Fix omitting of chunk on Seek()

querier.go

@@ -15,7 +15,6 @@ package tsdb
 
 import (
 	"fmt"
-	"sort"
 	"strings"
 
 	"github.com/prometheus/tsdb/chunks"
@@ -671,25 +670,13 @@ func (it *chunkSeriesIterator) Seek(t int64) (ok bool) {
 		t = it.mint
 	}
 
-	// Only do binary search forward to stay in line with other iterators
-	// that can only move forward.
-	x := sort.Search(len(it.chunks[it.i:]), func(i int) bool {
-		return it.chunks[it.i+i].MinTime >= t
-	})
-	x += it.i
-
-	// If the timestamp was not found, it might be in the last chunk.
-	if x == len(it.chunks) {
-		x--
-
-		// Go to previous chunk if the chunk doesn't exactly start with t.
-		// If we are already at the first chunk, we use it as it's the best we have.
-	} else if x > 0 && it.chunks[x].MinTime > t {
-		x--
+	for ; it.chunks[it.i].MaxTime < t; it.i++ {
+		if it.i == len(it.chunks)-1 {
+			return false
+		}
 	}
 
-	it.i = x
-	it.cur = it.chunks[x].Chunk.Iterator()
+	it.cur = it.chunks[it.i].Chunk.Iterator()
 	if len(it.intervals) > 0 {
 		it.cur = &deletedIterator{it: it.cur, intervals: it.intervals}
 	}

querier_test.go

@@ -1028,7 +1028,7 @@ func TestSeriesIterator(t *testing.T) {
 }
 
 // Regression for: https://github.com/prometheus/tsdb/pull/97
-func TestCSIteratorDoubleSeek(t *testing.T) {
+func TestChunkSeriesIterator_DoubleSeek(t *testing.T) {
 	chkMetas := []*ChunkMeta{
 		chunkFromSamples([]sample{}),
 		chunkFromSamples([]sample{{1, 1}, {2, 2}, {3, 3}}),
@@ -1043,6 +1043,28 @@ func TestCSIteratorDoubleSeek(t *testing.T) {
 	require.Equal(t, float64(2), v)
 }
 
+// Regression when seeked chunks were still found via binary search and we always
+// skipped to the end when seeking a value in the current chunk.
+func TestChunkSeriesIterator_SeekInCurrentChunk(t *testing.T) {
+	metas := []*ChunkMeta{
+		chunkFromSamples([]sample{}),
+		chunkFromSamples([]sample{{1, 2}, {3, 4}, {5, 6}, {7, 8}}),
+		chunkFromSamples([]sample{}),
+	}
+
+	it := newChunkSeriesIterator(metas, nil, 1, 7)
+
+	require.True(t, it.Next())
+	ts, v := it.At()
+	require.Equal(t, int64(1), ts)
+	require.Equal(t, float64(2), v)
+
+	require.True(t, it.Seek(4))
+	ts, v = it.At()
+	require.Equal(t, int64(5), ts)
+	require.Equal(t, float64(6), v)
+}
+
 func TestPopulatedCSReturnsValidChunkSlice(t *testing.T) {
 	lbls := []labels.Labels{labels.New(labels.Label{"a", "b"})}
 	chunkMetas := [][]*ChunkMeta{