thanos-io/thanos · error

decode result into ValueTypeMatrix

Error message

decode result into ValueTypeMatrix

What it means

After the envelope decodes, QueryRange sees data.resultType == "matrix" and unmarshals data.result into prometheus/common's model.Matrix. This error wraps a failure to decode the raw result JSON into that type — the samples/series inside data.result do not match the expected matrix JSON structure (arrays of {metric, values} objects).

Solutions

1. Log m.Data.Result (raw JSON) at the call site to inspect the actual sample structure.
2. Confirm the server is genuine Prometheus/Thanos and check its version; upgrade if a known result-encoding bug exists.
3. Check for response-rewriting middleware or caches in the path and bypass them to test directly.
4. Validate the query itself does not hit a federated/gateway layer that reformats results.

if err != nil && strings.Contains(err.Error(), "decode result into ValueTypeMatrix") {
    // capture raw result for debugging; suspect server/middleware corruption
}

When it happens

Trigger: QueryRange (via Exec) receives a 200 response whose resultType is "matrix" but whose result payload cannot decode into model.Matrix — e.g. values arrays containing non-numeric strings, malformed sample pairs, or a nonstandard result emitted by a proxy/modified server.

Common situations: A third-party or older server claiming resultType matrix but emitting differently shaped samples; a caching proxy serving a corrupted/cached body; custom Prometheus forks or response-rewriting middleware.

Understand the failure class

Background: "failed to unmarshal" / json.Unmarshal errors: why parsing a response into a Go struct fails and how to fix it — this error's family across 23 libraries.

Related errors

• unmarshal response
• unmarshal query instant response
• unmarshal query range response
• unmarshal build info API response
• unmarshal marker JSON

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/77c04d4de500d770. Report an issue: GitHub.

Appendix: source

Thrown at pkg/promclient/promclient.go:589

		} `json:"data"`

		Error     string `json:"error,omitempty"`
		ErrorType string `json:"errorType,omitempty"`
		// Extra fields supported by Thanos Querier.
		Warnings []string `json:"warnings"`
	}

	if err = json.Unmarshal(body, &m); err != nil {
		return nil, nil, nil, errors.Wrap(err, "unmarshal query range response")
	}

	var matrixResult model.Matrix

	// Decode the Result depending on the ResultType
	switch m.Data.ResultType {
	case string(parser.ValueTypeMatrix):
		if err = json.Unmarshal(m.Data.Result, &matrixResult); err != nil {
			return nil, nil, nil, errors.Wrap(err, "decode result into ValueTypeMatrix")
		}
	default:
		if m.Warnings != nil {
			return nil, nil, nil, errors.Errorf("error: %s, type: %s, warning: %s", m.Error, m.ErrorType, strings.Join(m.Warnings, ", "))
		}
		if m.Error != "" {
			return nil, nil, nil, errors.Errorf("error: %s, type: %s", m.Error, m.ErrorType)
		}

		return nil, nil, nil, errors.Errorf("received status code: 200, unknown response type: '%q'", m.Data.ResultType)
	}
	return matrixResult, m.Warnings, m.Data.Explanation, nil
}

// Scalar response consists of array with mixed types so it needs to be
// unmarshaled separately.
func convertScalarJSONToVector(scalarJSONResult json.RawMessage) (model.Vector, error) {
	var (

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