diff --git a/examples/api/chat_example.py b/examples/api/chat_example.py
index b7781ef5..393b004e 100644
--- a/examples/api/chat_example.py
+++ b/examples/api/chat_example.py
@@ -54,7 +54,7 @@ def chat_example4():
         memory_chat.memory_service.consolidate_memory()
 
         response = memory_chat.chat_with_memory(query="你知道我的乐器爱好是什么？",
-                                                add_messages=False)
+                                                history_message_strategy=None)
         print("回答2：\n" + response.message.content)
         print("记忆2：\n" + response.meta_data["memories"])
 
diff --git a/memoryscope/core/chat/api_memory_chat.py b/memoryscope/core/chat/api_memory_chat.py
index d1e8d491..6a8078f7 100644
--- a/memoryscope/core/chat/api_memory_chat.py
+++ b/memoryscope/core/chat/api_memory_chat.py
@@ -1,4 +1,4 @@
-from typing import List, Optional
+from typing import List, Optional, Literal
 
 from memoryscope.constants.common_constants import MEMORIES
 from memoryscope.constants.language_constants import DEFAULT_HUMAN_NAME
@@ -126,7 +126,7 @@ class ApiMemoryChat(BaseMemoryChat):
                          system_prompt: Optional[str] = None,
                          memory_prompt: Optional[str] = None,
                          extra_memories: Optional[str] = None,
-                         add_messages: bool = True,
+                         history_message_strategy: Literal["auto", None] | int = "auto",
                          remember_response: bool = True,
                          **kwargs):
         """
@@ -138,7 +138,11 @@ class ApiMemoryChat(BaseMemoryChat):
             system_prompt (str, optional): System prompt. Defaults to the system_prompt in "memory_chat_prompt.yaml".
             memory_prompt (str, optional): Memory prompt. Defaults to the memory_prompt in "memory_chat_prompt.yaml".
             extra_memories (str, optional): Manually added user memory in this function.
-            add_messages (bool, optional): whether add not memorized messages to LLM.
+            history_message_strategy ("auto", None, int):
+                - If it is set to "auto"， the history messages in the conversation will retain those that have not
+                    yet been summarized. Default to "auto".
+                - If it is set to None， no conversation history will be saved.
+                - If it is set to an integer value "n", the most recent "n" messages will be retained.
             remember_response (bool, optional): Flag indicating whether to save the AI's response to memory.
                 Defaults to False.
         Returns:
@@ -181,8 +185,15 @@ class ApiMemoryChat(BaseMemoryChat):
         chat_messages.append(system_message)
 
         # Include past conversation history in the message list
-        if add_messages:
-            history_messages = self.memory_service.read_message()
+        if history_message_strategy:
+            history_messages = []
+
+            if history_message_strategy == "auto":
+                history_messages = self.memory_service.read_message()
+
+            elif isinstance(history_message_strategy, int):
+                history_messages = self.memory_service.chat_messages[-history_message_strategy:]
+
             if history_messages:
                 chat_messages.extend(history_messages)
 
diff --git a/memoryscope/core/chat/base_memory_chat.py b/memoryscope/core/chat/base_memory_chat.py
index 5707c398..e311f072 100644
--- a/memoryscope/core/chat/base_memory_chat.py
+++ b/memoryscope/core/chat/base_memory_chat.py
@@ -1,5 +1,5 @@
 from abc import ABCMeta, abstractmethod
-from typing import Optional
+from typing import Optional, Literal
 
 from memoryscope.core.service.base_memory_service import BaseMemoryService
 from memoryscope.core.utils.logger import Logger
@@ -32,9 +32,30 @@ class BaseMemoryChat(metaclass=ABCMeta):
                          system_prompt: Optional[str] = None,
                          memory_prompt: Optional[str] = None,
                          extra_memories: Optional[str] = None,
-                         add_messages: bool = True,
+                         history_message_strategy: Literal["auto", None] | int = "auto",
                          remember_response: bool = True,
                          **kwargs):
+        """
+        The core function that carries out conversation with memory accepts user queries through query and returns the
+        conversation results through model_response. The retrieved memories are stored in the memories within meta_data.
+        Args:
+            query (str, optional): User's query, includes the user's question.
+            role_name (str, optional): User's role name.
+            system_prompt (str, optional): System prompt. Defaults to the system_prompt in "memory_chat_prompt.yaml".
+            memory_prompt (str, optional): Memory prompt. Defaults to the memory_prompt in "memory_chat_prompt.yaml".
+            extra_memories (str, optional): Manually added user memory in this function.
+            history_message_strategy ("auto", None, int):
+                - If it is set to "auto"， the history messages in the conversation will retain those that have not
+                    yet been summarized. Default to "auto".
+                - If it is set to None， no conversation history will be saved.
+                - If it is set to an integer value "n", the most recent "n" messages will be retained.
+            remember_response (bool, optional): Flag indicating whether to save the AI's response to memory.
+                Defaults to False.
+        Returns:
+            - ModelResponse: In non-streaming mode, returns a complete AI response.
+            - ModelResponseGen: In streaming mode, returns a generator yielding AI response parts.
+            - Memories: To obtain the memory by invoking the method of model_response.meta_data[MEMORIES]
+        """
         raise NotImplementedError
 
     def run(self):
diff --git a/memoryscope/core/chat/cli_memory_chat.py b/memoryscope/core/chat/cli_memory_chat.py
index 3d610468..150c79b3 100644
--- a/memoryscope/core/chat/cli_memory_chat.py
+++ b/memoryscope/core/chat/cli_memory_chat.py
@@ -1,6 +1,6 @@
 import os
 import time
-from typing import Optional
+from typing import Optional, Literal
 
 import questionary
 
@@ -40,7 +40,7 @@ class CliMemoryChat(ApiMemoryChat):
                          system_prompt: Optional[str] = None,
                          memory_prompt: Optional[str] = None,
                          extra_memories: Optional[str] = None,
-                         add_messages: bool = True,
+                         history_message_strategy: Literal["auto", None] | int = "auto",
                          remember_response: bool = True,
                          **kwargs):
         resp = super().chat_with_memory(query=query,
@@ -48,7 +48,7 @@ class CliMemoryChat(ApiMemoryChat):
                                         system_prompt=system_prompt,
                                         memory_prompt=memory_prompt,
                                         extra_memories=extra_memories,
-                                        add_messages=add_messages,
+                                        history_message_strategy=history_message_strategy,
                                         remember_response=remember_response,
                                         **kwargs)
 
diff --git a/memoryscope/core/operation/backend_operation.py b/memoryscope/core/operation/backend_operation.py
index fd6a55a4..e4b4a41c 100644
--- a/memoryscope/core/operation/backend_operation.py
+++ b/memoryscope/core/operation/backend_operation.py
@@ -103,7 +103,7 @@ class BackendOperation(BaseWorkflow, BaseOperation):
             if self._loop_switch:
                 self.run_operation()
 
-    def run_operation_backend(self):
+    def start_operation_backend(self):
         """
         Initiates the background operation loop if it's not already running.
         Sets the _loop_switch to True and submits the _loop_operation to a thread from the global thread pool.
diff --git a/memoryscope/core/operation/base_operation.py b/memoryscope/core/operation/base_operation.py
index 600e3dd4..b5276a7c 100644
--- a/memoryscope/core/operation/base_operation.py
+++ b/memoryscope/core/operation/base_operation.py
@@ -50,7 +50,7 @@ class BaseOperation(metaclass=ABCMeta):
         """
         raise NotImplementedError
 
-    def run_operation_backend(self):
+    def start_operation_backend(self):
         """
         Placeholder method for running an operation specific to the backend.
         Intended to be overridden by subclasses if backend operations are required.
diff --git a/memoryscope/core/service/base_memory_service.py b/memoryscope/core/service/base_memory_service.py
index d997fa98..68acc566 100644
--- a/memoryscope/core/service/base_memory_service.py
+++ b/memoryscope/core/service/base_memory_service.py
@@ -28,6 +28,7 @@ class BaseMemoryService(metaclass=ABCMeta):
         self.kwargs = kwargs
 
         self._operation_dict: Dict[str, BaseOperation] = {}
+        self.chat_messages: List[Message] = []
         self.logger = Logger.get_logger()
 
     @property
@@ -51,7 +52,7 @@ class BaseMemoryService(metaclass=ABCMeta):
     def init_service(self, **kwargs):
         raise NotImplementedError
 
-    def start_backend_service(self):
+    def start_backend_service(self, name: str = None):
         pass
 
     def stop_backend_service(self, wait_service_end: bool = False):
diff --git a/memoryscope/core/service/memory_scope_service.py b/memoryscope/core/service/memory_scope_service.py
index 88c644d4..e60dfd2f 100644
--- a/memoryscope/core/service/memory_scope_service.py
+++ b/memoryscope/core/service/memory_scope_service.py
@@ -37,7 +37,6 @@ class MemoryScopeService(BaseMemoryService):
         if assistant_name:
             self.context.meta_data["assistant_name"] = assistant_name
 
-        self.chat_messages: List[Message] = []
         self.message_lock = threading.Lock()
 
     def add_messages(self, messages: List[Message] | Message):
@@ -89,13 +88,17 @@ class MemoryScopeService(BaseMemoryService):
         for name, operation_config in self.memory_operations_conf.items():
             self.register_operation(name, operation_config, **kwargs)
 
-    def start_backend_service(self):
+    def start_backend_service(self, name: str = None):
         """
         Start all backend operations.
         """
-        for _, operation in self._operation_dict.items():
-            if operation.operation_type == "backend":
-                operation.run_operation_backend()
+        for op_name, operation in self._operation_dict.items():
+            if name:
+                if op_name == name:
+                    operation.start_operation_backend()
+            else:
+                if operation.operation_type == "backend":
+                    operation.start_operation_backend()
 
     def stop_backend_service(self, wait_service_end: bool = False):
         """
diff --git a/memoryscope/core/worker/backend/update_insight_worker.py b/memoryscope/core/worker/backend/update_insight_worker.py
index fbc7698b..51f8d7e9 100644
--- a/memoryscope/core/worker/backend/update_insight_worker.py
+++ b/memoryscope/core/worker/backend/update_insight_worker.py
@@ -56,14 +56,15 @@ class UpdateInsightWorker(MemoryBaseWorker):
             return insight_node, filtered_nodes, max_score
 
         if use_dummy_ranker:
-            key_vector: List[float] = self.embedding_model.call(text=insight_node.key).embedding_results
-            if not key_vector:
-                self.logger.warning(f"embedding call {insight_node.key} failed!")
-                return insight_node, filtered_nodes, max_score
+            if not insight_node.key_vector:
+                key_vector: List[float] = self.embedding_model.call(text=insight_node.key).embedding_results
+                if not key_vector:
+                    self.logger.warning(f"embedding call {insight_node.key} failed!")
+                    return insight_node, filtered_nodes, max_score
 
-            insight_node.key_vector = key_vector
-            documents_vector = [x.vector for x in obs_nodes]
-            score_recall_list = cosine_similarity(key_vector, documents_vector)
+                insight_node.key_vector = key_vector
+
+            score_recall_list = cosine_similarity(insight_node.key_vector, [x.vector for x in obs_nodes])
             assert len(score_recall_list) == len(obs_nodes), \
                 f"size is not as excepted. {len(score_recall_list)} v.s. {len(obs_nodes)}"