diff --git a/weed/storage/needle_map_boltdb.go b/weed/storage/needle_map_boltdb.go
index cbcc786af..96c29cab6 100644
--- a/weed/storage/needle_map_boltdb.go
+++ b/weed/storage/needle_map_boltdb.go
@@ -19,6 +19,7 @@ type BoltDbNeedleMap struct {
 
 var boltdbBucket = []byte("weed")
 
+// TODO avoid using btree to count deletions.
 func NewBoltDbNeedleMap(dbFileName string, indexFile *os.File) (m *BoltDbNeedleMap, err error) {
 	m = &BoltDbNeedleMap{dbFileName: dbFileName}
 	m.indexFile = indexFile
diff --git a/weed/storage/needle_map_leveldb.go b/weed/storage/needle_map_leveldb.go
index 78dffaf7d..dfe3ccc0a 100644
--- a/weed/storage/needle_map_leveldb.go
+++ b/weed/storage/needle_map_leveldb.go
@@ -17,6 +17,7 @@ type LevelDbNeedleMap struct {
 	baseNeedleMapper
 }
 
+// TODO avoid using btree to count deletions.
 func NewLevelDbNeedleMap(dbFileName string, indexFile *os.File) (m *LevelDbNeedleMap, err error) {
 	m = &LevelDbNeedleMap{dbFileName: dbFileName}
 	m.indexFile = indexFile