feat(metrics): add cluster_session guage

apps/emqx/src/emqx_cm.erl

@@ -124,7 +124,8 @@
     {?CHAN_TAB, 'channels.count', 'channels.max'},
     {?CHAN_TAB, 'sessions.count', 'sessions.max'},
     {?CHAN_CONN_TAB, 'connections.count', 'connections.max'},
-    {?CHAN_LIVE_TAB, 'live_connections.count', 'live_connections.max'}
+    {?CHAN_LIVE_TAB, 'live_connections.count', 'live_connections.max'},
+    {?CHAN_REG_TAB, 'cluster_sessions.count', 'cluster_sessions.max'}
 ]).
 
 %% Batch drain

apps/emqx/src/emqx_cm_registry.erl

@@ -99,7 +99,7 @@ unregister_channel({ClientId, ChanPid}) when is_binary(ClientId), is_pid(ChanPid
     case is_enabled() of
         true ->
             mria:dirty_delete_object(?CHAN_REG_TAB, record(ClientId, ChanPid)),
-            %% insert unregistration history after unrestration
+            %% insert unregistration history after unregstration
             ok = when_hist_enabled(fun() -> insert_hist_d(ClientId) end);
         false ->
             ok

apps/emqx/src/emqx_cm_registry_keeper.erl

@@ -172,7 +172,7 @@ cleanup_delay() ->
             %% prepare for online config change
             Default;
         RetainSeconds ->
-            Min = max(1, timer:seconds(RetainSeconds div 4)),
+            Min = max(timer:seconds(1), timer:seconds(RetainSeconds) div 4),
             min(Min, Default)
     end.
 
@@ -188,5 +188,7 @@ now_ts() ->
     erlang:system_time(seconds).
 
 do_count(Since) ->
-    Ms = ets:fun2ms(fun(#channel{pid = V}) -> is_pid(V) orelse (is_integer(V) andalso (V >= Since)) end),
+    Ms = ets:fun2ms(fun(#channel{pid = V}) ->
+        is_pid(V) orelse (is_integer(V) andalso (V >= Since))
+    end),
     ets:select_count(?CHAN_REG_TAB, Ms).

apps/emqx/src/emqx_stats.erl

@@ -99,7 +99,11 @@
     [
         'sessions.count',
         %% Maximum Number of Concurrent Sessions
-        'sessions.max'
+        'sessions.max',
+        %% Count of Sessions in the cluster
+        'cluster_sessions.count',
+        %% Maximum Number of Sessions in the cluster
+        'cluster_sessions.max'
     ]
 ).
 
@@ -164,6 +168,8 @@ names() ->
         emqx_connections_max,
         emqx_live_connections_count,
         emqx_live_connections_max,
+        emqx_cluster_sessions_count,
+        emqx_cluster_sessions_max,
         emqx_sessions_count,
         emqx_sessions_max,
         emqx_channels_count,

apps/emqx_dashboard/src/emqx_dashboard_monitor.erl

@@ -415,6 +415,7 @@ getstats(Key) ->
 
 stats(connections) -> emqx_stats:getstat('connections.count');
 stats(live_connections) -> emqx_stats:getstat('live_connections.count');
+stats(cluster_sessions) -> emqx_stats:getstat('cluster_sessions.count');
 stats(topics) -> emqx_stats:getstat('topics.count');
 stats(subscriptions) -> emqx_stats:getstat('subscriptions.count');
 stats(received) -> emqx_metrics:val('messages.received');

apps/emqx_dashboard/src/emqx_dashboard_monitor_api.erl

@@ -194,6 +194,12 @@ swagger_desc(live_connections) ->
         "Connections at the time of sampling."
         " Can only represent the approximate state"
     >>;
+swagger_desc(cluster_sessions) ->
+    <<
+        "Total number of sessions in the cluster at the time of sampling. "
+        "It includes expired sessions when `broker.session_history_retain` is set to a duration greater than `0s`. "
+        "Can only represent the approximate state"
+    >>;
 swagger_desc(received_msg_rate) ->
     swagger_desc_format("Dropped messages ", per);
 %swagger_desc(received_bytes_rate) -> swagger_desc_format("Received bytes ", per);

apps/emqx_management/src/emqx_mgmt.erl

@@ -145,6 +145,7 @@ node_info() ->
         ),
         connections => ets:info(?CHAN_TAB, size),
         live_connections => ets:info(?CHAN_LIVE_TAB, size),
+        cluster_sessions => ets:info(?CHAN_REG_TAB, size),
         node_status => 'running',
         uptime => proplists:get_value(uptime, BrokerInfo),
         version => iolist_to_binary(proplists:get_value(version, BrokerInfo)),

apps/emqx_management/src/emqx_mgmt_api_nodes.erl

@@ -160,6 +160,19 @@ fields(node_info) ->
                 non_neg_integer(),
                 #{desc => <<"Number of clients currently connected to this node">>, example => 0}
             )},
+        {cluster_sessions,
+            mk(
+                non_neg_integer(),
+                #{
+                    desc =>
+                        <<
+                            "By default, it includes only those sessions that have not expired. "
+                            "If the `broker.session_history_retain` config is set to a duration greater than `0s`, "
+                            "this count will also include sessions that expired within the specified retain time"
+                        >>,
+                    example => 0
+                }
+            )},
         {load1,
             mk(
                 float(),

apps/emqx_management/src/emqx_mgmt_api_stats.erl

@@ -89,6 +89,10 @@ fields(node_stats_data) ->
         stats_schema('delayed.max', <<"Historical maximum number of delayed messages">>),
         stats_schema('live_connections.count', <<"Number of current live connections">>),
         stats_schema('live_connections.max', <<"Historical maximum number of live connections">>),
+        stats_schema('cluster_sessions.count', <<"Number of sessions in the cluster">>),
+        stats_schema(
+            'cluster_sessions.max', <<"Historical maximum number of sessions in the cluster">>
+        ),
         stats_schema('retained.count', <<"Number of currently retained messages">>),
         stats_schema('retained.max', <<"Historical maximum number of retained messages">>),
         stats_schema('sessions.count', <<"Number of current sessions">>),

apps/emqx_prometheus/src/emqx_prometheus.erl

@@ -251,7 +251,7 @@ add_collect_family(Name, Data, Callback, Type) ->
 
 %% behaviour
 fetch_from_local_node(Mode) ->
-    {node(self()), #{
+    {node(), #{
         stats_data => stats_data(Mode),
         vm_data => vm_data(Mode),
         cluster_data => cluster_data(Mode),
@@ -308,6 +308,8 @@ emqx_collect(K = emqx_sessions_count, D) -> gauge_metrics(?MG(K, D));
 emqx_collect(K = emqx_sessions_max, D) -> gauge_metrics(?MG(K, D));
 emqx_collect(K = emqx_channels_count, D) -> gauge_metrics(?MG(K, D));
 emqx_collect(K = emqx_channels_max, D) -> gauge_metrics(?MG(K, D));
+emqx_collect(K = emqx_cluster_sessions_count, D) -> gauge_metrics(?MG(K, D));
+emqx_collect(K = emqx_cluster_sessions_max, D) -> gauge_metrics(?MG(K, D));
 %% pub/sub stats
 emqx_collect(K = emqx_topics_count, D) -> gauge_metrics(?MG(K, D));
 emqx_collect(K = emqx_topics_max, D) -> gauge_metrics(?MG(K, D));
@@ -500,6 +502,8 @@ stats_metric_meta() ->
         {emqx_sessions_max, gauge, 'sessions.max'},
         {emqx_channels_count, gauge, 'channels.count'},
         {emqx_channels_max, gauge, 'channels.max'},
+        {emqx_cluster_sessions_count, gauge, 'cluster_sessions.count'},
+        {emqx_cluster_sessions_max, gauge, 'cluster_sessions.max'},
         %% pub/sub stats
         {emqx_suboptions_count, gauge, 'suboptions.count'},
         {emqx_suboptions_max, gauge, 'suboptions.max'},

apps/emqx_telemetry/src/emqx_telemetry.app.src

@@ -1,6 +1,6 @@
 {application, emqx_telemetry, [
     {description, "Report telemetry data for EMQX Opensource edition"},
-    {vsn, "0.1.3"},
+    {vsn, "0.2.0"},
     {registered, [emqx_telemetry_sup, emqx_telemetry]},
     {mod, {emqx_telemetry_app, []}},
     {applications, [

apps/emqx_telemetry/src/emqx_telemetry.erl

@@ -303,6 +303,9 @@ active_plugins() ->
 num_clients() ->
     emqx_stats:getstat('live_connections.count').
 
+num_cluster_sessions() ->
+    emqx_stats:getstat('cluster_sessions.count').
+
 messages_sent() ->
     emqx_metrics:val('messages.sent').
 
@@ -348,6 +351,7 @@ get_telemetry(State0 = #state{node_uuid = NodeUUID, cluster_uuid = ClusterUUID})
         {nodes_uuid, nodes_uuid()},
         {active_plugins, active_plugins()},
         {num_clients, num_clients()},
+        {num_cluster_sessions, num_cluster_sessions()},
         {messages_received, messages_received()},
         {messages_sent, messages_sent()},
         {build_info, build_info()},

rel/i18n/emqx_mgmt_api_clients.hocon

@@ -61,9 +61,12 @@ set_keepalive_seconds.label:
 """Set the online client keepalive by seconds"""
 
 get_sessions_count.desc:
-"""Get the number of sessions. By default it returns the number of non-expired sessions.
+"""Get the total number of sessions in the cluster.
-if `broker.session_history_retain` is set to a duration greater than `0s`,
+By default, it includes only those sessions that have not expired.
-this API can also count expired sessions by providing the `since` parameter."""
+If the `broker.session_history_retain` config is set to a duration greater than 0s,
+this count will also include sessions that expired within the specified retain time.
+By specifying the `since` parameter, it can return the number of sessions that have expired within the specified time."""
+
 get_sessions_count.label:
 """Count number of sessions"""