Fix FindAtOrAfter where seek position is between two smallchunks

and add a test that covers that case.

Signed-off-by: Bryan Boreham <bryan@weave.works>

Author: bboreham

pkg/chunk/encoding/bigchunk.go

@@ -273,6 +273,14 @@ func (it *bigchunkIterator) FindAtOrAfter(target model.Time) bool {
 			return true
 		}
 	}
+	// Timestamp is after the end of that chunk - if there is another chunk
+	// then the position we need is at the beginning of it.
+	if it.i+1 < len(it.chunks) {
+		it.i++
+		it.curr = it.chunks[it.i].Iterator(it.curr)
+		it.curr.Next()
+		return true
+	}
 	return false
 }
 

pkg/chunk/encoding/chunk_test.go

@@ -147,6 +147,14 @@ func testChunkSeek(t *testing.T, encoding Encoding, samples int) {
 
 	iter := chunk.NewIterator(nil)
 	for i := 0; i < samples; i += samples / 10 {
+		if i > 0 {
+			// Seek one millisecond before the actual time
+			require.True(t, iter.FindAtOrAfter(model.Time(i*step-1)), "1ms before step %d not found", i)
+			sample := iter.Value()
+			require.EqualValues(t, model.Time(i*step), sample.Timestamp)
+			require.EqualValues(t, model.SampleValue(i), sample.Value)
+		}
+		// Now seek to exactly the right time
 		require.True(t, iter.FindAtOrAfter(model.Time(i*step)))
 		sample := iter.Value()
 		require.EqualValues(t, model.Time(i*step), sample.Timestamp)