0111 unregister session with timestamp

apps/emqx/include/emqx_cm.hrl

@@ -23,7 +23,7 @@
 -define(CHAN_INFO_TAB, emqx_channel_info).
 -define(CHAN_LIVE_TAB, emqx_channel_live).
 
-%% Mria/Mnesia Tables for channel management.
+%% Mria table for session registraition.
 -define(CHAN_REG_TAB, emqx_channel_registry).
 
 -define(T_KICK, 5_000).
@@ -32,4 +32,11 @@
 
 -define(CM_POOL, emqx_cm_pool).
 
+%% Registered sessions.
+-record(channel, {
+    chid :: emqx_types:clientid() | '_',
+    %% pid field is extended in 5.6.0 to support recording unregistration timestamp.
+    pid :: pid() | non_neg_integer() | '$1'
+}).
+
 -endif.

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

@@ -1,5 +1,5 @@
 %%--------------------------------------------------------------------
-%% Copyright (c) 2019-2023 EMQ Technologies Co., Ltd. All Rights Reserved.
+%% Copyright (c) 2019-2024 EMQ Technologies Co., Ltd. All Rights Reserved.
 %%
 %% Licensed under the Apache License, Version 2.0 (the "License");
 %% you may not use this file except in compliance with the License.
@@ -19,14 +19,9 @@
 
 -behaviour(gen_server).
 
--include("emqx.hrl").
--include("emqx_cm.hrl").
--include("logger.hrl").
--include("types.hrl").
-
 -export([start_link/0]).
 
--export([is_enabled/0]).
+-export([is_enabled/0, is_hist_enabled/0]).
 
 -export([
     register_channel/1,
@@ -50,10 +45,13 @@
     do_cleanup_channels/1
 ]).
 
--define(REGISTRY, ?MODULE).
--define(LOCK, {?MODULE, cleanup_down}).
+-include("emqx.hrl").
+-include("emqx_cm.hrl").
+-include("logger.hrl").
+-include("types.hrl").
 
--record(channel, {chid, pid}).
+-define(REGISTRY, ?MODULE).
+-define(NODE_DOWN_CLEANUP_LOCK, {?MODULE, cleanup_down}).
 
 %% @doc Start the global channel registry.
 -spec start_link() -> startlink_ret().
@@ -69,6 +67,11 @@ start_link() ->
 is_enabled() ->
     emqx:get_config([broker, enable_session_registry]).
 
+%% @doc Is the global session registration history enabled?
+-spec is_hist_enabled() -> boolean().
+is_hist_enabled() ->
+    retain_duration() > 0.
+
 %% @doc Register a global channel.
 -spec register_channel(
     emqx_types:clientid()
@@ -78,8 +81,11 @@ register_channel(ClientId) when is_binary(ClientId) ->
     register_channel({ClientId, self()});
 register_channel({ClientId, ChanPid}) when is_binary(ClientId), is_pid(ChanPid) ->
     case is_enabled() of
-        true -> mria:dirty_write(?CHAN_REG_TAB, record(ClientId, ChanPid));
-        false -> ok
+        true ->
+            ok = when_hist_enabled(fun() -> delete_hist_d(ClientId) end),
+            mria:dirty_write(?CHAN_REG_TAB, record(ClientId, ChanPid));
+        false ->
+            ok
     end.
 
 %% @doc Unregister a global channel.
@@ -91,18 +97,45 @@ unregister_channel(ClientId) when is_binary(ClientId) ->
     unregister_channel({ClientId, self()});
 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));
-        false -> ok
+        true ->
+            mria:dirty_delete_object(?CHAN_REG_TAB, record(ClientId, ChanPid)),
+            %% insert unregistration history after unregstration
+            ok = when_hist_enabled(fun() -> insert_hist_d(ClientId) end);
+        false ->
+            ok
     end.
 
 %% @doc Lookup the global channels.
 -spec lookup_channels(emqx_types:clientid()) -> list(pid()).
 lookup_channels(ClientId) ->
-    [ChanPid || #channel{pid = ChanPid} <- mnesia:dirty_read(?CHAN_REG_TAB, ClientId)].
+    lists:filtermap(
+        fun
+            (#channel{pid = ChanPid}) when is_pid(ChanPid) ->
+                case is_pid_down(ChanPid) of
+                    true ->
+                        false;
+                    _ ->
+                        {true, ChanPid}
+                end;
+            (_) ->
+                false
+        end,
+        mnesia:dirty_read(?CHAN_REG_TAB, ClientId)
+    ).
+
+%% Return 'true' or 'false' if it's a local pid.
+%% Otherwise return 'unknown'.
+is_pid_down(Pid) when node(Pid) =:= node() ->
+    not erlang:is_process_alive(Pid);
+is_pid_down(_) ->
+    unknown.
 
 record(ClientId, ChanPid) ->
     #channel{chid = ClientId, pid = ChanPid}.
 
+hist(ClientId) ->
+    #channel{chid = ClientId, pid = now_ts()}.
+
 %%--------------------------------------------------------------------
 %% gen_server callbacks
 %%--------------------------------------------------------------------
@@ -158,15 +191,96 @@ code_change(_OldVsn, State, _Extra) ->
 
 cleanup_channels(Node) ->
     global:trans(
-        {?LOCK, self()},
+        {?NODE_DOWN_CLEANUP_LOCK, self()},
         fun() ->
             mria:transaction(?CM_SHARD, fun ?MODULE:do_cleanup_channels/1, [Node])
         end
     ).
 
 do_cleanup_channels(Node) ->
-    Pat = [{#channel{pid = '$1', _ = '_'}, [{'==', {node, '$1'}, Node}], ['$_']}],
+    Pat = [
+        {
+            #channel{pid = '$1', _ = '_'},
+            _Match = [{'andalso', {is_pid, '$1'}, {'==', {node, '$1'}, Node}}],
+            _Return = ['$_']
+        }
+    ],
     lists:foreach(fun delete_channel/1, mnesia:select(?CHAN_REG_TAB, Pat, write)).
 
 delete_channel(Chan) ->
-    mnesia:delete_object(?CHAN_REG_TAB, Chan, write).
+    mnesia:delete_object(?CHAN_REG_TAB, Chan, write),
+    ok = when_hist_enabled(fun() -> insert_hist_t(Chan#channel.chid) end).
+
+%%--------------------------------------------------------------------
+%% History entry operations
+%%--------------------------------------------------------------------
+
+when_hist_enabled(F) ->
+    case is_hist_enabled() of
+        true ->
+            _ = F();
+        false ->
+            ok
+    end,
+    ok.
+
+%% Insert unregistration history in a transaction when unregistering the last channel for a clientid.
+insert_hist_t(ClientId) ->
+    case delete_hist_t(ClientId) of
+        true ->
+            ok;
+        false ->
+            mnesia:write(?CHAN_REG_TAB, hist(ClientId), write)
+    end.
+
+%% Dirty insert unregistration history.
+%% Since dirty opts are used, async pool workers may race deletes and inserts,
+%% so there could be more than one history records for a clientid,
+%% but it should be eventually consistent after the client re-registers or the periodic cleanup.
+insert_hist_d(ClientId) ->
+    %% delete old hist records first
+    case delete_hist_d(ClientId) of
+        true ->
+            ok;
+        false ->
+            mria:dirty_write(?CHAN_REG_TAB, hist(ClientId))
+    end.
+
+%% Current timestamp in seconds.
+now_ts() ->
+    erlang:system_time(seconds).
+
+%% Delete all history records for a clientid, return true if there is a Pid found.
+delete_hist_t(ClientId) ->
+    fold_hist(
+        fun(Hist) -> mnesia:delete_object(?CHAN_REG_TAB, Hist, write) end,
+        mnesia:read(?CHAN_REG_TAB, ClientId, write)
+    ).
+
+%% Delete all history records for a clientid, return true if there is a Pid found.
+delete_hist_d(ClientId) ->
+    fold_hist(
+        fun(Hist) -> mria:dirty_delete_object(?CHAN_REG_TAB, Hist) end,
+        mnesia:dirty_read(?CHAN_REG_TAB, ClientId)
+    ).
+
+%% Fold over the history records, return true if there is a Pid found.
+fold_hist(F, List) ->
+    lists:foldl(
+        fun(#channel{pid = Ts} = Record, HasPid) ->
+            case is_integer(Ts) of
+                true ->
+                    ok = F(Record),
+                    HasPid;
+                false ->
+                    true
+            end
+        end,
+        false,
+        List
+    ).
+
+%% Return the session registration history retain duration.
+-spec retain_duration() -> non_neg_integer().
+retain_duration() ->
+    emqx:get_config([broker, session_history_retain]).