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Merged
songy23 merged 2 commits into from
Nov 9, 2026
Merged

[exporter/prometheus] Preserve exponential histogram zero thresholds #52834

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eaebe2c
[exporter/prometheus] Preserve exponential histogram zero thresholds
ArthurSens Nov 6, 2026
e2472e5
Add changelog entries for zero threshold preservation
ArthurSens Nov 6, 2026
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5 changes: 5 additions & 0 deletions .chloggen/52834-prometheus-remote-write-zero-threshold.yaml
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@@ -0,0 +1,5 @@
change_type: bug_fix
component: pkg/translator/prometheusremotewrite
note: Preserve the zero threshold when converting exponential histograms to Prometheus remote-write v1 and v2 native histograms.
issues: [52834]
change_logs: [user, api]
5 changes: 5 additions & 0 deletions .chloggen/52834-prometheus-zero-threshold.yaml
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@@ -0,0 +1,5 @@
change_type: bug_fix
component: exporter/prometheus
note: Preserve the zero threshold when converting exponential histograms to Prometheus native histograms.
issues: [52834]
change_logs: [user]
14 changes: 2 additions & 12 deletions exporter/prometheusexporter/collector.go
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Expand Up @@ -192,12 +192,7 @@ func (c *collector) convertMetric(metric pmetric.Metric, resourceAttrs pcommon.M
return nil, errUnknownMetricType
}

// defaultZeroThreshold matches the remote-write translator's default for native histograms
// when an explicit zero threshold is not provided in the datapoint.
const (
defaultZeroThreshold = 1e-128
cbnhScale = -53
)
const cbnhScale = -53

func bucketsToNativeMap(buckets pmetric.ExponentialHistogramDataPointBuckets, scaleDown int32) map[int]int64 {
counts := buckets.BucketCounts()
Expand Down Expand Up @@ -247,11 +242,6 @@ func (c *collector) convertExponentialHistogram(metric pmetric.Metric, resourceA
pos := bucketsToNativeMap(dp.Positive(), scaleDown)
neg := bucketsToNativeMap(dp.Negative(), scaleDown)

zeroThresh := dp.ZeroThreshold()
if zeroThresh == 0 {
zeroThresh = defaultZeroThreshold
}

// Use created timestamp if start time is set (> 0), else zero value.
created := time.Time{}
if dp.StartTimestamp().AsTime().Unix() > 0 {
Expand All @@ -266,7 +256,7 @@ func (c *collector) convertExponentialHistogram(metric pmetric.Metric, resourceA
neg,
dp.ZeroCount(),
schema,
zeroThresh,
dp.ZeroThreshold(),
created,
attributes...,
)
Expand Down
57 changes: 54 additions & 3 deletions exporter/prometheusexporter/collector_test.go
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Expand Up @@ -907,12 +907,12 @@ func TestAccumulateExponentialHistograms(t *testing.T) {
wantZeroThresh float64
}{
{
name: "NativeHistogram basic (default zero threshold)",
name: "NativeHistogram basic (zero threshold)",
wantCount: 10,
wantSum: 42.0,
wantSchema: 0,
wantZeroCount: 4,
wantZeroThresh: defaultZeroThreshold,
wantZeroThresh: 0,
metric: func(ts time.Time, withStartTime bool) (metric pmetric.Metric) {
metric = pmetric.NewMetric()
metric.SetName("test_native_hist")
Expand All @@ -926,7 +926,7 @@ func TestAccumulateExponentialHistograms(t *testing.T) {
dp.SetZeroCount(4)
dp.SetCount(10)
dp.SetSum(42.0)
dp.SetZeroThreshold(0) // trigger defaultZeroThreshold
dp.SetZeroThreshold(0)
dp.Attributes().PutStr("label_1", "1")
dp.Attributes().PutStr("label_2", "2")
dp.SetTimestamp(pcommon.NewTimestampFromTime(ts))
Expand Down Expand Up @@ -1289,3 +1289,54 @@ func TestTargetInfoIdentifyingResourceAttributes(t *testing.T) {
})
}
}

func TestConvertExponentialHistogramZeroThreshold(t *testing.T) {
tests := []struct {
name string
threshold float64
setThreshold bool
offset int32
}{
{name: "unset threshold", offset: -432},
{name: "explicit zero threshold", setThreshold: true, offset: -432},
{name: "nonzero threshold", threshold: 0.5, setThreshold: true},
}
for _, tt := range tests {
t.Run(tt.name, func(t *testing.T) {
metric := pmetric.NewMetric()
metric.SetName("test_native_histogram")
hist := metric.SetEmptyExponentialHistogram()
hist.SetAggregationTemporality(pmetric.AggregationTemporalityCumulative)
dp := hist.DataPoints().AppendEmpty()
dp.SetScale(0)
dp.SetCount(3)
dp.SetSum(0)
dp.SetZeroCount(1)
if tt.setThreshold {
dp.SetZeroThreshold(tt.threshold)
}
dp.Positive().SetOffset(tt.offset)
dp.Positive().BucketCounts().FromRaw([]uint64{1})
dp.Negative().SetOffset(tt.offset)
dp.Negative().BucketCounts().FromRaw([]uint64{1})
c := newCollector(&Config{}, zap.NewNop())
m, err := c.convertExponentialHistogram(metric, pcommon.NewMap(), "", "", "", pcommon.NewMap())
require.NoError(t, err)
out := &io_prometheus_client.Metric{}
require.NoError(t, m.Write(out))
h := out.GetHistogram()
require.Equal(t, tt.threshold, h.GetZeroThreshold())
require.Equal(t, uint64(3), h.GetSampleCount())
require.Equal(t, uint64(1), h.GetZeroCount())
require.Equal(t, 0.0, h.GetSampleSum())
require.Len(t, h.PositiveSpan, 1)
require.Len(t, h.NegativeSpan, 1)
require.Equal(t, tt.offset+1, h.PositiveSpan[0].GetOffset())
require.Equal(t, tt.offset+1, h.NegativeSpan[0].GetOffset())
require.Equal(t, uint32(1), h.PositiveSpan[0].GetLength())
require.Equal(t, uint32(1), h.NegativeSpan[0].GetLength())
require.Equal(t, []int64{1}, h.PositiveDelta)
require.Equal(t, []int64{1}, h.NegativeDelta)
})
}
}
11 changes: 2 additions & 9 deletions pkg/translator/prometheusremotewrite/histograms.go
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Expand Up @@ -18,8 +18,6 @@ import (
"go.uber.org/multierr"
)

const defaultZeroThreshold = 1e-128

// explicitToNHCB converts an OTLP explicit-bucket histogram data point to a
// Prometheus histogram with custom buckets (schema -53) via Prometheus' own
// convertnhcb helper. Exactly one of the returned histograms is non-nil.
Expand Down Expand Up @@ -149,7 +147,8 @@ func exponentialToNativeHistogram(p pmetric.ExponentialHistogramDataPoint) (prom
ResetHint: prompb.Histogram_UNKNOWN,
Schema: scale,

ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: p.ZeroCount()},
ZeroThreshold: p.ZeroThreshold(),
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: p.ZeroCount()},

PositiveSpans: pSpans,
PositiveDeltas: pDeltas,
Expand All @@ -159,12 +158,6 @@ func exponentialToNativeHistogram(p pmetric.ExponentialHistogramDataPoint) (prom
Timestamp: convertTimeStamp(p.Timestamp()),
}

if p.ZeroThreshold() != 0 {
h.ZeroThreshold = p.ZeroThreshold()
} else {
h.ZeroThreshold = defaultZeroThreshold
}

if p.Flags().NoRecordedValue() {
h.Sum = math.Float64frombits(value.StaleNaN)
h.Count = &prompb.Histogram_CountInt{CountInt: value.StaleNaN}
Expand Down
41 changes: 34 additions & 7 deletions pkg/translator/prometheusremotewrite/histograms_test.go
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Expand Up @@ -528,6 +528,33 @@ func TestExponentialToNativeHistogram(t *testing.T) {
wantNativeHist func() prompb.Histogram
wantErrMessage string
}{
{
name: "preserve zero threshold with tiny positive and negative buckets",
exponentialHist: func() pmetric.ExponentialHistogramDataPoint {
pt := pmetric.NewExponentialHistogramDataPoint()
pt.SetScale(0)
pt.SetCount(2)
pt.SetSum(0)
pt.SetZeroCount(0)
pt.SetZeroThreshold(0)
// At scale 0, bucket -432 has upper bound 2^-431, below 1e-128.
pt.Positive().SetOffset(-432)
pt.Positive().BucketCounts().FromRaw([]uint64{1})
pt.Negative().SetOffset(-432)
pt.Negative().BucketCounts().FromRaw([]uint64{1})
return pt
},
wantNativeHist: func() prompb.Histogram {
return prompb.Histogram{
Count: &prompb.Histogram_CountInt{CountInt: 2},
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []prompb.BucketSpan{{Offset: -431, Length: 1}},
PositiveDeltas: []int64{1},
NegativeSpans: []prompb.BucketSpan{{Offset: -431, Length: 1}},
NegativeDeltas: []int64{1},
}
},
},
{
name: "convert exp. to native histogram",
exponentialHist: func() pmetric.ExponentialHistogramDataPoint {
Expand All @@ -552,7 +579,7 @@ func TestExponentialToNativeHistogram(t *testing.T) {
Count: &prompb.Histogram_CountInt{CountInt: 4},
Sum: 10.1,
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 1},
NegativeSpans: []prompb.BucketSpan{{Offset: 2, Length: 2}},
NegativeDeltas: []int64{1, 0},
Expand Down Expand Up @@ -650,7 +677,7 @@ func TestExponentialToNativeHistogram(t *testing.T) {
Count: &prompb.Histogram_CountInt{CountInt: 6},
Sum: 10.1,
Schema: 8,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 1},
PositiveSpans: []prompb.BucketSpan{{Offset: 2, Length: 3}},
PositiveDeltas: []int64{1, 0, 0}, // 1, 1, 1
Expand Down Expand Up @@ -682,7 +709,7 @@ func TestExponentialToNativeHistogram(t *testing.T) {
Count: &prompb.Histogram_CountInt{CountInt: 6},
Sum: 10.1,
Schema: 8,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 1},
PositiveSpans: []prompb.BucketSpan{{Offset: 1, Length: 2}},
PositiveDeltas: []int64{1, 1}, // 0+1, 1+1 = 1, 2
Expand Down Expand Up @@ -785,15 +812,15 @@ func TestPrometheusConverter_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &prompb.Histogram_CountInt{CountInt: 7},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []prompb.BucketSpan{{Offset: 0, Length: 2}},
PositiveDeltas: []int64{4, -2},
},
{
Count: &prompb.Histogram_CountInt{CountInt: 4},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []prompb.BucketSpan{{Offset: 0, Length: 3}},
PositiveDeltas: []int64{4, -2, -1},
Expand Down Expand Up @@ -851,7 +878,7 @@ func TestPrometheusConverter_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &prompb.Histogram_CountInt{CountInt: 7},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []prompb.BucketSpan{{Offset: 0, Length: 2}},
PositiveDeltas: []int64{4, -2},
Expand All @@ -867,7 +894,7 @@ func TestPrometheusConverter_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &prompb.Histogram_CountInt{CountInt: 4},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &prompb.Histogram_ZeroCountInt{ZeroCountInt: 0},
NegativeSpans: []prompb.BucketSpan{{Offset: 0, Length: 3}},
NegativeDeltas: []int64{4, -2, -1},
Expand Down
7 changes: 1 addition & 6 deletions pkg/translator/prometheusremotewrite/histograms_v2.go
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Expand Up @@ -102,11 +102,6 @@ func exponentialToNativeHistogramV2(p pmetric.ExponentialHistogramDataPoint) (wr
pSpans, pDeltas := convertBucketsLayoutV2(p.Positive(), scaleDown)
nSpans, nDeltas := convertBucketsLayoutV2(p.Negative(), scaleDown)

zeroThreshold := p.ZeroThreshold()
if zeroThreshold == 0 {
zeroThreshold = defaultZeroThreshold
}

h := writev2.Histogram{
// The counter reset detection must be compatible with Prometheus to
// safely set ResetHint to NO. This is not ensured currently.
Expand All @@ -121,7 +116,7 @@ func exponentialToNativeHistogramV2(p pmetric.ExponentialHistogramDataPoint) (wr
Schema: scale,

ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: p.ZeroCount()},
ZeroThreshold: zeroThreshold,
ZeroThreshold: p.ZeroThreshold(),

PositiveSpans: pSpans,
PositiveDeltas: pDeltas,
Expand Down
41 changes: 34 additions & 7 deletions pkg/translator/prometheusremotewrite/histograms_v2_test.go
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Expand Up @@ -553,6 +553,33 @@ func TestExponentialToNativeHistogramV2(t *testing.T) {
wantNativeHist func() writev2.Histogram
wantErrMessage string
}{
{
name: "preserve zero threshold with tiny positive and negative buckets",
exponentialHist: func() pmetric.ExponentialHistogramDataPoint {
pt := pmetric.NewExponentialHistogramDataPoint()
pt.SetScale(0)
pt.SetCount(2)
pt.SetSum(0)
pt.SetZeroCount(0)
pt.SetZeroThreshold(0)
// At scale 0, bucket -432 has upper bound 2^-431, below 1e-128.
pt.Positive().SetOffset(-432)
pt.Positive().BucketCounts().FromRaw([]uint64{1})
pt.Negative().SetOffset(-432)
pt.Negative().BucketCounts().FromRaw([]uint64{1})
return pt
},
wantNativeHist: func() writev2.Histogram {
return writev2.Histogram{
Count: &writev2.Histogram_CountInt{CountInt: 2},
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []writev2.BucketSpan{{Offset: -431, Length: 1}},
PositiveDeltas: []int64{1},
NegativeSpans: []writev2.BucketSpan{{Offset: -431, Length: 1}},
NegativeDeltas: []int64{1},
}
},
},
{
name: "convert exp. to native histogram",
exponentialHist: func() pmetric.ExponentialHistogramDataPoint {
Expand All @@ -577,7 +604,7 @@ func TestExponentialToNativeHistogramV2(t *testing.T) {
Count: &writev2.Histogram_CountInt{CountInt: 4},
Sum: 10.1,
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 1},
NegativeSpans: []writev2.BucketSpan{{Offset: 2, Length: 2}},
NegativeDeltas: []int64{1, 0},
Expand Down Expand Up @@ -641,7 +668,7 @@ func TestExponentialToNativeHistogramV2(t *testing.T) {
Count: &writev2.Histogram_CountInt{CountInt: 6},
Sum: 10.1,
Schema: 8,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 1},
PositiveSpans: []writev2.BucketSpan{{Offset: 2, Length: 3}},
PositiveDeltas: []int64{1, 0, 0}, // 1, 1, 1
Expand Down Expand Up @@ -673,7 +700,7 @@ func TestExponentialToNativeHistogramV2(t *testing.T) {
Count: &writev2.Histogram_CountInt{CountInt: 6},
Sum: 10.1,
Schema: 8,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 1},
PositiveSpans: []writev2.BucketSpan{{Offset: 1, Length: 2}},
PositiveDeltas: []int64{1, 1}, // 0+1, 1+1 = 1, 2
Expand Down Expand Up @@ -806,15 +833,15 @@ func TestPrometheusConverterV2_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &writev2.Histogram_CountInt{CountInt: 7},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []writev2.BucketSpan{{Offset: 0, Length: 2}},
PositiveDeltas: []int64{4, -2},
},
{
Count: &writev2.Histogram_CountInt{CountInt: 4},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []writev2.BucketSpan{{Offset: 0, Length: 3}},
PositiveDeltas: []int64{4, -2, -1},
Expand Down Expand Up @@ -875,7 +902,7 @@ func TestPrometheusConverterV2_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &writev2.Histogram_CountInt{CountInt: 7},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 0},
PositiveSpans: []writev2.BucketSpan{{Offset: 0, Length: 2}},
PositiveDeltas: []int64{4, -2},
Expand All @@ -894,7 +921,7 @@ func TestPrometheusConverterV2_addExponentialHistogramDataPoints(t *testing.T) {
{
Count: &writev2.Histogram_CountInt{CountInt: 4},
Schema: 1,
ZeroThreshold: defaultZeroThreshold,
ZeroThreshold: 0,
ZeroCount: &writev2.Histogram_ZeroCountInt{ZeroCountInt: 0},
NegativeSpans: []writev2.BucketSpan{{Offset: 0, Length: 3}},
NegativeDeltas: []int64{4, -2, -1},
Expand Down
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