Fix appendable: check whether last val was a histogram (#14613)

* Fix appendable: check whether last val was a histogram

When appending a float, we were checking whether lastValue was equal to
current value, but we didn't check whether last value was a float value.

Signed-off-by: Oleg Zaytsev <mail@olegzaytsev.com>

storage/errors.go

@@ -18,6 +18,7 @@ import "fmt"
 type errDuplicateSampleForTimestamp struct {
 	timestamp           int64
 	existing            float64
+	existingIsHistogram bool
 	newValue            float64
 }
 
@@ -29,13 +30,26 @@ func NewDuplicateFloatErr(t int64, existing, newValue float64) error {
 	}
 }
 
+// NewDuplicateHistogramToFloatErr describes an error where a new float sample is sent for same timestamp as previous histogram.
+func NewDuplicateHistogramToFloatErr(t int64, newValue float64) error {
+	return errDuplicateSampleForTimestamp{
+		timestamp:           t,
+		existingIsHistogram: true,
+		newValue:            newValue,
+	}
+}
+
 func (e errDuplicateSampleForTimestamp) Error() string {
 	if e.timestamp == 0 {
 		return "duplicate sample for timestamp"
 	}
+	if e.existingIsHistogram {
+		return fmt.Sprintf("duplicate sample for timestamp %d; overrides not allowed: existing is a histogram, new value %g", e.timestamp, e.newValue)
+	}
 	return fmt.Sprintf("duplicate sample for timestamp %d; overrides not allowed: existing %g, new value %g", e.timestamp, e.existing, e.newValue)
 }
 
+// Is implements the anonymous interface checked by errors.Is.
 // Every errDuplicateSampleForTimestamp compares equal to the global ErrDuplicateSampleForTimestamp.
 func (e errDuplicateSampleForTimestamp) Is(t error) bool {
 	if t == ErrDuplicateSampleForTimestamp {

storage/errors_test.go

@@ -0,0 +1,38 @@
+// Copyright 2014 The Prometheus Authors
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+// http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package storage
+
+import (
+	"fmt"
+	"testing"
+
+	"github.com/stretchr/testify/require"
+)
+
+func TestErrDuplicateSampleForTimestamp(t *testing.T) {
+	// All errDuplicateSampleForTimestamp are ErrDuplicateSampleForTimestamp
+	require.ErrorIs(t, ErrDuplicateSampleForTimestamp, errDuplicateSampleForTimestamp{})
+
+	// Same type only is if it has same properties.
+	err := NewDuplicateFloatErr(1_000, 10, 20)
+	sameErr := NewDuplicateFloatErr(1_000, 10, 20)
+	differentErr := NewDuplicateFloatErr(1_001, 30, 40)
+
+	require.ErrorIs(t, err, sameErr)
+	require.NotErrorIs(t, err, differentErr)
+
+	// Also works when err is wrapped.
+	require.ErrorIs(t, fmt.Errorf("failed: %w", err), sameErr)
+	require.NotErrorIs(t, fmt.Errorf("failed: %w", err), differentErr)
+}

tsdb/head_append.go

@@ -466,6 +466,9 @@ func (s *memSeries) appendable(t int64, v float64, headMaxt, minValidTime, oooTi
 			// like federation and erroring out at that time would be extremely noisy.
 			// This only checks against the latest in-order sample.
 			// The OOO headchunk has its own method to detect these duplicates.
+			if s.lastHistogramValue != nil || s.lastFloatHistogramValue != nil {
+				return false, 0, storage.NewDuplicateHistogramToFloatErr(t, v)
+			}
 			if math.Float64bits(s.lastValue) != math.Float64bits(v) {
 				return false, 0, storage.NewDuplicateFloatErr(t, s.lastValue, v)
 			}

tsdb/head_test.go

@@ -5919,6 +5919,35 @@ func TestPostingsCardinalityStats(t *testing.T) {
 	require.Equal(t, statsForSomeLabel1, head.PostingsCardinalityStats("n", 1))
 }
 
+func TestHeadAppender_AppendFloatWithSameTimestampAsPreviousHistogram(t *testing.T) {
+	head, _ := newTestHead(t, DefaultBlockDuration, wlog.CompressionNone, false)
+	t.Cleanup(func() { head.Close() })
+
+	ls := labels.FromStrings(labels.MetricName, "test")
+
+	{
+		// Append a float 10.0 @ 1_000
+		app := head.Appender(context.Background())
+		_, err := app.Append(0, ls, 1_000, 10.0)
+		require.NoError(t, err)
+		require.NoError(t, app.Commit())
+	}
+
+	{
+		// Append a float histogram @ 2_000
+		app := head.Appender(context.Background())
+		h := tsdbutil.GenerateTestHistogram(1)
+		_, err := app.AppendHistogram(0, ls, 2_000, h, nil)
+		require.NoError(t, err)
+		require.NoError(t, app.Commit())
+	}
+
+	app := head.Appender(context.Background())
+	_, err := app.Append(0, ls, 2_000, 10.0)
+	require.Error(t, err)
+	require.ErrorIs(t, err, storage.NewDuplicateHistogramToFloatErr(2_000, 10.0))
+}
+
 func TestHeadAppender_AppendCTZeroSample(t *testing.T) {
 	type appendableSamples struct {
 		ts  int64