grafana/k6 · error

metric %q is not a gauge

Error message

metric %q is not a gauge

What it means

getOrCreateGauge looks up the name in the gauges sync.Map and type-asserts to otelMetric.Float64Gauge. If a value exists but is not a gauge, the same metric name was registered earlier as another instrument type; a naming collision in registry state makes dispatch fail. Internal consistency error, not user-caused.

Source

Thrown at internal/output/opentelemetry/registry.go:116

		r.rateCounters.Store(totalName, totalCounter)
		r.logger.Debugf("registered counter metric %q", totalName)
	} else {
		totalCounter, ok = storedTotalCounter.(otelMetric.Int64Counter)
		if !ok {
			return nil, fmt.Errorf("metric %q stored not as counter", totalName)
		}
	}

	return totalCounter, nil
}

func (r *registry) getOrCreateGauge(name, unit string) (otelMetric.Float64Gauge, error) {
	if gauge, ok := r.gauges.Load(name); ok {
		if v, ok := gauge.(otelMetric.Float64Gauge); ok {
			return v, nil
		}

		return nil, fmt.Errorf("metric %q is not a gauge", name)
	}

	opts := []otelMetric.Float64GaugeOption{}
	if unit != "" {
		opts = append(opts, otelMetric.WithUnit(unit))
	}

	gauge, err := r.meter.Float64Gauge(name, opts...)
	if err != nil {
		return nil, fmt.Errorf("failed to create gauge for %q: %w", name, err)
	}

	r.logger.Debugf("registered gauge metric %q ", name)

	r.gauges.Store(name, gauge)
	return gauge, nil
}

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Rename the gauge metric to avoid name collisions with counters/histograms
2. Use distinct names per metric type

When it happens

Trigger: Thrown at internal/output/opentelemetry/registry.go:116 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of grafana/k6@01ffac6f24 (2026-08-18). Data as JSON: /api/errors/8558fbc7d6f41781. Report an issue: GitHub.