Optimising dependencies/dependents funcs to not produce new slices each request

Signed-off-by: Danny Kopping <danny.kopping@grafana.com>

rules/group.go

@@ -892,35 +892,31 @@ func NewGroupMetrics(reg prometheus.Registerer) *Metrics {
 // output metric produced by another recording rule in its expression (i.e. as its "input").
 type dependencyMap map[Rule][]Rule
 
-// dependents returns all rules which use the output of the given rule as one of their inputs.
-func (m dependencyMap) dependents(r Rule) []Rule {
-	if len(m) == 0 {
-		return nil
-	}
-
-	return m[r]
+// dependents returns the count of rules which use the output of the given rule as one of their inputs.
+func (m dependencyMap) dependents(r Rule) int {
+	return len(m[r])
 }
 
-// dependencies returns all the rules on which the given rule is dependent for input.
-func (m dependencyMap) dependencies(r Rule) []Rule {
+// dependencies returns the count of rules on which the given rule is dependent for input.
+func (m dependencyMap) dependencies(r Rule) int {
 	if len(m) == 0 {
-		return nil
+		return 0
 	}
 
-	var parents []Rule
-	for parent, children := range m {
+	var count int
+	for _, children := range m {
 		if len(children) == 0 {
 			continue
 		}
 
 		for _, child := range children {
 			if child == r {
-				parents = append(parents, parent)
+				count++
 			}
 		}
 	}
 
-	return parents
+	return count
 }
 
 func (m dependencyMap) isIndependent(r Rule) bool {
@@ -928,7 +924,7 @@ func (m dependencyMap) isIndependent(r Rule) bool {
 		return false
 	}
 
-	return len(m.dependents(r)) == 0 && len(m.dependencies(r)) == 0
+	return m.dependents(r)+m.dependencies(r) == 0
 }
 
 // buildDependencyMap builds a data-structure which contains the relationships between rules within a group.

rules/manager_test.go

@@ -1419,20 +1419,37 @@ func TestDependencyMap(t *testing.T) {
 	expr, err = parser.ParseExpr("user:requests:rate1m <= 0")
 	require.NoError(t, err)
 	rule2 := NewAlertingRule("ZeroRequests", expr, 0, 0, labels.Labels{}, labels.Labels{}, labels.EmptyLabels(), "", true, log.NewNopLogger())
+
+	expr, err = parser.ParseExpr("sum by (user) (rate(requests[5m]))")
+	require.NoError(t, err)
+	rule3 := NewRecordingRule("user:requests:rate5m", expr, labels.Labels{})
+
+	expr, err = parser.ParseExpr("increase(user:requests:rate1m[1h])")
+	require.NoError(t, err)
+	rule4 := NewRecordingRule("user:requests:increase1h", expr, labels.Labels{})
+
 	group := NewGroup(GroupOptions{
 		Name:     "rule_group",
 		Interval: time.Second,
-		Rules:    []Rule{rule, rule2},
+		Rules:    []Rule{rule, rule2, rule3, rule4},
 		Opts:     opts,
 	})
 
-	require.Equal(t, []Rule{rule2}, group.dependencyMap.dependents(rule))
-	require.Len(t, group.dependencyMap.dependencies(rule), 0)
+	require.Zero(t, group.dependencyMap.dependencies(rule))
+	require.Equal(t, 2, group.dependencyMap.dependents(rule))
 	require.False(t, group.dependencyMap.isIndependent(rule))
 
-	require.Len(t, group.dependencyMap.dependents(rule2), 0)
-	require.Equal(t, []Rule{rule}, group.dependencyMap.dependencies(rule2))
+	require.Zero(t, group.dependencyMap.dependents(rule2))
+	require.Equal(t, 1, group.dependencyMap.dependencies(rule2))
 	require.False(t, group.dependencyMap.isIndependent(rule2))
+
+	require.Zero(t, group.dependencyMap.dependents(rule3))
+	require.Zero(t, group.dependencyMap.dependencies(rule3))
+	require.True(t, group.dependencyMap.isIndependent(rule3))
+
+	require.Zero(t, group.dependencyMap.dependents(rule4))
+	require.Equal(t, 1, group.dependencyMap.dependencies(rule4))
+	require.False(t, group.dependencyMap.isIndependent(rule4))
 }
 
 func TestNoDependency(t *testing.T) {