Alerting: Handle NaN in reducers (#22053)

- Fix bug with NaN in alerting - Closes #21953
- Alert reducers (avg/max/etc) drop null values from their calculation. This change makes it so NaN values are handled in the same way as null values.

pkg/services/alerting/conditions/reducer.go

@@ -29,7 +29,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 	case "avg":
 		validPointsCount := 0
 		for _, point := range series.Points {
-			if point[0].Valid {
+			if isValid(point[0]) {
 				value += point[0].Float64
 				validPointsCount++
 				allNull = false
@@ -40,7 +40,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 		}
 	case "sum":
 		for _, point := range series.Points {
-			if point[0].Valid {
+			if isValid(point[0]) {
 				value += point[0].Float64
 				allNull = false
 			}
@@ -48,7 +48,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 	case "min":
 		value = math.MaxFloat64
 		for _, point := range series.Points {
-			if point[0].Valid {
+			if isValid(point[0]) {
 				allNull = false
 				if value > point[0].Float64 {
 					value = point[0].Float64
@@ -58,7 +58,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 	case "max":
 		value = -math.MaxFloat64
 		for _, point := range series.Points {
-			if point[0].Valid {
+			if isValid(point[0]) {
 				allNull = false
 				if value < point[0].Float64 {
 					value = point[0].Float64
@@ -71,7 +71,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 	case "last":
 		points := series.Points
 		for i := len(points) - 1; i >= 0; i-- {
-			if points[i][0].Valid {
+			if isValid(points[i][0]) {
 				value = points[i][0].Float64
 				allNull = false
 				break
@@ -80,7 +80,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 	case "median":
 		var values []float64
 		for _, v := range series.Points {
-			if v[0].Valid {
+			if isValid(v[0]) {
 				allNull = false
 				values = append(values, v[0].Float64)
 			}
@@ -100,7 +100,7 @@ func (s *queryReducer) Reduce(series *tsdb.TimeSeries) null.Float {
 		allNull, value = calculateDiff(series, allNull, value, percentDiff)
 	case "count_non_null":
 		for _, v := range series.Points {
-			if v[0].Valid {
+			if isValid(v[0]) {
 				value++
 			}
 		}
@@ -129,7 +129,7 @@ func calculateDiff(series *tsdb.TimeSeries, allNull bool, value float64, fn func
 	)
 	// get the newest point
 	for i = len(points) - 1; i >= 0; i-- {
-		if points[i][0].Valid {
+		if isValid(points[i][0]) {
 			allNull = false
 			first = points[i][0].Float64
 			break
@@ -139,7 +139,7 @@ func calculateDiff(series *tsdb.TimeSeries, allNull bool, value float64, fn func
 		// get the oldest point
 		points = points[0:i]
 		for i := 0; i < len(points); i++ {
-			if points[i][0].Valid {
+			if isValid(points[i][0]) {
 				allNull = false
 				val := fn(first, points[i][0].Float64)
 				value = math.Abs(val)
@@ -150,6 +150,10 @@ func calculateDiff(series *tsdb.TimeSeries, allNull bool, value float64, fn func
 	return allNull, value
 }
 
+func isValid(f null.Float) bool {
+	return f.Valid && !math.IsNaN(f.Float64)
+}
+
 var diff = func(newest, oldest float64) float64 {
 	return newest - oldest
 }

pkg/services/alerting/conditions/reducer_test.go

@@ -1,6 +1,7 @@
 package conditions
 
 import (
+	"math"
 	"testing"
 
 	. "github.com/smartystreets/goconvey/convey"
@@ -181,6 +182,21 @@ func TestSimpleReducer(t *testing.T) {
 
 			So(reducer.Reduce(series).Valid, ShouldEqual, false)
 		})
+
+		Convey("min should work with NaNs", func() {
+			result := testReducer("min", math.NaN(), math.NaN(), math.NaN())
+			So(result, ShouldEqual, float64(0))
+		})
+
+		Convey("isValid should treat NaN as invalid", func() {
+			result := isValid(null.FloatFrom(math.NaN()))
+			So(result, ShouldBeFalse)
+		})
+
+		Convey("isValid should treat invalid null.Float as invalid", func() {
+			result := isValid(null.FloatFromPtr(nil))
+			So(result, ShouldBeFalse)
+		})
 	})
 }