perf(gateway): skip materialising member list subscribers (#2184)

fluxer_gateway/src/guild/guild_member_list_subs.erl

@@ -14,10 +14,12 @@
     retain_only_session_list/3,
     unsubscribe_session/2,
     get_list_subs/2,
+    has_subs/2,
     get_session_ranges/3,
     list_ids/1,
     fold_list_subs/4,
     fold_lists/3,
+    fold_list_ids/3,
     foreach_list/2,
     is_subscribed/3
 ]).
@@ -121,6 +123,13 @@ lookup_list(Tab, Key) ->
 get_list_subs(ListId, Tab) ->
     collect_list(Tab, ets:next(Tab, {ListId, <<>>}), ListId, #{}).
 
+-spec has_subs(binary(), ets:table()) -> boolean().
+has_subs(ListId, Tab) ->
+    case ets:next(Tab, {ListId, <<>>}) of
+        {ListId, SessionId} when is_binary(SessionId) -> true;
+        _ -> false
+    end.
+
 -spec get_session_ranges(binary(), binary(), ets:table()) -> [range()].
 get_session_ranges(SessionId, ListId, Tab) ->
     case ets:lookup(Tab, {ListId, SessionId}) of
@@ -142,6 +151,10 @@ fold_list_subs(ListId, Tab, Fun, Acc0) ->
 fold_lists(Fun, Acc0, Tab) ->
     fold_lists_loop(Fun, Acc0, Tab, ets:next(Tab, {<<>>, <<>>})).
 
+-spec fold_list_ids(fun((binary(), Acc) -> Acc), Acc, ets:table()) -> Acc when Acc :: term().
+fold_list_ids(Fun, Acc0, Tab) ->
+    fold_list_ids_loop(Fun, Acc0, Tab, ets:next(Tab, {<<>>, <<>>})).
+
 -spec foreach_list(fun((binary(), list_subs()) -> term()), ets:table()) -> ok.
 foreach_list(Fun, Tab) ->
     _ = fold_lists(
@@ -201,6 +214,17 @@ fold_lists_loop(Fun, Acc, Tab, {ListId, _} = Key) when is_binary(ListId) ->
     NextListKey = skip_past_list(Tab, Key, ListId),
     fold_lists_loop(Fun, Acc2, Tab, NextListKey).
 
+-spec fold_list_ids_loop(fun((binary(), Acc) -> Acc), Acc, ets:table(), term()) -> Acc when
+    Acc :: term().
+fold_list_ids_loop(_Fun, Acc, _Tab, '$end_of_table') ->
+    Acc;
+fold_list_ids_loop(_Fun, Acc, _Tab, {idx_tab, _}) ->
+    Acc;
+fold_list_ids_loop(Fun, Acc, Tab, {ListId, _} = Key) when is_binary(ListId) ->
+    Acc2 = Fun(ListId, Acc),
+    NextListKey = skip_past_list(Tab, Key, ListId),
+    fold_list_ids_loop(Fun, Acc2, Tab, NextListKey).
+
 -spec skip_past_list(ets:table(), term(), binary()) -> term().
 skip_past_list(Tab, Key, ListId) ->
     case ets:next(Tab, Key) of

fluxer_gateway/src/guild/guild_member_list_write.erl

@@ -180,10 +180,10 @@ broadcast_channel_engine_connection_change(UserId, State, SubsTab) ->
     guild_state().
 fold_connection_change_lists(GuildId, UserId, State, SubsTab) ->
     Sessions = maps:get(sessions, State, #{}),
-    guild_member_list_subs:fold_lists(
-        fun(ListId, ListSubs, AccState) ->
+    guild_member_list_subs:fold_list_ids(
+        fun(ListId, AccState) ->
             sync_connection_change_for_list(
-                GuildId, UserId, ListId, ListSubs, Sessions, AccState
+                GuildId, UserId, ListId, SubsTab, Sessions, AccState
             )
         end,
         State,
@@ -200,10 +200,10 @@ fold_connection_change_lists(GuildId, UserId, State, SubsTab) ->
 dispatch_user_change_to_subscribed_lists(
     UserId, OldMember, NewMember, SubsTab, State
 ) ->
-    guild_member_list_subs:fold_lists(
-        fun(ListId, ListSubs, AccState) ->
+    guild_member_list_subs:fold_list_ids(
+        fun(ListId, AccState) ->
             dispatch_user_change_to_list(
-                UserId, OldMember, NewMember, ListId, ListSubs, AccState
+                UserId, OldMember, NewMember, ListId, SubsTab, AccState
             )
         end,
         State,
@@ -215,14 +215,14 @@ dispatch_user_change_to_subscribed_lists(
     map() | undefined,
     map() | undefined,
     list_id(),
-    guild_member_list_subs:list_subs(),
+    ets:table(),
     guild_state()
 ) -> guild_state().
 dispatch_user_change_to_list(
-    UserId, OldMember, NewMember, ListId, ListSubs, State
+    UserId, OldMember, NewMember, ListId, SubsTab, State
 ) ->
     State1 = apply_user_change_to_channel_store(UserId, ListId, OldMember, NewMember, State),
-    queue_list_sync_if_subscribed(ListId, ListSubs, State1).
+    queue_list_sync_if_subscribed(ListId, SubsTab, State1).
 
 -spec apply_user_change_to_channel_store(
     user_id(), list_id(), map() | undefined, map() | undefined, guild_state()
@@ -253,14 +253,14 @@ apply_channel_member_change(_UserId, _ListId, _OldMember, _NewMember, _State) ->
     integer(),
     user_id(),
     list_id(),
-    guild_member_list_subs:list_subs(),
+    ets:table(),
     map(),
     guild_state()
 ) -> guild_state().
-sync_connection_change_for_list(_GuildId, _UserId, ListId, ListSubs, _Sessions, State) ->
+sync_connection_change_for_list(_GuildId, _UserId, ListId, SubsTab, _Sessions, State) ->
     case guild_member_list_channel_engine:is_engine_list(ListId, State) of
         true ->
-            queue_list_sync_if_subscribed(ListId, ListSubs, State);
+            queue_list_sync_if_subscribed(ListId, SubsTab, State);
         false ->
             State
     end.
@@ -295,13 +295,11 @@ rebuild_channel_store(ListId, State) ->
         false -> State
     end.
 
--spec queue_list_sync_if_subscribed(
-    list_id(), guild_member_list_subs:list_subs(), guild_state()
-) -> guild_state().
-queue_list_sync_if_subscribed(ListId, ListSubs, State) ->
-    case map_size(ListSubs) of
-        0 -> State;
-        _ -> guild_member_list_sync_batch:queue_list_sync(ListId, State)
+-spec queue_list_sync_if_subscribed(list_id(), ets:table(), guild_state()) -> guild_state().
+queue_list_sync_if_subscribed(ListId, SubsTab, State) ->
+    case guild_member_list_subs:has_subs(ListId, SubsTab) of
+        false -> State;
+        true -> guild_member_list_sync_batch:queue_list_sync(ListId, State)
     end.
 
 -spec flush_pending_member_list_syncs(guild_state()) -> guild_state().
@@ -319,9 +317,11 @@ apply_user_change_to_channel_store_updates_engine_test() ->
     ?assert(maps:is_key(<<"123">>, maps:get(channel_member_list_engines, State1))).
 
 sync_connection_change_ignores_zero_list_test() ->
+    SubsTab = guild_member_list_subs:new(),
     ?assertEqual(
         #{},
-        sync_connection_change_for_list(1, 2, <<"0">>, #{}, #{}, #{})
-    ).
+        sync_connection_change_for_list(1, 2, <<"0">>, SubsTab, #{}, #{})
+    ),
+    guild_member_list_subs:destroy(SubsTab).
 
 -endif.