thanos-io/thanos · error

unrecognized matcher type

Error message

unrecognized matcher type %d

What it means

While converting Prometheus label matchers to Thanos proto matchers, the matcher's MatchType did not match any of the four known types (equal, not-equal, regexp, not-regexp). This indicates a version mismatch with the vendored Prometheus library that introduced a new match type, or memory corruption of the matcher — user queries cannot normally produce it.

Solutions

1. Add an explicit case for the new labels.MatchType in the switch in PromMatchersToMatchers and map it to the corresponding storepb LabelMatcher_Type, then regenerate/check storepb bindings.
2. If the matcher type should never reach the store API, validate and reject it earlier at the API layer so internal conversion never sees an unknown type.
3. Write a unit test iterating all labels.MatchType values through PromMatchersToMatchers to catch unmapped enum values at compile/test time instead of at runtime.
4. If a Prometheus upgrade added the type, pin or upgrade the Prometheus dependency deliberately and port the mapping as part of the upgrade.

When it happens

Trigger: Thrown at pkg/store/storepb/custom.go:388 when the library encounters an invalid state.

Common situations: See trigger scenarios.

AI-assisted analysis of thanos-io/thanos@35b8b99117 (2026-09-07). Data as JSON: /api/errors/92bc571df3f6bde4. Report an issue: GitHub.

Appendix: source

Thrown at pkg/store/storepb/custom.go:388

// PromMatchersToMatchers returns proto matchers from Prometheus matchers.
// NOTE: It allocates memory.
func PromMatchersToMatchers(ms ...*labels.Matcher) ([]LabelMatcher, error) {
	res := make([]LabelMatcher, 0, len(ms))
	for _, m := range ms {
		var t LabelMatcher_Type

		switch m.Type {
		case labels.MatchEqual:
			t = LabelMatcher_EQ
		case labels.MatchNotEqual:
			t = LabelMatcher_NEQ
		case labels.MatchRegexp:
			t = LabelMatcher_RE
		case labels.MatchNotRegexp:
			t = LabelMatcher_NRE
		default:
			return nil, errors.Errorf("unrecognized matcher type %d", m.Type)
		}
		res = append(res, LabelMatcher{Type: t, Name: m.Name, Value: m.Value})
	}
	return res, nil
}

// MatchersToPromMatchers returns Prometheus matchers from proto matchers.
// NOTE: It allocates memory.
func MatchersToPromMatchers(ms ...LabelMatcher) ([]*labels.Matcher, error) {
	res := make([]*labels.Matcher, 0, len(ms))
	for i := range ms {
		pm, err := MatcherToPromMatcher(ms[i])
		if err != nil {
			return nil, err
		}
		res = append(res, pm)
	}
	return res, nil

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