fix(buffer): fix `replayq` usages in buffer workers (5.0)

https://emqx.atlassian.net/browse/EMQX-8700

Fixes a few errors in the usage of `replayq` queues.

- Close `replayq` when `emqx_resource_worker` terminates.
- Do not keep old references to `replayq` after any `pop`s.
- Clear `replayq`'s data directories when removing a resource.

apps/emqx_resource/src/emqx_resource_worker.erl

@@ -53,6 +53,8 @@
 
 -export([reply_after_query/7, batch_reply_after_query/7]).
 
+-export([clear_disk_queue_dir/2]).
+
 -elvis([{elvis_style, dont_repeat_yourself, disable}]).
 
 -define(Q_ITEM(REQUEST), {q_item, REQUEST}).
@@ -176,6 +178,7 @@ init({Id, Index, Opts}) ->
         resume_interval => maps:get(resume_interval, Opts, HCItvl),
         tref => undefined
     },
+    ?tp(resource_worker_init, #{id => Id, index => Index}),
     {ok, blocked, St, {next_event, cast, resume}}.
 
 running(enter, _, St) ->
@@ -232,7 +235,9 @@ blocked(info, Info, _Data) ->
 terminate(_Reason, #{id := Id, index := Index, queue := Q}) ->
     emqx_resource_metrics:inflight_set(Id, Index, 0),
     emqx_resource_metrics:queuing_set(Id, Index, queue_count(Q)),
-    gproc_pool:disconnect_worker(Id, {Id, Index}).
+    gproc_pool:disconnect_worker(Id, {Id, Index}),
+    replayq:close(Q),
+    ok.
 
 code_change(_OldVsn, State, _Extra) ->
     {ok, State}.
@@ -432,7 +437,11 @@ flush(Data0) ->
             {Q1, QAckRef, Batch0} = replayq:pop(Q0, #{count_limit => BatchSize}),
             Batch = [Item || ?Q_ITEM(Item) <- Batch0],
             IsBatch = BatchSize =/= 1,
-            do_flush(Data0, #{
+            %% We *must* use the new queue, because we currently can't
+            %% `nack' a `pop'.
+            %% Maybe we could re-open the queue?
+            Data1 = Data0#{queue := Q1},
+            do_flush(Data1, #{
                 new_queue => Q1,
                 is_batch => IsBatch,
                 batch => Batch,
@@ -463,24 +472,35 @@ do_flush(Data0, #{is_batch := false, batch := Batch, ack_ref := QAckRef, new_que
         %% failed and is not async; keep the request in the queue to
         %% be retried
         {true, false} ->
-            {next_state, blocked, Data1};
+            %% Note: currently, we cannot safely pop an item from
+            %% `replayq', keep the old reference to the queue and
+            %% later try to append new items to the old ref: by
+            %% popping an item, we may cause the side effect of
+            %% closing an open segment and opening a new one, and the
+            %% later `append' with the old file descriptor will fail
+            %% with `einval' because it has been closed.  So we are
+            %% forced to re-append the item, changing the order of
+            %% requests...
+            ok = replayq:ack(Q1, QAckRef),
+            SentBatch = mark_as_sent(Batch),
+            Q2 = append_queue(Id, Index, Q1, SentBatch),
+            Data2 = Data1#{queue := Q2},
+            {next_state, blocked, Data2};
         %% failed and is async; remove the request from the queue, as
         %% it is already in inflight table
         {true, true} ->
             ok = replayq:ack(Q1, QAckRef),
             emqx_resource_metrics:queuing_set(Id, Index, queue_count(Q1)),
-            Data = Data1#{queue := Q1},
+            {next_state, blocked, Data1};
-            {next_state, blocked, Data};
         %% success; just ack
         {false, _} ->
             ok = replayq:ack(Q1, QAckRef),
             emqx_resource_metrics:queuing_set(Id, Index, queue_count(Q1)),
-            Data2 = Data1#{queue := Q1},
             case replayq:count(Q1) > 0 of
                 true ->
-                    {keep_state, Data2, [{next_event, internal, flush}]};
+                    {keep_state, Data1, [{next_event, internal, flush}]};
                 false ->
-                    {keep_state, Data2}
+                    {keep_state, Data1}
             end
     end;
 do_flush(Data0, #{is_batch := true, batch := Batch, ack_ref := QAckRef, new_queue := Q1}) ->
@@ -498,28 +518,39 @@ do_flush(Data0, #{is_batch := true, batch := Batch, ack_ref := QAckRef, new_queu
         %% failed and is not async; keep the request in the queue to
         %% be retried
         {true, false} ->
-            {next_state, blocked, Data1};
+            %% Note: currently, we cannot safely pop an item from
+            %% `replayq', keep the old reference to the queue and
+            %% later try to append new items to the old ref: by
+            %% popping an item, we may cause the side effect of
+            %% closing an open segment and opening a new one, and the
+            %% later `append' with the old file descriptor will fail
+            %% with `einval' because it has been closed.  So we are
+            %% forced to re-append the item, changing the order of
+            %% requests...
+            ok = replayq:ack(Q1, QAckRef),
+            SentBatch = mark_as_sent(Batch),
+            Q2 = append_queue(Id, Index, Q1, SentBatch),
+            Data2 = Data1#{queue := Q2},
+            {next_state, blocked, Data2};
         %% failed and is async; remove the request from the queue, as
         %% it is already in inflight table
         {true, true} ->
             ok = replayq:ack(Q1, QAckRef),
             emqx_resource_metrics:queuing_set(Id, Index, queue_count(Q1)),
-            Data = Data1#{queue := Q1},
+            {next_state, blocked, Data1};
-            {next_state, blocked, Data};
         %% success; just ack
         {false, _} ->
             ok = replayq:ack(Q1, QAckRef),
             emqx_resource_metrics:queuing_set(Id, Index, queue_count(Q1)),
             CurrentCount = replayq:count(Q1),
-            Data2 = Data1#{queue := Q1},
             case {CurrentCount > 0, CurrentCount >= BatchSize} of
                 {false, _} ->
-                    {keep_state, Data2};
+                    {keep_state, Data1};
                 {true, true} ->
-                    {keep_state, Data2, [{next_event, internal, flush}]};
+                    {keep_state, Data1, [{next_event, internal, flush}]};
                 {true, false} ->
-                    Data3 = ensure_flush_timer(Data2),
+                    Data2 = ensure_flush_timer(Data1),
-                    {keep_state, Data3}
+                    {keep_state, Data2}
             end
     end.
 
@@ -874,6 +905,15 @@ disk_queue_dir(Id, Index) ->
     QDir = binary_to_list(Id) ++ ":" ++ integer_to_list(Index),
     filename:join([emqx:data_dir(), "resource_worker", node(), QDir]).
 
+clear_disk_queue_dir(Id, Index) ->
+    ReplayQDir = disk_queue_dir(Id, Index),
+    case file:del_dir_r(ReplayQDir) of
+        {error, enoent} ->
+            ok;
+        Res ->
+            Res
+    end.
+
 ensure_flush_timer(Data = #{tref := undefined, batch_time := T}) ->
     Ref = make_ref(),
     TRef = erlang:send_after(T, self(), {flush, Ref}),

apps/emqx_resource/src/emqx_resource_worker_sup.erl

@@ -67,7 +67,8 @@ stop_workers(ResId, Opts) ->
     WorkerPoolSize = worker_pool_size(Opts),
     lists:foreach(
         fun(Idx) ->
-            ensure_worker_removed(ResId, Idx)
+            ensure_worker_removed(ResId, Idx),
+            ensure_disk_queue_dir_absent(ResId, Idx)
         end,
         lists:seq(1, WorkerPoolSize)
     ),
@@ -127,6 +128,10 @@ ensure_worker_removed(ResId, Idx) ->
             {error, Reason}
     end.
 
+ensure_disk_queue_dir_absent(ResourceId, Index) ->
+    ok = emqx_resource_worker:clear_disk_queue_dir(ResourceId, Index),
+    ok.
+
 ensure_worker_pool_removed(ResId) ->
     try
         gproc_pool:delete(ResId)

apps/emqx_resource/test/emqx_connector_demo.erl

@@ -88,6 +88,19 @@ on_query(_InstId, block, #{pid := Pid}) ->
 on_query(_InstId, resume, #{pid := Pid}) ->
     Pid ! resume,
     ok;
+on_query(_InstId, {big_payload, Payload}, #{pid := Pid}) ->
+    ReqRef = make_ref(),
+    From = {self(), ReqRef},
+    Pid ! {From, {big_payload, Payload}},
+    receive
+        {ReqRef, ok} ->
+            ?tp(connector_demo_big_payload, #{payload => Payload}),
+            ok;
+        {ReqRef, incorrect_status} ->
+            {error, {recoverable_error, incorrect_status}}
+    after 1000 ->
+        {error, timeout}
+    end;
 on_query(_InstId, {inc_counter, N}, #{pid := Pid}) ->
     ReqRef = make_ref(),
     From = {self(), ReqRef},
@@ -216,6 +229,9 @@ counter_loop(
             {{FromPid, ReqRef}, {inc, _N}} when Status == blocked ->
                 FromPid ! {ReqRef, incorrect_status},
                 State#{incorrect_status_count := IncorrectCount + 1};
+            {{FromPid, ReqRef}, {big_payload, _Payload}} when Status == blocked ->
+                FromPid ! {ReqRef, incorrect_status},
+                State#{incorrect_status_count := IncorrectCount + 1};
             {get, ReplyFun} ->
                 apply_reply(ReplyFun, Num),
                 State;

apps/emqx_resource/test/emqx_resource_SUITE.erl

@@ -1116,6 +1116,88 @@ t_retry_batch(_Config) ->
     ),
     ok.
 
+t_delete_and_re_create_with_same_name(_Config) ->
+    {ok, _} = emqx_resource:create(
+        ?ID,
+        ?DEFAULT_RESOURCE_GROUP,
+        ?TEST_RESOURCE,
+        #{name => test_resource},
+        #{
+            query_mode => sync,
+            batch_size => 1,
+            worker_pool_size => 2,
+            queue_seg_bytes => 100,
+            resume_interval => 1_000
+        }
+    ),
+    %% pre-condition: we should have just created a new queue
+    Queuing0 = emqx_resource_metrics:queuing_get(?ID),
+    ?assertEqual(0, Queuing0),
+    ?check_trace(
+        begin
+            ?assertMatch(ok, emqx_resource:simple_sync_query(?ID, block)),
+            NumRequests = 10,
+            {ok, SRef} = snabbkaffe:subscribe(
+                ?match_event(#{?snk_kind := resource_worker_appended_to_queue}),
+                %% +1 because the first request will fail,
+                %% block the resource, and will be
+                %% re-appended to the queue.
+                NumRequests + 1,
+                _Timeout = 5_000
+            ),
+            %% ensure replayq offloads to disk
+            Payload = binary:copy(<<"a">>, 119),
+            lists:foreach(
+                fun(N) ->
+                    {error, _} =
+                        emqx_resource:query(
+                            ?ID,
+                            {big_payload, <<(integer_to_binary(N))/binary, Payload/binary>>}
+                        )
+                end,
+                lists:seq(1, NumRequests)
+            ),
+
+            {ok, _} = snabbkaffe:receive_events(SRef),
+
+            %% ensure that stuff got enqueued into disk
+            Queuing1 = emqx_resource_metrics:queuing_get(?ID),
+            ?assertEqual(NumRequests, Queuing1),
+
+            %% now, we delete the resource
+            ok = emqx_resource:remove_local(?ID),
+            ?assertEqual({error, not_found}, emqx_resource_manager:lookup(?ID)),
+
+            %% re-create the resource with the *same name*
+            {{ok, _}, {ok, _Events}} =
+                ?wait_async_action(
+                    emqx_resource:create(
+                        ?ID,
+                        ?DEFAULT_RESOURCE_GROUP,
+                        ?TEST_RESOURCE,
+                        #{name => test_resource},
+                        #{
+                            query_mode => async,
+                            batch_size => 1,
+                            worker_pool_size => 2,
+                            queue_seg_bytes => 100,
+                            resume_interval => 1_000
+                        }
+                    ),
+                    #{?snk_kind := resource_worker_enter_blocked},
+                    5_000
+                ),
+
+            %% it shouldn't have anything enqueued, as it's a fresh resource
+            Queuing2 = emqx_resource_metrics:queuing_get(?ID),
+            ?assertEqual(0, Queuing2),
+
+            ok
+        end,
+        []
+    ),
+    ok.
+
 %%------------------------------------------------------------------------------
 %% Helpers
 %%------------------------------------------------------------------------------