diff --git a/shards/mishards/service_handler.py b/shards/mishards/service_handler.py
index 28c1a31ed5..5ba801f9b5 100644
--- a/shards/mishards/service_handler.py
+++ b/shards/mishards/service_handler.py
@@ -29,11 +29,17 @@ class ServiceHandler(milvus_pb2_grpc.MilvusServiceServicer):
     def _reduce(self, source_ids, ids, source_diss, diss, k, reverse):
         sort_f = (lambda x, y: x >= y) if reverse else (lambda x, y: x <= y)
 
+        if len(ids) == 0:
+            return source_ids, source_diss
+
+        if len(source_ids) == 0:
+            return ids, diss
+
         src_last = len(source_diss) - 1
-        if sort_f(source_diss[src_last], diss[0]):
+        if sort_f(source_diss[src_last], diss[0]) and len(source_ids) >= k:
             return source_ids, source_diss
         last = len(diss) - 1
-        if sort_f(diss[last], source_diss[0]):
+        if sort_f(diss[last], source_diss[0]) and len(ids) >= k:
             return ids, diss
 
         source_diss.extend(diss)