diff --git a/app/app.yaml b/app/app.yaml
index 0f36fe0..92c1536 100644
--- a/app/app.yaml
+++ b/app/app.yaml
@@ -33,12 +33,13 @@ app:
     allow_multiple_trace_ids_in_tracing_result: false
     # use external apm data to fill trace data, default: false
     call_apm_api_to_supplement_trace: false
-    # source data for tracing, default: all (set to empty means all)
+    # source data for tracing, default: [trace_id, syscall, tcp_seq, x_request_id] (equals to empty)
     # available options: [trace_id, syscall, tcp_seq, x_request_id, dns]
+    # in default settings, we do not trace DNS protocol
     # each source means one of tracing method enabled
     #   trace_id: global seq through requests
     #   syscall: eBPF tracing through process/threads
     #   tcp_seq: network layer tracing through TCP seq
     #   x_request_id: application layer tracing through X-Request-ID/http header
-    #   dns: DNS protocol tracing through DNS transaction-id (request_id)
+    #   dns: DNS protocol tracing through DNS transaction-id (request_id), IT'S DISABLED BY DEFAULT, REQUIRED ENABLED MANUALLY IF NEEDED
     tracing_source: []
\ No newline at end of file
diff --git a/app/app/application/l7_flow_tracing.py b/app/app/application/l7_flow_tracing.py
index 3d56990..82ca0fa 100644
--- a/app/app/application/l7_flow_tracing.py
+++ b/app/app/application/l7_flow_tracing.py
@@ -2,9 +2,8 @@
 import uuid
 import pandas as pd
 from log import logger
-from typing import List, Dict, Set, Callable
+from typing import List, Dict, Set, Callable, Tuple
 
-from ast import Tuple
 from pandas import DataFrame
 from collections import defaultdict
 from data.querier_client import Querier
@@ -223,11 +222,12 @@
 TRACING_SRC_SYSCALL = "syscall"
 TRACING_SRC_TCP_SEQ = "tcp_seq"
 TRACING_SRC_X_REQ_ID = "x_request_id"
+# 默认不开启 dns 追踪
 TRACING_SRC_DNS = "dns"
 
 DEFAULT_TRACING_SOURCE = [
     TRACING_SRC_TRACE_ID, TRACING_SRC_SYSCALL, TRACING_SRC_TCP_SEQ,
-    TRACING_SRC_X_REQ_ID, TRACING_SRC_DNS
+    TRACING_SRC_X_REQ_ID
 ]
 
 
@@ -282,7 +282,7 @@ async def query_and_trace_flowmetas(
             max_iteration: int = config.max_iteration,
             network_delay_us: int = config.network_delay_us,
             host_clock_offset_us: int = config.host_clock_offset_us,
-            app_spans_from_api: list = []) -> Tuple(list, list):
+            app_spans_from_api: list = []) -> Tuple[Set, list]:
         """多次迭代，查询可追踪到的所有 l7_flow_log 的摘要
         参数说明：
         time_filter: 查询的时间范围过滤条件，SQL表达式
@@ -312,7 +312,7 @@ async def query_and_trace_flowmetas(
         dataframe_flowmetas = await self.query_flowmetas("1=1", base_filter)
         if type(dataframe_flowmetas) != DataFrame or dataframe_flowmetas.empty:
             # when app_spans_from_api got values from api, return it
-            return [], app_spans_from_api
+            return set(), app_spans_from_api
         l7_flow_ids = set(dataframe_flowmetas['_id'])  # set(flow._id)
 
         # 用于下一轮迭代，记录元信息
@@ -430,6 +430,7 @@ async def query_and_trace_flowmetas(
                             # 写入 trace_id_index 时，遇到空 trace_id 有可能会复用 index，导致重复
                             # 于是，这里可能导致误查询，需要额外过滤一下 len(new_trace_id_arr)=0(trace_id='') 的情况
                             new_trace_id_flow_delete_index.append(index)
+
                     if new_trace_id_flow_delete_index:
                         new_trace_id_flows = new_trace_id_flows.drop(
                             new_trace_id_flow_delete_index).reset_index(
diff --git a/app/app/common/const.py b/app/app/common/const.py
index cace2c5..abe4b6b 100644
--- a/app/app/common/const.py
+++ b/app/app/common/const.py
@@ -45,7 +45,7 @@
     TAP_SIDE_CLIENT_HYPERVISOR: 4,
     TAP_SIDE_CLIENT_GATEWAY_HYPERVISOR: 5,
     TAP_SIDE_CLIENT_GATEWAY: 6,
-    TAP_SIDE_SERVER_GATEWAY: 6,  # 由于可能多次穿越网关区域，c-gw和s-gw还需要重排
+    TAP_SIDE_SERVER_GATEWAY: 7,  # 由于可能多次穿越网关区域，c-gw和s-gw还需要重排
     TAP_SIDE_SERVER_GATEWAY_HYPERVISOR: 8,
     TAP_SIDE_SERVER_HYPERVISOR: 9,
     TAP_SIDE_SERVER_POD_NODE: 10,
diff --git a/app/app/config.py b/app/app/config.py
index b6b17ec..f9e0dd5 100644
--- a/app/app/config.py
+++ b/app/app/config.py
@@ -26,7 +26,7 @@ def parse_spec(self, cfg):
             'call_apm_api_to_supplement_trace', False)
         self.tracing_source = spec.get(
             'tracing_source',
-            ["trace_id", "syscall", "tcp_seq", "x_request_id", "dns"])
+            ["trace_id", "syscall", "tcp_seq", "x_request_id"])
 
     def parse_querier(self, cfg):
         querier = cfg.get('querier', dict())