app/vmselect/promql: remove duplicated logic of filling NaN values for histograms

Removed logic was used to fill nan values with lower buckets values: [1 2 3 nan nan nan] => [1 2 3 3 3 3].
Since buckets are now fixed from lower ones to upper this happens in the main loop, so there is no need in a second one.

Signed-off-by: Zakhar Bessarab <z.bessarab@victoriametrics.com>

app/vmselect/promql/exec_test.go

@@ -4471,7 +4471,7 @@ func TestExecSuccess(t *testing.T) {
 		),0.01)`
 		r := netstorage.Result{
 			MetricName: metricNameExpected,
-			Values:     []float64{18.57, 18.57, 18.57, 18.57, 18.57, 18.57},
+			Values:     []float64{30, 30, 30, 30, 30, 30},
 			Timestamps: timestampsExpected,
 		}
 		r.MetricName.Tags = []storage.Tag{{

app/vmselect/promql/transform.go

@@ -1044,29 +1044,18 @@ func fixBrokenBuckets(i int, xss []leTimeseries) {
 	// Buckets are already sorted by le, so their values must be in ascending order,
 	// since the next bucket includes all the previous buckets.
 	// If the next bucket has lower value than the current bucket,
-	// then the current bucket must be substituted with the next bucket value.
+	// then the next bucket must be substituted with the current bucket value.
 	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/2819
 	if len(xss) < 2 {
 		return
 	}
-	// Fill NaN in upper buckets with the first non-NaN value found in lower buckets.
-	for j := len(xss) - 1; j >= 0; j-- {
+
+	// Substitute upper bucket values with lower bucket values if the upper values are NaN
+	// or are bigger than the lower bucket values.
+	vNext := xss[0].ts.Values[0]
+	for j := 1; j < len(xss); j++ {
 		v := xss[j].ts.Values[i]
-		if !math.IsNaN(v) {
-			j++
-			for j < len(xss) {
-				xss[j].ts.Values[i] = v
-				j++
-			}
-			break
-		}
-	}
-	// Substitute lower bucket values with upper values if the lower values are NaN
-	// or are bigger than the upper bucket values.
-	vNext := xss[len(xss)-1].ts.Values[i]
-	for j := len(xss) - 2; j >= 0; j-- {
-		v := xss[j].ts.Values[i]
-		if math.IsNaN(v) || v > vNext {
+		if math.IsNaN(v) || vNext > v {
 			xss[j].ts.Values[i] = vNext
 		} else {
 			vNext = v

app/vmselect/promql/transform_test.go

@@ -32,11 +32,11 @@ func TestFixBrokenBuckets(t *testing.T) {
 	f(nil, []float64{})
 	f([]float64{1}, []float64{1})
 	f([]float64{1, 2}, []float64{1, 2})
-	f([]float64{2, 1}, []float64{1, 1})
+	f([]float64{2, 1}, []float64{2, 2})
 	f([]float64{1, 2, 3, nan, nan}, []float64{1, 2, 3, 3, 3})
-	f([]float64{5, 1, 2, 3, nan}, []float64{1, 1, 2, 3, 3})
-	f([]float64{1, 5, 2, nan, 6, 3}, []float64{1, 2, 2, 3, 3, 3})
-	f([]float64{5, 10, 4, 3}, []float64{3, 3, 3, 3})
+	f([]float64{5, 1, 2, 3, nan}, []float64{5, 5, 5, 5, 5})
+	f([]float64{1, 5, 2, nan, 6, 3}, []float64{1, 5, 5, 5, 6, 6})
+	f([]float64{5, 10, 4, 3}, []float64{5, 10, 10, 10})
 }
 
 func TestVmrangeBucketsToLE(t *testing.T) {