fix(sessds): Delay unsubscribe until full ack of in-flight messages
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ieQu1
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@ -62,7 +62,10 @@
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first_seqno_qos2 = 0 :: emqx_persistent_session_ds:seqno(),
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%% Sequence numbers that have to be committed for the batch:
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last_seqno_qos1 = 0 :: emqx_persistent_session_ds:seqno(),
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last_seqno_qos2 = 0 :: emqx_persistent_session_ds:seqno()
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last_seqno_qos2 = 0 :: emqx_persistent_session_ds:seqno(),
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%% This stream belongs to an unsubscribed topic-filter, and is
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%% marked for deletion:
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unsubscribed = false :: boolean()
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}).
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%% Session metadata keys:
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@ -93,7 +93,7 @@ find_new_streams(S) ->
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(_Key, #srs{it_end = end_of_stream}, Acc) ->
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Acc;
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(Key, Stream, Acc) ->
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case is_fully_acked(Comm1, Comm2, Stream) of
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case is_fully_acked(Comm1, Comm2, Stream) andalso not Stream#srs.unsubscribed of
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true ->
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[{Key, Stream} | Acc];
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false ->
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@ -124,25 +124,26 @@ find_new_streams(S) ->
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%% This way, messages from the same topic/shard are never reordered.
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-spec renew_streams(emqx_persistent_session_ds_state:t()) -> emqx_persistent_session_ds_state:t().
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renew_streams(S0) ->
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S1 = remove_fully_replayed_streams(S0),
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S1 = remove_unsubscribed_streams(S0),
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S2 = remove_fully_replayed_streams(S1),
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emqx_topic_gbt:fold(
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fun(Key, _Subscription = #{start_time := StartTime, id := SubId}, S2) ->
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fun(Key, _Subscription = #{start_time := StartTime, id := SubId}, Acc) ->
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TopicFilter = emqx_topic:words(emqx_trie_search:get_topic(Key)),
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Streams = select_streams(
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SubId,
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emqx_ds:get_streams(?PERSISTENT_MESSAGE_DB, TopicFilter, StartTime),
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S2
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Acc
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),
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lists:foldl(
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fun(I, Acc) ->
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ensure_iterator(TopicFilter, StartTime, SubId, I, Acc)
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fun(I, Acc1) ->
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ensure_iterator(TopicFilter, StartTime, SubId, I, Acc1)
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end,
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S2,
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Acc,
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Streams
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)
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end,
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S1,
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emqx_persistent_session_ds_state:get_subscriptions(S1)
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S2,
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emqx_persistent_session_ds_state:get_subscriptions(S2)
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).
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-spec del_subscription(
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@ -150,11 +151,33 @@ renew_streams(S0) ->
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) ->
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emqx_persistent_session_ds_state:t().
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del_subscription(SubId, S0) ->
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%% NOTE: this function only marks the streams for deletion,
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%% instead of outright deleting them.
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%%
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%% It's done for two reasons:
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%%
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%% - MQTT standard states that the broker MUST process acks for
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%% all sent messages, and it MAY keep on sending buffered
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%% messages:
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%% https://docs.oasis-open.org/mqtt/mqtt/v5.0/os/mqtt-v5.0-os.html#_Toc3901186
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%%
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%% - Deleting the streams may lead to gaps in the sequence number
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%% series, and lead to problems with acknowledgement tracking, we
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%% avoid that by delaying the deletion.
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%%
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%% When the stream is marked for deletion, the session won't fetch
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%% _new_ batches from it. Actual deletion is done by
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%% `renew_streams', when it detects that all in-flight messages
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%% from the stream have been acked by the client.
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emqx_persistent_session_ds_state:fold_streams(
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fun(Key, _, Acc) ->
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fun(Key, ReplayState, Acc) ->
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case Key of
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{SubId, _Stream} ->
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emqx_persistent_session_ds_state:del_stream(Key, Acc);
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%% This stream belongs to a deleted subscription.
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%% Mark for deletion:
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emqx_persistent_session_ds_state:put_stream(
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Key, ReplayState#srs{unsubscribed = true}, Acc
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);
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_ ->
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Acc
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end
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@ -184,6 +207,10 @@ ensure_iterator(TopicFilter, StartTime, SubId, {{RankX, RankY}, Stream}, S) ->
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it_end = Iterator
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},
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emqx_persistent_session_ds_state:put_stream(Key, NewStreamState, S);
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SRS = #srs{unsubscribed = true} ->
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%% The session resubscribed to the stream after
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%% unsubscribing. Spare the stream:
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emqx_persistent_session_ds_state:put_stream(Key, SRS#srs{unsubscribed = false}, S);
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#srs{} ->
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S
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end.
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@ -222,6 +249,27 @@ select_streams(SubId, RankX, Streams0, S) ->
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lists:takewhile(fun({{_, Y}, _}) -> Y =:= MinRankY end, Streams)
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end.
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%% @doc Remove fully acked streams for the deleted subscriptions.
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-spec remove_unsubscribed_streams(emqx_persistent_session_ds_state:t()) ->
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emqx_persistent_session_ds_state:t().
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remove_unsubscribed_streams(S0) ->
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CommQos1 = emqx_persistent_session_ds_state:get_seqno(?committed(?QOS_1), S0),
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CommQos2 = emqx_persistent_session_ds_state:get_seqno(?committed(?QOS_2), S0),
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emqx_persistent_session_ds_state:fold_streams(
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fun(Key, ReplayState, S1) ->
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case
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ReplayState#srs.unsubscribed andalso is_fully_acked(CommQos1, CommQos2, ReplayState)
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of
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true ->
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emqx_persistent_session_ds_state:del_stream(Key, S1);
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false ->
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S1
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end
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end,
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S0,
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S0
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).
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%% @doc Advance RankY for each RankX that doesn't have any unreplayed
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%% streams.
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%%
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