fix(sessds): avoid accumulating QoS0-only ranges in memory

apps/emqx/src/emqx_persistent_message_ds_replayer.erl

@@ -186,7 +186,9 @@ poll(PreprocFun, SessionId, Inflight0, WindowSize) when WindowSize > 0, WindowSi
         true ->
             %% TODO: Wrap this in `mria:async_dirty/2`?
             Streams = shuffle(get_streams(SessionId)),
-            fetch(PreprocFun, SessionId, Inflight0, Streams, FreeSpace, [])
+            {Publihes, Inflight} = fetch(PreprocFun, SessionId, Inflight0, Streams, FreeSpace, []),
+            %% Discard now irrelevant QoS0-only ranges, if any.
+            {Publihes, discard_committed(SessionId, Inflight)}
     end.
 
 %% Which seqno this track is committed until.
@@ -300,9 +302,9 @@ discard_committed(
 
 find_checkpoints(Ranges) ->
     lists:foldl(
-        fun(#ds_pubrange{stream = StreamRef, until = Until}, Acc) ->
+        fun(#ds_pubrange{stream = StreamRef} = Range, Acc) ->
             %% For each stream, remember the last range over this stream.
-            Acc#{StreamRef => Until}
+            Acc#{StreamRef => Range}
         end,
         #{},
         Ranges
@@ -312,7 +314,7 @@ discard_committed_ranges(
     SessionId,
     Commits,
     Checkpoints,
-    Ranges = [Range = #ds_pubrange{until = Until, stream = StreamRef} | Rest]
+    Ranges = [Range = #ds_pubrange{stream = StreamRef} | Rest]
 ) ->
     case discard_committed_range(Commits, Range) of
         discard ->
@@ -321,11 +323,11 @@ discard_committed_ranges(
             %% over this stream (i.e. a checkpoint).
             RangeKept =
                 case maps:get(StreamRef, Checkpoints) of
-                    CP when CP > Until ->
+                    Range ->
+                        [checkpoint_range(Range)];
+                    _Previous ->
                         discard_range(Range),
-                        [];
-                    Until ->
-                        [checkpoint_range(Range)]
+                        []
                 end,
             %% Since we're (intentionally) not using transactions here, it's important to
             %% issue database writes in the same order in which ranges are stored: from