Merge pull request #12361 from rabbitmq/mergify/bp/v4.0.x/pr-12358

QQ: fix off-by-one bug in release cursor effects. (backport #12358)

deps/rabbit/src/rabbit_fifo.erl

@@ -1064,7 +1064,7 @@ handle_aux(_RaState, cast, tick, #?AUX{name = Name,
                undefined ->
                    [{release_cursor, ra_aux:last_applied(RaAux)}];
                Smallest ->
-                   [{release_cursor, Smallest}]
+                   [{release_cursor, Smallest - 1}]
            end,
     {no_reply, Aux, RaAux, Effs};
 handle_aux(_RaState, cast, eol, #?AUX{name = Name} = Aux, RaAux) ->
@@ -2915,7 +2915,10 @@ release_cursor(LastSmallest, Smallest)
   when is_integer(LastSmallest) andalso
        is_integer(Smallest) andalso
        Smallest > LastSmallest ->
-    [{release_cursor, Smallest}];
+    [{release_cursor, Smallest - 1}];
+release_cursor(undefined, Smallest)
+  when is_integer(Smallest) ->
+    [{release_cursor, Smallest - 1}];
 release_cursor(_, _) ->
     [].
 

deps/rabbit/test/rabbit_fifo_SUITE.erl

@@ -2347,6 +2347,31 @@ aux_test(_) ->
     ?assert(X > 0.0),
     ok.
 
+handle_aux_tick_test(Config) ->
+    _ = ra_machine_ets:start_link(),
+    Aux0 = init_aux(aux_test),
+    LastApplied = 1,
+    MacState0 = init(#{name => ?FUNCTION_NAME,
+                       queue_resource => rabbit_misc:r("/", queue, ?FUNCTION_NAME_B),
+                       single_active_consumer_on => false}),
+    State0 = #{machine_state => MacState0,
+               log => mock_log,
+               last_applied => LastApplied},
+    {MacState1, _} = enq(Config, 1, 1, first, MacState0),
+    State1 = State0#{machine_state => MacState1},
+    meck:expect(ra_log, last_index_term, fun (_) -> {1, 0} end),
+    ?assertEqual(1, rabbit_fifo:smallest_raft_index(MacState1)),
+    %% the release cursor should be 1 lower than the smallest raft index
+    {no_reply, _, _,
+     [{release_cursor, 0}]} = handle_aux(leader, cast, tick, Aux0, State1),
+    timer:sleep(10),
+
+    persistent_term:put(quorum_queue_checkpoint_config, {1, 0, 1}),
+    {no_reply, _, _,
+     [{checkpoint, 1, _},
+      {release_cursor, 0}]} = handle_aux(follower, cast, force_checkpoint, Aux0, State1),
+    ok.
+
 
 %% machine version conversion test