func BenchmarkLabelMatching(b *testing.B) {
	s, closer := NewTestStorage(b, 1)
	defer closer.Close()

	h := fnv.New64a()
	lbl := func(x int) clientmodel.LabelValue {
		h.Reset()
		h.Write([]byte(fmt.Sprintf("%d", x)))
		return clientmodel.LabelValue(fmt.Sprintf("%d", h.Sum64()))
	}

	M := 32
	met := clientmodel.Metric{}
	for i := 0; i < M; i++ {
		met["label_a"] = lbl(i)
		for j := 0; j < M; j++ {
			met["label_b"] = lbl(j)
			for k := 0; k < M; k++ {
				met["label_c"] = lbl(k)
				for l := 0; l < M; l++ {
					met["label_d"] = lbl(l)
					s.Append(&clientmodel.Sample{
						Metric:    met.Clone(),
						Timestamp: 0,
						Value:     1,
					})
				}
			}
		}
	}
	s.WaitForIndexing()

	newMatcher := func(matchType metric.MatchType, name clientmodel.LabelName, value clientmodel.LabelValue) *metric.LabelMatcher {
		lm, err := metric.NewLabelMatcher(matchType, name, value)
		if err != nil {
			b.Fatalf("error creating label matcher: %s", err)
		}
		return lm
	}

	var matcherTests = []metric.LabelMatchers{
		{
			newMatcher(metric.Equal, "label_a", lbl(1)),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(3)),
			newMatcher(metric.Equal, "label_c", lbl(3)),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(3)),
			newMatcher(metric.Equal, "label_c", lbl(3)),
			newMatcher(metric.NotEqual, "label_d", lbl(3)),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(3)),
			newMatcher(metric.Equal, "label_b", lbl(3)),
			newMatcher(metric.Equal, "label_c", lbl(3)),
			newMatcher(metric.NotEqual, "label_d", lbl(3)),
		},
		{
			newMatcher(metric.RegexMatch, "label_a", ".+"),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(3)),
			newMatcher(metric.RegexMatch, "label_a", ".+"),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(1)),
			newMatcher(metric.RegexMatch, "label_c", "("+lbl(3)+"|"+lbl(10)+")"),
		},
		{
			newMatcher(metric.Equal, "label_a", lbl(3)),
			newMatcher(metric.Equal, "label_a", lbl(4)),
			newMatcher(metric.RegexMatch, "label_c", "("+lbl(3)+"|"+lbl(10)+")"),
		},
	}

	b.ReportAllocs()
	b.ResetTimer()

	for i := 0; i < b.N; i++ {
		benchLabelMatchingRes = map[clientmodel.Fingerprint]clientmodel.COWMetric{}
		for _, mt := range matcherTests {
			benchLabelMatchingRes = s.MetricsForLabelMatchers(mt...)
		}
	}
	// Stop timer to not count the storage closing.
	b.StopTimer()
}