app/vmselect/promql: adjust the provided window only for range functions with dt in denominator

This should fix range function calculations such as `changes(m[d])` where `d` is smaller
than the scrape interval.

Updates https://github.com/VictoriaMetrics/VictoriaMetrics/issues/72

app/vmselect/promql/eval.go

@@ -597,6 +597,7 @@ func getRollupConfigs(name string, rf rollupFunc, start, end, step, window int64
 			End:             end,
 			Step:            step,
 			Window:          window,
+			MayAdjustWindow: rollupFuncsMayAdjustWindow[name],
 			Timestamps:      sharedTimestamps,
 		}
 	}

app/vmselect/promql/rollup.go

@@ -50,6 +50,13 @@ var rollupFuncs = map[string]newRollupFunc{
 	"rollup_increase":    newRollupFuncOneArg(rollupFake), // + rollupFuncsRemoveCounterResets
 }
 
+var rollupFuncsMayAdjustWindow = map[string]bool{
+	"deriv":      true,
+	"deriv_fast": true,
+	"irate":      true,
+	"rate":       true,
+}
+
 var rollupFuncsRemoveCounterResets = map[string]bool{
 	"increase":        true,
 	"irate":           true,
@@ -121,6 +128,13 @@ type rollupConfig struct {
 	Step   int64
 	Window int64
 
+	// Whether window may be adjusted to 2 x interval between data points.
+	// This is needed for functions which have dt in the denominator
+	// such as rate, deriv, etc.
+	// Without the adjustement their value would jump in unexpected directions
+	// when using window smaller than 2 x scrape_interval.
+	MayAdjustWindow bool
+
 	Timestamps []int64
 }
 
@@ -163,7 +177,7 @@ func (rc *rollupConfig) Do(dstValues []float64, values []float64, timestamps []i
 	if window <= 0 {
 		window = rc.Step
 	}
-	if window < maxPrevInterval {
+	if rc.MayAdjustWindow && window < maxPrevInterval {
 		window = maxPrevInterval
 	}
 	rfa := getRollupFuncArg()
@@ -300,7 +314,7 @@ func newRollupHoltWinters(args []interface{}) (rollupFunc, error) {
 		// before calling rollup funcs.
 		values := rfa.values
 		if len(values) == 0 {
-			return nan
+			return rfa.prevValue
 		}
 		sf := sfs[rfa.idx]
 		if sf <= 0 || sf >= 1 {
@@ -358,21 +372,21 @@ func linearRegression(rfa *rollupFuncArg) (float64, float64) {
 	values := rfa.values
 	timestamps := rfa.timestamps
 	if len(values) == 0 {
-		return nan, nan
+		return rfa.prevValue, 0
 	}
 
 	// See https://en.wikipedia.org/wiki/Simple_linear_regression#Numerical_example
 	tFirst := rfa.prevTimestamp
 	vSum := rfa.prevValue
+	tSum := float64(0)
+	tvSum := float64(0)
+	ttSum := float64(0)
 	n := 1.0
 	if math.IsNaN(rfa.prevValue) {
 		tFirst = timestamps[0]
 		vSum = 0
 		n = 0
 	}
-	tSum := float64(0)
-	tvSum := float64(0)
-	ttSum := float64(0)
 	for i, v := range values {
 		dt := float64(timestamps[i]-tFirst) * 1e-3
 		vSum += v
@@ -402,7 +416,11 @@ func newRollupQuantile(args []interface{}) (rollupFunc, error) {
 		// before calling rollup funcs.
 		values := rfa.values
 		if len(values) == 0 {
-			return nan
+			return rfa.prevValue
+		}
+		if len(values) == 1 {
+			// Fast path - only a single value.
+			return values[0]
 		}
 		hf := histogram.GetFast()
 		for _, v := range values {
@@ -424,7 +442,7 @@ func rollupAvg(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return nan
+		return rfa.prevValue
 	}
 	var sum float64
 	for _, v := range values {
@@ -438,7 +456,7 @@ func rollupMin(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return nan
+		return rfa.prevValue
 	}
 	minValue := values[0]
 	for _, v := range values {
@@ -454,7 +472,7 @@ func rollupMax(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return nan
+		return rfa.prevValue
 	}
 	maxValue := values[0]
 	for _, v := range values {
@@ -470,7 +488,7 @@ func rollupSum(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return nan
+		return rfa.prevValue
 	}
 	var sum float64
 	for _, v := range values {
@@ -484,8 +502,11 @@ func rollupCount(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	return float64(len(values))
 }
 
@@ -501,8 +522,15 @@ func rollupStdvar(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
+	if len(values) == 1 {
+		// Fast path.
+		return values[0]
+	}
 	var avg float64
 	var count float64
 	var q float64
@@ -528,7 +556,7 @@ func rollupDelta(rfa *rollupFuncArg) float64 {
 		values = values[1:]
 	}
 	if len(values) == 0 {
-		return nan
+		return 0
 	}
 	return values[len(values)-1] - prevValue
 }
@@ -538,14 +566,17 @@ func rollupIdelta(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	lastValue := values[len(values)-1]
 	values = values[:len(values)-1]
 	if len(values) == 0 {
 		prevValue := rfa.prevValue
 		if math.IsNaN(prevValue) {
-			return nan
+			return 0
 		}
 		return lastValue - prevValue
 	}
@@ -576,7 +607,7 @@ func rollupDerivFast(rfa *rollupFuncArg) float64 {
 		timestamps = timestamps[1:]
 	}
 	if len(values) == 0 {
-		return nan
+		return 0
 	}
 	vEnd := values[len(values)-1]
 	tEnd := timestamps[len(timestamps)-1]
@@ -591,8 +622,11 @@ func rollupIderiv(rfa *rollupFuncArg) float64 {
 	values := rfa.values
 	timestamps := rfa.timestamps
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	vEnd := values[len(values)-1]
 	tEnd := timestamps[len(timestamps)-1]
 	values = values[:len(values)-1]
@@ -601,7 +635,7 @@ func rollupIderiv(rfa *rollupFuncArg) float64 {
 	prevTimestamp := rfa.prevTimestamp
 	if len(values) == 0 {
 		if math.IsNaN(prevValue) {
-			return nan
+			return 0
 		}
 	} else {
 		prevValue = values[len(values)-1]
@@ -616,13 +650,15 @@ func rollupChanges(rfa *rollupFuncArg) float64 {
 	// There is no need in handling NaNs here, since they must be cleaned up
 	// before calling rollup funcs.
 	values := rfa.values
+	prevValue := rfa.prevValue
+	n := 0
+	if math.IsNaN(prevValue) {
 		if len(values) == 0 {
 			return nan
 		}
-	n := 0
-	prevValue := rfa.prevValue
-	if math.IsNaN(prevValue) {
 		prevValue = values[0]
+		values = values[1:]
+		n++
 	}
 	for _, v := range values {
 		if v != prevValue {
@@ -638,15 +674,18 @@ func rollupResets(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	prevValue := rfa.prevValue
 	if math.IsNaN(prevValue) {
 		prevValue = values[0]
 		values = values[1:]
 	}
 	if len(values) == 0 {
-		return nan
+		return 0
 	}
 	n := 0
 	for _, v := range values {
@@ -681,7 +720,7 @@ func rollupLast(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return nan
+		return rfa.prevValue
 	}
 	return values[len(values)-1]
 }
@@ -691,8 +730,11 @@ func rollupDistinct(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	m := make(map[float64]struct{})
 	for _, v := range values {
 		m[v] = struct{}{}
@@ -708,8 +750,11 @@ func rollupIntegrate(rfa *rollupFuncArg) float64 {
 	values := rfa.values
 	timestamps := rfa.timestamps
 	if len(values) == 0 {
+		if math.IsNaN(rfa.prevValue) {
 			return nan
 		}
+		return 0
+	}
 	prevValue := rfa.prevValue
 	if math.IsNaN(prevValue) {
 		prevValue = values[0]
@@ -718,7 +763,7 @@ func rollupIntegrate(rfa *rollupFuncArg) float64 {
 		timestamps = timestamps[1:]
 	}
 	if len(values) == 0 {
-		return nan
+		return 0
 	}
 
 	var sum float64

app/vmselect/promql/rollup_test.go

@@ -190,7 +190,7 @@ func TestRollupNewRollupFuncSuccess(t *testing.T) {
 	}
 
 	f("default_rollup", 34)
-	f("changes", 10)
+	f("changes", 11)
 	f("delta", -89)
 	f("deriv", -266.85860231406065)
 	f("deriv_fast", -712)
@@ -209,6 +209,8 @@ func TestRollupNewRollupFuncSuccess(t *testing.T) {
 	f("first_over_time", 123)
 	f("last_over_time", 34)
 	f("integrate", 61.0275)
+	f("distinct_over_time", 8)
+	f("ideriv", 0)
 }
 
 func TestRollupNewRollupFuncError(t *testing.T) {
@@ -268,14 +270,14 @@ func TestRollupNoWindowNoPoints(t *testing.T) {
 		rc := rollupConfig{
 			Func:   rollupDelta,
 			Start:  120,
-			End:    144,
+			End:    148,
 			Step:   4,
 			Window: 0,
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{2, 2, 2, 0, 0, 0, nan}
+		valuesExpected := []float64{2, 0, 0, 0, 0, 0, 0, nan}
-		timestampsExpected := []int64{120, 124, 128, 132, 136, 140, 144}
+		timestampsExpected := []int64{120, 124, 128, 132, 136, 140, 144, 148}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
 }
@@ -305,7 +307,7 @@ func TestRollupWindowNoPoints(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{34, 34, nan, nan}
+		valuesExpected := []float64{34, nan, nan, nan}
 		timestampsExpected := []int64{141, 151, 161, 171}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
@@ -316,14 +318,14 @@ func TestRollupNoWindowPartialPoints(t *testing.T) {
 		rc := rollupConfig{
 			Func:   rollupFirst,
 			Start:  0,
-			End:    20,
+			End:    25,
 			Step:   5,
 			Window: 0,
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, 123, 123, 123, 123}
+		valuesExpected := []float64{nan, 123, 123, 123, 34, 34}
-		timestampsExpected := []int64{0, 5, 10, 15, 20}
+		timestampsExpected := []int64{0, 5, 10, 15, 20, 25}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
 	t.Run("afterEnd", func(t *testing.T) {
@@ -395,7 +397,7 @@ func TestRollupWindowPartialPoints(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, 54, 44, nan}
+		valuesExpected := []float64{nan, 54, 44, 34}
 		timestampsExpected := []int64{0, 50, 100, 150}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
@@ -496,7 +498,7 @@ func TestRollupFuncsNoWindow(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, 33, -87, 0}
+		valuesExpected := []float64{0, 33, -87, 0}
 		timestampsExpected := []int64{10, 50, 90, 130}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
@@ -510,10 +512,24 @@ func TestRollupFuncsNoWindow(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, 3, 4, 3, 0}
+		valuesExpected := []float64{nan, 4, 4, 3, 0}
 		timestampsExpected := []int64{0, 40, 80, 120, 160}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
+	t.Run("changes_small_window", func(t *testing.T) {
+		rc := rollupConfig{
+			Func:   rollupChanges,
+			Start:  0,
+			End:    45,
+			Step:   9,
+			Window: 9,
+		}
+		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
+		values := rc.Do(nil, testValues, testTimestamps)
+		valuesExpected := []float64{nan, 1, 1, 1, 1, 0}
+		timestampsExpected := []int64{0, 9, 18, 27, 36, 45}
+		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
+	})
 	t.Run("resets", func(t *testing.T) {
 		rc := rollupConfig{
 			Func:   rollupResets,
@@ -552,7 +568,7 @@ func TestRollupFuncsNoWindow(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, -2879.310344827587, 558.0608793686592, 422.84569138276544, 0}
+		valuesExpected := []float64{0, -2879.310344827587, 558.0608793686592, 422.84569138276544, 0}
 		timestampsExpected := []int64{0, 40, 80, 120, 160}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})
@@ -580,7 +596,7 @@ func TestRollupFuncsNoWindow(t *testing.T) {
 		}
 		rc.Timestamps = getTimestamps(rc.Start, rc.End, rc.Step)
 		values := rc.Do(nil, testValues, testTimestamps)
-		valuesExpected := []float64{nan, 39.81519810323691, 32.080952292598795, 5.2493385826745405, 0}
+		valuesExpected := []float64{nan, 39.81519810323691, 32.080952292598795, 5.2493385826745405, 5.830951894845301}
 		timestampsExpected := []int64{0, 40, 80, 120, 160}
 		testRowsEqual(t, values, rc.Timestamps, valuesExpected, timestampsExpected)
 	})