diff --git a/mem0/memory/main.py b/mem0/memory/main.py
index f0f9cbae..14f980f2 100644
--- a/mem0/memory/main.py
+++ b/mem0/memory/main.py
@@ -582,7 +582,7 @@ class Memory(MemoryBase):
 
         new_metadata = metadata or {}
         new_metadata["data"] = data
-        new_metadata["hash"] = existing_memory.payload.get("hash")
+        new_metadata["hash"] = hashlib.md5(data.encode()).hexdigest()
         new_metadata["created_at"] = existing_memory.payload.get("created_at")
         new_metadata["updated_at"] = datetime.now(pytz.timezone("US/Pacific")).isoformat()
 
diff --git a/mem0/vector_stores/base.py b/mem0/vector_stores/base.py
index 974f120f..21f47f3a 100644
--- a/mem0/vector_stores/base.py
+++ b/mem0/vector_stores/base.py
@@ -38,7 +38,7 @@ class VectorStoreBase(ABC):
         pass
 
     @abstractmethod
-    def delete_col(self, name):
+    def delete_col(self):
         """Delete a collection."""
         pass
 
@@ -46,3 +46,8 @@ class VectorStoreBase(ABC):
     def col_info(self, name):
         """Get information about a collection."""
         pass
+
+    @abstractmethod
+    def list(self, filters=None, limit=None):
+        """List all memories."""
+        pass