storage: make histogram reset handling consistent in chainSampleIterator (#12779)

storage: make histogram reset handling consistent in chainSampleIterator

---------

Signed-off-by: György Krajcsovits <gyorgy.krajcsovits@grafana.com>

storage/merge.go

@@ -523,8 +523,12 @@ func (c *chainSampleIterator) AtHistogram() (int64, *histogram.Histogram) {
 	}
 	t, h := c.curr.AtHistogram()
 	// If the current sample is not consecutive with the previous one, we
-	// cannot be sure anymore that there was no counter reset.
-	if !c.consecutive && h.CounterResetHint == histogram.NotCounterReset {
+	// cannot be sure anymore about counter resets for counter histograms.
+	// TODO(beorn7): If a `NotCounterReset` sample is followed by a
+	// non-consecutive `CounterReset` sample, we could keep the hint as
+	// `CounterReset`. But then we needed to track the previous sample
+	// in more detail, which might not be worth it.
+	if !c.consecutive && h.CounterResetHint != histogram.GaugeType {
 		h.CounterResetHint = histogram.UnknownCounterReset
 	}
 	return t, h

storage/merge_test.go

@@ -24,6 +24,7 @@ import (
 
 	"github.com/stretchr/testify/require"
 
+	"github.com/prometheus/prometheus/model/histogram"
 	"github.com/prometheus/prometheus/model/labels"
 	"github.com/prometheus/prometheus/tsdb/chunkenc"
 	"github.com/prometheus/prometheus/tsdb/chunks"
@@ -384,16 +385,36 @@ func TestMergeChunkQuerierWithNoVerticalChunkSeriesMerger(t *testing.T) {
 	}
 }
 
+func histogramSample(ts int64, hint histogram.CounterResetHint) hSample {
+	h := tsdbutil.GenerateTestHistogram(int(ts + 1))
+	h.CounterResetHint = hint
+	return hSample{t: ts, h: h}
+}
+
+func floatHistogramSample(ts int64, hint histogram.CounterResetHint) fhSample {
+	fh := tsdbutil.GenerateTestFloatHistogram(int(ts + 1))
+	fh.CounterResetHint = hint
+	return fhSample{t: ts, fh: fh}
+}
+
+// Shorthands for counter reset hints.
+const (
+	uk = histogram.UnknownCounterReset
+	cr = histogram.CounterReset
+	nr = histogram.NotCounterReset
+	ga = histogram.GaugeType
+)
+
 func TestCompactingChunkSeriesMerger(t *testing.T) {
 	m := NewCompactingChunkSeriesMerger(ChainedSeriesMerge)
 
 	// histogramSample returns a histogram that is unique to the ts.
 	histogramSample := func(ts int64) hSample {
-		return hSample{t: ts, h: tsdbutil.GenerateTestHistogram(int(ts + 1))}
+		return histogramSample(ts, uk)
 	}
 
 	floatHistogramSample := func(ts int64) fhSample {
-		return fhSample{t: ts, fh: tsdbutil.GenerateTestFloatHistogram(int(ts + 1))}
+		return floatHistogramSample(ts, uk)
 	}
 
 	for _, tc := range []struct {
@@ -573,10 +594,131 @@ func TestCompactingChunkSeriesMerger(t *testing.T) {
 
 			require.Equal(t, expErr, actErr)
 			require.Equal(t, expChks, actChks)
+
+			actSamples := chunks.ChunkMetasToSamples(actChks)
+			expSamples := chunks.ChunkMetasToSamples(expChks)
+			require.Equal(t, expSamples, actSamples)
 		})
 	}
 }
 
+func TestCompactingChunkSeriesMergerHistogramCounterResetHint(t *testing.T) {
+	m := NewCompactingChunkSeriesMerger(ChainedSeriesMerge)
+
+	for sampleType, sampleFunc := range map[string]func(int64, histogram.CounterResetHint) chunks.Sample{
+		"histogram":       func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return histogramSample(ts, hint) },
+		"float histogram": func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return floatHistogramSample(ts, hint) },
+	} {
+		for name, tc := range map[string]struct {
+			input    []ChunkSeries
+			expected ChunkSeries
+		}{
+			"histogram counter reset hint kept in single series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+				),
+			},
+			"histogram not counter reset hint kept in single series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+				),
+			},
+			"histogram counter reset hint kept in multiple equal series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+					),
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+				),
+			},
+			"histogram not counter reset hint kept in multiple equal series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+					),
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+				),
+			},
+			"histogram counter reset hint dropped from differing series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, cr), sampleFunc(15, uk)},
+					),
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, cr), sampleFunc(12, uk), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, cr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, uk), sampleFunc(12, uk), sampleFunc(15, uk)},
+				),
+			},
+			"histogram counter not reset hint dropped from differing series": {
+				input: []ChunkSeries{
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, nr), sampleFunc(15, uk)},
+					),
+					NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+						[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+						[]chunks.Sample{sampleFunc(10, nr), sampleFunc(12, uk), sampleFunc(15, uk)},
+					),
+				},
+				expected: NewListChunkSeriesFromSamples(labels.FromStrings("bar", "baz"),
+					[]chunks.Sample{sampleFunc(0, nr), sampleFunc(5, uk)},
+					[]chunks.Sample{sampleFunc(10, uk), sampleFunc(12, uk), sampleFunc(15, uk)},
+				),
+			},
+		} {
+			t.Run(sampleType+"/"+name, func(t *testing.T) {
+				merged := m(tc.input...)
+				require.Equal(t, tc.expected.Labels(), merged.Labels())
+				actChks, actErr := ExpandChunks(merged.Iterator(nil))
+				expChks, expErr := ExpandChunks(tc.expected.Iterator(nil))
+
+				require.Equal(t, expErr, actErr)
+				require.Equal(t, expChks, actChks)
+
+				actSamples := chunks.ChunkMetasToSamples(actChks)
+				expSamples := chunks.ChunkMetasToSamples(expChks)
+				require.Equal(t, expSamples, actSamples)
+			})
+		}
+	}
+}
+
 func TestConcatenatingChunkSeriesMerger(t *testing.T) {
 	m := NewConcatenatingChunkSeriesMerger()
 
@@ -804,102 +946,243 @@ func (m *mockChunkSeriesSet) Err() error { return nil }
 func (m *mockChunkSeriesSet) Warnings() annotations.Annotations { return nil }
 
 func TestChainSampleIterator(t *testing.T) {
-	for _, tc := range []struct {
-		input    []chunkenc.Iterator
-		expected []chunks.Sample
-	}{
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}}),
-			},
-			expected: []chunks.Sample{fSample{0, 0}, fSample{1, 1}},
-		},
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}}),
-				NewListSeriesIterator(samples{fSample{2, 2}, fSample{3, 3}}),
+	for sampleType, sampleFunc := range map[string]func(int64) chunks.Sample{
+		"float":           func(ts int64) chunks.Sample { return fSample{ts, float64(ts)} },
+		"histogram":       func(ts int64) chunks.Sample { return histogramSample(ts, uk) },
+		"float histogram": func(ts int64) chunks.Sample { return floatHistogramSample(ts, uk) },
+	} {
+		for name, tc := range map[string]struct {
+			input    []chunkenc.Iterator
+			expected []chunks.Sample
+		}{
+			"single iterator": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0), sampleFunc(1)},
 			},
-			expected: []chunks.Sample{fSample{0, 0}, fSample{1, 1}, fSample{2, 2}, fSample{3, 3}},
-		},
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{3, 3}}),
-				NewListSeriesIterator(samples{fSample{1, 1}, fSample{4, 4}}),
-				NewListSeriesIterator(samples{fSample{2, 2}, fSample{5, 5}}),
+			"non overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1)}),
+					NewListSeriesIterator(samples{sampleFunc(2), sampleFunc(3)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0), sampleFunc(1), sampleFunc(2), sampleFunc(3)},
 			},
-			expected: []chunks.Sample{
-				fSample{0, 0}, fSample{1, 1}, fSample{2, 2}, fSample{3, 3}, fSample{4, 4}, fSample{5, 5},
+			"overlapping but distinct iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(3)}),
+					NewListSeriesIterator(samples{sampleFunc(1), sampleFunc(4)}),
+					NewListSeriesIterator(samples{sampleFunc(2), sampleFunc(5)}),
+				},
+				expected: []chunks.Sample{
+					sampleFunc(0), sampleFunc(1), sampleFunc(2), sampleFunc(3), sampleFunc(4), sampleFunc(5),
+				},
 			},
-		},
-		// Overlap.
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}}),
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{2, 2}}),
-				NewListSeriesIterator(samples{fSample{2, 2}, fSample{3, 3}}),
-				NewListSeriesIterator(samples{}),
-				NewListSeriesIterator(samples{}),
-				NewListSeriesIterator(samples{}),
+			"overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1)}),
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(2)}),
+					NewListSeriesIterator(samples{sampleFunc(2), sampleFunc(3)}),
+					NewListSeriesIterator(samples{}),
+					NewListSeriesIterator(samples{}),
+					NewListSeriesIterator(samples{}),
+				},
+				expected: []chunks.Sample{sampleFunc(0), sampleFunc(1), sampleFunc(2), sampleFunc(3)},
 			},
-			expected: []chunks.Sample{fSample{0, 0}, fSample{1, 1}, fSample{2, 2}, fSample{3, 3}},
-		},
+		} {
+			t.Run(sampleType+"/"+name, func(t *testing.T) {
+				merged := ChainSampleIteratorFromIterators(nil, tc.input)
+				actual, err := ExpandSamples(merged, nil)
+				require.NoError(t, err)
+				require.Equal(t, tc.expected, actual)
+			})
+		}
+	}
+}
+
+func TestChainSampleIteratorHistogramCounterResetHint(t *testing.T) {
+	for sampleType, sampleFunc := range map[string]func(int64, histogram.CounterResetHint) chunks.Sample{
+		"histogram":       func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return histogramSample(ts, hint) },
+		"float histogram": func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return floatHistogramSample(ts, hint) },
 	} {
-		merged := ChainSampleIteratorFromIterators(nil, tc.input)
-		actual, err := ExpandSamples(merged, nil)
-		require.NoError(t, err)
-		require.Equal(t, tc.expected, actual)
+		for name, tc := range map[string]struct {
+			input    []chunkenc.Iterator
+			expected []chunks.Sample
+		}{
+			"single iterator": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, cr), sampleFunc(2, uk)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0, uk), sampleFunc(1, cr), sampleFunc(2, uk)},
+			},
+			"single iterator gauge": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, ga), sampleFunc(1, ga), sampleFunc(2, ga)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0, ga), sampleFunc(1, ga), sampleFunc(2, ga)},
+			},
+			"overlapping iterators gauge": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, ga), sampleFunc(1, ga), sampleFunc(2, ga), sampleFunc(4, ga)}),
+					NewListSeriesIterator(samples{sampleFunc(0, ga), sampleFunc(1, ga), sampleFunc(3, ga), sampleFunc(5, ga)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0, ga), sampleFunc(1, ga), sampleFunc(2, ga), sampleFunc(3, ga), sampleFunc(4, ga), sampleFunc(5, ga)},
+			},
+			"non overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, uk)}),
+					NewListSeriesIterator(samples{sampleFunc(2, cr), sampleFunc(3, cr)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0, uk), sampleFunc(1, uk), sampleFunc(2, uk), sampleFunc(3, cr)},
+			},
+			"overlapping but distinct iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(3, uk), sampleFunc(5, cr)}),
+					NewListSeriesIterator(samples{sampleFunc(1, uk), sampleFunc(2, cr), sampleFunc(4, cr)}),
+				},
+				expected: []chunks.Sample{
+					sampleFunc(0, uk), sampleFunc(1, uk), sampleFunc(2, cr), sampleFunc(3, uk), sampleFunc(4, uk), sampleFunc(5, uk),
+				},
+			},
+			"overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, cr), sampleFunc(2, cr)}),
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, cr), sampleFunc(2, cr)}),
+				},
+				expected: []chunks.Sample{sampleFunc(0, uk), sampleFunc(1, uk), sampleFunc(2, uk)},
+			},
+		} {
+			t.Run(sampleType+"/"+name, func(t *testing.T) {
+				merged := ChainSampleIteratorFromIterators(nil, tc.input)
+				actual, err := ExpandSamples(merged, nil)
+				require.NoError(t, err)
+				require.Equal(t, tc.expected, actual)
+			})
+		}
 	}
 }
 
 func TestChainSampleIteratorSeek(t *testing.T) {
-	for _, tc := range []struct {
-		input    []chunkenc.Iterator
-		seek     int64
-		expected []chunks.Sample
-	}{
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}, fSample{2, 2}}),
+	for sampleType, sampleFunc := range map[string]func(int64) chunks.Sample{
+		"float":           func(ts int64) chunks.Sample { return fSample{ts, float64(ts)} },
+		"histogram":       func(ts int64) chunks.Sample { return histogramSample(ts, uk) },
+		"float histogram": func(ts int64) chunks.Sample { return floatHistogramSample(ts, uk) },
+	} {
+		for name, tc := range map[string]struct {
+			input    []chunkenc.Iterator
+			seek     int64
+			expected []chunks.Sample
+		}{
+			"single iterator": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1), sampleFunc(2)}),
+				},
+				seek:     1,
+				expected: []chunks.Sample{sampleFunc(1), sampleFunc(2)},
 			},
-			seek:     1,
-			expected: []chunks.Sample{fSample{1, 1}, fSample{2, 2}},
-		},
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}}),
-				NewListSeriesIterator(samples{fSample{2, 2}, fSample{3, 3}}),
+			"non overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1)}),
+					NewListSeriesIterator(samples{sampleFunc(2), sampleFunc(3)}),
+				},
+				seek:     2,
+				expected: []chunks.Sample{sampleFunc(2), sampleFunc(3)},
 			},
-			seek:     2,
-			expected: []chunks.Sample{fSample{2, 2}, fSample{3, 3}},
-		},
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{3, 3}}),
-				NewListSeriesIterator(samples{fSample{1, 1}, fSample{4, 4}}),
-				NewListSeriesIterator(samples{fSample{2, 2}, fSample{5, 5}}),
+			"overlapping but distinct iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(3)}),
+					NewListSeriesIterator(samples{sampleFunc(1), sampleFunc(4)}),
+					NewListSeriesIterator(samples{sampleFunc(2), sampleFunc(5)}),
+				},
+				seek:     2,
+				expected: []chunks.Sample{sampleFunc(2), sampleFunc(3), sampleFunc(4), sampleFunc(5)},
 			},
-			seek:     2,
-			expected: []chunks.Sample{fSample{2, 2}, fSample{3, 3}, fSample{4, 4}, fSample{5, 5}},
-		},
-		{
-			input: []chunkenc.Iterator{
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{2, 2}, fSample{3, 3}}),
-				NewListSeriesIterator(samples{fSample{0, 0}, fSample{1, 1}, fSample{2, 2}}),
+			"overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(2), sampleFunc(3)}),
+					NewListSeriesIterator(samples{sampleFunc(0), sampleFunc(1), sampleFunc(2)}),
+				},
+				seek:     0,
+				expected: []chunks.Sample{sampleFunc(0), sampleFunc(1), sampleFunc(2), sampleFunc(3)},
 			},
-			seek:     0,
-			expected: []chunks.Sample{fSample{0, 0}, fSample{1, 1}, fSample{2, 2}, fSample{3, 3}},
-		},
+		} {
+			t.Run(sampleType+"/"+name, func(t *testing.T) {
+				merged := ChainSampleIteratorFromIterators(nil, tc.input)
+				actual := []chunks.Sample{}
+				switch merged.Seek(tc.seek) {
+				case chunkenc.ValFloat:
+					t, f := merged.At()
+					actual = append(actual, fSample{t, f})
+				case chunkenc.ValHistogram:
+					t, h := merged.AtHistogram()
+					actual = append(actual, hSample{t, h})
+				case chunkenc.ValFloatHistogram:
+					t, fh := merged.AtFloatHistogram()
+					actual = append(actual, fhSample{t, fh})
+				}
+				s, err := ExpandSamples(merged, nil)
+				require.NoError(t, err)
+				actual = append(actual, s...)
+				require.Equal(t, tc.expected, actual)
+			})
+		}
+	}
+}
+
+func TestChainSampleIteratorSeekHistogramCounterResetHint(t *testing.T) {
+	for sampleType, sampleFunc := range map[string]func(int64, histogram.CounterResetHint) chunks.Sample{
+		"histogram":       func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return histogramSample(ts, hint) },
+		"float histogram": func(ts int64, hint histogram.CounterResetHint) chunks.Sample { return floatHistogramSample(ts, hint) },
 	} {
-		merged := ChainSampleIteratorFromIterators(nil, tc.input)
-		actual := []chunks.Sample{}
-		if merged.Seek(tc.seek) == chunkenc.ValFloat {
-			t, f := merged.At()
-			actual = append(actual, fSample{t, f})
+		for name, tc := range map[string]struct {
+			input    []chunkenc.Iterator
+			seek     int64
+			expected []chunks.Sample
+		}{
+			"single iterator": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, cr), sampleFunc(2, uk)}),
+				},
+				seek:     1,
+				expected: []chunks.Sample{sampleFunc(1, uk), sampleFunc(2, uk)},
+			},
+			"non overlapping iterators": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, uk)}),
+					NewListSeriesIterator(samples{sampleFunc(2, cr), sampleFunc(3, cr)}),
+				},
+				seek:     2,
+				expected: []chunks.Sample{sampleFunc(2, uk), sampleFunc(3, cr)},
+			},
+			"non overlapping iterators seek to internal reset": {
+				input: []chunkenc.Iterator{
+					NewListSeriesIterator(samples{sampleFunc(0, cr), sampleFunc(1, uk)}),
+					NewListSeriesIterator(samples{sampleFunc(2, cr), sampleFunc(3, cr)}),
+				},
+				seek:     3,
+				expected: []chunks.Sample{sampleFunc(3, uk)},
+			},
+		} {
+			t.Run(sampleType+"/"+name, func(t *testing.T) {
+				merged := ChainSampleIteratorFromIterators(nil, tc.input)
+				actual := []chunks.Sample{}
+				switch merged.Seek(tc.seek) {
+				case chunkenc.ValFloat:
+					t, f := merged.At()
+					actual = append(actual, fSample{t, f})
+				case chunkenc.ValHistogram:
+					t, h := merged.AtHistogram()
+					actual = append(actual, hSample{t, h})
+				case chunkenc.ValFloatHistogram:
+					t, fh := merged.AtFloatHistogram()
+					actual = append(actual, fhSample{t, fh})
+				}
+				s, err := ExpandSamples(merged, nil)
+				require.NoError(t, err)
+				actual = append(actual, s...)
+				require.Equal(t, tc.expected, actual)
+			})
 		}
-		s, err := ExpandSamples(merged, nil)
-		require.NoError(t, err)
-		actual = append(actual, s...)
-		require.Equal(t, tc.expected, actual)
 	}
 }
 

storage/series_test.go

@@ -430,35 +430,36 @@ func testHistogramsSeriesToChunks(t *testing.T, test histogramTest) {
 	require.Equal(t, len(test.expectedCounterResetHeaders), len(chks))
 
 	// Decode all encoded samples and assert they are equal to the original ones.
-	encodedSamples := expandHistogramSamples(chks)
+	encodedSamples := chunks.ChunkMetasToSamples(chks)
 	require.Equal(t, len(test.samples), len(encodedSamples))
 
 	for i, s := range test.samples {
+		encodedSample := encodedSamples[i]
 		switch expectedSample := s.(type) {
 		case hSample:
-			encodedSample, ok := encodedSamples[i].(hSample)
-			require.True(t, ok, "expect histogram", fmt.Sprintf("at idx %d", i))
+			require.Equal(t, chunkenc.ValHistogram, encodedSample.Type(), "expect histogram", fmt.Sprintf("at idx %d", i))
+			h := encodedSample.H()
 			// Ignore counter reset if not gauge here, will check on chunk level.
 			if expectedSample.h.CounterResetHint != histogram.GaugeType {
-				encodedSample.h.CounterResetHint = histogram.UnknownCounterReset
+				h.CounterResetHint = histogram.UnknownCounterReset
 			}
 			if value.IsStaleNaN(expectedSample.h.Sum) {
-				require.True(t, value.IsStaleNaN(encodedSample.h.Sum), fmt.Sprintf("at idx %d", i))
+				require.True(t, value.IsStaleNaN(h.Sum), fmt.Sprintf("at idx %d", i))
 				continue
 			}
-			require.Equal(t, *expectedSample.h, *encodedSample.h.Compact(0), fmt.Sprintf("at idx %d", i))
+			require.Equal(t, *expectedSample.h, *h.Compact(0), fmt.Sprintf("at idx %d", i))
 		case fhSample:
-			encodedSample, ok := encodedSamples[i].(fhSample)
-			require.True(t, ok, "expect float histogram", fmt.Sprintf("at idx %d", i))
+			require.Equal(t, chunkenc.ValFloatHistogram, encodedSample.Type(), "expect float histogram", fmt.Sprintf("at idx %d", i))
+			fh := encodedSample.FH()
 			// Ignore counter reset if not gauge here, will check on chunk level.
 			if expectedSample.fh.CounterResetHint != histogram.GaugeType {
-				encodedSample.fh.CounterResetHint = histogram.UnknownCounterReset
+				fh.CounterResetHint = histogram.UnknownCounterReset
 			}
 			if value.IsStaleNaN(expectedSample.fh.Sum) {
-				require.True(t, value.IsStaleNaN(encodedSample.fh.Sum), fmt.Sprintf("at idx %d", i))
+				require.True(t, value.IsStaleNaN(fh.Sum), fmt.Sprintf("at idx %d", i))
 				continue
 			}
-			require.Equal(t, *expectedSample.fh, *encodedSample.fh.Compact(0), fmt.Sprintf("at idx %d", i))
+			require.Equal(t, *expectedSample.fh, *fh.Compact(0), fmt.Sprintf("at idx %d", i))
 		default:
 			t.Error("internal error, unexpected type")
 		}
@@ -469,29 +470,6 @@ func testHistogramsSeriesToChunks(t *testing.T, test histogramTest) {
 	}
 }
 
-func expandHistogramSamples(chunks []chunks.Meta) (result []chunks.Sample) {
-	if len(chunks) == 0 {
-		return
-	}
-
-	for _, chunk := range chunks {
-		it := chunk.Chunk.Iterator(nil)
-		for vt := it.Next(); vt != chunkenc.ValNone; vt = it.Next() {
-			switch vt {
-			case chunkenc.ValHistogram:
-				t, h := it.AtHistogram()
-				result = append(result, hSample{t: t, h: h})
-			case chunkenc.ValFloatHistogram:
-				t, fh := it.AtFloatHistogram()
-				result = append(result, fhSample{t: t, fh: fh})
-			default:
-				panic("unexpected value type")
-			}
-		}
-	}
-	return
-}
-
 func getCounterResetHint(chunk chunks.Meta) chunkenc.CounterResetHeader {
 	switch chk := chunk.Chunk.(type) {
 	case *chunkenc.HistogramChunk:

tsdb/chunks/chunks.go

@@ -207,6 +207,34 @@ func PopulatedChunk(numSamples int, minTime int64) (Meta, error) {
 	return ChunkFromSamples(samples)
 }
 
+// ChunkMetasToSamples converts a slice of chunk meta data to a slice of samples.
+// Used in tests to compare the content of chunks.
+func ChunkMetasToSamples(chunks []Meta) (result []Sample) {
+	if len(chunks) == 0 {
+		return
+	}
+
+	for _, chunk := range chunks {
+		it := chunk.Chunk.Iterator(nil)
+		for vt := it.Next(); vt != chunkenc.ValNone; vt = it.Next() {
+			switch vt {
+			case chunkenc.ValFloat:
+				t, v := it.At()
+				result = append(result, sample{t: t, f: v})
+			case chunkenc.ValHistogram:
+				t, h := it.AtHistogram()
+				result = append(result, sample{t: t, h: h})
+			case chunkenc.ValFloatHistogram:
+				t, fh := it.AtFloatHistogram()
+				result = append(result, sample{t: t, fh: fh})
+			default:
+				panic("unexpected value type")
+			}
+		}
+	}
+	return
+}
+
 // Iterator iterates over the chunks of a single time series.
 type Iterator interface {
 	// At returns the current meta.