diff --git a/apps/emqx/src/emqx_metrics.erl b/apps/emqx/src/emqx_metrics.erl
index 2757ea492..2c8088c48 100644
--- a/apps/emqx/src/emqx_metrics.erl
+++ b/apps/emqx/src/emqx_metrics.erl
@@ -146,7 +146,6 @@
          {counter, 'messages.dropped.expired'},  % QoS2 Messages expired
          {counter, 'messages.dropped.no_subscribers'},  % Messages dropped
          {counter, 'messages.forward'},       % Messages forward
-         {counter, 'messages.retained'},      % Messages retained
          {counter, 'messages.delayed'},       % Messages delayed
          {counter, 'messages.delivered'},     % Messages delivered
          {counter, 'messages.acked'}          % Messages acked
@@ -207,7 +206,7 @@ stop() -> gen_server:stop(?SERVER).
 
 %% BACKW: v4.3.0
 upgrade_retained_delayed_counter_type() ->
-    Ks = ['messages.retained', 'messages.delayed'],
+    Ks = ['messages.delayed'],
     gen_server:call(?SERVER, {set_type_to_counter, Ks}, infinity).
 
 %%--------------------------------------------------------------------
@@ -556,7 +555,7 @@ reserved_idx('messages.dropped')             -> 109;
 reserved_idx('messages.dropped.expired')     -> 110;
 reserved_idx('messages.dropped.no_subscribers') -> 111;
 reserved_idx('messages.forward')             -> 112;
-reserved_idx('messages.retained')            -> 113;
+%%reserved_idx('messages.retained')            -> 113; %% keep the index, new metrics can use this
 reserved_idx('messages.delayed')             -> 114;
 reserved_idx('messages.delivered')           -> 115;
 reserved_idx('messages.acked')               -> 116;
@@ -592,4 +591,3 @@ reserved_idx('olp.gc')                       -> 303;
 reserved_idx('olp.new_conn')                 -> 304;
 
 reserved_idx(_)                              -> undefined.
-
diff --git a/apps/emqx/test/emqx_metrics_SUITE.erl b/apps/emqx/test/emqx_metrics_SUITE.erl
index f47e028bc..8b277e898 100644
--- a/apps/emqx/test/emqx_metrics_SUITE.erl
+++ b/apps/emqx/test/emqx_metrics_SUITE.erl
@@ -71,19 +71,10 @@ t_inc_dec(_) ->
     with_metrics_server(
       fun() ->
         ?assertEqual(0, emqx_metrics:val('bytes.received')),
-        ?assertEqual(0, emqx_metrics:val('messages.retained')),
         ok = emqx_metrics:inc('bytes.received'),
         ok = emqx_metrics:inc('bytes.received', 2),
         ok = emqx_metrics:inc('bytes.received', 2),
-        ?assertEqual(5, emqx_metrics:val('bytes.received')),
-        ok = emqx_metrics:inc('messages.retained', 2),
-        ok = emqx_metrics:inc('messages.retained', 2),
-        ?assertEqual(4, emqx_metrics:val('messages.retained')),
-        ok = emqx_metrics:dec('messages.retained'),
-        ok = emqx_metrics:dec('messages.retained', 1),
-        ?assertEqual(2, emqx_metrics:val('messages.retained')),
-        ok = emqx_metrics:set('messages.retained', 3),
-        ?assertEqual(3, emqx_metrics:val('messages.retained'))
+        ?assertEqual(5, emqx_metrics:val('bytes.received'))
       end).
 
 t_inc_recv(_) ->
@@ -162,21 +153,12 @@ t_trans(_) ->
         ok = emqx_metrics:trans(inc, 'bytes.received'),
         ok = emqx_metrics:trans(inc, 'bytes.received', 2),
         ?assertEqual(0, emqx_metrics:val('bytes.received')),
-        ok = emqx_metrics:trans(inc, 'messages.retained', 2),
-        ok = emqx_metrics:trans(inc, 'messages.retained', 2),
-        ?assertEqual(0, emqx_metrics:val('messages.retained')),
         ok = emqx_metrics:commit(),
         ?assertEqual(3, emqx_metrics:val('bytes.received')),
-        ?assertEqual(4, emqx_metrics:val('messages.retained')),
-        ok = emqx_metrics:trans(dec, 'messages.retained'),
-        ok = emqx_metrics:trans(dec, 'messages.retained', 1),
-        ?assertEqual(4, emqx_metrics:val('messages.retained')),
-        ok = emqx_metrics:commit(),
-        ?assertEqual(2, emqx_metrics:val('messages.retained'))
+        ok = emqx_metrics:commit()
       end).
 
 with_metrics_server(Fun) ->
     {ok, _} = emqx_metrics:start_link(),
     _ = Fun(),
     ok = emqx_metrics:stop().
-
diff --git a/apps/emqx/test/emqx_proper_types.erl b/apps/emqx/test/emqx_proper_types.erl
index 32aba9674..fcae60294 100644
--- a/apps/emqx/test/emqx_proper_types.erl
+++ b/apps/emqx/test/emqx_proper_types.erl
@@ -288,7 +288,7 @@ systopic_metrics() ->
               <<"messages/qos2/received">>, <<"messages/qos2/sent">>,
               <<"messages/publish">>, <<"messages/dropped">>,
               <<"messages/dropped/expired">>, <<"messages/dropped/no_subscribers">>,
-              <<"messages/forward">>, <<"messages/retained">>,
+              <<"messages/forward">>,
               <<"messages/delayed">>, <<"messages/delivered">>,
               <<"messages/acked">>],
     ?LET({Nodename, T},
diff --git a/apps/emqx_retainer/src/emqx_retainer.erl b/apps/emqx_retainer/src/emqx_retainer.erl
index e1780cc08..51a28897c 100644
--- a/apps/emqx_retainer/src/emqx_retainer.erl
+++ b/apps/emqx_retainer/src/emqx_retainer.erl
@@ -37,7 +37,9 @@
         , clean/0
         , delete/1
         , page_read/3
-        , post_config_update/5]).
+        , post_config_update/5
+        , stats_fun/0
+        ]).
 
 %% gen_server callbacks
 -export([ init/1
@@ -69,6 +71,7 @@
 -callback match_messages(context(), topic(), cursor()) -> {ok, list(), cursor()}.
 -callback clear_expired(context()) -> ok.
 -callback clean(context()) -> ok.
+-callback size(context()) -> non_neg_integer().
 
 %%--------------------------------------------------------------------
 %% Hook API
@@ -185,6 +188,9 @@ post_config_update(_, _UpdateReq, NewConf, OldConf, _AppEnvs) ->
 call(Req) ->
     gen_server:call(?MODULE, Req, infinity).
 
+stats_fun() ->
+    gen_server:cast(?MODULE, ?FUNCTION_NAME).
+
 %%--------------------------------------------------------------------
 %% gen_server callbacks
 %%--------------------------------------------------------------------
@@ -226,6 +232,12 @@ handle_call(Req, _From, State) ->
     ?LOG(error, "Unexpected call: ~p", [Req]),
     {reply, ignored, State}.
 
+handle_cast(stats_fun, #{context := Context} = State) ->
+    Mod = get_backend_module(),
+    Size = Mod:size(Context),
+    emqx_stats:setstat('retained.count', 'retained.max', Size),
+    {noreply, State};
+
 handle_cast(Msg, State) ->
     ?LOG(error, "Unexpected cast: ~p", [Msg]),
     {noreply, State}.
@@ -485,8 +497,11 @@ close_resource(_) ->
 load(Context) ->
     _ = emqx:hook('session.subscribed', {?MODULE, on_session_subscribed, [Context]}),
     _ = emqx:hook('message.publish', {?MODULE, on_message_publish, [Context]}),
+    emqx_stats:update_interval(emqx_retainer_stats, fun ?MODULE:stats_fun/0),
     ok.
 
 unload() ->
     emqx:unhook('message.publish', {?MODULE, on_message_publish}),
-    emqx:unhook('session.subscribed', {?MODULE, on_session_subscribed}).
+    emqx:unhook('session.subscribed', {?MODULE, on_session_subscribed}),
+    emqx_stats:cancel_update(emqx_retainer_stats),
+    ok.
diff --git a/apps/emqx_retainer/src/emqx_retainer_mnesia.erl b/apps/emqx_retainer/src/emqx_retainer_mnesia.erl
index 89db7108a..cc2cd8f44 100644
--- a/apps/emqx_retainer/src/emqx_retainer_mnesia.erl
+++ b/apps/emqx_retainer/src/emqx_retainer_mnesia.erl
@@ -30,7 +30,9 @@
         , page_read/4
         , match_messages/3
         , clear_expired/1
-        , clean/1]).
+        , clean/1
+        , size/1
+        ]).
 
 -export([create_resource/1]).
 
@@ -73,7 +75,6 @@ store_retained(_, Msg =#message{topic = Topic}) ->
     ExpiryTime = emqx_retainer:get_expiry_time(Msg),
     case is_table_full() of
         false ->
-            ok = emqx_metrics:inc('messages.retained'),
             mria:dirty_write(?TAB,
                              #retained{topic = topic2tokens(Topic),
                                        msg = Msg,
@@ -156,6 +157,10 @@ match_messages(_, Topic, Cursor) ->
 clean(_) ->
     _ = mria:clear_table(?TAB),
     ok.
+
+size(_) ->
+    table_size().
+
 %%--------------------------------------------------------------------
 %% Internal functions
 %%--------------------------------------------------------------------