grafana/k6 · error

unable to run Thresholds; reason: unknown sink type

Error message

unable to run Thresholds; reason: unknown sink type

What it means

Thresholds.Run switches on the concrete sink type of the metric the thresholds apply to; the default branch fires when the metric's Sink is not one of the supported types (Counter, Gauge, Trend, Rate). This means thresholds were configured on a metric whose sink implementation the threshold engine cannot read — an internal/registration inconsistency rather than a user expression problem.

Source

Thrown at metrics/thresholds.go:214

		// Parse the percentile thresholds and insert them in
		// the sinks mapping.
		for _, threshold := range ts.Thresholds {
			if threshold.parsed.AggregationMethod != tokenPercentile {
				continue
			}

			key := fmt.Sprintf("p(%g)", threshold.parsed.AggregationValue.Float64)
			ts.sinked[key] = sinkImpl.P(threshold.parsed.AggregationValue.Float64 / 100)
		}
	case *RateSink:
		// We want to avoid division by zero, which
		// would lead to [#2520](https://github.com/grafana/k6/issues/2520)
		if sinkImpl.Total > 0 {
			ts.sinked["rate"] = float64(sinkImpl.Trues) / float64(sinkImpl.Total)
		}
	default:
		return false, fmt.Errorf("unable to run Thresholds; reason: unknown sink type")
	}

	return ts.runAll(duration)
}

// Parse parses the Thresholds and fills each Threshold.parsed field with the result.
// It effectively asserts they are syntaxically correct.
func (ts *Thresholds) Parse() error {
	for _, t := range ts.Thresholds {
		parsed, err := parseThresholdExpression(t.Source)
		if err != nil {
			return err
		}

		t.parsed = parsed
	}

	return nil

View on GitHub (pinned to 01ffac6f24)

Solutions

1. Check which metric the thresholds are defined on and verify it was registered with a standard type (counter, gauge, trend, rate)
2. If using a custom metric/extension, ensure its sink implements one of the known sink types
3. Report as a k6 bug if the metric is a built-in type

When it happens

Trigger: Thrown at metrics/thresholds.go:214 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/69e52ed3dd3de279. Report an issue: GitHub.