Alerting: Elide requests to Loki if nothing should be recorded (#65011)

Exit early if no log streams or annotations

pkg/services/ngalert/state/historian/annotation.go

@@ -62,6 +62,11 @@ func (h *AnnotationBackend) Record(ctx context.Context, rule history_model.RuleM
 	panel := parsePanelKey(rule, logger)
 
 	errCh := make(chan error, 1)
+	if len(annotations) == 0 {
+		close(errCh)
+		return errCh
+	}
+
 	go func() {
 		defer close(errCh)
 		errCh <- h.recordAnnotations(ctx, panel, annotations, rule.OrgID, logger)
@@ -180,10 +185,6 @@ func buildAnnotations(rule history_model.RuleMeta, states []state.StateTransitio
 }
 
 func (h *AnnotationBackend) recordAnnotations(ctx context.Context, panel *panelKey, annotations []annotations.Item, orgID int64, logger log.Logger) error {
-	if len(annotations) == 0 {
-		return nil
-	}
-
 	if panel != nil {
 		dashID, err := h.dashboards.getID(ctx, panel.orgID, panel.dashUID)
 		if err != nil {

pkg/services/ngalert/state/historian/loki.go

@@ -72,7 +72,13 @@ func (h *RemoteLokiBackend) TestConnection(ctx context.Context) error {
 func (h *RemoteLokiBackend) Record(ctx context.Context, rule history_model.RuleMeta, states []state.StateTransition) <-chan error {
 	logger := h.log.FromContext(ctx)
 	streams := statesToStreams(rule, states, h.externalLabels, logger)
+
 	errCh := make(chan error, 1)
+	if len(streams) == 0 {
+		close(errCh)
+		return errCh
+	}
+
 	go func() {
 		defer close(errCh)
 

pkg/services/ngalert/state/historian/loki_test.go

@@ -311,6 +311,18 @@ grafana_alerting_state_history_writes_total{org="1"} 2
 		)
 		require.NoError(t, err)
 	})
+
+	t.Run("elides request if nothing to send", func(t *testing.T) {
+		req := NewFakeRequester()
+		loki := createTestLokiBackend(req, metrics.NewHistorianMetrics(prometheus.NewRegistry()))
+		rule := createTestRule()
+		states := []state.StateTransition{}
+
+		err := <-loki.Record(context.Background(), rule, states)
+
+		require.NoError(t, err)
+		require.Nil(t, req.lastRequest)
+	})
 }
 
 func createTestLokiBackend(req client.Requester, met *metrics.Historian) *RemoteLokiBackend {