refactor: rm iterators from DS `#session{}` record

apps/emqx/include/emqx_session.hrl

@@ -49,9 +49,7 @@
     %% Awaiting PUBREL Timeout (Unit: millisecond)
     await_rel_timeout :: timeout(),
     %% Created at
-    created_at :: pos_integer(),
-    %% Durable storage iterators for existing subscriptions
-    iterators = [] :: [emqx_ds_replay:replay_id()]
+    created_at :: pos_integer()
 }).
 
 -endif.

apps/emqx/src/emqx_persistent_session_ds.erl

@@ -85,7 +85,7 @@ open_session(ClientID) ->
     ?WHEN_ENABLED(emqx_ds:session_open(ClientID)).
 
 -spec add_subscription(emqx_types:topic(), emqx_ds:session_id()) ->
-    {ok, emqx_ds:iterator_id(), _IsNew :: boolean()} | {skipped, disabled}.
+    {ok, emqx_ds:iterator_id(), IsNew :: boolean()} | {skipped, disabled}.
 add_subscription(TopicFilterBin, DSSessionID) ->
     ?WHEN_ENABLED(
         begin

apps/emqx/src/emqx_session.erl

@@ -169,14 +169,8 @@
 -spec init_and_open(emqx_types:clientid(), options()) -> session().
 init_and_open(ClientID, Options) ->
     Session0 = emqx_session:init(Options),
-    IteratorIDs =
-        case emqx_persistent_session_ds:open_session(ClientID) of
-            {skipped, disabled} ->
-                [];
-            {_IsNew, _DSSessionID, Iterators0} ->
-                Iterators0
-        end,
-    Session0#session{iterators = IteratorIDs}.
+    _ = emqx_persistent_session_ds:open_session(ClientID),
+    Session0.
 
 -spec init(options()) -> session().
 init(Opts) ->
@@ -274,9 +268,7 @@ info(awaiting_rel_max, #session{max_awaiting_rel = Max}) ->
 info(await_rel_timeout, #session{await_rel_timeout = Timeout}) ->
     Timeout;
 info(created_at, #session{created_at = CreatedAt}) ->
-    CreatedAt;
-info(iterators, #session{iterators = IteratorIds}) ->
-    IteratorIds.
+    CreatedAt.
 
 %% @doc Get stats of the session.
 -spec stats(session()) -> emqx_types:stats().
@@ -325,15 +317,8 @@ is_subscriptions_full(#session{
 -spec add_persistent_subscription(emqx_types:topic(), emqx_types:clientid(), session()) ->
     session().
 add_persistent_subscription(TopicFilterBin, ClientId, Session) ->
-    case emqx_persistent_session_ds:add_subscription(TopicFilterBin, ClientId) of
-        {skipped, disabled} ->
-            Session;
-        {ok, IteratorID, _IsNew = true} ->
-            Iterators = Session#session.iterators,
-            Session#session{iterators = [IteratorID | Iterators]};
-        {ok, _IteratorID, _IsNew = false} ->
-            Session
-    end.
+    _ = emqx_persistent_session_ds:add_subscription(TopicFilterBin, ClientId),
+    Session.
 
 %%--------------------------------------------------------------------
 %% Client -> Broker: UNSUBSCRIBE

apps/emqx/test/emqx_persistent_messages_SUITE.erl

@@ -148,18 +148,15 @@ t_session_subscription_iterators(Config) ->
             ct:pal("publishing 4"),
             Message4 = emqx_message:make(AnotherTopic, Payload4),
             publish(Node1, Message4),
-            IteratorIds = get_iterator_ids(Node1, ClientId),
             emqtt:stop(Client),
             #{
-                messages => [Message1, Message2, Message3, Message4],
-                iterator_ids => IteratorIds
+                messages => [Message1, Message2, Message3, Message4]
             }
         end,
         fun(Results, Trace) ->
             ct:pal("trace:\n  ~p", [Trace]),
             #{
-                messages := [_Message1, Message2, Message3 | _],
-                iterator_ids := IteratorIds
+                messages := [_Message1, Message2, Message3 | _]
             } = Results,
             case ?of_kind(ds_session_subscription_added, Trace) of
                 [] ->
@@ -182,10 +179,9 @@ t_session_subscription_iterators(Config) ->
                     ),
                     ok
             end,
-            ?assertMatch([_], IteratorIds),
             ?assertMatch({ok, [_]}, get_all_iterator_ids(Node1)),
-            ?assertMatch({ok, [_]}, get_all_iterator_ids(Node2)),
-            [IteratorId] = IteratorIds,
+            {ok, [IteratorId]} = get_all_iterator_ids(Node1),
+            ?assertMatch({ok, [IteratorId]}, get_all_iterator_ids(Node2)),
             ReplayMessages1 = erpc:call(Node1, fun() -> consume(?DS_SHARD, IteratorId) end),
             ExpectedMessages = [Message2, Message3],
             ?assertEqual(ExpectedMessages, ReplayMessages1),
@@ -284,7 +280,4 @@ get_mqtt_port(Node, Type) ->
     Port.
 
 get_all_iterator_ids(Node) ->
-    Fn = fun(K, _V, Acc) -> [K | Acc] end,
-    erpc:call(Node, fun() ->
-        emqx_ds_storage_layer:foldl_iterator_prefix(?DS_SHARD, <<>>, Fn, [])
-    end).
+    erpc:call(Node, emqx_ds_storage_layer, list_iterator_prefix, [?DS_SHARD, <<>>]).

apps/emqx/test/emqx_proper_types.erl

@@ -147,8 +147,7 @@ sessioninfo() ->
             awaiting_rel = awaiting_rel(),
             max_awaiting_rel = non_neg_integer(),
             await_rel_timeout = safty_timeout(),
-            created_at = timestamp(),
-            iterators = []
+            created_at = timestamp()
         },
         emqx_session:info(Session)
     ).

apps/emqx_durable_storage/src/emqx_ds.erl

@@ -15,6 +15,7 @@
 %%--------------------------------------------------------------------
 -module(emqx_ds).
 
+-include_lib("stdlib/include/ms_transform.hrl").
 -include_lib("snabbkaffe/include/snabbkaffe.hrl").
 
 %% API:
@@ -124,17 +125,15 @@ message_stats() ->
 %%
 %% Note: session API doesn't handle session takeovers, it's the job of
 %% the broker.
--spec session_open(emqx_types:clientid()) -> {_New :: boolean(), session_id(), [iterator_id()]}.
+-spec session_open(emqx_types:clientid()) -> {_New :: boolean(), session_id()}.
 session_open(ClientID) ->
     case mnesia:dirty_read(?SESSION_TAB, ClientID) of
-        [#session{iterators = Iterators}] ->
-            IteratorIDs = maps:values(Iterators),
-            {false, ClientID, IteratorIDs};
+        [#session{}] ->
+            {false, ClientID};
         [] ->
-            Iterators = #{},
-            Session = #session{id = ClientID, iterators = Iterators},
+            Session = #session{id = ClientID},
             mria:dirty_write(?SESSION_TAB, Session),
-            {true, ClientID, _IteratorIDs = []}
+            {true, ClientID}
     end.
 
 %% @doc Called when a client reconnects with `clean session=true' or

apps/emqx_durable_storage/src/emqx_ds_int.hrl

@@ -21,8 +21,10 @@
 -define(DS_SHARD, emqx_ds_shard).
 
 -record(session, {
+    %% same as clientid
     id :: emqx_ds:session_id(),
-    iterators :: #{emqx_topic:words() => emqx_ds:iterator_id()}
+    %% for future usage
+    props = #{} :: map()
 }).
 
 -record(iterator_ref, {

apps/emqx_durable_storage/src/emqx_ds_storage_layer.erl

@@ -19,6 +19,7 @@
     discard_iterator/2,
     is_iterator_present/2,
     discard_iterator_prefix/2,
+    list_iterator_prefix/2,
     foldl_iterator_prefix/4
 ]).
 
@@ -203,7 +204,17 @@ discard_iterator(Shard, ReplayID) ->
 -spec discard_iterator_prefix(emqx_ds:shard(), binary()) ->
     ok | {error, _TODO}.
 discard_iterator_prefix(Shard, KeyPrefix) ->
-    do_discard_iterator_prefix(Shard, KeyPrefix).
+    case do_discard_iterator_prefix(Shard, KeyPrefix) of
+        {ok, _} -> ok;
+        Error -> Error
+    end.
+
+-spec list_iterator_prefix(
+    emqx_ds:shard(),
+    binary()
+) -> {ok, [emqx_ds:iterator_id()]} | {error, _TODO}.
+list_iterator_prefix(Shard, KeyPrefix) ->
+    do_list_iterator_prefix(Shard, KeyPrefix).
 
 -spec foldl_iterator_prefix(
     emqx_ds:shard(),
@@ -377,7 +388,11 @@ open_restore_iterator(#{module := Mod, data := Data}, It = #it{replay = Replay},
 
 %%
 
--define(KEY_REPLAY_STATE(ReplayID), <<(ReplayID)/binary, "rs">>).
+-define(KEY_REPLAY_STATE(IteratorId), <<(IteratorId)/binary, "rs">>).
+-define(KEY_REPLAY_STATE_PAT(KeyReplayState), begin
+    <<IteratorId:(size(KeyReplayState) - 2)/binary, "rs">> = (KeyReplayState),
+    IteratorId
+end).
 
 -define(ITERATION_WRITE_OPTS, []).
 -define(ITERATION_READ_OPTS, []).
@@ -424,6 +439,13 @@ restore_iterator_state(
     It = #it{shard = Shard, gen = Gen, replay = {TopicFilter, StartTime}},
     open_restore_iterator(meta_get_gen(Shard, Gen), It, State).
 
+do_list_iterator_prefix(Shard, KeyPrefix) ->
+    Fn = fun(K0, _V, Acc) ->
+        K = ?KEY_REPLAY_STATE_PAT(K0),
+        [K | Acc]
+    end,
+    do_foldl_iterator_prefix(Shard, KeyPrefix, Fn, []).
+
 do_discard_iterator_prefix(Shard, KeyPrefix) ->
     #db{handle = DBHandle, cf_iterator = CF} = meta_lookup(Shard, db),
     Fn = fun(K, _V, _Acc) -> ok = rocksdb:delete(DBHandle, CF, K, ?ITERATION_WRITE_OPTS) end,

apps/emqx_durable_storage/test/emqx_ds_SUITE.erl

@@ -169,7 +169,7 @@ t_session_subscription_idempotency(Config) ->
             %% Exactly one iterator should have been opened.
             ?assertMatch({ok, [_]}, get_all_iterator_ids(Node1)),
             ?assertMatch(
-                {_IsNew = false, ClientId, _},
+                {_IsNew = false, ClientId},
                 erpc:call(Node1, emqx_ds, session_open, [ClientId])
             ),
             ok