diff --git a/repositories/summary.go b/repositories/summary.go
index f151780..603d24b 100644
--- a/repositories/summary.go
+++ b/repositories/summary.go
@@ -16,7 +16,14 @@ func NewSummaryRepository(db *gorm.DB) *SummaryRepository {
 
 func (r *SummaryRepository) GetAll() ([]*models.Summary, error) {
 	var summaries []*models.Summary
-	if err := r.db.Find(&summaries).Error; err != nil {
+	if err := r.db.
+		Order("from_time asc").
+		Preload("Projects", "type = ?", models.SummaryProject).
+		Preload("Languages", "type = ?", models.SummaryLanguage).
+		Preload("Editors", "type = ?", models.SummaryEditor).
+		Preload("OperatingSystems", "type = ?", models.SummaryOS).
+		Preload("Machines", "type = ?", models.SummaryMachine).
+		Find(&summaries).Error; err != nil {
 		return nil, err
 	}
 	return summaries, nil
diff --git a/services/aggregation.go b/services/aggregation.go
index 32f0122..415b6eb 100644
--- a/services/aggregation.go
+++ b/services/aggregation.go
@@ -1,9 +1,11 @@
 package services
 
 import (
+	"errors"
 	"github.com/emvi/logbuch"
 	"github.com/muety/wakapi/config"
 	"runtime"
+	"sync"
 	"time"
 
 	"github.com/go-co-op/gocron"
@@ -14,11 +16,14 @@ const (
 	aggregateIntervalDays int = 1
 )
 
+var lock = sync.Mutex{}
+
 type AggregationService struct {
 	config           *config.Config
 	userService      IUserService
 	summaryService   ISummaryService
 	heartbeatService IHeartbeatService
+	inProgress       map[string]bool
 }
 
 func NewAggregationService(userService IUserService, summaryService ISummaryService, heartbeatService IHeartbeatService) *AggregationService {
@@ -27,6 +32,7 @@ func NewAggregationService(userService IUserService, summaryService ISummaryServ
 		userService:      userService,
 		summaryService:   summaryService,
 		heartbeatService: heartbeatService,
+		inProgress:       map[string]bool{},
 	}
 }
 
@@ -49,6 +55,11 @@ func (srv *AggregationService) Schedule() {
 }
 
 func (srv *AggregationService) Run(userIds map[string]bool) error {
+	if err := srv.lockUsers(userIds); err != nil {
+		return err
+	}
+	defer srv.unlockUsers(userIds)
+
 	jobs := make(chan *AggregationJob)
 	summaries := make(chan *models.Summary)
 
@@ -145,6 +156,28 @@ func (srv *AggregationService) trigger(jobs chan<- *AggregationJob, userIds map[
 	return nil
 }
 
+func (srv *AggregationService) lockUsers(userIds map[string]bool) error {
+	lock.Lock()
+	defer lock.Unlock()
+	for uid := range userIds {
+		if _, ok := srv.inProgress[uid]; ok {
+			return errors.New("aggregation already in progress for at least of the request users")
+		}
+	}
+	for uid := range userIds {
+		srv.inProgress[uid] = true
+	}
+	return nil
+}
+
+func (srv *AggregationService) unlockUsers(userIds map[string]bool) {
+	lock.Lock()
+	defer lock.Unlock()
+	for uid := range userIds {
+		delete(srv.inProgress, uid)
+	}
+}
+
 func generateUserJobs(userId string, from time.Time, jobs chan<- *AggregationJob) {
 	var to time.Time