some routing optimisation

- handle the very common "message goes through single exchange" case
  specially
- use a gb_set in all other cases - it performs much better than a set
  for smaller sets, and not too badly for very large sets either.

1 files changed, 12 insertions, 3 deletions

diff --git a/src/rabbit_exchange.erl b/src/rabbit_exchange.erl
index 61a24388f2..4c0f341ffc 100644
--- a/src/rabbit_exchange.erl
+++ b/src/rabbit_exchange.erl
@@ -228,7 +228,7 @@ info_all(VHostPath, Items) -> map(VHostPath, fun (X) -> info(X, Items) end).
 
 publish(X = #exchange{name = XName}, Delivery) ->
     rabbit_router:deliver(
-      route(Delivery, {queue:from_list([X]), sets:from_list([XName]), []}),
+      route(Delivery, {queue:from_list([X]), XName, []}),
       Delivery).
 
 route(Delivery, {WorkList, SeenXs, QNames}) ->
@@ -252,13 +252,22 @@ process_alternate(_X, Results) ->
     Results.
 
 process_route(#resource{kind = exchange} = XName,
+              {_WorkList, XName, _QNames} = Acc) ->
+    Acc;
+process_route(#resource{kind = exchange} = XName,
+              {WorkList, #resource{kind = exchange} = SeenX, QNames}) ->
+    {case lookup(XName) of
+         {ok, X}            -> queue:in(X, WorkList);
+         {error, not_found} -> WorkList
+     end, gb_sets:from_list([SeenX, XName]), QNames};
+process_route(#resource{kind = exchange} = XName,
               {WorkList, SeenXs, QNames} = Acc) ->
-    case sets:is_element(XName, SeenXs) of
+    case gb_sets:is_element(XName, SeenXs) of
         true  -> Acc;
         false -> {case lookup(XName) of
                       {ok, X}            -> queue:in(X, WorkList);
                       {error, not_found} -> WorkList
-                  end, sets:add_element(XName, SeenXs), QNames}
+                  end, gb_sets:add_element(XName, SeenXs), QNames}
     end;
 process_route(#resource{kind = queue} = QName,
               {WorkList, SeenXs, QNames}) ->