[query] Remove empty series from output when dropping NaNs (#1682)

src/query/api/v1/handler/prometheus/native/common.go

@@ -240,12 +240,37 @@ func parseQuery(r *http.Request) (string, error) {
 	return queries[0], nil
 }
 
+func filterNaNSeries(series []*ts.Series) []*ts.Series {
+	filtered := series[:0]
+	for _, s := range series {
+		dps := s.Values().Datapoints()
+		hasVal := false
+		for _, dp := range dps {
+			if !math.IsNaN(dp.Value) {
+				hasVal = true
+				break
+			}
+		}
+
+		if hasVal {
+			filtered = append(filtered, s)
+		}
+	}
+
+	return filtered
+}
+
 func renderResultsJSON(
 	w io.Writer,
 	series []*ts.Series,
 	params models.RequestParams,
 	keepNans bool,
 ) {
+	// NB: if dropping NaNs, drop series with only NaNs from output entirely.
+	if !keepNans {
+		series = filterNaNSeries(series)
+	}
+
 	jw := json.NewWriter(w)
 	jw.BeginObject()
 

src/query/api/v1/handler/prometheus/native/common_test.go

@@ -37,6 +37,7 @@ import (
 	"github.com/m3db/m3/src/query/util/logging"
 	xtest "github.com/m3db/m3/src/x/test"
 
+	"github.com/golang/mock/gomock"
 	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
 )
@@ -351,14 +352,6 @@ func TestRenderResultsJSONWithDroppedNaNs(t *testing.T) {
 						]
 					],
 					"step_size_ms": 10000
-				},
-				{
-					"metric": {
-						"biz": "baz",
-						"qux": "qaz"
-					},
-					"values": [],
-					"step_size_ms": 10000
 				}
 			]
 		}
@@ -429,3 +422,40 @@ func mustPrettyJSON(t *testing.T, str string) string {
 	require.NoError(t, err)
 	return string(pretty)
 }
+
+func TestSanitizeSeries(t *testing.T) {
+	ctrl := gomock.NewController(t)
+	defer ctrl.Finish()
+
+	nan := math.NaN()
+	testData := []struct {
+		name string
+		data []float64
+	}{
+		{"1", []float64{nan, nan, nan, nan}},
+		{"2", []float64{nan, nan, nan, 1}},
+		{"3", []float64{nan, nan, nan, nan}},
+		{"4", []float64{nan, nan, 1, nan}},
+		{"5", []float64{1, 1, 1, 1}},
+		{"6", []float64{nan, nan, nan, nan}},
+	}
+
+	series := make([]*ts.Series, 0, len(testData))
+	tags := models.NewTags(0, models.NewTagOptions())
+	for _, d := range testData {
+		vals := ts.NewMockValues(ctrl)
+		dps := make(ts.Datapoints, 0, len(d.data))
+		for _, p := range d.data {
+			dps = append(dps, ts.Datapoint{Value: p})
+		}
+
+		vals.EXPECT().Datapoints().Return(dps)
+		series = append(series, ts.NewSeries([]byte(d.name), vals, tags))
+	}
+
+	series = filterNaNSeries(series)
+	require.Equal(t, 3, len(series))
+	assert.Equal(t, "2", string(series[0].Name()))
+	assert.Equal(t, "4", string(series[1].Name()))
+	assert.Equal(t, "5", string(series[2].Name()))
+}

src/query/generated/mocks/generate.go

@@ -22,6 +22,7 @@
 //go:generate sh -c "mockgen -package=downsample $PACKAGE/src/cmd/services/m3coordinator/downsample Downsampler,MetricsAppender,SamplesAppender | genclean -pkg $PACKAGE/src/cmd/services/m3coordinator/downsample -out $GOPATH/src/$PACKAGE/src/cmd/services/m3coordinator/downsample/downsample_mock.go"
 //go:generate sh -c "mockgen -package=storage -destination=$GOPATH/src/$PACKAGE/src/query/storage/storage_mock.go $PACKAGE/src/query/storage Storage"
 //go:generate sh -c "mockgen -package=m3 -destination=$GOPATH/src/$PACKAGE/src/query/storage/m3/m3_mock.go $PACKAGE/src/query/storage/m3 Storage"
+//go:generate sh -c "mockgen -package=ts -destination=$GOPATH/src/$PACKAGE/src/query/ts/ts_mock.go $PACKAGE/src/query/ts Values"
 //go:generate sh -c "mockgen -package=block -destination=$GOPATH/src/$PACKAGE/src/query/block/block_mock.go $PACKAGE/src/query/block Block,StepIter,SeriesIter,Builder,Step,UnconsolidatedBlock,UnconsolidatedStepIter,UnconsolidatedSeriesIter,UnconsolidatedStep"
 //go:generate sh -c "mockgen -package=ingest -destination=$GOPATH/src/$PACKAGE/src/cmd/services/m3coordinator/ingest/write_mock.go $PACKAGE/src/cmd/services/m3coordinator/ingest DownsamplerAndWriter"
 //go:generate sh -c "mockgen -package=transform -destination=$GOPATH/src/$PACKAGE/src/query/executor/transform/types_mock.go $PACKAGE/src/query/executor/transform OpNode"