diff --git a/apps/emqx_exhook/src/emqx_exhook_mngr.erl b/apps/emqx_exhook/src/emqx_exhook_mngr.erl
index 9df1e19ef..d91652904 100644
--- a/apps/emqx_exhook/src/emqx_exhook_mngr.erl
+++ b/apps/emqx_exhook/src/emqx_exhook_mngr.erl
@@ -300,7 +300,9 @@ put_pool_size(Val) ->
     persistent_term:put({?APP, pool_size}, Val).
 
 get_pool_size() ->
-    persistent_term:get({?APP, pool_size}).
+    %% Avoid the scenario that the parameter is not set after
+    %% the hot upgrade completed.
+    persistent_term:get({?APP, pool_size}, erlang:system_info(schedulers)).
 
 save(Name, ServerState) ->
     Saved = persistent_term:get(?APP, []),
diff --git a/apps/emqx_exhook/test/emqx_exhook_demo_svr.erl b/apps/emqx_exhook/test/emqx_exhook_demo_svr.erl
index aa1d02a15..b1e3801b2 100644
--- a/apps/emqx_exhook/test/emqx_exhook_demo_svr.erl
+++ b/apps/emqx_exhook/test/emqx_exhook_demo_svr.erl
@@ -295,7 +295,7 @@ on_session_terminated(Req, Md) ->
      | {error, grpc_cowboy_h:error_response()}.
 on_message_publish(#{message := #{from := From} = Msg} = Req, Md) ->
     ?MODULE:in({?FUNCTION_NAME, Req}),
-    io:format(standard_error, "fun: ~p, req: ~0p~n", [?FUNCTION_NAME, Req]),
+    %io:format("fun: ~p, req: ~0p~n", [?FUNCTION_NAME, Req]),
     %% some cases for testing
     case From of
         <<"baduser">> ->