SmallestNonzeroFloat64,
sum: 3 * math.SmallestNonzeroFloat64,
Expand Down