diff --git a/api/db/db_models.py b/api/db/db_models.py
index ecd65ad1d..d0f08a7a0 100644
--- a/api/db/db_models.py
+++ b/api/db/db_models.py
@@ -36,18 +36,7 @@ from api.utils.json_encode import json_dumps, json_loads
 from api.utils.configs import deserialize_b64, serialize_b64
 
 from common.time_utils import current_timestamp, timestamp_to_date, date_string_to_timestamp
-
-
-def singleton(cls, *args, **kw):
-    instances = {}
-
-    def _singleton():
-        key = str(cls) + str(os.getpid())
-        if key not in instances:
-            instances[key] = cls(*args, **kw)
-        return instances[key]
-
-    return _singleton
+from common.decorator import singleton
 
 
 CONTINUOUS_FIELD_TYPE = {IntegerField, FloatField, DateTimeField}
diff --git a/common/decorator.py b/common/decorator.py
new file mode 100644
index 000000000..f45a41a9d
--- /dev/null
+++ b/common/decorator.py
@@ -0,0 +1,27 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+import os
+
+def singleton(cls, *args, **kw):
+    instances = {}
+
+    def _singleton():
+        key = str(cls) + str(os.getpid())
+        if key not in instances:
+            instances[key] = cls(*args, **kw)
+        return instances[key]
+
+    return _singleton
\ No newline at end of file
diff --git a/rag/utils/__init__.py b/rag/utils/__init__.py
index 19d952d58..f3a696318 100644
--- a/rag/utils/__init__.py
+++ b/rag/utils/__init__.py
@@ -15,23 +15,10 @@
 #
 
 import os
-
 import tiktoken
 
 from api.utils.file_utils import get_project_base_directory
 
-
-def singleton(cls, *args, **kw):
-    instances = {}
-
-    def _singleton():
-        key = str(cls) + str(os.getpid())
-        if key not in instances:
-            instances[key] = cls(*args, **kw)
-        return instances[key]
-
-    return _singleton
-
 tiktoken_cache_dir = get_project_base_directory()
 os.environ["TIKTOKEN_CACHE_DIR"] = tiktoken_cache_dir
 # encoder = tiktoken.encoding_for_model("gpt-3.5-turbo")
diff --git a/rag/utils/azure_sas_conn.py b/rag/utils/azure_sas_conn.py
index d1737546b..771d5afdf 100644
--- a/rag/utils/azure_sas_conn.py
+++ b/rag/utils/azure_sas_conn.py
@@ -19,7 +19,7 @@ import os
 import time
 from io import BytesIO
 from rag import settings
-from rag.utils import singleton
+from common.decorator import singleton
 from azure.storage.blob import ContainerClient
 
 
diff --git a/rag/utils/azure_spn_conn.py b/rag/utils/azure_spn_conn.py
index 4b6b861f4..e5a194aa8 100644
--- a/rag/utils/azure_spn_conn.py
+++ b/rag/utils/azure_spn_conn.py
@@ -18,7 +18,7 @@ import logging
 import os
 import time
 from rag import settings
-from rag.utils import singleton
+from common.decorator import singleton
 from azure.identity import ClientSecretCredential, AzureAuthorityHosts
 from azure.storage.filedatalake import FileSystemClient
 
diff --git a/rag/utils/es_conn.py b/rag/utils/es_conn.py
index 1ebdf4fef..e662428ba 100644
--- a/rag/utils/es_conn.py
+++ b/rag/utils/es_conn.py
@@ -26,7 +26,7 @@ from elasticsearch_dsl import UpdateByQuery, Q, Search, Index
 from elastic_transport import ConnectionTimeout
 from rag import settings
 from rag.settings import TAG_FLD, PAGERANK_FLD
-from rag.utils import singleton
+from common.decorator import singleton
 from api.utils.file_utils import get_project_base_directory
 from api.utils.common import convert_bytes
 from rag.utils.doc_store_conn import DocStoreConnection, MatchExpr, OrderByExpr, MatchTextExpr, MatchDenseExpr, \
diff --git a/rag/utils/infinity_conn.py b/rag/utils/infinity_conn.py
index 0d85d25e6..1d6dbd091 100644
--- a/rag/utils/infinity_conn.py
+++ b/rag/utils/infinity_conn.py
@@ -27,7 +27,7 @@ from infinity.connection_pool import ConnectionPool
 from infinity.errors import ErrorCode
 from rag import settings
 from rag.settings import PAGERANK_FLD, TAG_FLD
-from rag.utils import singleton
+from common.decorator import singleton
 import pandas as pd
 from api.utils.file_utils import get_project_base_directory
 from rag.nlp import is_english
diff --git a/rag/utils/minio_conn.py b/rag/utils/minio_conn.py
index ff15c2bbf..1777de0e5 100644
--- a/rag/utils/minio_conn.py
+++ b/rag/utils/minio_conn.py
@@ -21,7 +21,7 @@ from minio.commonconfig import CopySource
 from minio.error import S3Error
 from io import BytesIO
 from rag import settings
-from rag.utils import singleton
+from common.decorator import singleton
 
 
 @singleton
diff --git a/rag/utils/opendal_conn.py b/rag/utils/opendal_conn.py
index 1293516a9..41abdf343 100644
--- a/rag/utils/opendal_conn.py
+++ b/rag/utils/opendal_conn.py
@@ -4,7 +4,7 @@ import pymysql
 from urllib.parse import quote_plus
 
 from api.utils.configs import get_base_config
-from rag.utils import singleton
+from common.decorator import singleton
 
 
 CREATE_TABLE_SQL = """
diff --git a/rag/utils/opensearch_conn.py b/rag/utils/opensearch_conn.py
index fc7d82cf9..3c2cf376b 100644
--- a/rag/utils/opensearch_conn.py
+++ b/rag/utils/opensearch_conn.py
@@ -26,7 +26,7 @@ from opensearchpy import UpdateByQuery, Q, Search, Index
 from opensearchpy import ConnectionTimeout
 from rag import settings
 from rag.settings import TAG_FLD, PAGERANK_FLD
-from rag.utils import singleton
+from common.decorator import singleton
 from api.utils.file_utils import get_project_base_directory
 from rag.utils.doc_store_conn import DocStoreConnection, MatchExpr, OrderByExpr, MatchTextExpr, MatchDenseExpr, \
     FusionExpr
diff --git a/rag/utils/oss_conn.py b/rag/utils/oss_conn.py
index 3e75d70fc..a34bd2323 100644
--- a/rag/utils/oss_conn.py
+++ b/rag/utils/oss_conn.py
@@ -19,7 +19,7 @@ from botocore.exceptions import ClientError
 from botocore.config import Config
 import time
 from io import BytesIO
-from rag.utils import singleton
+from common.decorator import singleton
 from rag import settings
 
 
diff --git a/rag/utils/redis_conn.py b/rag/utils/redis_conn.py
index 63010576e..2b295eacf 100644
--- a/rag/utils/redis_conn.py
+++ b/rag/utils/redis_conn.py
@@ -20,7 +20,7 @@ import uuid
 
 import valkey as redis
 from rag import settings
-from rag.utils import singleton
+from common.decorator import singleton
 from valkey.lock import Lock
 import trio
 
diff --git a/rag/utils/s3_conn.py b/rag/utils/s3_conn.py
index 2a1e08185..190f18b51 100644
--- a/rag/utils/s3_conn.py
+++ b/rag/utils/s3_conn.py
@@ -20,7 +20,7 @@ from botocore.exceptions import ClientError
 from botocore.config import Config
 import time
 from io import BytesIO
-from rag.utils import singleton
+from common.decorator import singleton
 from rag import settings
 
 @singleton
diff --git a/test/unit_test/common/test_decorator.py b/test/unit_test/common/test_decorator.py
new file mode 100644
index 000000000..a4bc4a24e
--- /dev/null
+++ b/test/unit_test/common/test_decorator.py
@@ -0,0 +1,79 @@
+#
+#  Copyright 2025 The InfiniFlow Authors. All Rights Reserved.
+#
+#  Licensed under the Apache License, Version 2.0 (the "License");
+#  you may not use this file except in compliance with the License.
+#  You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+#  Unless required by applicable law or agreed to in writing, software
+#  distributed under the License is distributed on an "AS IS" BASIS,
+#  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+#  See the License for the specific language governing permissions and
+#  limitations under the License.
+#
+
+from common.decorator import singleton
+
+
+# Test class for demonstration
+@singleton
+class TestClass:
+    def __init__(self):
+        self.counter = 0
+
+    def increment(self):
+        self.counter += 1
+        return self.counter
+
+
+# Test cases
+class TestSingleton:
+
+    def test_state_persistence(self):
+        """Test that instance state persists across multiple calls"""
+        instance1 = TestClass()
+        instance1.increment()
+        instance1.increment()
+
+        instance2 = TestClass()
+        assert instance2.counter == 2  # State should persist
+
+    def test_multiple_calls_consistency(self):
+        """Test consistency across multiple calls"""
+        instances = [TestClass() for _ in range(5)]
+
+        # All references should point to the same object
+        first_instance = instances[0]
+        for instance in instances:
+            assert instance is first_instance
+
+    def test_instance_methods_work(self):
+        """Test that instance methods work correctly"""
+        instance = TestClass()
+
+        # Test method calls
+        result1 = instance.increment()
+        result2 = instance.increment()
+
+        assert result1 == 3
+        assert result2 == 4
+        assert instance.counter == 4
+
+
+# Test decorator itself
+def test_singleton_decorator_returns_callable():
+    """Test that the decorator returns a callable"""
+
+    class PlainClass:
+        pass
+
+    decorated_class = singleton(PlainClass)
+
+    # Should return a function
+    assert callable(decorated_class)
+
+    # Calling should return an instance of PlainClass
+    instance = decorated_class()
+    assert isinstance(instance, PlainClass)