Refactoring

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

rules/group.go

@@ -437,7 +437,7 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 		eval := func(i int, rule Rule, async bool) {
 			defer func() {
 				if async {
-					g.opts.ConcurrencyController.Done()
+					g.opts.ConcurrentEvalsController.Done()
 				}
 			}()
 
@@ -569,7 +569,7 @@ func (g *Group) Eval(ctx context.Context, ts time.Time) {
 
 		// If the rule has no dependencies, it can run concurrently because no other rules in this group depend on its output.
 		// Try run concurrently if there are slots available.
-		if g.dependencyMap.isIndependent(rule) && g.opts.ConcurrencyController.Allow() {
+		if g.dependencyMap.isIndependent(rule) && g.opts.ConcurrentEvalsController != nil && g.opts.ConcurrentEvalsController.Allow() {
 			go eval(i, rule, true)
 		} else {
 			eval(i, rule, false)
@@ -888,8 +888,8 @@ func NewGroupMetrics(reg prometheus.Registerer) *Metrics {
 }
 
 // dependencyMap is a data-structure which contains the relationships between rules within a group.
-// It is used to describe the dependency associations between recording rules in a group whereby one rule uses the
-// output metric produced by another recording rule in its expression (i.e. as its "input").
+// It is used to describe the dependency associations between rules in a group whereby one rule uses the
+// output metric produced by another rule in its expression (i.e. as its "input").
 type dependencyMap map[Rule][]Rule
 
 // dependents returns the count of rules which use the output of the given rule as one of their inputs.
@@ -905,10 +905,6 @@ func (m dependencyMap) dependencies(r Rule) int {
 
 	var count int
 	for _, children := range m {
-		if len(children) == 0 {
-			continue
-		}
-
 		for _, child := range children {
 			if child == r {
 				count++
@@ -919,6 +915,8 @@ func (m dependencyMap) dependencies(r Rule) int {
 	return count
 }
 
+// isIndependent determines whether the given rule is not dependent on another rule for its input, nor is any other rule
+// dependent on its output.
 func (m dependencyMap) isIndependent(r Rule) bool {
 	if m == nil {
 		return false
@@ -928,6 +926,16 @@ func (m dependencyMap) isIndependent(r Rule) bool {
 }
 
 // buildDependencyMap builds a data-structure which contains the relationships between rules within a group.
+//
+// Alert rules, by definition, cannot have any dependents - but they can have dependencies. Any recording rule on whose
+// output an Alert rule depends will not be able to run concurrently.
+//
+// There is a class of rule expressions which are considered "indeterminate", because either relationships cannot be
+// inferred, or concurrent evaluation of rules depending on these series would produce undefined/unexpected behaviour:
+//   - wildcard queriers like {cluster="prod1"} which would match every series with that label selector
+//   - any "meta" series (series produced by Prometheus itself) like ALERTS, ALERTS_FOR_STATE
+//
+// Rules which are independent can run concurrently with no side-effects.
 func buildDependencyMap(rules []Rule) dependencyMap {
 	dependencies := make(dependencyMap)
 

rules/manager.go

@@ -115,10 +115,10 @@ type ManagerOptions struct {
 	OutageTolerance           time.Duration
 	ForGracePeriod            time.Duration
 	ResendDelay               time.Duration
+	GroupLoader               GroupLoader
 	MaxConcurrentEvals        int64
 	ConcurrentEvalsEnabled    bool
-	ConcurrencyController  ConcurrencyController
-	GroupLoader            GroupLoader
+	ConcurrentEvalsController ConcurrentRuleEvalController
 
 	Metrics *Metrics
 }
@@ -134,7 +134,7 @@ func NewManager(o *ManagerOptions) *Manager {
 		o.GroupLoader = FileLoader{}
 	}
 
-	o.ConcurrencyController = NewConcurrencyController(o.ConcurrentEvalsEnabled, o.MaxConcurrentEvals)
+	o.ConcurrentEvalsController = NewConcurrentRuleEvalController(o.ConcurrentEvalsEnabled, o.MaxConcurrentEvals)
 
 	m := &Manager{
 		groups: map[string]*Group{},
@@ -410,16 +410,26 @@ func SendAlerts(s Sender, externalURL string) NotifyFunc {
 	}
 }
 
-type ConcurrencyController struct {
+// ConcurrentRuleEvalController controls whether rules can be evaluated concurrently. Its purpose it to bound the amount
+// of concurrency in rule evaluations so they do not overwhelm the Prometheus server with additional query load.
+// Concurrency is controlled globally, not on a per-group basis.
+type ConcurrentRuleEvalController interface {
+	Allow() bool
+	Done()
+}
+
+// concurrentRuleEvalController holds a weighted semaphore which controls the concurrent evaluation of rules.
+type concurrentRuleEvalController struct {
 	enabled bool
 	sema    *semaphore.Weighted
 }
 
-func NewConcurrencyController(enabled bool, maxConcurrency int64) ConcurrencyController {
-	return ConcurrencyController{enabled: enabled, sema: semaphore.NewWeighted(maxConcurrency)}
+func NewConcurrentRuleEvalController(enabled bool, maxConcurrency int64) ConcurrentRuleEvalController {
+	return concurrentRuleEvalController{enabled: enabled, sema: semaphore.NewWeighted(maxConcurrency)}
 }
 
-func (c ConcurrencyController) Allow() bool {
+// Allow determines whether any concurrency slots are available.
+func (c concurrentRuleEvalController) Allow() bool {
 	if !c.enabled {
 		return false
 	}
@@ -427,7 +437,8 @@ func (c ConcurrencyController) Allow() bool {
 	return c.sema.TryAcquire(1)
 }
 
-func (c ConcurrencyController) Done() {
+// Done releases a concurrent evaluation slot.
+func (c concurrentRuleEvalController) Done() {
 	if !c.enabled {
 		return
 	}

rules/manager_test.go

@@ -1471,7 +1471,53 @@ func TestNoDependency(t *testing.T) {
 	})
 
 	// A group with only one rule cannot have dependencies.
+	require.Empty(t, group.dependencyMap)
+}
+
+func TestDependenciesEdgeCases(t *testing.T) {
+	ctx := context.Background()
+	opts := &ManagerOptions{
+		Context: ctx,
+		Logger:  log.NewNopLogger(),
+	}
+
+	t.Run("empty group", func(t *testing.T) {
+		group := NewGroup(GroupOptions{
+			Name:     "rule_group",
+			Interval: time.Second,
+			Rules:    []Rule{}, // empty group
+			Opts:     opts,
+		})
+
+		expr, err := parser.ParseExpr("sum by (user) (rate(requests[1m]))")
+		require.NoError(t, err)
+		rule := NewRecordingRule("user:requests:rate1m", expr, labels.Labels{})
+
+		// A group with no rules has no dependency map, but doesn't panic if the map is queried.
+		require.Nil(t, group.dependencyMap)
 		require.False(t, group.dependencyMap.isIndependent(rule))
+	})
+
+	t.Run("rules which reference no series", func(t *testing.T) {
+		expr, err := parser.ParseExpr("one")
+		require.NoError(t, err)
+		rule1 := NewRecordingRule("1", expr, labels.Labels{})
+
+		expr, err = parser.ParseExpr("two")
+		require.NoError(t, err)
+		rule2 := NewRecordingRule("2", expr, labels.Labels{})
+
+		group := NewGroup(GroupOptions{
+			Name:     "rule_group",
+			Interval: time.Second,
+			Rules:    []Rule{rule1, rule2},
+			Opts:     opts,
+		})
+
+		// A group with rules which reference no series will still produce a dependency map
+		require.True(t, group.dependencyMap.isIndependent(rule1))
+		require.True(t, group.dependencyMap.isIndependent(rule2))
+	})
 }
 
 func TestNoMetricSelector(t *testing.T) {
@@ -1596,10 +1642,23 @@ func TestDependencyMapUpdatesOnGroupUpdate(t *testing.T) {
 	require.NoError(t, err)
 
 	for h, g := range ruleManager.groups {
+		const ruleName = "job:http_requests:rate5m"
+		var rr *RecordingRule
+
+		for _, r := range g.rules {
+			if r.Name() == ruleName {
+				rr = r.(*RecordingRule)
+			}
+		}
+
+		require.NotEmptyf(t, rr, "expected to find %q recording rule in fixture", ruleName)
+
 		// Dependency maps must change because the groups would've been updated.
 		require.NotEqual(t, orig[h], g.dependencyMap)
 		// We expect there to be some dependencies since the new rule group contains a dependency.
 		require.Greater(t, len(g.dependencyMap), 0)
+		require.Equal(t, 1, g.dependencyMap.dependents(rr))
+		require.Zero(t, g.dependencyMap.dependencies(rr))
 	}
 }
 
@@ -1625,17 +1684,16 @@ func TestAsyncRuleEvaluation(t *testing.T) {
 				inflightQueries.Add(-1)
 			}()
 
-			// Artificially delay all query executions to highly concurrent execution improvement.
+			// Artificially delay all query executions to highlight concurrent execution improvement.
 			time.Sleep(artificialDelay)
 
-			// return a stub sample
+			// Return a stub sample.
 			return promql.Vector{
 				promql.Sample{Metric: labels.FromStrings("__name__", "test"), T: ts.UnixMilli(), F: 12345},
 			}, nil
 		},
 	})
 
-	// Evaluate groups manually to show the impact of async rule evaluations.
 	groups, errs := ruleManager.LoadGroups(time.Second, labels.EmptyLabels(), "", nil, files...)
 	require.Empty(t, errs)
 	require.Len(t, groups, 1)
@@ -1688,7 +1746,7 @@ func TestAsyncRuleEvaluation(t *testing.T) {
 
 		for _, group := range groups {
 			// Allow up to 2 concurrent rule evaluations.
-			group.opts.ConcurrencyController = NewConcurrencyController(true, 2)
+			group.opts.ConcurrentEvalsController = NewConcurrentRuleEvalController(true, 2)
 			require.Len(t, group.rules, expectedRules)
 
 			start := time.Now()
@@ -1749,17 +1807,16 @@ func TestBoundedRuleEvalConcurrency(t *testing.T) {
 				inflightQueries.Add(-1)
 			}()
 
-			// Artificially delay all query executions to highly concurrent execution improvement.
+			// Artificially delay all query executions to highlight concurrent execution improvement.
 			time.Sleep(artificialDelay)
 
-			// return a stub sample
+			// Return a stub sample.
 			return promql.Vector{
 				promql.Sample{Metric: labels.FromStrings("__name__", "test"), T: ts.UnixMilli(), F: 12345},
 			}, nil
 		},
 	})
 
-	// Evaluate groups manually to show the impact of async rule evaluations.
 	groups, errs := ruleManager.LoadGroups(time.Second, labels.EmptyLabels(), "", nil, files...)
 	require.Empty(t, errs)
 	require.Len(t, groups, groupCount)