Perfomance: Preallocate slices (#61580)

pkg/services/ngalert/notifier/alertmanager.go

@@ -403,7 +403,7 @@ func (am *Alertmanager) buildIntegrationsMap(receivers []*apimodels.PostableApiR
 
 // buildReceiverIntegrations builds a list of integration notifiers off of a receiver config.
 func (am *Alertmanager) buildReceiverIntegrations(receiver *apimodels.PostableApiReceiver, tmpl *alerting.Template) ([]*alerting.Integration, error) {
-	var integrations []*alerting.Integration
+	integrations := make([]*alerting.Integration, 0, len(receiver.GrafanaManagedReceivers))
 	for i, r := range receiver.GrafanaManagedReceivers {
 		n, err := am.buildReceiverIntegration(r, tmpl)
 		if err != nil {

pkg/services/ngalert/notifier/receivers.go

@@ -130,7 +130,7 @@ func (am *Alertmanager) GetReceivers(ctx context.Context) []apimodels.Receiver {
 	am.reloadConfigMtx.RLock()
 	defer am.reloadConfigMtx.RUnlock()
 
-	var apiReceivers []apimodels.Receiver
+	apiReceivers := make([]apimodels.Receiver, 0, len(am.Base.GetReceivers()))
 	for _, rcv := range am.Base.GetReceivers() {
 		// Build integrations slice for each receiver.
 		integrations := make([]*models.Integration, 0, len(rcv.Integrations()))

pkg/services/ngalert/state/manager.go

@@ -184,7 +184,7 @@ func (st *Manager) ResetStateByRuleUID(ctx context.Context, ruleKey ngModels.Ale
 func (st *Manager) ProcessEvalResults(ctx context.Context, evaluatedAt time.Time, alertRule *ngModels.AlertRule, results eval.Results, extraLabels data.Labels) []StateTransition {
 	logger := st.log.FromContext(ctx)
 	logger.Debug("State manager processing evaluation results", "resultCount", len(results))
-	var states []StateTransition
+	states := make([]StateTransition, 0, len(results))
 
 	for _, result := range results {
 		s := st.setNextState(ctx, alertRule, result, extraLabels, logger)
@@ -383,10 +383,10 @@ func (st *Manager) deleteStaleStatesFromCache(ctx context.Context, logger log.Lo
 	// TODO: We will need to change this when we support images without screenshots as each series will have a different image
 	var resolvedImage *ngModels.Image
 
-	var resolvedStates []StateTransition
 	staleStates := st.cache.deleteRuleStates(alertRule.GetKey(), func(s *State) bool {
 		return stateIsStale(evaluatedAt, s.LastEvaluationTime, alertRule.IntervalSeconds)
 	})
+	resolvedStates := make([]StateTransition, 0, len(staleStates))
 
 	for _, s := range staleStates {
 		logger.Info("Detected stale state entry", "cacheID", s.CacheID, "state", s.State, "reason", s.StateReason)

pkg/services/ngalert/store/deltas.go

@@ -58,7 +58,9 @@ func CalculateChanges(ctx context.Context, ruleReader RuleReader, groupKey model
 		existingGroupRulesUIDs[r.UID] = r
 	}
 
-	var toAdd, toDelete []*models.AlertRule
+	//nolint:prealloc // difficult logic
+	var toAdd []*models.AlertRule
+	//nolint:prealloc // difficult logic
 	var toUpdate []RuleDelta
 	loadedRulesByUID := map[string]*models.AlertRule{} // auxiliary cache to avoid unnecessary queries if there are multiple moves from the same group
 	for _, r := range submittedRules {
@@ -110,6 +112,7 @@ func CalculateChanges(ctx context.Context, ruleReader RuleReader, groupKey model
 		continue
 	}
 
+	toDelete := make([]*models.AlertRule, 0, len(existingGroupRulesUIDs))
 	for _, rule := range existingGroupRulesUIDs {
 		toDelete = append(toDelete, rule)
 	}

pkg/services/pluginsettings/service/service.go

@@ -49,7 +49,7 @@ func (s *Service) GetPluginSettings(ctx context.Context, args *pluginsettings.Ge
 		return nil, err
 	}
 
-	var result []*pluginsettings.InfoDTO
+	result := make([]*pluginsettings.InfoDTO, 0, len(ps))
 	for _, p := range ps {
 		result = append(result, &pluginsettings.InfoDTO{
 			OrgID:         p.OrgID,

pkg/services/provisioning/values/values.go

@@ -255,8 +255,8 @@ func transformInterface(i interface{}) (interface{}, interface{}, error) {
 }
 
 func transformSlice(i []interface{}) (interface{}, interface{}, error) {
-	var transformedSlice []interface{}
-	var rawSlice []interface{}
+	transformedSlice := make([]interface{}, 0, len(i))
+	rawSlice := make([]interface{}, 0, len(i))
 	for _, val := range i {
 		transformed, raw, err := transformInterface(val)
 		if err != nil {

pkg/services/publicdashboards/commands/generate_datasources/generate.go

@@ -56,7 +56,7 @@ func getDatasourcePluginSlugs(baseUrl string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
-	var slugs []string
+	slugs := make([]string, 0, len(res.Items))
 	for _, meta := range res.Items {
 		slugs = append(slugs, meta.Slug)
 	}

pkg/services/publicdashboards/service/query.go

@@ -88,7 +88,7 @@ func (pd *PublicDashboardServiceImpl) FindAnnotations(ctx context.Context, reqDT
 		}
 	}
 
-	var results []models.AnnotationEvent
+	results := make([]models.AnnotationEvent, 0, len(uniqueEvents))
 	for _, result := range uniqueEvents {
 		results = append(results, result)
 	}

pkg/services/searchV2/allowed_actions.go

@@ -100,7 +100,7 @@ func (s *StandardSearchService) createAllowedActions(ctx context.Context, orgId
 		dsActionsByUid = make(map[string][]string)
 	}
 
-	var out [][]allowedActions
+	out := make([][]allowedActions, 0, len(references))
 	for _, ref := range references {
 		var actions []allowedActions
 

pkg/services/searchV2/index.go

@@ -776,13 +776,12 @@ func (i *searchIndex) updateDashboard(ctx context.Context, orgID int64, index *o
 		return err
 	}
 
-	var actualPanelIDs []string
-
 	if location != "" {
 		location += "/"
 	}
 	location += dash.uid
 	panelDocs := getDashboardPanelDocs(dash, location)
+	actualPanelIDs := make([]string, 0, len(panelDocs))
 	for _, panelDoc := range panelDocs {
 		actualPanelIDs = append(actualPanelIDs, string(panelDoc.ID().Term()))
 		batch.Update(panelDoc.ID(), panelDoc)

pkg/services/secrets/kvstore/plugin.go

@@ -190,7 +190,7 @@ func (kv *SecretsKVStorePlugin) WithFallbackEnabled(fn func() error) error {
 }
 
 func parseKeys(keys []*smp.Key) []Key {
-	var newKeys []Key
+	newKeys := make([]Key, 0, len(keys))
 
 	for _, k := range keys {
 		newKey := Key{OrgId: k.OrgId, Namespace: k.Namespace, Type: k.Type}
@@ -201,7 +201,7 @@ func parseKeys(keys []*smp.Key) []Key {
 }
 
 func parseItems(items []*smp.Item) []Item {
-	var newItems []Item
+	newItems := make([]Item, 0, len(items))
 
 	for _, i := range items {
 		newItem := Item{OrgId: &i.Key.OrgId, Namespace: &i.Key.Namespace, Type: &i.Key.Type, Value: i.Value}

pkg/services/sqlstore/migrations/accesscontrol/action_migrator.go

@@ -54,7 +54,8 @@ func (m *actionNameMigrator) migrateActionNames() error {
 		"alert.rules:update":       accesscontrol.ActionAlertingRuleUpdate,
 	}
 
-	var oldActionNames, newActionNames []interface{}
+	oldActionNames := make([]interface{}, 0, len(actionNameMapping))
+	newActionNames := make([]interface{}, 0, len(actionNameMapping))
 	for oldName, newName := range actionNameMapping {
 		oldActionNames = append(oldActionNames, oldName)
 		newActionNames = append(newActionNames, newName)

pkg/services/sqlstore/migrations/accesscontrol/team_membership.go

@@ -47,7 +47,7 @@ func (p *teamPermissionMigrator) setRolePermissions(roleID int64, permissions []
 	}
 
 	// Then insert new permissions
-	var newPermissions []accesscontrol.Permission
+	newPermissions := make([]accesscontrol.Permission, 0, len(permissions))
 	now := time.Now()
 	for _, permission := range permissions {
 		permission.RoleID = roleID