diff --git a/paddle/fluid/operators/async_listen_and_serv_op.cc b/paddle/fluid/operators/async_listen_and_serv_op.cc
index ec0ddedf3d13b319c54b00de593fa43ac945ee9f..bdb20240f69449d44c2ec89d2f3cb0d206f0b9b2 100644
--- a/paddle/fluid/operators/async_listen_and_serv_op.cc
+++ b/paddle/fluid/operators/async_listen_and_serv_op.cc
@@ -96,6 +96,8 @@ void AsyncListenAndServOp::RunImpl(const framework::Scope &scope,
       block_list.push_back(blkid);
     }
   }
+  PADDLE_ENFORCE_EQ(grad_map_str.size(), block_list.size(),
+                    "grad num should be equal to optimize block num");
   auto optimize_prepared = executor.Prepare(*program, block_list);
 
   std::unordered_map<std::string,
@@ -107,7 +109,8 @@ void AsyncListenAndServOp::RunImpl(const framework::Scope &scope,
 
   rpc_service_->SetScope(&recv_scope);
   rpc_service_->SetDevCtx(&dev_ctx);
-  // TODO(qiao) set proper fields for table lookup and update
+
+  // set proper fields for table lookup and update
   rpc_service_->SetExecutor(&executor);
   VLOG(3) << "prefetch block id is " << prefetch_block->ID();
   auto prefetch_prepared = executor.Prepare(*program, prefetch_block->ID());
@@ -142,6 +145,7 @@ void AsyncListenAndServOp::RunImpl(const framework::Scope &scope,
       }
       AsyncExecuteBlock(&executor, grad_to_prepared[recv_var_name].get(),
                         &recv_scope);
+      // TODO(qiao): explain why
       if (var->IsType<framework::SelectedRows>()) {
         var->GetMutable<framework::SelectedRows>()->mutable_rows()->clear();
       }
diff --git a/paddle/fluid/operators/detail/async_grpc_server.cc b/paddle/fluid/operators/detail/async_grpc_server.cc
index 7e45bc6b2f5dda6bd9cb91e6b860acf877bae67a..b9a228e1d2fc6d4b6c2ad0d449c19769b8eadc83 100644
--- a/paddle/fluid/operators/detail/async_grpc_server.cc
+++ b/paddle/fluid/operators/detail/async_grpc_server.cc
@@ -91,7 +91,7 @@ class RequestGet final : public RequestBase {
                       framework::Scope* scope,
                       const platform::DeviceContext* dev_ctx)
       : RequestBase(service, cq, dev_ctx), responder_(&ctx_), scope_(scope) {
-    int method_id = static_cast<int>(detail::GrpcMethod::kGetVariable);
+    auto method_id = static_cast<int>(detail::GrpcMethod::kGetVariable);
     service_->RequestAsyncUnary(method_id, &ctx_, &request_, &responder_, cq_,
                                 cq_, this);
   }