diff --git a/maro/rl/agent/abs_agent.py b/maro/rl/agent/abs_agent.py
index 0aa9afd76..03967875d 100644
--- a/maro/rl/agent/abs_agent.py
+++ b/maro/rl/agent/abs_agent.py
@@ -27,11 +27,9 @@ class AbsAgent(ABC):
             choosing actions and optimizing models.
         experience_pool (AbsStore): A data store that stores experiences generated by the experience shaper.
     """
-    def __init__(self,
-                 name: str,
-                 algorithm: AbsAlgorithm,
-                 experience_pool: AbsStore
-                 ):
+    def __init__(
+        self, name: str, algorithm: AbsAlgorithm, experience_pool: AbsStore
+    ):
         self._name = name
         self._algorithm = algorithm
         self._experience_pool = experience_pool
@@ -82,10 +80,13 @@ def load_model_dict_from_file(self, file_path):
 
     def dump_model_dict(self, dir_path: str):
         """Dump models to disk."""
-        torch.save({model_key: model.state_dict() for model_key, model in self._algorithm.model_dict.items()},
-                   os.path.join(dir_path, self._name))
+        torch.save(
+            {model_key: model.state_dict() for model_key, model in self._algorithm.model_dict.items()},
+            os.path.join(dir_path, self._name)
+        )
 
-    def dump_experience_store(self, dir_path: str):
+    def dump_experience_pool(self, dir_path: str):
         """Dump the experience pool to disk."""
-        with open(os.path.join(dir_path, self._name)) as fp:
+        os.makedirs(dir_path, exist_ok=True)
+        with open(os.path.join(dir_path, self._name), "wb") as fp:
             pickle.dump(self._experience_pool, fp)
diff --git a/maro/rl/storage/column_based_store.py b/maro/rl/storage/column_based_store.py
index 8709a8d8e..46398185e 100644
--- a/maro/rl/storage/column_based_store.py
+++ b/maro/rl/storage/column_based_store.py
@@ -53,6 +53,15 @@ def __next__(self):
     def __getitem__(self, index: int):
         return {k: lst[index] for k, lst in self._store.items()}
 
+    def __getstate__(self):
+        """A patch for picking the object with lambda.
+        Using the default ``__dict__`` would make the object unpicklable due to the lambda function involved in the
+        ``defaultdict`` definition of the ``_store`` attribute.
+        """
+        obj_dict = self.__dict__
+        obj_dict["_store"] = dict(obj_dict["_store"])
+        return obj_dict
+
     @property
     def capacity(self):
         """Store capacity.
@@ -92,8 +101,9 @@ def put(self, contents: dict, overwrite_indexes: Sequence = None) -> List[int]:
             self._size += added_size
             return list(range(self._size - added_size, self._size))
         else:
-            write_indexes = get_update_indexes(self._size, added_size, self._capacity, self._overwrite_type,
-                                               overwrite_indexes=overwrite_indexes)
+            write_indexes = get_update_indexes(
+                self._size, added_size, self._capacity, self._overwrite_type, overwrite_indexes=overwrite_indexes
+            )
             self.update(write_indexes, contents)
             self._size = min(self._capacity, self._size + added_size)
             return write_indexes
@@ -125,7 +135,7 @@ def apply_multi_filters(self, filters: Sequence[Callable]):
 
         Args:
             filters (Sequence[Callable]): Filter list, each item is a lambda function,
-                                          e.g., [lambda d: d['a'] == 1 and d['b'] == 1].
+                e.g., [lambda d: d['a'] == 1 and d['b'] == 1].
         Returns:
             Filtered indexes and corresponding objects.
         """