feat(buffer_worker): decouple query mode from underlying connector call mode

Fixes https://emqx.atlassian.net/browse/EMQX-9129

Currently, if an user configures a bridge with query mode sync, then
all calls to the underlying driver/connector ("inner calls") will
always be synchronous, regardless of its support for async calls.

Since buffer workers always support async queries ("outer calls"), we
should decouple those two call modes (inner and outer), and avoid
exposing the inner call configuration to user to avoid complexity.

There are two situations when we want to force synchronous calls to
the underlying connector even if it supports async:

1) When using `simple_sync_query`, since we are bypassing the buffer
workers;
2) When retrying the inflight window, to avoid overwhelming the
driver.

apps/emqx_resource/src/emqx_resource.erl

@@ -265,7 +265,7 @@ query(ResId, Request, Opts) ->
             IsBufferSupported = is_buffer_supported(Module),
             case {IsBufferSupported, QM} of
                 {true, _} ->
-                    %% only Kafka so far
+                    %% only Kafka producer so far
                     Opts1 = Opts#{is_buffer_supported => true},
                     emqx_resource_buffer_worker:simple_async_query(ResId, Request, Opts1);
                 {false, sync} ->

apps/emqx_resource/src/emqx_resource_buffer_worker.erl

@@ -140,7 +140,7 @@ simple_sync_query(Id, Request) ->
     QueryOpts = simple_query_opts(),
     emqx_resource_metrics:matched_inc(Id),
     Ref = make_request_ref(),
-    Result = call_query(sync, Id, Index, Ref, ?SIMPLE_QUERY(Request), QueryOpts),
+    Result = call_query(force_sync, Id, Index, Ref, ?SIMPLE_QUERY(Request), QueryOpts),
     _ = handle_query_result(Id, Result, _HasBeenSent = false),
     Result.
 
@@ -152,7 +152,7 @@ simple_async_query(Id, Request, QueryOpts0) ->
     QueryOpts = maps:merge(simple_query_opts(), QueryOpts0),
     emqx_resource_metrics:matched_inc(Id),
     Ref = make_request_ref(),
-    Result = call_query(async, Id, Index, Ref, ?SIMPLE_QUERY(Request), QueryOpts),
+    Result = call_query(async_if_possible, Id, Index, Ref, ?SIMPLE_QUERY(Request), QueryOpts),
     _ = handle_query_result(Id, Result, _HasBeenSent = false),
     Result.
 
@@ -377,7 +377,7 @@ retry_inflight_sync(Ref, QueryOrBatch, Data0) ->
     } = Data0,
     ?tp(buffer_worker_retry_inflight, #{query_or_batch => QueryOrBatch, ref => Ref}),
     QueryOpts = #{simple_query => false},
-    Result = call_query(sync, Id, Index, Ref, QueryOrBatch, QueryOpts),
+    Result = call_query(force_sync, Id, Index, Ref, QueryOrBatch, QueryOpts),
     ReplyResult =
         case QueryOrBatch of
             ?QUERY(ReplyTo, _, HasBeenSent, _ExpireAt) ->
@@ -566,7 +566,7 @@ do_flush(
     %% unwrap when not batching (i.e., batch size == 1)
     [?QUERY(ReplyTo, _, HasBeenSent, _ExpireAt) = Request] = Batch,
     QueryOpts = #{inflight_tid => InflightTID, simple_query => false},
-    Result = call_query(configured, Id, Index, Ref, Request, QueryOpts),
+    Result = call_query(async_if_possible, Id, Index, Ref, Request, QueryOpts),
     Reply = ?REPLY(ReplyTo, HasBeenSent, Result),
     case reply_caller(Id, Reply, QueryOpts) of
         %% Failed; remove the request from the queue, as we cannot pop
@@ -651,7 +651,7 @@ do_flush(#{queue := Q1} = Data0, #{
         inflight_tid := InflightTID
     } = Data0,
     QueryOpts = #{inflight_tid => InflightTID, simple_query => false},
-    Result = call_query(configured, Id, Index, Ref, Batch, QueryOpts),
+    Result = call_query(async_if_possible, Id, Index, Ref, Batch, QueryOpts),
     case batch_reply_caller(Id, Result, Batch, QueryOpts) of
         %% Failed; remove the request from the queue, as we cannot pop
         %% from it again, but we'll retry it using the inflight table.
@@ -883,17 +883,13 @@ handle_async_worker_down(Data0, Pid) ->
     mark_inflight_items_as_retriable(Data, WorkerMRef),
     {keep_state, Data}.
 
-call_query(QM0, Id, Index, Ref, Query, QueryOpts) ->
-    ?tp(call_query_enter, #{id => Id, query => Query, query_mode => QM0}),
+-spec call_query(force_sync | async_if_possible, _, _, _, _, _) -> _.
+call_query(QM, Id, Index, Ref, Query, QueryOpts) ->
+    ?tp(call_query_enter, #{id => Id, query => Query, query_mode => QM}),
     case emqx_resource_manager:lookup_cached(Id) of
         {ok, _Group, #{status := stopped}} ->
             ?RESOURCE_ERROR(stopped, "resource stopped or disabled");
         {ok, _Group, Resource} ->
-            QM =
-                case QM0 =:= configured of
-                    true -> maps:get(query_mode, Resource);
-                    false -> QM0
-                end,
             do_call_query(QM, Id, Index, Ref, Query, QueryOpts, Resource);
         {error, not_found} ->
             ?RESOURCE_ERROR(not_found, "resource not found")
@@ -1511,9 +1507,9 @@ inc_sent_success(Id, _HasBeenSent = true) ->
 inc_sent_success(Id, _HasBeenSent) ->
     emqx_resource_metrics:success_inc(Id).
 
-call_mode(sync, _) -> sync;
-call_mode(async, always_sync) -> sync;
-call_mode(async, async_if_possible) -> async.
+call_mode(force_sync, _) -> sync;
+call_mode(async_if_possible, always_sync) -> sync;
+call_mode(async_if_possible, async_if_possible) -> async.
 
 assert_ok_result(ok) ->
     true;

apps/emqx_resource/test/emqx_connector_demo.erl

@@ -146,6 +146,12 @@ on_query(_InstId, {sleep_before_reply, For}, #{pid := Pid}) ->
         {error, timeout}
     end.
 
+on_query_async(_InstId, block, ReplyFun, #{pid := Pid}) ->
+    Pid ! {block, ReplyFun},
+    {ok, Pid};
+on_query_async(_InstId, resume, ReplyFun, #{pid := Pid}) ->
+    Pid ! {resume, ReplyFun},
+    {ok, Pid};
 on_query_async(_InstId, {inc_counter, N}, ReplyFun, #{pid := Pid}) ->
     Pid ! {inc, N, ReplyFun},
     {ok, Pid};
@@ -274,6 +280,10 @@ counter_loop(
             block ->
                 ct:pal("counter recv: ~p", [block]),
                 State#{status => blocked};
+            {block, ReplyFun} ->
+                ct:pal("counter recv: ~p", [block]),
+                apply_reply(ReplyFun, ok),
+                State#{status => blocked};
             {block_now, ReplyFun} ->
                 ct:pal("counter recv: ~p", [block_now]),
                 apply_reply(
@@ -284,6 +294,11 @@ counter_loop(
                 {messages, Msgs} = erlang:process_info(self(), messages),
                 ct:pal("counter recv: ~p, buffered msgs: ~p", [resume, length(Msgs)]),
                 State#{status => running};
+            {resume, ReplyFun} ->
+                {messages, Msgs} = erlang:process_info(self(), messages),
+                ct:pal("counter recv: ~p, buffered msgs: ~p", [resume, length(Msgs)]),
+                apply_reply(ReplyFun, ok),
+                State#{status => running};
             {inc, N, ReplyFun} when Status == running ->
                 %ct:pal("async counter recv: ~p", [{inc, N}]),
                 apply_reply(ReplyFun, ok),

apps/emqx_resource/test/emqx_resource_SUITE.erl

@@ -2561,6 +2561,84 @@ do_t_recursive_flush() ->
     ),
     ok.
 
+t_call_mode_uncoupled_from_query_mode(_Config) ->
+    DefaultOpts = #{
+        batch_size => 1,
+        batch_time => 5,
+        worker_pool_size => 1
+    },
+    ?check_trace(
+        begin
+            %% We check that we can call the buffer workers with async
+            %% calls, even if the underlying connector itself only
+            %% supports sync calls.
+            emqx_connector_demo:set_callback_mode(always_sync),
+            {ok, _} = emqx_resource:create(
+                ?ID,
+                ?DEFAULT_RESOURCE_GROUP,
+                ?TEST_RESOURCE,
+                #{name => test_resource},
+                DefaultOpts#{query_mode => async}
+            ),
+            ?tp_span(
+                async_query_sync_driver,
+                #{},
+                ?assertMatch(
+                    {ok, {ok, _}},
+                    ?wait_async_action(
+                        emqx_resource:query(?ID, {inc_counter, 1}),
+                        #{?snk_kind := buffer_worker_flush_ack},
+                        500
+                    )
+                )
+            ),
+            ?assertEqual(ok, emqx_resource:remove_local(?ID)),
+
+            %% And we check the converse: a connector that allows async
+            %% calls can be called synchronously, but the underlying
+            %% call should be async.
+            emqx_connector_demo:set_callback_mode(async_if_possible),
+            {ok, _} = emqx_resource:create(
+                ?ID,
+                ?DEFAULT_RESOURCE_GROUP,
+                ?TEST_RESOURCE,
+                #{name => test_resource},
+                DefaultOpts#{query_mode => sync}
+            ),
+            ?tp_span(
+                sync_query_async_driver,
+                #{},
+                ?assertEqual(ok, emqx_resource:query(?ID, {inc_counter, 2}))
+            ),
+            ?assertEqual(ok, emqx_resource:remove_local(?ID)),
+            ?tp(sync_query_async_driver, #{}),
+            ok
+        end,
+        fun(Trace0) ->
+            Trace1 = trace_between_span(Trace0, async_query_sync_driver),
+            ct:pal("async query calling sync driver\n  ~p", [Trace1]),
+            ?assert(
+                ?strict_causality(
+                    #{?snk_kind := async_query, request := {inc_counter, 1}},
+                    #{?snk_kind := call_query, call_mode := sync},
+                    Trace1
+                )
+            ),
+
+            Trace2 = trace_between_span(Trace0, sync_query_async_driver),
+            ct:pal("sync query calling async driver\n  ~p", [Trace2]),
+            ?assert(
+                ?strict_causality(
+                    #{?snk_kind := sync_query, request := {inc_counter, 2}},
+                    #{?snk_kind := call_query_async},
+                    Trace2
+                )
+            ),
+
+            ok
+        end
+    ).
+
 %%------------------------------------------------------------------------------
 %% Helpers
 %%------------------------------------------------------------------------------
@@ -2742,3 +2820,8 @@ assert_async_retry_fail_then_succeed_inflight(Trace) ->
         )
     ),
     ok.
+
+trace_between_span(Trace0, Marker) ->
+    {Trace1, [_ | _]} = ?split_trace_at(#{?snk_kind := Marker, ?snk_span := {complete, _}}, Trace0),
+    {[_ | _], [_ | Trace2]} = ?split_trace_at(#{?snk_kind := Marker, ?snk_span := start}, Trace1),
+    Trace2.

changes/ce/feat-10206.en.md

@@ -0,0 +1,7 @@
+Decouple the query mode from the underlying call mode for buffer
+workers.
+
+Prior to this change, setting the query mode of a resource
+such as a bridge to `sync` would force the buffer to call the
+underlying connector in a synchronous way, even if it supports async
+calls.

lib-ee/emqx_ee_bridge/test/emqx_ee_bridge_dynamo_SUITE.erl

@@ -291,7 +291,7 @@ t_setup_via_config_and_publish(Config) ->
         end,
         fun(Trace0) ->
             Trace = ?of_kind(dynamo_connector_query_return, Trace0),
-            ?assertMatch([#{result := {ok, _}}], Trace),
+            ?assertMatch([#{result := ok}], Trace),
             ok
         end
     ),
@@ -328,7 +328,7 @@ t_setup_via_http_api_and_publish(Config) ->
         end,
         fun(Trace0) ->
             Trace = ?of_kind(dynamo_connector_query_return, Trace0),
-            ?assertMatch([#{result := {ok, _}}], Trace),
+            ?assertMatch([#{result := ok}], Trace),
             ok
         end
     ),

lib-ee/emqx_ee_bridge/test/emqx_ee_bridge_gcp_pubsub_SUITE.erl

@@ -1013,7 +1013,6 @@ t_publish_timeout(Config) ->
     do_econnrefused_or_timeout_test(Config, timeout).
 
 do_econnrefused_or_timeout_test(Config, Error) ->
-    QueryMode = ?config(query_mode, Config),
     ResourceId = ?config(resource_id, Config),
     TelemetryTable = ?config(telemetry_table, Config),
     Topic = <<"t/topic">>,
@@ -1021,15 +1020,8 @@ do_econnrefused_or_timeout_test(Config, Error) ->
     Message = emqx_message:make(Topic, Payload),
     ?check_trace(
         begin
-            case {QueryMode, Error} of
-                {sync, _} ->
-                    {_, {ok, _}} =
-                        ?wait_async_action(
-                            emqx:publish(Message),
-                            #{?snk_kind := gcp_pubsub_request_failed, recoverable_error := true},
-                            15_000
-                        );
-                {async, econnrefused} ->
+            case Error of
+                econnrefused ->
                     %% at the time of writing, async requests
                     %% are never considered expired by ehttpc
                     %% (even if they arrive late, or never
@@ -1049,7 +1041,7 @@ do_econnrefused_or_timeout_test(Config, Error) ->
                             },
                             15_000
                         );
-                {async, timeout} ->
+                timeout ->
                     %% at the time of writing, async requests
                     %% are never considered expired by ehttpc
                     %% (even if they arrive late, or never
@@ -1067,18 +1059,13 @@ do_econnrefused_or_timeout_test(Config, Error) ->
             end
         end,
         fun(Trace) ->
-            case {QueryMode, Error} of
-                {sync, _} ->
+            case Error of
+                econnrefused ->
                     ?assertMatch(
                         [#{reason := Error, connector := ResourceId} | _],
                         ?of_kind(gcp_pubsub_request_failed, Trace)
                     );
-                {async, econnrefused} ->
-                    ?assertMatch(
-                        [#{reason := Error, connector := ResourceId} | _],
-                        ?of_kind(gcp_pubsub_request_failed, Trace)
-                    );
-                {async, timeout} ->
+                timeout ->
                     ?assertMatch(
                         [_, _ | _],
                         ?of_kind(gcp_pubsub_response, Trace)
@@ -1088,11 +1075,11 @@ do_econnrefused_or_timeout_test(Config, Error) ->
         end
     ),
 
-    case {Error, QueryMode} of
+    case Error of
         %% apparently, async with disabled queue doesn't mark the
         %% message as dropped; and since it never considers the
         %% response expired, this succeeds.
-        {econnrefused, async} ->
+        econnrefused ->
             wait_telemetry_event(TelemetryTable, queuing, ResourceId, #{
                 timeout => 10_000, n_events => 1
             }),
@@ -1114,7 +1101,7 @@ do_econnrefused_or_timeout_test(Config, Error) ->
                 } when Matched >= 1 andalso Inflight + Queueing + Dropped + Failed =< 2,
                 CurrentMetrics
             );
-        {timeout, async} ->
+        timeout ->
             wait_until_gauge_is(inflight, 0, _Timeout = 400),
             wait_until_gauge_is(queuing, 0, _Timeout = 400),
             assert_metrics(
@@ -1129,21 +1116,6 @@ do_econnrefused_or_timeout_test(Config, Error) ->
                     late_reply => 2
                 },
                 ResourceId
-            );
-        {_, sync} ->
-            wait_until_gauge_is(queuing, 0, 500),
-            wait_until_gauge_is(inflight, 1, 500),
-            assert_metrics(
-                #{
-                    dropped => 0,
-                    failed => 0,
-                    inflight => 1,
-                    matched => 1,
-                    queuing => 0,
-                    retried => 0,
-                    success => 0
-                },
-                ResourceId
             )
     end,
 
@@ -1267,7 +1239,6 @@ t_failure_no_body(Config) ->
 
 t_unrecoverable_error(Config) ->
     ResourceId = ?config(resource_id, Config),
-    QueryMode = ?config(query_mode, Config),
     TestPid = self(),
     FailureNoBodyHandler =
         fun(Req0, State) ->
@@ -1298,33 +1269,16 @@ t_unrecoverable_error(Config) ->
     Message = emqx_message:make(Topic, Payload),
     ?check_trace(
         {_, {ok, _}} =
-            case QueryMode of
-                sync ->
-                    ?wait_async_action(
-                        emqx:publish(Message),
-                        #{?snk_kind := gcp_pubsub_request_failed},
-                        5_000
-                    );
-                async ->
-                    ?wait_async_action(
-                        emqx:publish(Message),
-                        #{?snk_kind := gcp_pubsub_response},
-                        5_000
-                    )
-            end,
+            ?wait_async_action(
+                emqx:publish(Message),
+                #{?snk_kind := gcp_pubsub_response},
+                5_000
+            ),
         fun(Trace) ->
-            case QueryMode of
-                sync ->
-                    ?assertMatch(
-                        [#{reason := killed}],
-                        ?of_kind(gcp_pubsub_request_failed, Trace)
-                    );
-                async ->
-                    ?assertMatch(
-                        [#{response := {error, killed}}],
-                        ?of_kind(gcp_pubsub_response, Trace)
-                    )
-            end,
+            ?assertMatch(
+                [#{response := {error, killed}}],
+                ?of_kind(gcp_pubsub_response, Trace)
+            ),
             ok
         end
     ),

lib-ee/emqx_ee_bridge/test/emqx_ee_bridge_influxdb_SUITE.erl

@@ -532,10 +532,12 @@ t_start_ok(Config) ->
     },
     ?check_trace(
         begin
-            ?assertEqual(ok, send_message(Config, SentData)),
             case QueryMode of
-                async -> ct:sleep(500);
-                sync -> ok
+                async ->
+                    ?assertMatch(ok, send_message(Config, SentData)),
+                    ct:sleep(500);
+                sync ->
+                    ?assertMatch({ok, 204, _}, send_message(Config, SentData))
             end,
             PersistedData = query_by_clientid(ClientId, Config),
             Expected = #{
@@ -689,10 +691,12 @@ t_const_timestamp(Config) ->
         <<"payload">> => Payload,
         <<"timestamp">> => erlang:system_time(millisecond)
     },
-    ?assertEqual(ok, send_message(Config, SentData)),
     case QueryMode of
-        async -> ct:sleep(500);
-        sync -> ok
+        async ->
+            ?assertMatch(ok, send_message(Config, SentData)),
+            ct:sleep(500);
+        sync ->
+            ?assertMatch({ok, 204, _}, send_message(Config, SentData))
     end,
     PersistedData = query_by_clientid(ClientId, Config),
     Expected = #{foo => <<"123">>},
@@ -745,7 +749,12 @@ t_boolean_variants(Config) ->
                 <<"timestamp">> => erlang:system_time(millisecond),
                 <<"payload">> => Payload
             },
-            ?assertEqual(ok, send_message(Config, SentData)),
+            case QueryMode of
+                sync ->
+                    ?assertMatch({ok, 204, _}, send_message(Config, SentData));
+                async ->
+                    ?assertMatch(ok, send_message(Config, SentData))
+            end,
             case QueryMode of
                 async -> ct:sleep(500);
                 sync -> ok
@@ -841,10 +850,9 @@ t_bad_timestamp(Config) ->
                     );
                 {sync, false} ->
                     ?assertEqual(
-                        {error,
-                            {unrecoverable_error, [
-                                {error, {bad_timestamp, <<"bad_timestamp">>}}
-                            ]}},
+                        {error, [
+                            {error, {bad_timestamp, <<"bad_timestamp">>}}
+                        ]},
                         Return
                     );
                 {sync, true} ->
@@ -964,7 +972,7 @@ t_write_failure(Config) ->
                                 {error, {resource_error, #{reason := timeout}}},
                                 send_message(Config, SentData)
                             ),
-                            #{?snk_kind := buffer_worker_flush_nack},
+                            #{?snk_kind := handle_async_reply, action := nack},
                             1_000
                         );
                 async ->
@@ -978,13 +986,13 @@ t_write_failure(Config) ->
         fun(Trace0) ->
             case QueryMode of
                 sync ->
-                    Trace = ?of_kind(buffer_worker_flush_nack, Trace0),
+                    Trace = ?of_kind(handle_async_reply, Trace0),
                     ?assertMatch([_ | _], Trace),
                     [#{result := Result} | _] = Trace,
                     ?assert(
                         {error, {error, {closed, "The connection was lost."}}} =:= Result orelse
                             {error, {error, closed}} =:= Result orelse
-                            {error, {recoverable_error, {error, econnrefused}}} =:= Result,
+                            {error, {recoverable_error, econnrefused}} =:= Result,
                         #{got => Result}
                     );
                 async ->
@@ -1006,7 +1014,6 @@ t_write_failure(Config) ->
     ok.
 
 t_missing_field(Config) ->
-    QueryMode = ?config(query_mode, Config),
     BatchSize = ?config(batch_size, Config),
     IsBatch = BatchSize > 1,
     {ok, _} =
@@ -1034,8 +1041,7 @@ t_missing_field(Config) ->
             {ok, _} =
                 snabbkaffe:block_until(
                     ?match_n_events(NEvents, #{
-                        ?snk_kind := influxdb_connector_send_query_error,
-                        mode := QueryMode
+                        ?snk_kind := influxdb_connector_send_query_error
                     }),
                     _Timeout1 = 10_000
                 ),

lib-ee/emqx_ee_connector/test/emqx_ee_connector_influxdb_SUITE.erl

@@ -94,7 +94,7 @@ perform_lifecycle_check(PoolName, InitialConfig) ->
         emqx_resource:get_instance(PoolName),
     ?assertEqual({ok, connected}, emqx_resource:health_check(PoolName)),
     % % Perform query as further check that the resource is working as expected
-    ?assertMatch(ok, emqx_resource:query(PoolName, test_query())),
+    ?assertMatch({ok, 204, _}, emqx_resource:query(PoolName, test_query())),
     ?assertEqual(ok, emqx_resource:stop(PoolName)),
     % Resource will be listed still, but state will be changed and healthcheck will fail
     % as the worker no longer exists.
@@ -116,7 +116,7 @@ perform_lifecycle_check(PoolName, InitialConfig) ->
     {ok, ?CONNECTOR_RESOURCE_GROUP, #{status := InitialStatus}} =
         emqx_resource:get_instance(PoolName),
     ?assertEqual({ok, connected}, emqx_resource:health_check(PoolName)),
-    ?assertMatch(ok, emqx_resource:query(PoolName, test_query())),
+    ?assertMatch({ok, 204, _}, emqx_resource:query(PoolName, test_query())),
     % Stop and remove the resource in one go.
     ?assertEqual(ok, emqx_resource:remove_local(PoolName)),
     ?assertEqual({error, not_found}, ecpool:stop_sup_pool(ReturnedPoolName)),