promql: Support histogram in value string representation

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

promql/engine_test.go

@@ -2455,10 +2455,11 @@ func TestSparseHistogramRate(t *testing.T) {
 	require.NoError(t, test.Run())
 	engine := test.QueryEngine()
 
-	queryString := fmt.Sprintf("rate(%s[1m])", seriesName)
+	//queryString := fmt.Sprintf("rate(%s[1m])", seriesName)
+	queryString := fmt.Sprintf("%s", seriesName)
 	qry, err := engine.NewInstantQuery(test.Queryable(), queryString, timestamp.Time(int64(5*time.Minute/time.Millisecond)))
 	require.NoError(t, err)
 	res := qry.Exec(test.Context())
 	require.NoError(t, res.Err)
-	// fmt.Println(res)
+	fmt.Println(res)
 }

promql/value.go

@@ -87,9 +87,13 @@ type Point struct {
 }
 
 func (p Point) String() string {
-	// TODO(beorn7): Support Histogram.
-	v := strconv.FormatFloat(p.V, 'f', -1, 64)
-	return fmt.Sprintf("%v @[%v]", v, p.T)
+	var s string
+	if p.H != nil {
+		s = p.H.String()
+	} else {
+		s = strconv.FormatFloat(p.V, 'f', -1, 64)
+	}
+	return fmt.Sprintf("%s @[%v]", s, p.T)
 }
 
 // MarshalJSON implements json.Marshaler.

storage/memoized_iterator.go

@@ -80,8 +80,12 @@ func (b *MemoizedSeriesIterator) Seek(t int64) bool {
 		if !b.ok {
 			return false
 		}
+		if b.it.ChunkEncoding() == chunkenc.EncHistogram {
+			b.lastTime, _ = b.it.AtHistogram()
+		} else {
 			b.lastTime, _ = b.it.At()
 		}
+	}
 
 	if b.lastTime >= t {
 		return true
@@ -102,12 +106,20 @@ func (b *MemoizedSeriesIterator) Next() bool {
 	}
 
 	// Keep track of the previous element.
+	if b.it.ChunkEncoding() == chunkenc.EncHistogram {
+		b.prevTime, b.prev
+	} else {
 		b.prevTime, b.prevValue = b.it.At()
+	}
 
 	b.ok = b.it.Next()
 	if b.ok {
+		if b.it.ChunkEncoding() == chunkenc.EncHistogram {
+			b.lastTime, _ = b.it.AtHistogram()
+		} else {
 			b.lastTime, _ = b.it.At()
 		}
+	}
 
 	return b.ok
 }