app/vmselect/promql: move needSilenceIntervalForRollupFunc from eval.go to rollup.go

This should improve maintainability of the code related to rollup functions,
since it is located in rollup.go

While at it, properly return empty results from holt_winters(), rate_over_sum(),
sum2_over_time(), geomean_over_time() and distinct_over_time() when there are no real samples
on the selected lookbehind window. Previously the previous sample value was mistakenly
returned from these functions.

app/vmselect/promql/eval.go

@@ -1687,7 +1687,7 @@ func evalRollupFuncNoCache(qt *querytracer.Tracer, ec *EvalConfig, funcName stri
 	tfss := searchutils.ToTagFilterss(me.LabelFilterss)
 	tfss = searchutils.JoinTagFilterss(tfss, ec.EnforcedTagFilterss)
 	minTimestamp := ec.Start
-	if needSilenceIntervalForRollupFunc(funcName) {
+	if needSilenceIntervalForRollupFunc[funcName] {
 		minTimestamp -= maxSilenceInterval()
 	}
 	if window > ec.Step {
@@ -1788,56 +1788,6 @@ func maxSilenceInterval() int64 {
 	return d
 }
 
-func needSilenceIntervalForRollupFunc(funcName string) bool {
-	// All the rollup functions, which do not rely on the previous sample
-	// before the lookbehind window (aka prevValue and realPrevValue), do not need silence interval.
-	switch strings.ToLower(funcName) {
-	case "default_rollup":
-		// The default_rollup implicitly relies on the previous samples in order to fill gaps.
-		// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5388
-		return true
-	case
-		"absent_over_time",
-		"avg_over_time",
-		"count_eq_over_time",
-		"count_gt_over_time",
-		"count_le_over_time",
-		"count_ne_over_time",
-		"count_over_time",
-		"first_over_time",
-		"histogram_over_time",
-		"hoeffding_bound_lower",
-		"hoeffding_bound_upper",
-		"last_over_time",
-		"mad_over_time",
-		"max_over_time",
-		"median_over_time",
-		"min_over_time",
-		"predict_linear",
-		"present_over_time",
-		"quantile_over_time",
-		"quantiles_over_time",
-		"range_over_time",
-		"share_gt_over_time",
-		"share_le_over_time",
-		"share_eq_over_time",
-		"stale_samples_over_time",
-		"stddev_over_time",
-		"stdvar_over_time",
-		"sum_over_time",
-		"tfirst_over_time",
-		"timestamp",
-		"timestamp_with_name",
-		"tlast_over_time",
-		"tmax_over_time",
-		"tmin_over_time",
-		"zscore_over_time":
-		return false
-	default:
-		return true
-	}
-}
-
 func evalRollupWithIncrementalAggregate(qt *querytracer.Tracer, funcName string, keepMetricNames bool,
 	iafc *incrementalAggrFuncContext, rss *netstorage.Results, rcs []*rollupConfig,
 	preFunc func(values []float64, timestamps []int64), sharedTimestamps []int64) ([]*timeseries, error) {

app/vmselect/promql/rollup.go

@@ -103,6 +103,42 @@ var rollupFuncs = map[string]newRollupFunc{
 	"zscore_over_time":       newRollupFuncOneArg(rollupZScoreOverTime),
 }
 
+// Functions, which need the previous sample before the lookbehind window for proper calculations.
+//
+// All the rollup functions, which do not rely on the previous sample
+// before the lookbehind window (aka prevValue and realPrevValue), do not need silence interval.
+var needSilenceIntervalForRollupFunc = map[string]bool{
+	"ascent_over_time":    true,
+	"changes":             true,
+	"decreases_over_time": true,
+	// The default_rollup implicitly relies on the previous samples in order to fill gaps.
+	// See https://github.com/VictoriaMetrics/VictoriaMetrics/issues/5388
+	"default_rollup":         true,
+	"delta":                  true,
+	"deriv_fast":             true,
+	"descent_over_time":      true,
+	"idelta":                 true,
+	"ideriv":                 true,
+	"increase":               true,
+	"increase_pure":          true,
+	"increases_over_time":    true,
+	"integrate":              true,
+	"irate":                  true,
+	"lag":                    true,
+	"lifetime":               true,
+	"rate":                   true,
+	"resets":                 true,
+	"rollup":                 true,
+	"rollup_candlestick":     true,
+	"rollup_delta":           true,
+	"rollup_deriv":           true,
+	"rollup_increase":        true,
+	"rollup_rate":            true,
+	"rollup_scrape_interval": true,
+	"scrape_interval":        true,
+	"tlast_change_over_time": true,
+}
+
 // rollupAggrFuncs are functions that can be passed to `aggr_over_time()`
 var rollupAggrFuncs = map[string]rollupFunc{
 	"absent_over_time":        rollupAbsent,
@@ -957,7 +993,7 @@ func newRollupHoltWinters(args []interface{}) (rollupFunc, error) {
 		// before calling rollup funcs.
 		values := rfa.values
 		if len(values) == 0 {
-			return rfa.prevValue
+			return nan
 		}
 		sf := sfs[rfa.idx]
 		if sf < 0 || sf > 1 {
@@ -1586,11 +1622,7 @@ func rollupRateOverSum(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	timestamps := rfa.timestamps
 	if len(timestamps) == 0 {
-		if math.IsNaN(rfa.prevValue) {
+		return nan
-			return nan
-		}
-		// Assume that the value didn't change since rfa.prevValue.
-		return 0
 	}
 	sum := float64(0)
 	for _, v := range rfa.values {
@@ -1610,7 +1642,7 @@ func rollupSum2(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return rfa.prevValue * rfa.prevValue
+		return nan
 	}
 	var sum2 float64
 	for _, v := range values {
@@ -1624,7 +1656,7 @@ func rollupGeomean(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		return rfa.prevValue
+		return nan
 	}
 	p := 1.0
 	for _, v := range values {
@@ -2268,10 +2300,7 @@ func rollupDistinct(rfa *rollupFuncArg) float64 {
 	// before calling rollup funcs.
 	values := rfa.values
 	if len(values) == 0 {
-		if math.IsNaN(rfa.prevValue) {
+		return nan
-			return nan
-		}
-		return 0
 	}
 	m := make(map[float64]struct{})
 	for _, v := range values {