Make master locator min-masters count queues and not bindings.

The min-masters locator was originally designed to count bindings,
but this was confusing for people wanting to distribute queues rather
than routes to queues. This was changed in 1d413ea
to count only queues which have at least one binding. But queues always
have bindings (default) and hence it's equivalent to listing queues.

Since default bindings are removed the location was broken. This commit
changes the location to actually list queues rather than bindings.

Author: hairyhum

src/rabbit_queue_location_min_masters.erl

@@ -38,45 +38,33 @@ description() ->
       <<"Locate queue master node from cluster node with least bound queues">>}].
 
 queue_master_location(#amqqueue{} = Q) ->
-    Cluster            = rabbit_queue_master_location_misc:all_nodes(Q),
-    VHosts             = rabbit_vhost:list(),
-    BoundQueueMasters  = get_bound_queue_masters_per_vhost(VHosts, []),
-    {_Count, MinMaster}= get_min_master(Cluster, BoundQueueMasters),
-    {ok, MinMaster}.
+    Cluster = rabbit_queue_master_location_misc:all_nodes(Q),
+    QueueNames = rabbit_amqqueue:list_names(),
+    MastersPerNode = lists:foldl(
+        fun(#resource{virtual_host = VHost, name = QueueName}, NodeMasters) ->
+            case rabbit_queue_master_location_misc:lookup_master(QueueName, VHost) of
+                {ok, Master} when is_atom(Master) ->
+                    case maps:is_key(Master, NodeMasters) of
+                        true -> maps:update_with(Master,
+                                                 fun(N) -> N + 1 end,
+                                                 NodeMasters);
+                        false -> NodeMasters
+                    end;
+                _ -> NodeMasters
+            end
+        end,
+        maps:from_list([{N, 0} || N <- Cluster]),
+        QueueNames),
 
-%%---------------------------------------------------------------------------
-%% Private helper functions
-%%---------------------------------------------------------------------------
-get_min_master(Cluster, BoundQueueMasters) ->
-    lists:min([ {count_masters(Node, BoundQueueMasters), Node} ||
-                  Node <- Cluster ]).
-
-count_masters(Node, Masters) ->
-    length([ X || X <- Masters, X == Node ]).
-
-get_bound_queue_masters_per_vhost([], Acc) ->
-    lists:flatten(Acc);
-get_bound_queue_masters_per_vhost([VHost|RemVHosts], Acc) ->
-    BoundQueueNames =
-        lists:filtermap(
-            fun(#binding{destination =#resource{kind = queue,
-                                                name = QueueName}}) ->
-                    {true, QueueName};
-               (_) ->
-                    false
-            end,
-            rabbit_binding:list(VHost)),
-    UniqQueueNames = lists:usort(BoundQueueNames),
-    BoundQueueMasters = get_queue_masters(VHost, UniqQueueNames, []),
-    get_bound_queue_masters_per_vhost(RemVHosts, [BoundQueueMasters|Acc]).
-
-
-get_queue_masters(_VHost, [], BoundQueueNodes) -> BoundQueueNodes;
-get_queue_masters(VHost, [QueueName | RemQueueNames], QueueMastersAcc) ->
-    QueueMastersAcc0 = case rabbit_queue_master_location_misc:lookup_master(
-                              QueueName, VHost) of
-                           {ok, Master} when is_atom(Master) ->
-                               [Master|QueueMastersAcc];
-                           _ -> QueueMastersAcc
-                       end,
-    get_queue_masters(VHost, RemQueueNames, QueueMastersAcc0).
+    {MinNode, _NMasters} = maps:fold(
+        fun(Node, NMasters, init) ->
+            {Node, NMasters};
+        (Node, NMasters, {MinNode, MinMasters}) ->
+            case NMasters < MinMasters of
+                true  -> {Node, NMasters};
+                false -> {MinNode, MinMasters}
+            end
+        end,
+        init,
+        MastersPerNode),
+    {ok, MinNode}.