Add builtinFuncs to ExecutionState.Funcs as desired to reduce memory usage.

CHANGELOG.md

@@ -5,6 +5,7 @@
 ### Features
 
 - [#2154](https://github.com/influxdata/kapacitor/pull/2154): Add ability to skip ssl verification with an alert post node. Thanks @itsHabib!
+- [#2177](https://github.com/influxdata/kapacitor/issues/2177): NewFunctions func occupies many memory when state_count has large working_cardinality
 
 ### Bugfixes
 

tick/stateful/eval_function_node.go

@@ -259,7 +259,7 @@ func eval(n NodeEvaluator, scope *Scope, executionState ExecutionState) (interfa
 }
 
 func lookupFunc(name string, funcs Funcs, scope ReadOnlyScope) Func {
-	f := funcs[name]
+	f := funcs.Get(name)
 	if f != nil {
 		return f
 	}

tick/stateful/execution_state.go

@@ -8,7 +8,7 @@ type ExecutionState struct {
 
 func CreateExecutionState() ExecutionState {
 	return ExecutionState{
-		Funcs: NewFunctions(),
+		Funcs: NewEmptyFuncs(),
 	}
 }
 

tick/stateful/functions.go

@@ -132,6 +132,29 @@ func FuncDomains(f Func) Domains {
 // Lookup for functions
 type Funcs map[string]Func
 
+func (funcs Funcs) Get(name string) Func {
+	if f := funcs[name]; f != nil {
+		return f
+	}
+	if f := statelessFuncs[name]; f != nil {
+		funcs[name] = f
+		return f
+	}
+	switch name {
+	case "sigma":
+		funcs[name] = &sigma{}
+		return funcs[name]
+	case "count":
+		funcs[name] = &count{}
+		return funcs[name]
+	case "spread":
+		funcs[name] = &spread{min: math.Inf(+1), max: math.Inf(-1)}
+		return funcs[name]
+	default:
+		return nil
+	}
+}
+
 var statelessFuncs Funcs
 
 var builtinFuncs Funcs
@@ -252,6 +275,11 @@ func NewFunctions() Funcs {
 	return funcs
 }
 
+// Return empty Funcs
+func NewEmptyFuncs() Funcs {
+	return make(Funcs, 0)
+}
+
 type math1Func func(float64) float64
 type math1 struct {
 	name string