Fix interjections even more

Signed-off-by: beorn7 <beorn@grafana.com>

tsdb/chunkenc/histo.go

@@ -387,7 +387,6 @@ func (a *HistoAppender) Recode(posInterjections, negInterjections []Interjection
 		}
 		app.AppendHistogram(tOld, hOld)
 	}
-
 	return hc, app
 }
 

tsdb/chunkenc/histo_meta.go

@@ -159,41 +159,36 @@ func compareSpans(a, b []histogram.Span) ([]Interjection, bool) {
 
 	av, aok := ai.Next()
 	bv, bok := bi.Next()
+loop:
 	for {
-		if aok && bok {
-			if av == bv { // both have an identical value. move on!
-				// finish WIP interjection and reset
+		switch {
+		case aok && bok:
+			switch {
+			case av == bv: // Both have an identical value. move on!
+				// Finish WIP interjection and reset.
 				if inter.num > 0 {
 					interjections = append(interjections, inter)
 				}
 				inter.num = 0
 				av, aok = ai.Next()
 				bv, bok = bi.Next()
-				if aok {
-					inter.pos++
-				}
-				continue
-			}
-			if av < bv { // b misses a value that is in a.
+				inter.pos++
+			case av < bv: // b misses a value that is in a.
 				return interjections, false
-			}
-			if av > bv { // a misses a value that is in b. forward b and recompare
+			case av > bv: // a misses a value that is in b. Forward b and recompare.
 				inter.num++
 				bv, bok = bi.Next()
-				continue
 			}
-		} else if aok && !bok { // b misses a value that is in a.
+		case aok && !bok: // b misses a value that is in a.
 			return interjections, false
-		} else if !aok && bok { // a misses a value that is in b. forward b and recompare
+		case !aok && bok: // a misses a value that is in b. Forward b and recompare.
 			inter.num++
-			inter.pos++
 			bv, bok = bi.Next()
-			continue
-		} else { // both iterators ran out. we're done
+		default: // Both iterators ran out. We're done.
 			if inter.num > 0 {
 				interjections = append(interjections, inter)
 			}
-			break
+			break loop
 		}
 	}
 

tsdb/chunkenc/histo_meta_test.go

@@ -187,6 +187,28 @@ func TestInterjection(t *testing.T) {
 			bucketsIn:  []int64{6, -3, 0},
 			bucketsOut: []int64{6, -3, 0, -3, 0},
 		},
+		{
+			description: "double prepond at the beginning and double append at the end",
+			spansA: []histogram.Span{
+				{Offset: -10, Length: 3},
+			},
+			spansB: []histogram.Span{
+				{Offset: -12, Length: 7},
+			},
+			valid: true,
+			interjections: []Interjection{
+				{
+					pos: 0,
+					num: 2,
+				},
+				{
+					pos: 3,
+					num: 2,
+				},
+			},
+			bucketsIn:  []int64{6, -3, 0},
+			bucketsOut: []int64{0, 0, 6, -3, 0, -3, 0},
+		},
 		{
 			description: "single removal of bucket at the start",
 			spansA: []histogram.Span{
@@ -218,7 +240,6 @@ func TestInterjection(t *testing.T) {
 			},
 			valid: false,
 		},
-		// TODO(beorn7): Add more scenarios.
 		{
 			description: "as described in doc comment",
 			spansA: []histogram.Span{

tsdb/head.go

@@ -16,7 +16,6 @@ package tsdb
 import (
 	"context"
 	"fmt"
-	"github.com/prometheus/prometheus/pkg/histogram"
 	"math"
 	"path/filepath"
 	"runtime"
@@ -32,6 +31,7 @@ import (
 	"go.uber.org/atomic"
 
 	"github.com/prometheus/prometheus/pkg/exemplar"
+	"github.com/prometheus/prometheus/pkg/histogram"
 	"github.com/prometheus/prometheus/pkg/labels"
 	"github.com/prometheus/prometheus/storage"
 	"github.com/prometheus/prometheus/tsdb/chunkenc"