diff --git a/include/emqttd.hrl b/include/emqttd.hrl
index ab4b6ee72..51bce2f6d 100644
--- a/include/emqttd.hrl
+++ b/include/emqttd.hrl
@@ -91,7 +91,6 @@
 -record(mqtt_client, {
     client_id     :: binary() | undefined,
     client_pid    :: pid(),
-    client_mon    :: reference(),
     username      :: binary() | undefined,
     peername      :: {inet:ip_address(), integer()},
     clean_sess    :: boolean(),
diff --git a/src/emqttd_cm.erl b/src/emqttd_cm.erl
index b3bfb242b..4c2c2b252 100644
--- a/src/emqttd_cm.erl
+++ b/src/emqttd_cm.erl
@@ -33,7 +33,7 @@
 %% API Exports 
 -export([start_link/2, pool/0]).
 
--export([lookup/1, register/1, unregister/1]).
+-export([lookup/1, lookup_proc/1, register/1, unregister/1]).
 
 -behaviour(gen_server2).
 
@@ -44,7 +44,7 @@
 %% gen_server2 priorities
 -export([prioritise_call/4, prioritise_cast/3, prioritise_info/3]).
 
--record(state, {id, statsfun}).
+-record(state, {id, statsfun, monitors}).
 
 -define(CM_POOL, ?MODULE).
 
@@ -68,16 +68,28 @@ start_link(Id, StatsFun) ->
 pool() -> ?CM_POOL.
 
 %%------------------------------------------------------------------------------
-%% @doc Lookup client pid with clientId
+%% @doc Lookup client by clientId
 %% @end
 %%------------------------------------------------------------------------------
 -spec lookup(ClientId :: binary()) -> mqtt_client() | undefined.
 lookup(ClientId) when is_binary(ClientId) ->
     case ets:lookup(mqtt_client, ClientId) of
-	[Client] -> Client;
-	[] -> undefined
+        [Client] -> Client;
+        [] -> undefined
 	end.
 
+%%------------------------------------------------------------------------------
+%% @doc Lookup client pid by clientId
+%% @end
+%%------------------------------------------------------------------------------
+-spec lookup_proc(ClientId :: binary()) -> pid() | undefined.
+lookup_proc(ClientId) when is_binary(ClientId) ->
+    try ets:lookup_element(mqtt_client, ClientId, #mqtt_client.client_pid) of
+        Pid -> Pid
+    catch
+        error:badarg -> undefined
+    end.
+
 %%------------------------------------------------------------------------------
 %% @doc Register clientId with pid.
 %% @end
@@ -102,15 +114,15 @@ unregister(ClientId) when is_binary(ClientId) ->
 
 init([Id, StatsFun]) ->
     gproc_pool:connect_worker(?CM_POOL, {?MODULE, Id}),
-    {ok, #state{id = Id, statsfun = StatsFun}}.
+    {ok, #state{id = Id, statsfun = StatsFun, monitors = dict:new()}}.
 
 prioritise_call(_Req, _From, _Len, _State) ->
     1.
 
 prioritise_cast(Msg, _Len, _State) ->
     case Msg of
-        {register, _Client}           -> 2;
-        {unregister, _ClientId, _Pid} -> 3;
+        {register,   _Client}         -> 2;
+        {unregister, _ClientId, _Pid} -> 9;
         _                             -> 1
     end.
 
@@ -123,28 +135,20 @@ handle_call(Req, _From, State) ->
 
 handle_cast({register, Client = #mqtt_client{client_id  = ClientId,
                                              client_pid = Pid}}, State) ->
-	case ets:lookup(mqtt_client, ClientId) of
-        [#mqtt_client{client_pid = Pid}] ->
-            ignore;
-        [#mqtt_client{client_pid = _OldPid, client_mon = MRef}] ->
-            %% demonitor
-            erlang:demonitor(MRef, [flush]);
-        [] ->
-            ok
-	end,
-    ets:insert(mqtt_client, Client#mqtt_client{client_mon = erlang:monitor(process, Pid)}),
-    {noreply, setstats(State)};
+    case lookup_proc(ClientId) of
+        Pid  ->
+            {noreply, State};
+        _None ->
+            ets:insert(mqtt_client, Client),
+            {noreply, setstats(monitor_client(ClientId, Pid, State))}
+	end;
 
 handle_cast({unregister, ClientId, Pid}, State) ->
-	case ets:lookup(mqtt_client, ClientId) of
-        [#mqtt_client{client_pid = Pid, client_mon = MRef}] ->
-            erlang:demonitor(MRef, [flush]),
+	case lookup_proc(ClientId) of
+        Pid ->
             ets:delete(mqtt_client, ClientId),
             {noreply, setstats(State)};
-        [_] ->
-            {noreply, State};
-        [] ->
-            lager:warning("CM(~s): Cannot find pid ~p", [ClientId, Pid]),
+        undefined ->
             {noreply, State}
     end;
 
@@ -152,16 +156,20 @@ handle_cast(Msg, State) ->
     lager:error("Unexpected Msg: ~p", [Msg]),
     {noreply, State}.
 
-handle_info({'DOWN', MRef, process, DownPid, Reason}, State) ->
-    MP = #mqtt_client{client_pid = DownPid, client_mon = MRef, _ = '_'},
-    case ets:match_object(mqtt_client, MP) of
-        [Client] ->
-            ?LOG(warning, "client ~p DOWN for ~p", [DownPid, Reason], Client),
-            ets:delete_object(mqtt_client, Client);
-        [] ->
-            ignore
-    end,
-    {noreply, setstats(State)};
+handle_info({'DOWN', MRef, process, DownPid, _Reason}, State = #state{monitors = MonDict}) ->
+    case dict:find(MRef, MonDict) of
+        {ok, {ClientId, DownPid}} ->
+            case lookup_proc(ClientId) of
+                DownPid ->
+                    ets:delete(mqtt_client, ClientId);
+                _ ->
+                    ignore
+            end,
+            {noreply, setstats(erase_monitor(MRef, State))};
+        error ->
+            lager:error("MRef of client ~p not found", [DownPid]),
+            {noreply, State}
+    end;
 
 handle_info(Info, State) ->
     lager:error("Unexpected Info: ~p", [Info]),
@@ -178,6 +186,13 @@ code_change(_OldVsn, State, _Extra) ->
 %%% Internal functions
 %%%=============================================================================
 
+monitor_client(ClientId, Pid, State = #state{monitors = Monintors}) ->
+    MRef = erlang:monitor(process, Pid),
+    State#state{monitors = dict:store(MRef, {ClientId, Pid}, Monintors)}.
+
+erase_monitor(MRef, State = #state{monitors = Monintors}) ->
+    State#state{monitors = dict:erase(MRef, Monintors)}.
+
 setstats(State = #state{statsfun = StatsFun}) ->
     StatsFun(ets:info(mqtt_client, size)), State.
 
diff --git a/src/emqttd_protocol.erl b/src/emqttd_protocol.erl
index 053b74e1a..29985f044 100644
--- a/src/emqttd_protocol.erl
+++ b/src/emqttd_protocol.erl
@@ -282,14 +282,18 @@ redeliver({?PUBREL, PacketId}, State) ->
 shutdown(_Error, #proto_state{client_id = undefined}) ->
     ignore;
 
-shutdown(conflict, #proto_state{client_id = ClientId}) ->
-    emqttd_cm:unregister(ClientId);
+shutdown(conflict, #proto_state{client_id = _ClientId}) ->
+    %% let it down
+    %% emqttd_cm:unregister(ClientId);
+    ignore;
 
 shutdown(Error, State = #proto_state{client_id = ClientId, will_msg = WillMsg}) ->
     ?LOG(info, "Shutdown for ~p", [Error], State),
     send_willmsg(ClientId, WillMsg),
     emqttd_broker:foreach_hooks('client.disconnected', [Error, ClientId]),
-    emqttd_cm:unregister(ClientId).
+    %% let it down
+    %% emqttd_cm:unregister(ClientId).
+    ok.
 
 willmsg(Packet) when is_record(Packet, mqtt_packet_connect) ->
     emqttd_message:from_packet(Packet).