[receiver/prometheusreceiver] does not handle native histograms with custom bucket correctly

[krajorama]

Component(s)

receiver/prometheus

What happened?

Description

Native histograms with custom buckets should be converted to explicit Otel histograms, not exponential Otel histograms with fake schema -53.

See https://prometheus.io/docs/specs/native_histograms/#custom-values

Steps to Reproduce

Add unit test to enable Prometheus parsing to produce NHCB.
Enable the native histograms feature gate.
No need for protobuf input, normal text will work.

Expected Result

Explicit histogram metric on Otel side.

Actual Result

I expect invalid exponential histogram.

Collector version

v0.128.0

Environment information

Environment

OS: (e.g., "Ubuntu 20.04")
Compiler(if manually compiled): (e.g., "go 14.2")

OpenTelemetry Collector configuration

Log output

Additional context

No response

Tip

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[github-actions]

Pinging code owners:

• receiver/prometheus: @Aneurysm9 @dashpole @ArthurSens @krajorama

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[github-actions]

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Pinging code owners:

• receiver/prometheusreceiver: @Aneurysm9 @dashpole @ArthurSens @krajorama

See Adding Labels via Comments if you do not have permissions to add labels yourself.

[jelly-afk]

Hi, I would like to work on this

[dashpole]

Great! Some pointers:

Right now, we always call addExponentialHistogramSeries in AppendHistogram:

opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/transaction.go

Line 335 in 02a4c4f

err = curMF.addExponentialHistogramSeries(t.getSeriesRef(ls, curMF.mtype), metricName, ls, atMs, h, fh)

We will want to add a special case where if the schema is -53, we set the Histogram fields, similar to

opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/metricfamily.go

Lines 393 to 411 in ac33209

	case pmetric.MetricTypeHistogram, pmetric.MetricTypeSummary:
	switch {
	case strings.HasSuffix(metricName, metricsSuffixSum):
	mg.sum = v
	mg.hasSum = true
	case strings.HasSuffix(metricName, metricsSuffixCount):
	// always use the timestamp from count, because is the only required field for histograms and summaries.
	mg.ts = t
	mg.count = v
	mg.hasCount = true
	case metricName == mf.metadata.MetricFamily+metricSuffixCreated:
	mg.createdSeconds = v
	default:
	boundary, err := getBoundary(mf.mtype, ls)
	if err != nil {
	return err
	}
	mg.complexValue = append(mg.complexValue, &dataPoint{value: v, boundary: boundary})
	}

We will also need to not set the mtype to Exponential histogram here if schema is -53:

opentelemetry-collector-contrib/receiver/prometheusreceiver/internal/transaction.go

Lines 247 to 248 in ac33209

	if curMf.mtype == pmetric.MetricTypeHistogram && mfKey.isExponentialHistogram {
	curMf.mtype = pmetric.MetricTypeExponentialHistogram