Fix more counterResetInAnyBucket edgecases

Case a) empty span is at the beginning of the spans.
Case b) two consequtive empty spans with positive offsets.

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

tsdb/chunkenc/float_histogram.go

@@ -339,11 +339,16 @@ func counterResetInAnyFloatBucket(oldBuckets []xorValue, newBuckets []float64, o
 		return false
 	}
 
-	oldSpanSliceIdx, newSpanSliceIdx := 0, 0                   // Index for the span slices.
+	var (
-	oldInsideSpanIdx, newInsideSpanIdx := uint32(0), uint32(0) // Index inside a span.
+		oldSpanSliceIdx, newSpanSliceIdx     int    = -1, -1 // Index for the span slices. Starts at -1 to indicate that the first non empty span is not yet found.
-	oldIdx, newIdx := oldSpans[0].Offset, newSpans[0].Offset
+		oldInsideSpanIdx, newInsideSpanIdx   uint32          // Index inside a span.
+		oldIdx, newIdx                       int32           // Index inside a bucket slice.
+		oldBucketSliceIdx, newBucketSliceIdx int             // Index inside bucket slice.
+	)
 
-	oldBucketSliceIdx, newBucketSliceIdx := 0, 0 // Index inside bucket slice.
+	// Find first non empty spans.
+	oldSpanSliceIdx, oldIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldIdx, oldSpans)
+	newSpanSliceIdx, newIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newIdx, newSpans)
 	oldVal, newVal := oldBuckets[0].value, newBuckets[0]
 
 	// Since we assume that new spans won't have missing buckets, there will never be a case
@@ -359,13 +364,12 @@ func counterResetInAnyFloatBucket(oldBuckets []xorValue, newBuckets []float64, o
 			// Moving ahead old bucket and span by 1 index.
 			if oldInsideSpanIdx+1 >= oldSpans[oldSpanSliceIdx].Length {
 				// Current span is over.
-				oldSpanSliceIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldSpans)
+				oldSpanSliceIdx, oldIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldIdx, oldSpans)
 				oldInsideSpanIdx = 0
 				if oldSpanSliceIdx >= len(oldSpans) {
 					// All old spans are over.
 					break
 				}
-				oldIdx += 1 + oldSpans[oldSpanSliceIdx].Offset
 			} else {
 				oldInsideSpanIdx++
 				oldIdx++
@@ -378,14 +382,13 @@ func counterResetInAnyFloatBucket(oldBuckets []xorValue, newBuckets []float64, o
 			// Moving ahead new bucket and span by 1 index.
 			if newInsideSpanIdx+1 >= newSpans[newSpanSliceIdx].Length {
 				// Current span is over.
-				newSpanSliceIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newSpans)
+				newSpanSliceIdx, newIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newIdx, newSpans)
 				newInsideSpanIdx = 0
 				if newSpanSliceIdx >= len(newSpans) {
 					// All new spans are over.
 					// This should not happen, old spans above should catch this first.
 					panic("new spans over before old spans in counterReset")
 				}
-				newIdx += 1 + newSpans[newSpanSliceIdx].Offset
 			} else {
 				newInsideSpanIdx++
 				newIdx++

tsdb/chunkenc/float_histogram_test.go

@@ -550,62 +550,193 @@ func assertRecodedFloatHistogramChunkOnAppend(t *testing.T, prevChunk Chunk, hAp
 }
 
 func TestFloatHistogramChunkAppendableWithEmptySpan(t *testing.T) {
-	h1 := &histogram.FloatHistogram{
+	tests := map[string]struct {
-		Schema:        0,
+		h1 *histogram.FloatHistogram
-		Count:         21,
+		h2 *histogram.FloatHistogram
-		Sum:           1234.5,
+	}{
-		ZeroThreshold: 0.001,
+		"empty span in old and new histogram": {
-		ZeroCount:     4,
+			h1: &histogram.FloatHistogram{
-		PositiveSpans: []histogram.Span{
+				Schema:        0,
-			{Offset: 0, Length: 4},
+				Count:         21,
-			{Offset: 0, Length: 0},
+				Sum:           1234.5,
-			{Offset: 0, Length: 3},
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 0, Length: 0},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 2, 1, 1, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 2, 1, 2, 2, 2, 2},
+			},
+			h2: &histogram.FloatHistogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 0, Length: 0},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 3, 1, 2, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 4, 2, 7, 5, 5, 2},
+			},
 		},
-		PositiveBuckets: []float64{1, 2, 1, 1, 1, 1, 1},
+		"empty span in old histogram": {
-		NegativeSpans: []histogram.Span{
+			h1: &histogram.FloatHistogram{
-			{Offset: 1, Length: 4},
+				Schema:        0,
-			{Offset: 2, Length: 0},
+				Count:         21,
-			{Offset: 2, Length: 3},
+				Sum:           1234.5,
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 1, Length: 0}, // This span will disappear.
+					{Offset: 2, Length: 4},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 2, 1, 1, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 2, 1, 2, 2, 2, 2},
+			},
+			h2: &histogram.FloatHistogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 3, Length: 4},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 3, 1, 2, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 4, 2, 7, 5, 5, 2},
+			},
 		},
-		NegativeBuckets: []float64{1, 2, 1, 2, 2, 2, 2},
+		"empty span in new histogram": {
-	}
+			h1: &histogram.FloatHistogram{
-	h2 := &histogram.FloatHistogram{
+				Schema:        0,
-		Schema:        0,
+				Count:         21,
-		Count:         37,
+				Sum:           1234.5,
-		Sum:           2345.6,
+				ZeroThreshold: 0.001,
-		ZeroThreshold: 0.001,
+				ZeroCount:     4,
-		ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
-		PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
-			{Offset: 0, Length: 4},
+					{Offset: 3, Length: 3},
-			{Offset: 0, Length: 0},
+				},
-			{Offset: 0, Length: 3},
+				PositiveBuckets: []float64{1, 2, 1, 1, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 2, 1, 2, 2, 2, 2},
+			},
+			h2: &histogram.FloatHistogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 1, Length: 0}, // This span is new.
+					{Offset: 2, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 3, 1, 2, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 4, 2, 7, 5, 5, 2},
+			},
 		},
-		PositiveBuckets: []float64{1, 3, 1, 2, 1, 1, 1},
+		"two empty spans mixing offsets": {
-		NegativeSpans: []histogram.Span{
+			h1: &histogram.FloatHistogram{
-			{Offset: 1, Length: 4},
+				Schema:        0,
-			{Offset: 2, Length: 0},
+				Count:         21,
-			{Offset: 2, Length: 3},
+				Sum:           1234.5,
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 1, Length: 0},
+					{Offset: 3, Length: 0},
+					{Offset: 4, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 2, 1, 1, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 2, 1, 2, 2, 2, 2},
+			},
+			h2: &histogram.FloatHistogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 3, Length: 0},
+					{Offset: 1, Length: 0},
+					{Offset: 4, Length: 3},
+				},
+				PositiveBuckets: []float64{1, 3, 1, 2, 1, 1, 1},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []float64{1, 4, 2, 7, 5, 5, 2},
+			},
 		},
-		NegativeBuckets: []float64{1, 4, 2, 7, 5, 5, 2},
 	}
 
-	c := Chunk(NewFloatHistogramChunk())
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			c := Chunk(NewFloatHistogramChunk())
 
-	// Create fresh appender and add the first histogram.
+			// Create fresh appender and add the first histogram.
-	app, err := c.Appender()
+			app, err := c.Appender()
-	require.NoError(t, err)
+			require.NoError(t, err)
-	require.Equal(t, 0, c.NumSamples())
+			require.Equal(t, 0, c.NumSamples())
 
-	_, _, _, err = app.AppendFloatHistogram(nil, 1, h1, true)
+			_, _, _, err = app.AppendFloatHistogram(nil, 1, tc.h1, true)
-	require.NoError(t, err)
+			require.NoError(t, err)
-	require.Equal(t, 1, c.NumSamples())
+			require.Equal(t, 1, c.NumSamples())
-	hApp, _ := app.(*FloatHistogramAppender)
+			hApp, _ := app.(*FloatHistogramAppender)
 
-	pI, nI, okToAppend, counterReset := hApp.appendable(h2)
+			pI, nI, okToAppend, counterReset := hApp.appendable(tc.h2)
-	require.Empty(t, pI)
+			require.Empty(t, pI)
-	require.Empty(t, nI)
+			require.Empty(t, nI)
-	require.True(t, okToAppend)
+			require.True(t, okToAppend)
-	require.False(t, counterReset)
+			require.False(t, counterReset)
+		})
+	}
 }
 
 func TestFloatHistogramChunkAppendableGauge(t *testing.T) {

tsdb/chunkenc/histogram.go

@@ -359,11 +359,16 @@ func counterResetInAnyBucket(oldBuckets, newBuckets []int64, oldSpans, newSpans
 		return false
 	}
 
-	oldSpanSliceIdx, newSpanSliceIdx := 0, 0                   // Index for the span slices.
+	var (
-	oldInsideSpanIdx, newInsideSpanIdx := uint32(0), uint32(0) // Index inside a span.
+		oldSpanSliceIdx, newSpanSliceIdx     int    = -1, -1 // Index for the span slices. Starts at -1 to indicate that the first non empty span is not yet found.
-	oldIdx, newIdx := oldSpans[0].Offset, newSpans[0].Offset
+		oldInsideSpanIdx, newInsideSpanIdx   uint32          // Index inside a span.
+		oldIdx, newIdx                       int32           // Index inside a bucket slice.
+		oldBucketSliceIdx, newBucketSliceIdx int             // Index inside bucket slice.
+	)
 
-	oldBucketSliceIdx, newBucketSliceIdx := 0, 0 // Index inside bucket slice.
+	// Find first non empty spans.
+	oldSpanSliceIdx, oldIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldIdx, oldSpans)
+	newSpanSliceIdx, newIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newIdx, newSpans)
 	oldVal, newVal := oldBuckets[0], newBuckets[0]
 
 	// Since we assume that new spans won't have missing buckets, there will never be a case
@@ -379,13 +384,12 @@ func counterResetInAnyBucket(oldBuckets, newBuckets []int64, oldSpans, newSpans
 			// Moving ahead old bucket and span by 1 index.
 			if oldInsideSpanIdx+1 >= oldSpans[oldSpanSliceIdx].Length {
 				// Current span is over.
-				oldSpanSliceIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldSpans)
+				oldSpanSliceIdx, oldIdx = nextNonEmptySpanSliceIdx(oldSpanSliceIdx, oldIdx, oldSpans)
 				oldInsideSpanIdx = 0
 				if oldSpanSliceIdx >= len(oldSpans) {
 					// All old spans are over.
 					break
 				}
-				oldIdx += 1 + oldSpans[oldSpanSliceIdx].Offset
 			} else {
 				oldInsideSpanIdx++
 				oldIdx++
@@ -398,14 +402,13 @@ func counterResetInAnyBucket(oldBuckets, newBuckets []int64, oldSpans, newSpans
 			// Moving ahead new bucket and span by 1 index.
 			if newInsideSpanIdx+1 >= newSpans[newSpanSliceIdx].Length {
 				// Current span is over.
-				newSpanSliceIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newSpans)
+				newSpanSliceIdx, newIdx = nextNonEmptySpanSliceIdx(newSpanSliceIdx, newIdx, newSpans)
 				newInsideSpanIdx = 0
 				if newSpanSliceIdx >= len(newSpans) {
 					// All new spans are over.
 					// This should not happen, old spans above should catch this first.
 					panic("new spans over before old spans in counterReset")
 				}
-				newIdx += 1 + newSpans[newSpanSliceIdx].Offset
 			} else {
 				newInsideSpanIdx++
 				newIdx++

tsdb/chunkenc/histogram_meta.go

@@ -489,8 +489,13 @@ func counterResetHint(crh CounterResetHeader, numRead uint16) histogram.CounterR
 }
 
 // Handle pathological case of empty span when advancing span idx.
-func nextNonEmptySpanSliceIdx(idx int, spans []histogram.Span) (newIdx int) {
+// Call it with idx==-1 to find the first non empty span.
-	for idx++; idx < len(spans) && spans[idx].Length == 0; idx++ {
+func nextNonEmptySpanSliceIdx(idx int, bucketIdx int32, spans []histogram.Span) (newIdx int, newBucketIdx int32) {
+	for idx++; idx < len(spans); idx++ {
+		if spans[idx].Length > 0 {
+			return idx, bucketIdx + spans[idx].Offset + 1
+		}
+		bucketIdx += spans[idx].Offset
 	}
-	return idx
+	return idx, 0
 }

tsdb/chunkenc/histogram_test.go

@@ -573,62 +573,193 @@ func assertSampleCount(t *testing.T, c Chunk, exp int64, vtype ValueType) {
 }
 
 func TestHistogramChunkAppendableWithEmptySpan(t *testing.T) {
-	h1 := &histogram.Histogram{
+	tests := map[string]struct {
-		Schema:        0,
+		h1 *histogram.Histogram
-		Count:         21,
+		h2 *histogram.Histogram
-		Sum:           1234.5,
+	}{
-		ZeroThreshold: 0.001,
+		"empty span in old and new histogram": {
-		ZeroCount:     4,
+			h1: &histogram.Histogram{
-		PositiveSpans: []histogram.Span{
+				Schema:        0,
-			{Offset: 0, Length: 4},
+				Count:         21,
-			{Offset: 0, Length: 0},
+				Sum:           1234.5,
-			{Offset: 0, Length: 3},
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 0, Length: 0},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 1, -1, 0, 0, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 1, -1, 1, 0, 0, 0},
+			},
+			h2: &histogram.Histogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 0, Length: 0},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 2, -2, 1, -1, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 3, -2, 5, -2, 0, -3},
+			},
 		},
-		PositiveBuckets: []int64{1, 1, -1, 0, 0, 0, 0},
+		"empty span in old histogram": {
-		NegativeSpans: []histogram.Span{
+			h1: &histogram.Histogram{
-			{Offset: 1, Length: 4},
+				Schema:        0,
-			{Offset: 2, Length: 0},
+				Count:         21,
-			{Offset: 2, Length: 3},
+				Sum:           1234.5,
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 1, Length: 0}, // This span will disappear.
+					{Offset: 2, Length: 4},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 1, -1, 0, 0, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 1, -1, 1, 0, 0, 0},
+			},
+			h2: &histogram.Histogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 3, Length: 4},
+					{Offset: 0, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 2, -2, 1, -1, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 3, -2, 5, -2, 0, -3},
+			},
 		},
-		NegativeBuckets: []int64{1, 1, -1, 1, 0, 0, 0},
+		"empty span in new histogram": {
-	}
+			h1: &histogram.Histogram{
-	h2 := &histogram.Histogram{
+				Schema:        0,
-		Schema:        0,
+				Count:         21,
-		Count:         37,
+				Sum:           1234.5,
-		Sum:           2345.6,
+				ZeroThreshold: 0.001,
-		ZeroThreshold: 0.001,
+				ZeroCount:     4,
-		ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
-		PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
-			{Offset: 0, Length: 4},
+					{Offset: 3, Length: 3},
-			{Offset: 0, Length: 0},
+				},
-			{Offset: 0, Length: 3},
+				PositiveBuckets: []int64{1, 1, -1, 0, 0, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 1, -1, 1, 0, 0, 0},
+			},
+			h2: &histogram.Histogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 1, Length: 0}, // This span is new.
+					{Offset: 2, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 2, -2, 1, -1, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 3, -2, 5, -2, 0, -3},
+			},
 		},
-		PositiveBuckets: []int64{1, 2, -2, 1, -1, 0, 0},
+		"two empty spans mixing offsets": {
-		NegativeSpans: []histogram.Span{
+			h1: &histogram.Histogram{
-			{Offset: 1, Length: 4},
+				Schema:        0,
-			{Offset: 2, Length: 0},
+				Count:         21,
-			{Offset: 2, Length: 3},
+				Sum:           1234.5,
+				ZeroThreshold: 0.001,
+				ZeroCount:     4,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 1, Length: 0},
+					{Offset: 3, Length: 0},
+					{Offset: 4, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 1, -1, 0, 0, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 1, -1, 1, 0, 0, 0},
+			},
+			h2: &histogram.Histogram{
+				Schema:        0,
+				Count:         37,
+				Sum:           2345.6,
+				ZeroThreshold: 0.001,
+				ZeroCount:     5,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 4},
+					{Offset: 3, Length: 0},
+					{Offset: 1, Length: 0},
+					{Offset: 4, Length: 3},
+				},
+				PositiveBuckets: []int64{1, 2, -2, 1, -1, 0, 0},
+				NegativeSpans: []histogram.Span{
+					{Offset: 1, Length: 4},
+					{Offset: 2, Length: 0},
+					{Offset: 2, Length: 3},
+				},
+				NegativeBuckets: []int64{1, 3, -2, 5, -2, 0, -3},
+			},
 		},
-		NegativeBuckets: []int64{1, 3, -2, 5, -2, 0, -3},
 	}
 
-	c := Chunk(NewHistogramChunk())
+	for name, tc := range tests {
+		t.Run(name, func(t *testing.T) {
+			c := Chunk(NewHistogramChunk())
 
-	// Create fresh appender and add the first histogram.
+			// Create fresh appender and add the first histogram.
-	app, err := c.Appender()
+			app, err := c.Appender()
-	require.NoError(t, err)
+			require.NoError(t, err)
-	require.Equal(t, 0, c.NumSamples())
+			require.Equal(t, 0, c.NumSamples())
 
-	_, _, _, err = app.AppendHistogram(nil, 1, h1, true)
+			_, _, _, err = app.AppendHistogram(nil, 1, tc.h1, true)
-	require.NoError(t, err)
+			require.NoError(t, err)
-	require.Equal(t, 1, c.NumSamples())
+			require.Equal(t, 1, c.NumSamples())
-	hApp, _ := app.(*HistogramAppender)
+			hApp, _ := app.(*HistogramAppender)
 
-	pI, nI, okToAppend, counterReset := hApp.appendable(h2)
+			pI, nI, okToAppend, counterReset := hApp.appendable(tc.h2)
-	require.Empty(t, pI)
+			require.Empty(t, pI)
-	require.Empty(t, nI)
+			require.Empty(t, nI)
-	require.True(t, okToAppend)
+			require.True(t, okToAppend)
-	require.False(t, counterReset)
+			require.False(t, counterReset)
+		})
+	}
 }
 
 func TestAtFloatHistogram(t *testing.T) {