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Fix CumulativeCount value of +Inf bucket created from exemplar (#…
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…1148)

* Fix `CumulativeCount` value of `+Inf` bucket created from exemplar

Signed-off-by: Balint Zsilavecz <balint.zsilavecz@skyscanner.net>

* Update prometheus/metric_test.go

Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>
Signed-off-by: Balint Zsilavecz <balint.zsilavecz@skyscanner.net>

* Clarify description of implicit `+Inf` bucket count

Signed-off-by: Balint Zsilavecz <balint.zsilavecz@skyscanner.net>

* Fix test variables

Signed-off-by: Balint Zsilavecz <balint.zsilavecz@skyscanner.net>

Signed-off-by: Balint Zsilavecz <balint.zsilavecz@skyscanner.net>
Co-authored-by: Bartlomiej Plotka <bwplotka@gmail.com>
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balintzs and bwplotka committed Nov 1, 2022
1 parent 8cc2b6c commit 1f93f64
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Showing 3 changed files with 9 additions and 5 deletions.
2 changes: 1 addition & 1 deletion prometheus/histogram.go
Original file line number Diff line number Diff line change
Expand Up @@ -613,7 +613,7 @@ func (h *constHistogram) Write(out *dto.Metric) error {
// to send it to Prometheus in the Collect method.
//
// buckets is a map of upper bounds to cumulative counts, excluding the +Inf
// bucket.
// bucket. The +Inf bucket is implicit, and its value is equal to the provided count.
//
// NewConstHistogram returns an error if the length of labelValues is not
// consistent with the variable labels in Desc or if Desc is invalid.
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2 changes: 1 addition & 1 deletion prometheus/metric.go
Original file line number Diff line number Diff line change
Expand Up @@ -187,7 +187,7 @@ func (m *withExemplarsMetric) Write(pb *dto.Metric) error {
} else {
// The +Inf bucket should be explicitly added if there is an exemplar for it, similar to non-const histogram logic in https://github.com/prometheus/client_golang/blob/main/prometheus/histogram.go#L357-L365.
b := &dto.Bucket{
CumulativeCount: proto.Uint64(pb.Histogram.Bucket[len(pb.Histogram.GetBucket())-1].GetCumulativeCount()),
CumulativeCount: proto.Uint64(pb.Histogram.GetSampleCount()),
UpperBound: proto.Float64(math.Inf(1)),
Exemplar: e,
}
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10 changes: 7 additions & 3 deletions prometheus/metric_test.go
Original file line number Diff line number Diff line change
Expand Up @@ -79,10 +79,14 @@ func TestWithExemplarsMetric(t *testing.T) {
}
}

infBucket := metric.GetHistogram().Bucket[len(metric.GetHistogram().Bucket)-1].GetUpperBound()
infBucket := metric.GetHistogram().Bucket[len(metric.GetHistogram().Bucket)-1]

if infBucket != math.Inf(1) {
t.Errorf("want %v, got %v", math.Inf(1), infBucket)
if want, got := math.Inf(1), infBucket.GetUpperBound(); want != got {
t.Errorf("want %v, got %v", want, got)
}

if want, got := uint64(4711), infBucket.GetCumulativeCount(); want != got {
t.Errorf("want %v, got %v", want, got)
}
})
}

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