diff --git a/reader/cloudtrail/cloudtrail.go b/reader/cloudtrail/cloudtrail.go
index e71682015..ec98fcfac 100644
--- a/reader/cloudtrail/cloudtrail.go
+++ b/reader/cloudtrail/cloudtrail.go
@@ -98,9 +98,9 @@ func (r *Reader) Reset() (err error) {
 }
 
 func (r *Reader) Close() error {
-	log.Debugf("runner[%v] syncMgr.stopSync...", r.Meta.RunnerName)
+	log.Infof("Runner[%v] syncMgr.stopSync...", r.Meta.RunnerName)
 	r.syncMgr.stopSync()
-	log.Debugf("runner[%v] syncMgr closed, wait for BufReader closed...", r.Meta.RunnerName)
+	log.Infof("Runner[%v] syncMgr closed, wait for BufReader closed...", r.Meta.RunnerName)
 	return r.BufReader.Close()
 }
 
@@ -185,10 +185,17 @@ func buildSyncOptions(conf conf.MapConf) (*syncOptions, error) {
 	if opts.interval, err = time.ParseDuration(s); err != nil {
 		return nil, invalidConfigError(reader.KeySyncInterval, s, err)
 	}
+	if opts.interval.Nanoseconds() <= 0 {
+		opts.interval = 5 * time.Minute
+	}
+
 	s, _ = conf.GetStringOr(reader.KeySyncConcurrent, "5")
 	if opts.concurrent, err = strconv.Atoi(s); err != nil {
 		return nil, invalidConfigError(reader.KeySyncInterval, s, err)
 	}
+	if opts.concurrent <= 0 {
+		opts.concurrent = 5
+	}
 
 	return &opts, nil
 }
@@ -231,24 +238,18 @@ func makeSyncSource(bucket, prefix string) string {
 func (mgr *syncManager) startSync() {
 	ticker := time.NewTicker(mgr.interval)
 	defer ticker.Stop()
-
-	if err := mgr.syncOnce(); err != nil {
-		log.Errorf("sync failed: %v", err)
-	}
-
-Sync:
 	for {
+		if err := mgr.syncOnce(); err != nil {
+			log.Errorf("Runner[%v] daemon sync once failed: %v", mgr.meta.RunnerName, err)
+		}
+
 		select {
-		case <-ticker.C:
-			if err := mgr.syncOnce(); err != nil {
-				log.Errorf("sync failed: %v", err)
-			}
 		case <-mgr.quitChan:
-			break Sync
+			log.Infof("Runner[%v] daemon has stopped from running", mgr.meta.RunnerName)
+			return
+		case <-ticker.C:
 		}
 	}
-
-	log.Info("sync stopped working")
 }
 
 func (mgr *syncManager) syncOnce() error {
@@ -261,8 +262,7 @@ func (mgr *syncManager) syncOnce() error {
 		concurrent: mgr.concurrent,
 		region:     mgr.region,
 	}
-	runner := newSyncRunner(ctx, mgr.quitChan)
-	return runner.Sync()
+	return newSyncRunner(ctx, mgr.quitChan).Sync()
 }
 
 func (mgr *syncManager) stopSync() {
@@ -317,32 +317,85 @@ func validTarget(target string) bool {
 	return false
 }
 
+const maximumFlushSyncedFilesOneTime = 10
+
+func storeSyncedFiles(f *os.File, syncedFiles map[string]bool) error {
+	if len(syncedFiles) <= 0 {
+		return nil
+	}
+
+	for path := range syncedFiles {
+		f.WriteString(filepath.Base(path))
+		f.WriteString("\n")
+	}
+
+	return f.Sync()
+}
+
+// Note: 非线程安全，需由调用者保证同步调用
 func (s *syncRunner) syncToDir() error {
-	log.Info("syncing from s3...")
+	log.Infof("Runner[%v] syncing from s3...", s.meta.RunnerName)
+
+	metastore, err := os.OpenFile(s.metastore, os.O_WRONLY|os.O_APPEND|os.O_CREATE, 0644)
+	if err != nil {
+		return fmt.Errorf("open metastore: %v", err)
+	}
+	defer metastore.Close()
 
 	s3url := newS3Url(s.source)
 	bucket, err := lookupBucket(s3url.Bucket(), s.auth, s.region)
 	if err != nil {
-		return err
+		return fmt.Errorf("lookup bucket: %v", err)
 	}
 
 	sourceFiles := make(map[string]bool)
 	sourceFiles, err = loadS3Files(bucket, s3url.Path(), sourceFiles, "")
 	if err != nil {
-		return err
+		return fmt.Errorf("load s3 files: %v", err)
 	}
 	if s.syncedFiles == nil {
 		s.syncedFiles, err = s.loadSyncedFiles()
 		if err != nil {
-			return err
+			return fmt.Errorf("load synced files: %v", err)
 		}
 	}
 
-	err = s.concurrentSyncToDir(s3url, bucket, sourceFiles)
-	if err != nil {
-		return err
-	}
-	return s.storeSyncedFiles(sourceFiles)
+	syncedChan := make(chan string, s.concurrent)
+	doneChan := make(chan struct{})
+	go func() {
+		syncedFiles := make(map[string]bool, maximumFlushSyncedFilesOneTime)
+		for file := range syncedChan {
+			syncedFiles[file] = true
+
+			if len(syncedFiles) < maximumFlushSyncedFilesOneTime {
+				continue
+			}
+
+			if err = storeSyncedFiles(metastore, syncedFiles); err != nil {
+				log.Errorf("Runner[%v] wrote synced files to %q failed: %v", s.meta.RunnerName, s.metastore)
+			} else {
+				log.Infof("Runner[%v] wrote %d synced files to %q", s.meta.RunnerName, len(syncedFiles), s.metastore)
+
+				// Note: 可能导致在 Sync 失败的情况下部分文件名重复输入到 metastore 中，但比丢失已同步记录重新处理一遍相同数据结果要更加合理
+				syncedFiles = make(map[string]bool, maximumFlushSyncedFilesOneTime)
+			}
+		}
+
+		if err = storeSyncedFiles(metastore, syncedFiles); err != nil {
+			log.Errorf("Runner[%v] wrote synced files to %q failed: %v", s.meta.RunnerName, s.metastore)
+		} else {
+			log.Infof("Runner[%v] wrote %d synced files to %q", s.meta.RunnerName, len(syncedFiles), s.metastore)
+		}
+
+		doneChan <- struct{}{}
+	}()
+
+	s.concurrentSyncToDir(syncedChan, s3url, bucket, sourceFiles)
+	close(syncedChan)
+
+	<-doneChan
+	log.Infof("Runner[%v] daemon has finished syncing", s.meta.RunnerName)
+	return nil
 }
 
 type s3Url struct {
@@ -445,28 +498,6 @@ func (s *syncRunner) loadSyncedFiles() (map[string]bool, error) {
 	return files, nil
 }
 
-func (s *syncRunner) storeSyncedFiles(files map[string]bool) error {
-	if len(files) <= 0 {
-		return nil
-	}
-
-	f, err := os.OpenFile(s.metastore, os.O_WRONLY|os.O_APPEND, 0644)
-	if err != nil {
-		return err
-	}
-	defer f.Close()
-
-	w := bufio.NewWriter(f)
-	for path := range files {
-		w.WriteString(filepath.Base(path))
-		w.WriteByte('\n')
-	}
-
-	log.Infof("write %d synced files to %q", len(files), s.metastore)
-
-	return w.Flush()
-}
-
 func relativePath(path string, filePath string) string {
 	if path == "." {
 		return strings.TrimPrefix(filePath, "/")
@@ -474,22 +505,22 @@ func relativePath(path string, filePath string) string {
 	return strings.TrimPrefix(strings.TrimPrefix(filePath, path), "/")
 }
 
-func (s *syncRunner) concurrentSyncToDir(s3url s3Url, bucket *s3.Bucket, sourceFiles map[string]bool) error {
-	doneChan := newDoneChan(s.concurrent)
+// concurrentSyncToDir 并发地获取 bucket 中的文件，并返回本次同步实际完成的文件
+func (s *syncRunner) concurrentSyncToDir(syncedChan chan string, s3url s3Url, bucket *s3.Bucket, sourceFiles map[string]bool) {
 	pool := newPool(s.concurrent)
-
 	var wg sync.WaitGroup
+
+DONE:
 	for s3file := range sourceFiles {
 		select {
 		case <-s.quitChan:
 			log.Warnf("Runner[%v] daemon has stopped, task is interrupted", s.meta.RunnerName)
-			return nil
+			break DONE
 		default:
 		}
 
-		//对于目录不同步
+		// 对于目录不同步
 		if strings.HasSuffix(s3file, string(os.PathSeparator)) {
-			delete(sourceFiles, s3file)
 			continue
 		}
 		basename := filepath.Base(s3file)
@@ -499,38 +530,31 @@ func (s *syncRunner) concurrentSyncToDir(s3url s3Url, bucket *s3.Bucket, sourceF
 			if filepath.Dir(filePath) != "." {
 				err := os.MkdirAll(filepath.Dir(filePath), 0755)
 				if err != nil {
-					return err
+					log.Errorf("Runner[%v] create local directory %q failed: %v", s.meta.RunnerName, filepath.Dir(filePath), err)
+					continue
 				}
 			}
 			<-pool
 			s.syncedFiles[basename] = true
 
-			log.Debugf("starting sync: s3://%s/%s -> %s", bucket.Name, s3file, filePath)
+			log.Debugf("Runner[%v] start syncing: s3://%s/%s -> %s", s.meta.RunnerName, bucket.Name, s3file, filePath)
 
 			wg.Add(1)
-			go func(doneChan chan error, filePath string, bucket *s3.Bucket, s3file string) {
+			go func(filePath string, bucket *s3.Bucket, s3file string) {
 				defer wg.Done()
-				syncSingleFile(doneChan, filePath, bucket, s3file)
-				pool <- 1
-			}(doneChan, filePath, bucket, s3file)
+				if err := writeFile(filePath, bucket, s3file); err != nil {
+					log.Errorf("Runner[%v] write file %q to local failed: %v", s.meta.RunnerName, s3file, err)
+					return
+				}
+				syncedChan <- s3file
+				log.Debugf("Runner[%v] sync completed: s3://%s/%s -> %s", s.meta.RunnerName, bucket.Name, s3file, filePath)
+				pool <- struct{}{}
+			}(filePath, bucket, s3file)
 		} else {
-			delete(sourceFiles, s3file)
-			log.Debugf("%s already synced, skip it...", unzipPath)
+			log.Debugf("Runner[%v] %q already synced, skipped this time", s.meta.RunnerName, unzipPath)
 		}
 	}
 	wg.Wait()
-
-	log.Info("sync done in this round")
-	return nil
-}
-
-func syncSingleFile(doneChan chan error, filePath string, bucket *s3.Bucket, file string) {
-	err := writeFile(filePath, bucket, file)
-	if err != nil {
-		doneChan <- err
-	}
-	log.Debugf("sync completed: s3://%s/%s -> %s", bucket.Name, file, filePath)
-	doneChan <- nil
 }
 
 func writeToFile(zipf *zip.File, filename string) error {
@@ -574,25 +598,10 @@ func writeFile(filename string, bucket *s3.Bucket, path string) error {
 	return ioutil.WriteFile(filename, data, os.FileMode(0644))
 }
 
-func newPool(concurrent int) chan int {
-	pool := make(chan int, concurrent)
+func newPool(concurrent int) chan struct{} {
+	pool := make(chan struct{}, concurrent)
 	for x := 0; x < concurrent; x++ {
-		pool <- 1
+		pool <- struct{}{}
 	}
 	return pool
 }
-
-func newDoneChan(concurrent int) chan error {
-	doneChan := make(chan error, concurrent)
-	go func() {
-		for {
-			select {
-			case err := <-doneChan:
-				if err != nil {
-					log.Error(err)
-				}
-			}
-		}
-	}()
-	return doneChan
-}