mdatagen Histogram Metric Compilation Error #13575
Description
Component(s)
cmd/mdatagen
Problem
When defining a histogram metric in the metrics: section of metadata.yaml, mdatagen generates Go code that fails to compile. The build fails with the following error:
internal/metadata/generated_metrics.go:50:5: dp.SetDoubleValue undefined (type pmetric.HistogramDataPoint has no field or method SetDoubleValue)
How to Reproduce
-
Create a minimal project structure with the following files:
metadata.yaml:
type: test status: class: receiver stability: development: [metrics] metrics: test.duration: description: Test histogram metric enabled: true unit: s histogram: value_type: double attributes: []
doc.go:
// Package testhistogramissue demonstrates mdatagen histogram bug. package testhistogramissue
go.mod:
module testhistogramissue go 1.22
-
Run mdatagen to generate the component files:
mdatagen metadata.yaml
-
Install dependencies:
go get go.opentelemetry.io/collector/pdata@v1.37.0 go get go.opentelemetry.io/collector/component@v1.37.0 go get go.opentelemetry.io/collector/receiver@v1.37.0 go get go.opentelemetry.io/collector/confmap@v1.37.0
-
Attempt to build the generated code:
go build ./internal/metadata
The build will fail with the error shown above.
Generated Code Issue
The problematic code is generated in internal/metadata/generated_metrics.go at line 50:
func (m *metricTestDuration) recordDataPoint(start pcommon.Timestamp, ts pcommon.Timestamp, val float64) {
if !m.config.Enabled {
return
}
dp := m.data.Histogram().DataPoints().AppendEmpty()
dp.SetStartTimestamp(start)
dp.SetTimestamp(ts)
dp.SetDoubleValue(val) // ← This line causes the compilation error
}Root Cause
The code generation template incorrectly assumes all metric types use the same data point methods. The template generates:
dp.SetDoubleValue(val)This works for pmetric.NumberDataPoint (used by Gauge and Sum metrics) but fails for pmetric.HistogramDataPoint.
What HistogramDataPoint Actually Requires
The pmetric.HistogramDataPoint type doesn't have SetDoubleValue() or SetIntValue() methods. Instead, it requires:
SetCount(uint64)- to set the number of observationsSetSum(float64)- to set the sum of observationsExplicitBounds().FromRaw([]float64)- to set bucket boundariesBucketCounts().FromRaw([]uint64)- to set the count per bucket
The current mdatagen template doesn't account for this structural difference between histogram and scalar metric types.
Environment
- OpenTelemetry Collector version: v1.37.0
- Go version: 1.24.4
- mdatagen: v0.131.0
Impact
This issue prevents the use of histogram metrics in the metrics: section of any OpenTelemetry Collector component. Currently, it seems that no components in opentelemetry-collector-contrib use histograms for component metrics. There are cases where it should arguably be used - such as latency distributions.
Additional Context
- This issue only affects component metrics (in the
metrics:section) - Histogram metrics in the
telemetry:section work correctly as they use a different code generation path via the OpenTelemetry SDK - The workaround is to use Gauge metrics instead of histograms, though this loses the benefits of histogram aggregation
Collector version
v1.37.0
Environment information
Environment
- OpenTelemetry Collector version: v1.37.0
- Go version: 1.24.4
- mdatagen: v0.131.0
OpenTelemetry Collector configuration
Log output
Additional context
No response
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