fix(dashboard): fix slow fetching of persistent session stats

apps/emqx/src/emqx_persistent_session_ds/emqx_persistent_session_bookkeeper.erl

@@ -41,8 +41,20 @@
 %% call/cast/info events
 -record(tally_subs, {}).
 -record(tally_disconnected_sessions, {}).
--record(get_subscription_count, {}).
--record(get_disconnected_session_count, {}).
+
+%%------------------------------------------------------------------------------
+%% Stat records & table
+%%------------------------------------------------------------------------------
+
+-record(stat_field, {name, value}).
+
+-define(tab, ?MODULE).
+-define(subs_count, subs_count).
+-define(disconnected_session_count, disconnected_session_count).
+-define(subs_count(VALUE), #stat_field{name = ?subs_count, value = VALUE}).
+-define(disconnected_session_count(VALUE), #stat_field{
+    name = ?disconnected_session_count, value = VALUE
+}).
 
 %%------------------------------------------------------------------------------
 %% API
@@ -57,7 +69,12 @@ start_link() ->
 get_subscription_count() ->
     case emqx_persistent_message:is_persistence_enabled() of
         true ->
-            gen_server:call(?MODULE, #get_subscription_count{}, infinity);
+            try ets:lookup(?tab, ?subs_count) of
+                [?subs_count(N)] -> N;
+                [] -> 0
+            catch
+                error:badarg -> 0
+            end;
         false ->
             0
     end.
@@ -67,7 +84,12 @@ get_subscription_count() ->
 get_disconnected_session_count() ->
     case emqx_persistent_message:is_persistence_enabled() of
         true ->
-            gen_server:call(?MODULE, #get_disconnected_session_count{}, infinity);
+            try ets:lookup(?tab, ?disconnected_session_count) of
+                [?disconnected_session_count(N)] -> N;
+                [] -> 0
+            catch
+                error:badarg -> 0
+            end;
         false ->
             0
     end.
@@ -80,8 +102,7 @@ init(_Opts) ->
     case emqx_persistent_message:is_persistence_enabled() of
         true ->
             State = #{
-                subs_count => 0,
-                disconnected_session_count => 0
+                tab => ets:new(?tab, [named_table, set, protected, {keypos, #stat_field.name}])
             },
             {ok, State, {continue, #tally_subs{}}};
         false ->
@@ -97,12 +118,6 @@ handle_continue(#tally_disconnected_sessions{}, State0) ->
     ensure_disconnected_sessions_tally_timer(),
     {noreply, State}.
 
-handle_call(#get_subscription_count{}, _From, State) ->
-    #{subs_count := N} = State,
-    {reply, N, State};
-handle_call(#get_disconnected_session_count{}, _From, State) ->
-    #{disconnected_session_count := N} = State,
-    {reply, N, State};
 handle_call(_Call, _From, State) ->
     {reply, {error, bad_call}, State}.
 
@@ -124,13 +139,15 @@ handle_info(_Info, State) ->
 %% Internal fns
 %%------------------------------------------------------------------------------
 
-tally_persistent_subscriptions(State0) ->
+tally_persistent_subscriptions(#{tab := Tab} = State) ->
     N = emqx_persistent_session_ds_state:total_subscription_count(),
-    State0#{subs_count := N}.
+    _ = ets:insert(Tab, ?subs_count(N)),
+    State.
 
-tally_disconnected_persistent_sessions(State0) ->
+tally_disconnected_persistent_sessions(#{tab := Tab} = State) ->
     N = do_tally_disconnected_persistent_sessions(),
-    State0#{disconnected_session_count := N}.
+    _ = ets:insert(Tab, ?disconnected_session_count(N)),
+    State.
 
 ensure_subs_tally_timer() ->
     Timeout = emqx_config:get([durable_sessions, subscription_count_refresh_interval]),

changes/ce/fix-14184.en.md

@@ -0,0 +1 @@
+Fix the display of total and live connection counts in the dashboard. Previously, the counts could be zero and slowly updated if there were a lot of persistent sessions.