Merge pull request #17189 from prometheus/krajo/native-histogram-schema-validation

fix(nativehistograms): validation should fail on unsupported schemas

model/histogram/float_histogram.go

@@ -798,7 +798,8 @@ func (h *FloatHistogram) AllReverseBucketIterator() BucketIterator[float64] {
 // create false positives here.
 func (h *FloatHistogram) Validate() error {
 	var nCount, pCount float64
-	if h.UsesCustomBuckets() {
+	switch {
+	case IsCustomBucketsSchema(h.Schema):
 		if err := checkHistogramCustomBounds(h.CustomValues, h.PositiveSpans, len(h.PositiveBuckets)); err != nil {
 			return fmt.Errorf("custom buckets: %w", err)
 		}
@@ -814,7 +815,7 @@ func (h *FloatHistogram) Validate() error {
 		if len(h.NegativeBuckets) > 0 {
 			return ErrHistogramCustomBucketsNegBuckets
 		}
-	} else {
+	case IsExponentialSchema(h.Schema):
 		if err := checkHistogramSpans(h.PositiveSpans, len(h.PositiveBuckets)); err != nil {
 			return fmt.Errorf("positive side: %w", err)
 		}
@@ -828,6 +829,8 @@ func (h *FloatHistogram) Validate() error {
 		if h.CustomValues != nil {
 			return ErrHistogramExpSchemaCustomBounds
 		}
+	default:
+		return InvalidSchemaError(h.Schema)
 	}
 	err := checkHistogramBuckets(h.PositiveBuckets, &pCount, false)
 	if err != nil {

model/histogram/generic.go

@@ -21,9 +21,11 @@ import (
 )
 
 const (
-	ExponentialSchemaMax int32 = 8
+	ExponentialSchemaMax         int32 = 8
-	ExponentialSchemaMin int32 = -4
+	ExponentialSchemaMaxReserved int32 = 52
-	CustomBucketsSchema  int32 = -53
+	ExponentialSchemaMin         int32 = -4
+	ExponentialSchemaMinReserved int32 = -9
+	CustomBucketsSchema          int32 = -53
 )
 
 var (
@@ -42,8 +44,13 @@ var (
 	ErrHistogramCustomBucketsNegSpans   = errors.New("custom buckets: must not have negative spans")
 	ErrHistogramCustomBucketsNegBuckets = errors.New("custom buckets: must not have negative buckets")
 	ErrHistogramExpSchemaCustomBounds   = errors.New("histogram with exponential schema must not have custom bounds")
+	ErrHistogramsInvalidSchema          = fmt.Errorf("histogram has an invalid schema, which must be between %d and %d for exponential buckets, or %d for custom buckets", ExponentialSchemaMin, ExponentialSchemaMax, CustomBucketsSchema)
 )
 
+func InvalidSchemaError(s int32) error {
+	return fmt.Errorf("%w, got schema %d", ErrHistogramsInvalidSchema, s)
+}
+
 func IsCustomBucketsSchema(s int32) bool {
 	return s == CustomBucketsSchema
 }
@@ -52,6 +59,14 @@ func IsExponentialSchema(s int32) bool {
 	return s >= ExponentialSchemaMin && s <= ExponentialSchemaMax
 }
 
+func IsExponentialSchemaReserved(s int32) bool {
+	return s >= ExponentialSchemaMinReserved && s <= ExponentialSchemaMaxReserved
+}
+
+func IsValidSchema(s int32) bool {
+	return IsCustomBucketsSchema(s) || IsExponentialSchema(s)
+}
+
 // BucketCount is a type constraint for the count in a bucket, which can be
 // float64 (for type FloatHistogram) or uint64 (for type Histogram).
 type BucketCount interface {

model/histogram/histogram.go

@@ -424,7 +424,8 @@ func resize[T any](items []T, n int) []T {
 // the total h.Count).
 func (h *Histogram) Validate() error {
 	var nCount, pCount uint64
-	if h.UsesCustomBuckets() {
+	switch {
+	case IsCustomBucketsSchema(h.Schema):
 		if err := checkHistogramCustomBounds(h.CustomValues, h.PositiveSpans, len(h.PositiveBuckets)); err != nil {
 			return fmt.Errorf("custom buckets: %w", err)
 		}
@@ -440,7 +441,7 @@ func (h *Histogram) Validate() error {
 		if len(h.NegativeBuckets) > 0 {
 			return ErrHistogramCustomBucketsNegBuckets
 		}
-	} else {
+	case IsExponentialSchema(h.Schema):
 		if err := checkHistogramSpans(h.PositiveSpans, len(h.PositiveBuckets)); err != nil {
 			return fmt.Errorf("positive side: %w", err)
 		}
@@ -454,6 +455,8 @@ func (h *Histogram) Validate() error {
 		if h.CustomValues != nil {
 			return ErrHistogramExpSchemaCustomBounds
 		}
+	default:
+		return InvalidSchemaError(h.Schema)
 	}
 	err := checkHistogramBuckets(h.PositiveBuckets, &pCount, true)
 	if err != nil {

model/histogram/histogram_test.go

@@ -1565,6 +1565,18 @@ func TestHistogramValidation(t *testing.T) {
 				CustomValues:    []float64{1, 2, 3, 4, 5, 6, 7, 8},
 			},
 		},
+		"schema too high": {
+			h: &Histogram{
+				Schema: 10,
+			},
+			errMsg: `histogram has an invalid schema, which must be between -4 and 8 for exponential buckets, or -53 for custom buckets, got schema 10`,
+		},
+		"schema too low": {
+			h: &Histogram{
+				Schema: -10,
+			},
+			errMsg: `histogram has an invalid schema, which must be between -4 and 8 for exponential buckets, or -53 for custom buckets, got schema -10`,
+		},
 	}
 
 	for testName, tc := range tests {

scrape/target.go

@@ -414,12 +414,12 @@ type maxSchemaAppender struct {
 
 func (app *maxSchemaAppender) AppendHistogram(ref storage.SeriesRef, lset labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
 	if h != nil {
-		if histogram.IsExponentialSchema(h.Schema) && h.Schema > app.maxSchema {
+		if histogram.IsExponentialSchemaReserved(h.Schema) && h.Schema > app.maxSchema {
 			h = h.ReduceResolution(app.maxSchema)
 		}
 	}
 	if fh != nil {
-		if histogram.IsExponentialSchema(fh.Schema) && fh.Schema > app.maxSchema {
+		if histogram.IsExponentialSchemaReserved(fh.Schema) && fh.Schema > app.maxSchema {
 			fh = fh.ReduceResolution(app.maxSchema)
 		}
 	}

storage/remote/codec.go

@@ -388,6 +388,7 @@ type concreteSeriesIterator struct {
 	histogramsCur int
 	curValType    chunkenc.ValueType
 	series        *concreteSeries
+	err           error
 }
 
 func newConcreteSeriesIterator(series *concreteSeries) chunkenc.Iterator {
@@ -404,10 +405,14 @@ func (c *concreteSeriesIterator) reset(series *concreteSeries) {
 	c.histogramsCur = -1
 	c.curValType = chunkenc.ValNone
 	c.series = series
+	c.err = nil
 }
 
 // Seek implements storage.SeriesIterator.
 func (c *concreteSeriesIterator) Seek(t int64) chunkenc.ValueType {
+	if c.err != nil {
+		return chunkenc.ValNone
+	}
 	if c.floatsCur == -1 {
 		c.floatsCur = 0
 	}
@@ -439,7 +444,7 @@ func (c *concreteSeriesIterator) Seek(t int64) chunkenc.ValueType {
 		if c.series.floats[c.floatsCur].Timestamp <= c.series.histograms[c.histogramsCur].Timestamp {
 			c.curValType = chunkenc.ValFloat
 		} else {
-			c.curValType = getHistogramValType(&c.series.histograms[c.histogramsCur])
+			c.curValType = chunkenc.ValHistogram
 		}
 		// When the timestamps do not overlap the cursor for the non-selected sample type has advanced too
 		// far; we decrement it back down here.
@@ -453,11 +458,26 @@ func (c *concreteSeriesIterator) Seek(t int64) chunkenc.ValueType {
 	case c.floatsCur < len(c.series.floats):
 		c.curValType = chunkenc.ValFloat
 	case c.histogramsCur < len(c.series.histograms):
-		c.curValType = getHistogramValType(&c.series.histograms[c.histogramsCur])
+		c.curValType = chunkenc.ValHistogram
+	}
+	if c.curValType == chunkenc.ValHistogram {
+		h := &c.series.histograms[c.histogramsCur]
+		c.curValType = getHistogramValType(h)
+		c.err = validateHistogramSchema(h)
+	}
+	if c.err != nil {
+		c.curValType = chunkenc.ValNone
 	}
 	return c.curValType
 }
 
+func validateHistogramSchema(h *prompb.Histogram) error {
+	if histogram.IsValidSchema(h.Schema) {
+		return nil
+	}
+	return histogram.InvalidSchemaError(h.Schema)
+}
+
 func getHistogramValType(h *prompb.Histogram) chunkenc.ValueType {
 	if h.IsFloatHistogram() {
 		return chunkenc.ValFloatHistogram
@@ -504,6 +524,9 @@ const noTS = int64(math.MaxInt64)
 
 // Next implements chunkenc.Iterator.
 func (c *concreteSeriesIterator) Next() chunkenc.ValueType {
+	if c.err != nil {
+		return chunkenc.ValNone
+	}
 	peekFloatTS := noTS
 	if c.floatsCur+1 < len(c.series.floats) {
 		peekFloatTS = c.series.floats[c.floatsCur+1].Timestamp
@@ -532,12 +555,21 @@ func (c *concreteSeriesIterator) Next() chunkenc.ValueType {
 		c.histogramsCur++
 		c.curValType = chunkenc.ValFloat
 	}
+
+	if c.curValType == chunkenc.ValHistogram {
+		h := &c.series.histograms[c.histogramsCur]
+		c.curValType = getHistogramValType(h)
+		c.err = validateHistogramSchema(h)
+	}
+	if c.err != nil {
+		c.curValType = chunkenc.ValNone
+	}
 	return c.curValType
 }
 
 // Err implements chunkenc.Iterator.
-func (*concreteSeriesIterator) Err() error {
+func (c *concreteSeriesIterator) Err() error {
-	return nil
+	return c.err
 }
 
 // chunkedSeriesSet implements storage.SeriesSet.

storage/remote/codec_test.go

@@ -548,6 +548,50 @@ func TestConcreteSeriesIterator_FloatAndHistogramSamples(t *testing.T) {
 	require.Equal(t, chunkenc.ValNone, it.Seek(1))
 }
 
+func TestConcreteSeriesIterator_InvalidHistogramSamples(t *testing.T) {
+	for _, schema := range []int32{-100, 100} {
+		t.Run(fmt.Sprintf("schema=%d", schema), func(t *testing.T) {
+			h := prompb.FromIntHistogram(2, &testHistogram)
+			h.Schema = schema
+			fh := prompb.FromFloatHistogram(4, testHistogram.ToFloat(nil))
+			fh.Schema = schema
+			series := &concreteSeries{
+				labels: labels.FromStrings("foo", "bar"),
+				floats: []prompb.Sample{
+					{Value: 1, Timestamp: 0},
+					{Value: 2, Timestamp: 3},
+				},
+				histograms: []prompb.Histogram{
+					h,
+					fh,
+				},
+			}
+			it := series.Iterator(nil)
+			require.Equal(t, chunkenc.ValFloat, it.Next())
+			require.Equal(t, chunkenc.ValNone, it.Next())
+			require.Error(t, it.Err())
+
+			it = series.Iterator(it)
+			require.Equal(t, chunkenc.ValFloat, it.Next())
+			require.Equal(t, chunkenc.ValNone, it.Next())
+			require.Error(t, it.Err())
+
+			it = series.Iterator(it)
+			require.Equal(t, chunkenc.ValNone, it.Seek(1))
+			require.Error(t, it.Err())
+
+			it = series.Iterator(it)
+			require.Equal(t, chunkenc.ValFloat, it.Seek(3))
+			require.Equal(t, chunkenc.ValNone, it.Next())
+			require.Error(t, it.Err())
+
+			it = series.Iterator(it)
+			require.Equal(t, chunkenc.ValNone, it.Seek(4))
+			require.Error(t, it.Err())
+		})
+	}
+}
+
 func TestFromQueryResultWithDuplicates(t *testing.T) {
 	ts1 := prompb.TimeSeries{
 		Labels: []prompb.Label{

storage/remote/otlptranslator/prometheusremotewrite/histograms.go

@@ -86,16 +86,16 @@ func (c *PrometheusConverter) addExponentialHistogramDataPoints(ctx context.Cont
 func exponentialToNativeHistogram(p pmetric.ExponentialHistogramDataPoint, temporality pmetric.AggregationTemporality) (*histogram.Histogram, annotations.Annotations, error) {
 	var annots annotations.Annotations
 	scale := p.Scale()
-	if scale < -4 {
+	if scale < histogram.ExponentialSchemaMin {
 		return nil, annots,
 			fmt.Errorf("cannot convert exponential to native histogram."+
-				" Scale must be >= -4, was %d", scale)
+				" Scale must be >= %d, was %d", histogram.ExponentialSchemaMin, scale)
 	}
 
 	var scaleDown int32
-	if scale > 8 {
+	if scale > histogram.ExponentialSchemaMax {
-		scaleDown = scale - 8
+		scaleDown = scale - histogram.ExponentialSchemaMax
-		scale = 8
+		scale = histogram.ExponentialSchemaMax
 	}
 
 	pSpans, pDeltas := convertBucketsLayout(p.Positive().BucketCounts().AsRaw(), p.Positive().Offset(), scaleDown, true)

storage/remote/write_handler.go

@@ -250,7 +250,7 @@ func (h *writeHandler) write(ctx context.Context, req *prompb.WriteRequest) (err
 	samplesWithInvalidLabels := 0
 	samplesAppended := 0
 
-	app := &timeLimitAppender{
+	app := &remoteWriteAppender{
 		Appender: h.appendable.Appender(ctx),
 		maxTime:  timestamp.FromTime(time.Now().Add(maxAheadTime)),
 	}
@@ -365,7 +365,7 @@ func (h *writeHandler) appendV1Histograms(app storage.Appender, hh []prompb.Hist
 // NOTE(bwplotka): TSDB storage is NOT idempotent, so we don't allow "partial retry-able" errors.
 // Once we have 5xx type of error, we immediately stop and rollback all appends.
 func (h *writeHandler) writeV2(ctx context.Context, req *writev2.Request) (_ WriteResponseStats, errHTTPCode int, _ error) {
-	app := &timeLimitAppender{
+	app := &remoteWriteAppender{
 		Appender: h.appendable.Appender(ctx),
 		maxTime:  timestamp.FromTime(time.Now().Add(maxAheadTime)),
 	}
@@ -642,7 +642,7 @@ type rwExporter struct {
 
 func (rw *rwExporter) ConsumeMetrics(ctx context.Context, md pmetric.Metrics) error {
 	otlpCfg := rw.config().OTLPConfig
-	app := &timeLimitAppender{
+	app := &remoteWriteAppender{
 		Appender: rw.appendable.Appender(ctx),
 		maxTime:  timestamp.FromTime(time.Now().Add(maxAheadTime)),
 	}
@@ -745,13 +745,13 @@ func hasDelta(md pmetric.Metrics) bool {
 	return false
 }
 
-type timeLimitAppender struct {
+type remoteWriteAppender struct {
 	storage.Appender
 
 	maxTime int64
 }
 
-func (app *timeLimitAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64, v float64) (storage.SeriesRef, error) {
+func (app *remoteWriteAppender) Append(ref storage.SeriesRef, lset labels.Labels, t int64, v float64) (storage.SeriesRef, error) {
 	if t > app.maxTime {
 		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
 	}
@@ -763,11 +763,18 @@ func (app *timeLimitAppender) Append(ref storage.SeriesRef, lset labels.Labels,
 	return ref, nil
 }
 
-func (app *timeLimitAppender) AppendHistogram(ref storage.SeriesRef, l labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
+func (app *remoteWriteAppender) AppendHistogram(ref storage.SeriesRef, l labels.Labels, t int64, h *histogram.Histogram, fh *histogram.FloatHistogram) (storage.SeriesRef, error) {
 	if t > app.maxTime {
 		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
 	}
 
+	if h != nil && histogram.IsExponentialSchemaReserved(h.Schema) && h.Schema > histogram.ExponentialSchemaMax {
+		h = h.ReduceResolution(histogram.ExponentialSchemaMax)
+	}
+	if fh != nil && histogram.IsExponentialSchemaReserved(fh.Schema) && fh.Schema > histogram.ExponentialSchemaMax {
+		fh = fh.ReduceResolution(histogram.ExponentialSchemaMax)
+	}
+
 	ref, err := app.Appender.AppendHistogram(ref, l, t, h, fh)
 	if err != nil {
 		return 0, err
@@ -775,7 +782,7 @@ func (app *timeLimitAppender) AppendHistogram(ref storage.SeriesRef, l labels.La
 	return ref, nil
 }
 
-func (app *timeLimitAppender) AppendExemplar(ref storage.SeriesRef, l labels.Labels, e exemplar.Exemplar) (storage.SeriesRef, error) {
+func (app *remoteWriteAppender) AppendExemplar(ref storage.SeriesRef, l labels.Labels, e exemplar.Exemplar) (storage.SeriesRef, error) {
 	if e.Ts > app.maxTime {
 		return 0, fmt.Errorf("%w: timestamp is too far in the future", storage.ErrOutOfBounds)
 	}

storage/remote/write_handler_test.go

@@ -1222,3 +1222,100 @@ func (m *mockAppendable) AppendCTZeroSample(_ storage.SeriesRef, l labels.Labels
 	m.samples = append(m.samples, mockSample{l, ct, 0})
 	return storage.SeriesRef(hash), nil
 }
+
+var (
+	highSchemaHistogram = &histogram.Histogram{
+		Schema: 10,
+		PositiveSpans: []histogram.Span{
+			{
+				Offset: -1,
+				Length: 2,
+			},
+		},
+		PositiveBuckets: []int64{1, 2},
+		NegativeSpans: []histogram.Span{
+			{
+				Offset: 0,
+				Length: 1,
+			},
+		},
+		NegativeBuckets: []int64{1},
+	}
+	reducedSchemaHistogram = &histogram.Histogram{
+		Schema: 8,
+		PositiveSpans: []histogram.Span{
+			{
+				Offset: 0,
+				Length: 1,
+			},
+		},
+		PositiveBuckets: []int64{4},
+		NegativeSpans: []histogram.Span{
+			{
+				Offset: 0,
+				Length: 1,
+			},
+		},
+		NegativeBuckets: []int64{1},
+	}
+)
+
+func TestHistogramsReduction(t *testing.T) {
+	for _, protoMsg := range []config.RemoteWriteProtoMsg{config.RemoteWriteProtoMsgV1, config.RemoteWriteProtoMsgV2} {
+		t.Run(string(protoMsg), func(t *testing.T) {
+			appendable := &mockAppendable{}
+			handler := NewWriteHandler(promslog.NewNopLogger(), nil, appendable, []config.RemoteWriteProtoMsg{protoMsg}, false)
+
+			var (
+				err     error
+				payload []byte
+			)
+
+			if protoMsg == config.RemoteWriteProtoMsgV1 {
+				payload, _, _, err = buildWriteRequest(nil, []prompb.TimeSeries{
+					{
+						Labels:     []prompb.Label{{Name: "__name__", Value: "test_metric1"}},
+						Histograms: []prompb.Histogram{prompb.FromIntHistogram(1, highSchemaHistogram)},
+					},
+					{
+						Labels:     []prompb.Label{{Name: "__name__", Value: "test_metric2"}},
+						Histograms: []prompb.Histogram{prompb.FromFloatHistogram(2, highSchemaHistogram.ToFloat(nil))},
+					},
+				}, nil, nil, nil, nil, "snappy")
+			} else {
+				payload, _, _, err = buildV2WriteRequest(promslog.NewNopLogger(), []writev2.TimeSeries{
+					{
+						LabelsRefs: []uint32{0, 1},
+						Histograms: []writev2.Histogram{writev2.FromIntHistogram(1, highSchemaHistogram)},
+					},
+					{
+						LabelsRefs: []uint32{0, 2},
+						Histograms: []writev2.Histogram{writev2.FromFloatHistogram(2, highSchemaHistogram.ToFloat(nil))},
+					},
+				}, []string{"__name__", "test_metric1", "test_metric2"},
+					nil, nil, nil, "snappy")
+			}
+			require.NoError(t, err)
+
+			req, err := http.NewRequest("", "", bytes.NewReader(payload))
+			require.NoError(t, err)
+
+			req.Header.Set("Content-Type", remoteWriteContentTypeHeaders[protoMsg])
+
+			recorder := httptest.NewRecorder()
+			handler.ServeHTTP(recorder, req)
+
+			resp := recorder.Result()
+			body, err := io.ReadAll(resp.Body)
+			require.NoError(t, err)
+			require.Equal(t, http.StatusNoContent, resp.StatusCode)
+			require.Empty(t, body)
+
+			require.Len(t, appendable.histograms, 2)
+			require.Equal(t, int64(1), appendable.histograms[0].t)
+			require.Equal(t, reducedSchemaHistogram, appendable.histograms[0].h)
+			require.Equal(t, int64(2), appendable.histograms[1].t)
+			require.Equal(t, reducedSchemaHistogram.ToFloat(nil), appendable.histograms[1].fh)
+		})
+	}
+}

tsdb/chunkenc/float_histogram.go

@@ -954,6 +954,12 @@ func (it *floatHistogramIterator) Next() ValueType {
 			it.err = err
 			return ValNone
 		}
+
+		if !histogram.IsValidSchema(schema) {
+			it.err = histogram.InvalidSchemaError(schema)
+			return ValNone
+		}
+
 		it.schema = schema
 		it.zThreshold = zeroThreshold
 		it.pSpans, it.nSpans = posSpans, negSpans

tsdb/chunkenc/float_histogram_test.go

@@ -14,6 +14,7 @@
 package chunkenc
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -1462,3 +1463,32 @@ func TestFloatHistogramEmptyBucketsWithGaps(t *testing.T) {
 	require.Equal(t, ValNone, it.Next())
 	require.NoError(t, it.Err())
 }
+
+func TestFloatHistogramIteratorFailIfSchemaInValid(t *testing.T) {
+	for _, schema := range []int32{-101, 101} {
+		t.Run(fmt.Sprintf("schema %d", schema), func(t *testing.T) {
+			h := &histogram.FloatHistogram{
+				Schema:        schema,
+				Count:         10,
+				Sum:           15.0,
+				ZeroThreshold: 1e-100,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 2},
+					{Offset: 1, Length: 2},
+				},
+				PositiveBuckets: []float64{1, 2, 3, 4},
+			}
+
+			c := NewFloatHistogramChunk()
+			app, err := c.Appender()
+			require.NoError(t, err)
+
+			_, _, _, err = app.AppendFloatHistogram(nil, 1, h, false)
+			require.NoError(t, err)
+
+			it := c.Iterator(nil)
+			require.Equal(t, ValNone, it.Next())
+			require.ErrorIs(t, it.Err(), histogram.ErrHistogramsInvalidSchema)
+		})
+	}
+}

tsdb/chunkenc/histogram.go

@@ -1077,6 +1077,12 @@ func (it *histogramIterator) Next() ValueType {
 			it.err = err
 			return ValNone
 		}
+
+		if !histogram.IsValidSchema(schema) {
+			it.err = histogram.InvalidSchemaError(schema)
+			return ValNone
+		}
+
 		it.schema = schema
 		it.zThreshold = zeroThreshold
 		it.pSpans, it.nSpans = posSpans, negSpans

tsdb/chunkenc/histogram_test.go

@@ -14,6 +14,7 @@
 package chunkenc
 
 import (
+	"fmt"
 	"testing"
 
 	"github.com/stretchr/testify/require"
@@ -1818,3 +1819,32 @@ func TestIntHistogramEmptyBucketsWithGaps(t *testing.T) {
 	require.Equal(t, ValNone, it.Next())
 	require.NoError(t, it.Err())
 }
+
+func TestHistogramIteratorFailIfSchemaInValid(t *testing.T) {
+	for _, schema := range []int32{-101, 101} {
+		t.Run(fmt.Sprintf("schema %d", schema), func(t *testing.T) {
+			h := &histogram.Histogram{
+				Schema:        schema,
+				Count:         10,
+				Sum:           15.0,
+				ZeroThreshold: 1e-100,
+				PositiveSpans: []histogram.Span{
+					{Offset: 0, Length: 2},
+					{Offset: 1, Length: 2},
+				},
+				PositiveBuckets: []int64{1, 2, 3, 4},
+			}
+
+			c := NewHistogramChunk()
+			app, err := c.Appender()
+			require.NoError(t, err)
+
+			_, _, _, err = app.AppendHistogram(nil, 1, h, false)
+			require.NoError(t, err)
+
+			it := c.Iterator(nil)
+			require.Equal(t, ValNone, it.Next())
+			require.ErrorIs(t, it.Err(), histogram.ErrHistogramsInvalidSchema)
+		})
+	}
+}