diff --git a/kag/common/checkpointer/bin_checkpointer.py b/kag/common/checkpointer/bin_checkpointer.py
index df1d7c96..980917fa 100644
--- a/kag/common/checkpointer/bin_checkpointer.py
+++ b/kag/common/checkpointer/bin_checkpointer.py
@@ -13,6 +13,8 @@
 import logging
 import transaction
 import threading
+
+import BTrees.OOBTree
 from ZODB import DB
 from ZODB.FileStorage import FileStorage
 from kag.common.checkpointer.base import CheckPointer
@@ -115,6 +117,8 @@ def open(self):
         with self._lock:
             storage = FileStorage(self._ckpt_file_path)
             db = DB(storage)
+            with db.transaction() as conn:
+                conn.root.data = BTrees.OOBTree.BTree()
             return db
 
     def read_from_ckpt(self, key):
@@ -129,7 +133,7 @@ def read_from_ckpt(self, key):
         """
         with self._lock:
             with self._ckpt.transaction() as conn:
-                obj = conn.root().get(key, None)
+                obj = conn.root.data.get(key, None)
             return obj
 
     def write_to_ckpt(self, key, value):
@@ -143,7 +147,7 @@ def write_to_ckpt(self, key, value):
         with self._lock:
             try:
                 with self._ckpt.transaction() as conn:
-                    conn.root()[key] = value
+                    conn.root.data[key] = value
             except Exception as e:
                 logger.warn(f"failed to write checkpoint {key} to db, info: {e}")
 
@@ -171,9 +175,9 @@ def exists(self, key):
         """
         with self._lock:
             with self._ckpt.transaction() as conn:
-                return key in conn.root()
+                return key in conn.root.data
 
     def size(self):
         with self._lock:
             with self._ckpt.transaction() as conn:
-                return len(conn.root())
+                return len(conn.root.data)