From aac482517f8bbffdfb5cd39749bbc84773942a97 Mon Sep 17 00:00:00 2001
From: Aliaksandr Valialkin <valyala@gmail.com>
Date: Thu, 25 Jul 2019 22:02:03 +0300
Subject: [PATCH] app/vmselect/promql: return NaN from `count()` over zero time
 series

This aligns `count` behavior with Prometheus.
---
 app/vmselect/promql/aggr.go                  | 6 +++++-
 app/vmselect/promql/aggr_incremental.go      | 7 ++++++-
 app/vmselect/promql/aggr_incremental_test.go | 2 +-
 app/vmselect/promql/exec_test.go             | 4 ++--
 4 files changed, 14 insertions(+), 5 deletions(-)

diff --git a/app/vmselect/promql/aggr.go b/app/vmselect/promql/aggr.go
index 51eaec99a1..a2bfdaad04 100644
--- a/app/vmselect/promql/aggr.go
+++ b/app/vmselect/promql/aggr.go
@@ -312,7 +312,11 @@ func aggrFuncCount(tss []*timeseries) []*timeseries {
 			}
 			count++
 		}
-		dst.Values[i] = float64(count)
+		v := float64(count)
+		if count == 0 {
+			v = nan
+		}
+		dst.Values[i] = v
 	}
 	return tss[:1]
 }
diff --git a/app/vmselect/promql/aggr_incremental.go b/app/vmselect/promql/aggr_incremental.go
index 8b0fe4a666..c4651a541d 100644
--- a/app/vmselect/promql/aggr_incremental.go
+++ b/app/vmselect/promql/aggr_incremental.go
@@ -348,7 +348,12 @@ func mergeAggrCount(dst, src *incrementalAggrContext) {
 }
 
 func finalizeAggrCount(iac *incrementalAggrContext) {
-	// Nothing to do
+	dstValues := iac.ts.Values
+	for i, v := range dstValues {
+		if v == 0 {
+			dstValues[i] = nan
+		}
+	}
 }
 
 func updateAggrSum2(iac *incrementalAggrContext, values []float64) {
diff --git a/app/vmselect/promql/aggr_incremental_test.go b/app/vmselect/promql/aggr_incremental_test.go
index 7e779a1247..f9a78b1367 100644
--- a/app/vmselect/promql/aggr_incremental_test.go
+++ b/app/vmselect/promql/aggr_incremental_test.go
@@ -81,7 +81,7 @@ func TestIncrementalAggr(t *testing.T) {
 	})
 	t.Run("count", func(t *testing.T) {
 		t.Parallel()
-		valuesExpected := []float64{6, 0, 5, 5}
+		valuesExpected := []float64{6, nan, 5, 5}
 		f("count", valuesExpected)
 	})
 	t.Run("sum2", func(t *testing.T) {
diff --git a/app/vmselect/promql/exec_test.go b/app/vmselect/promql/exec_test.go
index d81f8fc849..9af546031b 100644
--- a/app/vmselect/promql/exec_test.go
+++ b/app/vmselect/promql/exec_test.go
@@ -2353,10 +2353,10 @@ func TestExecSuccess(t *testing.T) {
 	})
 	t.Run(`count(multi-vector)`, func(t *testing.T) {
 		t.Parallel()
-		q := `count(label_set(10, "foo", "bar") or label_set((15-time()/100)^0.5, "baz", "sss"))`
+		q := `count(label_set(time()<1500, "foo", "bar") or label_set(time()<1800, "baz", "sss"))`
 		r := netstorage.Result{
 			MetricName: metricNameExpected,
-			Values:     []float64{2, 2, 2, 1, 1, 1},
+			Values:     []float64{2, 2, 2, 1, nan, nan},
 			Timestamps: timestampsExpected,
 		}
 		resultExpected := []netstorage.Result{r}