diff --git a/weed/filer/arangodb/arangodb_store.go b/weed/filer/arangodb/arangodb_store.go
index a39735108..c1445f026 100644
--- a/weed/filer/arangodb/arangodb_store.go
+++ b/weed/filer/arangodb/arangodb_store.go
@@ -109,11 +109,11 @@ func (store *ArangodbStore) connection(uris []string, user string, pass string,
 		}); err != nil {
 		return err
 	}
-
 	if _, _, err = store.collection.EnsurePersistentIndex(ctx, []string{"directory"},
 		&driver.EnsurePersistentIndexOptions{Name: "IDX_directory"}); err != nil {
 		return err
 	}
+
 	if _, _, err = store.collection.EnsureTTLIndex(ctx, "ttl", 1,
 		&driver.EnsureTTLIndexOptions{Name: "IDX_TTL"}); err != nil {
 		return err
@@ -291,8 +291,8 @@ func (store *ArangodbStore) DeleteEntry(ctx context.Context, fullpath util.FullP
 }
 
 func (store *ArangodbStore) DeleteFolderChildren(ctx context.Context, fullpath util.FullPath) error {
-	query := ""
-	query = fmt.Sprintf(`for d in files filter starts_with(d.directory, "%s") remove d._key in files`,
+	var query string
+	query = query + fmt.Sprintf(`filter starts_with(d.directory, "%s") remove d._key in files`,
 		strings.Join(strings.Split(string(fullpath), "/"), ","),
 		string(fullpath),
 	)
diff --git a/weed/filer/arangodb/readme.md b/weed/filer/arangodb/readme.md
index eb6411c2e..eaa8bd7a7 100644
--- a/weed/filer/arangodb/readme.md
+++ b/weed/filer/arangodb/readme.md
@@ -44,4 +44,9 @@ should there be one collection per bucket? would make deleting a bucket instant
 arangodb uses rocksdb in the background, so i am assuming things run in log time
 
 i am not sure how the prefix query scales compared to the recursive calls that some other stores do for folder deletion
-might need to change that
+might need to change that.
+
+
+ok, so if https://www.arangodb.com/docs/stable/indexing-index-basics.html#persistent-index is correct
+it should be log time to the number of files in the directory
+and constant time if you have full directory + file