Merged bug24889 into default

22 files changed, 558 insertions, 62 deletions

diff --git a/docs/rabbitmqctl.1.xml b/docs/rabbitmqctl.1.xml
index ded3ab48..1effd691 100644
--- a/docs/rabbitmqctl.1.xml
+++ b/docs/rabbitmqctl.1.xml
@@ -745,6 +745,99 @@
     </refsect2>
 
     <refsect2>
+      <title>Parameter Management</title>
+      <para>
+        Certain features of RabbitMQ (such as the federation plugin)
+        are controlled by dynamic,
+        cluster-wide <emphasis>parameters</emphasis>. Each parameter
+        consists of a component name, a key and a value. The
+        component name and key are strings, and the value is an
+        Erlang term. Parameters can be set, cleared and listed. In
+        general you should refer to the documentation for the feature
+        in question to see how to set parameters.
+      </para>
+      <variablelist>
+        <varlistentry>
+          <term><cmdsynopsis><command>set_parameter</command> <arg choice="req"><replaceable>component_name</replaceable></arg> <arg choice="req"><replaceable>key</replaceable></arg> <arg choice="req"><replaceable>value</replaceable></arg></cmdsynopsis></term>
+          <listitem>
+            <para>
+              Sets a parameter.
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term>component_name</term>
+                <listitem><para>
+                    The name of the component for which the
+                    parameter is being set.
+                </para></listitem>
+              </varlistentry>
+              <varlistentry>
+                <term>key</term>
+                <listitem><para>
+                    The key for which the parameter is being set.
+                </para></listitem>
+              </varlistentry>
+              <varlistentry>
+                <term>value</term>
+                <listitem><para>
+                    The value for the parameter, as an
+                    Erlang term. In most shells you are very likely to
+                    need to quote this.
+                </para></listitem>
+              </varlistentry>
+            </variablelist>
+            <para role="example-prefix">For example:</para>
+            <screen role="example">rabbitmqctl set_parameter federation local_username '&lt;&lt;"guest">>'</screen>
+            <para role="example">
+              This command sets the parameter <command>local_username</command> for the <command>federation</command> component to the Erlang term <command>&lt;&lt;"guest">></command>.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><cmdsynopsis><command>clear_parameter</command> <arg choice="req"><replaceable>component_name</replaceable></arg> <arg choice="req"><replaceable>key</replaceable></arg></cmdsynopsis></term>
+          <listitem>
+            <para>
+              Clears a parameter.
+            </para>
+            <variablelist>
+              <varlistentry>
+                <term>component_name</term>
+                <listitem><para>
+                    The name of the component for which the
+                    parameter is being cleared.
+                </para></listitem>
+              </varlistentry>
+              <varlistentry>
+                <term>key</term>
+                <listitem><para>
+                    The key for which the parameter is being cleared.
+                </para></listitem>
+              </varlistentry>
+            </variablelist>
+            <para role="example-prefix">For example:</para>
+            <screen role="example">rabbitmqctl clear_parameter federation local_username</screen>
+            <para role="example">
+              This command clears the parameter <command>local_username</command> for the <command>federation</command> component.
+            </para>
+          </listitem>
+        </varlistentry>
+        <varlistentry>
+          <term><cmdsynopsis><command>list_parameters</command></cmdsynopsis></term>
+          <listitem>
+            <para>
+              Lists all parameters.
+            </para>
+            <para role="example-prefix">For example:</para>
+            <screen role="example">rabbitmqctl list_parameters</screen>
+            <para role="example">
+              This command lists all parameters.
+            </para>
+          </listitem>
+        </varlistentry>
+      </variablelist>
+    </refsect2>
+
+    <refsect2>
       <title>Server Status</title>
       <para>
         The server status queries interrogate the server and return a list of
diff --git a/include/rabbit.hrl b/include/rabbit.hrl
index faf3059a..5c73c8b8 100644
--- a/include/rabbit.hrl
+++ b/include/rabbit.hrl
@@ -66,6 +66,8 @@
 
 -record(listener, {node, protocol, host, ip_address, port}).
 
+-record(runtime_parameters, {key, value}).
+
 -record(basic_message, {exchange_name, routing_keys = [], content, id,
                         is_persistent}).
 
diff --git a/src/mirrored_supervisor.erl b/src/mirrored_supervisor.erl
index 221f6a87..4fe93981 100644
--- a/src/mirrored_supervisor.erl
+++ b/src/mirrored_supervisor.erl
@@ -261,24 +261,19 @@ start_internal(Group, ChildSpecs) ->
 
 %%----------------------------------------------------------------------------
 
-init({overall, Group, Init}) ->
-    case Init of
-        {ok, {Restart, ChildSpecs}} ->
-            Delegate = {delegate, {?SUPERVISOR, start_link,
-                                   [?MODULE, {delegate, Restart}]},
-                        temporary, 16#ffffffff, supervisor, [?SUPERVISOR]},
-            Mirroring = {mirroring, {?MODULE, start_internal,
-                                     [Group, ChildSpecs]},
-                         permanent, 16#ffffffff, worker, [?MODULE]},
-            %% Important: Delegate MUST start before Mirroring so that
-            %% when we shut down from above it shuts down last, so
-            %% Mirroring does not see it die.
-            %%
-            %% See comment in handle_info('DOWN', ...) below
-            {ok, {{one_for_all, 0, 1}, [Delegate, Mirroring]}};
-        ignore ->
-            ignore
-    end;
+init({overall, _Group, ignore}) -> ignore;
+init({overall,  Group, {ok, {Restart, ChildSpecs}}}) ->
+    %% Important: Delegate MUST start before Mirroring so that when we
+    %% shut down from above it shuts down last, so Mirroring does not
+    %% see it die.
+    %%
+    %% See comment in handle_info('DOWN', ...) below
+    {ok, {{one_for_all, 0, 1},
+          [{delegate, {?SUPERVISOR, start_link, [?MODULE, {delegate, Restart}]},
+            temporary, 16#ffffffff, supervisor, [?SUPERVISOR]},
+           {mirroring, {?MODULE, start_internal, [Group, ChildSpecs]},
+            permanent, 16#ffffffff, worker, [?MODULE]}]}};
+
 
 init({delegate, Restart}) ->
     {ok, {Restart, []}};
@@ -306,9 +301,9 @@ handle_call({init, Overall}, _From,
     Delegate = child(Overall, delegate),
     erlang:monitor(process, Delegate),
     State1 = State#state{overall = Overall, delegate = Delegate},
-    case all_started([maybe_start(Group, Delegate, S) || S <- ChildSpecs]) of
-        true  -> {reply, ok, State1};
-        false -> {stop, shutdown, State1}
+    case errors([maybe_start(Group, Delegate, S) || S <- ChildSpecs]) of
+        []     -> {reply, ok, State1};
+        Errors -> {stop, {shutdown, Errors}, State1}
     end;
 
 handle_call({start_child, ChildSpec}, _From,
@@ -372,9 +367,9 @@ handle_info({'DOWN', _Ref, process, Pid, _Reason},
                           [start(Delegate, ChildSpec) || ChildSpec <- ChildSpecs];
             _          -> []
         end,
-    case all_started(R) of
-        true  -> {noreply, State};
-        false -> {stop, shutdown, State}
+    case errors(R) of
+        []     -> {noreply, State};
+        Errors -> {stop, {shutdown, Errors}, State}
     end;
 
 handle_info(Info, State) ->
@@ -468,7 +463,7 @@ delete_all(Group) ->
     [delete(Group, id(C)) ||
         C <- mnesia:select(?TABLE, [{MatchHead, [], ['$1']}])].
 
-all_started(Results) -> [] =:= [R || R = {error, _} <- Results].
+errors(Results) -> [E || {error, E} <- Results].
 
 %%----------------------------------------------------------------------------
 
diff --git a/src/mirrored_supervisor_tests.erl b/src/mirrored_supervisor_tests.erl
index fe56b530..e8baabe8 100644
--- a/src/mirrored_supervisor_tests.erl
+++ b/src/mirrored_supervisor_tests.erl
@@ -268,7 +268,7 @@ inc_group() ->
 get_group(Group) ->
     {Group, get(counter)}.
 
-call(Id, Msg) -> call(Id, Msg, 10000, 100).
+call(Id, Msg) -> call(Id, Msg, 1000, 100).
 
 call(Id, Msg, 0, _Decr) ->
     exit({timeout_waiting_for_server, {Id, Msg}, erlang:get_stacktrace()});
diff --git a/src/rabbit.erl b/src/rabbit.erl
index b1f786a0..5e579165 100644
--- a/src/rabbit.erl
+++ b/src/rabbit.erl
@@ -621,15 +621,12 @@ log_location(Type) ->
 rotate_logs(File, Suffix, Handler) ->
     rotate_logs(File, Suffix, Handler, Handler).
 
-rotate_logs(File, Suffix, OldHandler, NewHandler) ->
-    case File of
-        undefined -> ok;
-        tty       -> ok;
-        _         -> gen_event:swap_handler(
-                       error_logger,
-                       {OldHandler, swap},
-                       {NewHandler, {File, Suffix}})
-    end.
+rotate_logs(undefined, _Suffix, _OldHandler, _NewHandler) -> ok;
+rotate_logs(tty,       _Suffix, _OldHandler, _NewHandler) -> ok;
+rotate_logs(File,       Suffix,  OldHandler,  NewHandler) ->
+    gen_event:swap_handler(error_logger,
+                           {OldHandler, swap},
+                           {NewHandler, {File, Suffix}}).
 
 log_rotation_result({error, MainLogError}, {error, SaslLogError}) ->
     {error, {{cannot_rotate_main_logs, MainLogError},
diff --git a/src/rabbit_backing_queue.erl b/src/rabbit_backing_queue.erl
index 28c57bb0..dc144a0e 100644
--- a/src/rabbit_backing_queue.erl
+++ b/src/rabbit_backing_queue.erl
@@ -26,10 +26,8 @@
         ('empty' |
          %% Message,                  IsDelivered, AckTag, Remaining_Len
          {rabbit_types:basic_message(), boolean(), Ack, non_neg_integer()})).
--type(is_durable() :: boolean()).
 -type(attempt_recovery() :: boolean()).
 -type(purged_msg_count() :: non_neg_integer()).
--type(confirm_required() :: boolean()).
 -type(async_callback() :: fun ((atom(), fun ((atom(), state()) -> state())) -> 'ok')).
 -type(duration() :: ('undefined' | 'infinity' | number())).
 
diff --git a/src/rabbit_basic.erl b/src/rabbit_basic.erl
index 17d848da..734456d3 100644
--- a/src/rabbit_basic.erl
+++ b/src/rabbit_basic.erl
@@ -224,6 +224,5 @@ header_routes(HeadersTable) ->
            {array, Routes} -> [Route || {longstr, Route} <- Routes];
            undefined       -> [];
            {Type, _Val}    -> throw({error, {unacceptable_type_in_header,
-                                             Type,
-                                             binary_to_list(HeaderKey)}})
+                                             binary_to_list(HeaderKey), Type}})
        end || HeaderKey <- ?ROUTING_HEADERS]).
diff --git a/src/rabbit_control.erl b/src/rabbit_control.erl
index 573ed6a3..2dea2a2f 100644
--- a/src/rabbit_control.erl
+++ b/src/rabbit_control.erl
@@ -356,6 +356,23 @@ action(list_permissions, Node, [], Opts, Inform) ->
                              list_vhost_permissions, [VHost]}),
                       rabbit_auth_backend_internal:vhost_perms_info_keys());
 
+action(set_parameter, Node, [Component, Key, Value], _Opts, Inform) ->
+    Inform("Setting runtime parameter ~p for component ~p to ~p",
+           [Key, Component, Value]),
+    rpc_call(Node, rabbit_runtime_parameters, parse_set,
+             [list_to_binary(Component), list_to_binary(Key), Value]);
+
+action(clear_parameter, Node, [Component, Key], _Opts, Inform) ->
+    Inform("Clearing runtime parameter ~p for component ~p", [Key, Component]),
+    rpc_call(Node, rabbit_runtime_parameters, clear, [list_to_binary(Component),
+                                                      list_to_binary(Key)]);
+
+action(list_parameters, Node, Args = [], _Opts, Inform) ->
+    Inform("Listing runtime parameters", []),
+    display_info_list(
+      rpc_call(Node, rabbit_runtime_parameters, list_formatted, Args),
+      rabbit_runtime_parameters:info_keys());
+
 action(report, Node, _Args, _Opts, Inform) ->
     io:format("Reporting server status on ~p~n~n", [erlang:universaltime()]),
     [begin ok = action(Action, N, [], [], Inform), io:nl() end ||
diff --git a/src/rabbit_event.erl b/src/rabbit_event.erl
index 4ec141cf..3f1b20fe 100644
--- a/src/rabbit_event.erl
+++ b/src/rabbit_event.erl
@@ -139,6 +139,6 @@ notify_if(false, _Type, _Props) -> ok.
 notify(Type, Props) ->
     %% TODO: switch to os:timestamp() when we drop support for
     %% Erlang/OTP < R13B01
-    gen_event:notify(rabbit_event, #event{type = Type,
-                                          props = Props,
-                                          timestamp = now()}).
+    gen_event:notify(?MODULE, #event{type      = Type,
+                                     props     = Props,
+                                     timestamp = now()}).
diff --git a/src/rabbit_limiter.erl b/src/rabbit_limiter.erl
index 9fa6213b..2b15498e 100644
--- a/src/rabbit_limiter.erl
+++ b/src/rabbit_limiter.erl
@@ -192,7 +192,7 @@ terminate(_, _) ->
     ok.
 
 code_change(_, State, _) ->
-    State.
+    {ok, State}.
 
 %%----------------------------------------------------------------------------
 %% Internal plumbing
diff --git a/src/rabbit_misc.erl b/src/rabbit_misc.erl
index 0aacd654..706de835 100644
--- a/src/rabbit_misc.erl
+++ b/src/rabbit_misc.erl
@@ -40,7 +40,8 @@
 -export([upmap/2, map_in_order/2]).
 -export([table_filter/3]).
 -export([dirty_read_all/1, dirty_foreach_key/2, dirty_dump_log/1]).
--export([format/2, format_stderr/2, with_local_io/1, local_info_msg/2]).
+-export([format/2, format_many/1, format_stderr/2]).
+-export([with_local_io/1, local_info_msg/2]).
 -export([start_applications/1, stop_applications/1]).
 -export([unfold/2, ceil/1, queue_fold/3]).
 -export([sort_field_table/1]).
@@ -54,7 +55,7 @@
 -export([const_ok/0, const/1]).
 -export([ntoa/1, ntoab/1]).
 -export([is_process_alive/1]).
--export([pget/2, pget/3, pget_or_die/2]).
+-export([pget/2, pget/3, pget_or_die/2, pset/3]).
 -export([format_message_queue/2]).
 -export([append_rpc_all_nodes/4]).
 -export([multi_call/2]).
@@ -158,6 +159,7 @@
                              -> 'ok' | 'aborted').
 -spec(dirty_dump_log/1 :: (file:filename()) -> ok_or_error()).
 -spec(format/2 :: (string(), [any()]) -> string()).
+-spec(format_many/1 :: ([{string(), [any()]}]) -> string()).
 -spec(format_stderr/2 :: (string(), [any()]) -> 'ok').
 -spec(with_local_io/1 :: (fun (() -> A)) -> A).
 -spec(local_info_msg/2 :: (string(), [any()]) -> 'ok').
@@ -199,6 +201,7 @@
 -spec(pget/2 :: (term(), [term()]) -> term()).
 -spec(pget/3 :: (term(), [term()], term()) -> term()).
 -spec(pget_or_die/2 :: (term(), [term()]) -> term() | no_return()).
+-spec(pset/3 :: (term(), term(), [term()]) -> term()).
 -spec(format_message_queue/2 :: (any(), priority_queue:q()) -> term()).
 -spec(append_rpc_all_nodes/4 :: ([node()], atom(), atom(), [any()]) -> [any()]).
 -spec(multi_call/2 ::
@@ -551,6 +554,9 @@ dirty_dump_log1(LH, {K, Terms, BadBytes}) ->
 
 format(Fmt, Args) -> lists:flatten(io_lib:format(Fmt, Args)).
 
+format_many(List) ->
+    lists:flatten([io_lib:format(F ++ "~n", A) || {F, A} <- List]).
+
 format_stderr(Fmt, Args) ->
     case os:type() of
         {unix, _} ->
@@ -848,6 +854,8 @@ pget_or_die(K, P) ->
         V         -> V
     end.
 
+pset(Key, Value, List) -> [{Key, Value} | proplists:delete(Key, List)].
+
 format_message_queue(_Opt, MQ) ->
     Len = priority_queue:len(MQ),
     {Len,
diff --git a/src/rabbit_mnesia.erl b/src/rabbit_mnesia.erl
index c714d3a7..7e9346f9 100644
--- a/src/rabbit_mnesia.erl
+++ b/src/rabbit_mnesia.erl
@@ -296,6 +296,11 @@ table_definitions() ->
       [{record_name, exchange_serial},
        {attributes, record_info(fields, exchange_serial)},
        {match, #exchange_serial{name = exchange_name_match(), _='_'}}]},
+     {rabbit_runtime_parameters,
+      [{record_name, runtime_parameters},
+       {attributes, record_info(fields, runtime_parameters)},
+       {disc_copies, [node()]},
+       {match, #runtime_parameters{_='_'}}]},
      {rabbit_durable_queue,
       [{record_name, amqqueue},
        {attributes, record_info(fields, amqqueue)},
diff --git a/src/rabbit_nodes.erl b/src/rabbit_nodes.erl
index b6a9e263..1c23632d 100644
--- a/src/rabbit_nodes.erl
+++ b/src/rabbit_nodes.erl
@@ -57,8 +57,7 @@ diagnostics(Nodes) ->
                   "hosts, their running nodes and ports:", [Nodes]}] ++
         [diagnostics_host(Host) || Host <- Hosts] ++
         diagnostics0(),
-    lists:flatten([io_lib:format(F ++ "~n", A) || NodeDiag <- NodeDiags,
-                                                  {F, A}   <- [NodeDiag]]).
+    rabbit_misc:format_many(lists:flatten(NodeDiags)).
 
 diagnostics0() ->
     [{"~ncurrent node details:~n- node name: ~w", [node()]},
diff --git a/src/rabbit_plugins.erl b/src/rabbit_plugins.erl
index 2a93c8f2..00880fb2 100644
--- a/src/rabbit_plugins.erl
+++ b/src/rabbit_plugins.erl
@@ -245,7 +245,7 @@ format_plugins(Pattern, Opts, PluginsFile, PluginsDir) ->
                  {true,  true}  -> throw({error_string,
                                           "Cannot specify -m and -v together"})
              end,
-    OnlyEnabled = proplists:get_bool(?ENABLED_OPT, Opts),
+    OnlyEnabled    = proplists:get_bool(?ENABLED_OPT,     Opts),
     OnlyEnabledAll = proplists:get_bool(?ENABLED_ALL_OPT, Opts),
 
     AvailablePlugins = find_plugins(PluginsDir),
@@ -257,14 +257,10 @@ format_plugins(Pattern, Opts, PluginsFile, PluginsDir) ->
     Plugins = [ Plugin ||
                   Plugin = #plugin{name = Name} <- AvailablePlugins,
                   re:run(atom_to_list(Name), RE, [{capture, none}]) =:= match,
-                  if OnlyEnabled -> lists:member(Name, EnabledExplicitly);
-                     true        -> true
-                  end,
-                  if OnlyEnabledAll ->
-                          lists:member(Name, EnabledImplicitly) or
-                              lists:member(Name, EnabledExplicitly);
-                     true ->
-                          true
+                  if OnlyEnabled    ->  lists:member(Name, EnabledExplicitly);
+                     OnlyEnabledAll -> (lists:member(Name, EnabledExplicitly) or
+                                        lists:member(Name, EnabledImplicitly));
+                     true           -> true
                   end],
     Plugins1 = usort_plugins(Plugins),
     MaxWidth = lists:max([length(atom_to_list(Name)) ||
@@ -338,8 +334,8 @@ read_enabled_plugins(PluginsFile) ->
     case rabbit_file:read_term_file(PluginsFile) of
         {ok, [Plugins]} -> Plugins;
         {ok, []}        -> [];
-        {ok, [_|_]}      -> throw({error, {malformed_enabled_plugins_file,
-                                           PluginsFile}});
+        {ok, [_|_]}     -> throw({error, {malformed_enabled_plugins_file,
+                                          PluginsFile}});
         {error, enoent} -> [];
         {error, Reason} -> throw({error, {cannot_read_enabled_plugins_file,
                                           PluginsFile, Reason}})
diff --git a/src/rabbit_registry.erl b/src/rabbit_registry.erl
index 8c0ebcbe..637835c3 100644
--- a/src/rabbit_registry.erl
+++ b/src/rabbit_registry.erl
@@ -23,7 +23,8 @@
 -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2,
          code_change/3]).
 
--export([register/3, binary_to_type/1, lookup_module/2, lookup_all/1]).
+-export([register/3, unregister/2,
+         binary_to_type/1, lookup_module/2, lookup_all/1]).
 
 -define(SERVER, ?MODULE).
 -define(ETS_NAME, ?MODULE).
@@ -32,6 +33,7 @@
 
 -spec(start_link/0 :: () -> rabbit_types:ok_pid_or_error()).
 -spec(register/3 :: (atom(), binary(), atom()) -> 'ok').
+-spec(unregister/2 :: (atom(), binary()) -> 'ok').
 -spec(binary_to_type/1 ::
         (binary()) -> atom() | rabbit_types:error('not_found')).
 -spec(lookup_module/2 ::
@@ -50,6 +52,9 @@ start_link() ->
 register(Class, TypeName, ModuleName) ->
     gen_server:call(?SERVER, {register, Class, TypeName, ModuleName}, infinity).
 
+unregister(Class, TypeName) ->
+    gen_server:call(?SERVER, {unregister, Class, TypeName}, infinity).
+
 %% This is used with user-supplied arguments (e.g., on exchange
 %% declare), so we restrict it to existing atoms only.  This means it
 %% can throw a badarg, indicating that the type cannot have been
@@ -83,6 +88,10 @@ internal_register(Class, TypeName, ModuleName)
                       {{Class, internal_binary_to_type(TypeName)}, ModuleName}),
     ok.
 
+internal_unregister(Class, TypeName) ->
+    true = ets:delete(?ETS_NAME, {Class, internal_binary_to_type(TypeName)}),
+    ok.
+
 sanity_check_module(ClassModule, Module) ->
     case catch lists:member(ClassModule,
                             lists:flatten(
@@ -95,8 +104,9 @@ sanity_check_module(ClassModule, Module) ->
         true                  -> ok
     end.
 
-class_module(exchange)       -> rabbit_exchange_type;
-class_module(auth_mechanism) -> rabbit_auth_mechanism.
+class_module(exchange)          -> rabbit_exchange_type;
+class_module(auth_mechanism)    -> rabbit_auth_mechanism;
+class_module(runtime_parameter) -> rabbit_runtime_parameter.
 
 %%---------------------------------------------------------------------------
 
@@ -108,6 +118,10 @@ handle_call({register, Class, TypeName, ModuleName}, _From, State) ->
     ok = internal_register(Class, TypeName, ModuleName),
     {reply, ok, State};
 
+handle_call({unregister, Class, TypeName}, _From, State) ->
+    ok = internal_unregister(Class, TypeName),
+    {reply, ok, State};
+
 handle_call(Request, _From, State) ->
     {stop, {unhandled_call, Request}, State}.
 
diff --git a/src/rabbit_runtime_parameter.erl b/src/rabbit_runtime_parameter.erl
new file mode 100644
index 00000000..c7d30116
--- /dev/null
+++ b/src/rabbit_runtime_parameter.erl
@@ -0,0 +1,43 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at http://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%% Copyright (c) 2007-2012 VMware, Inc.  All rights reserved.
+%%
+
+-module(rabbit_runtime_parameter).
+
+-ifdef(use_specs).
+
+-type(validate_results() ::
+        'ok' | {error, string(), [term()]} | [validate_results()]).
+
+-callback validate(binary(), binary(), term()) -> validate_results().
+-callback validate_clear(binary(), binary()) -> validate_results().
+-callback notify(binary(), binary(), term()) -> 'ok'.
+-callback notify_clear(binary(), binary()) -> 'ok'.
+
+-else.
+
+-export([behaviour_info/1]).
+
+behaviour_info(callbacks) ->
+    [
+     {validate, 3},
+     {validate_clear, 2},
+     {notify, 3},
+     {notify_clear, 2}
+    ];
+behaviour_info(_Other) ->
+    undefined.
+
+-endif.
diff --git a/src/rabbit_runtime_parameters.erl b/src/rabbit_runtime_parameters.erl
new file mode 100644
index 00000000..172cee92
--- /dev/null
+++ b/src/rabbit_runtime_parameters.erl
@@ -0,0 +1,239 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at http://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%% Copyright (c) 2007-2012 VMware, Inc.  All rights reserved.
+%%
+
+-module(rabbit_runtime_parameters).
+
+-include("rabbit.hrl").
+
+-export([parse_set/3, set/3, clear/2, list/0, list/1, list_formatted/0,
+         lookup/2, value/2, value/3, info_keys/0]).
+
+%%----------------------------------------------------------------------------
+
+-ifdef(use_specs).
+
+-type(ok_or_error_string() :: 'ok' | {'error_string', string()}).
+
+-spec(parse_set/3 :: (binary(), binary(), string()) -> ok_or_error_string()).
+-spec(set/3 :: (binary(), binary(), term()) -> ok_or_error_string()).
+-spec(clear/2 :: (binary(), binary()) -> ok_or_error_string()).
+-spec(list/0 :: () -> [rabbit_types:infos()]).
+-spec(list/1 :: (binary()) -> [rabbit_types:infos()] | 'not_found').
+-spec(list_formatted/0 :: () -> [rabbit_types:infos()]).
+-spec(lookup/2 :: (binary(), binary()) -> rabbit_types:infos()).
+-spec(value/2 :: (binary(), binary()) -> term()).
+-spec(value/3 :: (binary(), binary(), term()) -> term()).
+-spec(info_keys/0 :: () -> rabbit_types:info_keys()).
+
+-endif.
+
+%%---------------------------------------------------------------------------
+
+-import(rabbit_misc, [pget/2, pset/3]).
+
+-define(TABLE, rabbit_runtime_parameters).
+
+%%---------------------------------------------------------------------------
+
+parse_set(Component, Key, String) ->
+    case parse(String) of
+        {ok, Term}  -> set(Component, Key, Term);
+        {errors, L} -> format_error(L)
+    end.
+
+set(Component, Key, Term) ->
+    case set0(Component, Key, Term) of
+        ok          -> ok;
+        {errors, L} -> format_error(L)
+    end.
+
+format_error(L) ->
+    {error_string, rabbit_misc:format_many([{"Validation failed~n", []} | L])}.
+
+set0(Component, Key, Term) ->
+    case lookup_component(Component) of
+        {ok, Mod} ->
+            case flatten_errors(validate(Term)) of
+                ok ->
+                    case flatten_errors(Mod:validate(Component, Key, Term)) of
+                        ok ->
+                            case mnesia_update(Component, Key, Term) of
+                                {old, Term} -> ok;
+                                _           -> Mod:notify(Component, Key, Term)
+                            end,
+                            ok;
+                        E ->
+                            E
+                    end;
+                E ->
+                    E
+            end;
+        E ->
+            E
+    end.
+
+mnesia_update(Component, Key, Term) ->
+    rabbit_misc:execute_mnesia_transaction(
+      fun () ->
+              Res = case mnesia:read(?TABLE, {Component, Key}, read) of
+                        []       -> new;
+                        [Params] -> {old, Params#runtime_parameters.value}
+                    end,
+              ok = mnesia:write(?TABLE, c(Component, Key, Term), write),
+              Res
+      end).
+
+clear(Component, Key) ->
+    case clear0(Component, Key) of
+        ok          -> ok;
+        {errors, L} -> format_error(L)
+    end.
+
+clear0(Component, Key) ->
+    case lookup_component(Component) of
+        {ok, Mod} -> case flatten_errors(Mod:validate_clear(Component, Key)) of
+                         ok -> mnesia_clear(Component, Key),
+                               Mod:notify_clear(Component, Key),
+                               ok;
+                         E  -> E
+                     end;
+        E         -> E
+    end.
+
+mnesia_clear(Component, Key) ->
+    ok = rabbit_misc:execute_mnesia_transaction(
+           fun () ->
+                   ok = mnesia:delete(?TABLE, {Component, Key}, write)
+           end).
+
+list() ->
+    [p(P) || P <- rabbit_misc:dirty_read_all(?TABLE)].
+
+list(Component) ->
+    case lookup_component(Component) of
+        {ok, _} -> Match = #runtime_parameters{key = {Component, '_'}, _ = '_'},
+                   [p(P) || P <- mnesia:dirty_match_object(?TABLE, Match)];
+        _       -> not_found
+    end.
+
+list_formatted() ->
+    [pset(value, format(pget(value, P)), P) || P <- list()].
+
+lookup(Component, Key) ->
+    case lookup0(Component, Key, rabbit_misc:const(not_found)) of
+        not_found -> not_found;
+        Params    -> p(Params)
+    end.
+
+value(Component, Key) ->
+    case lookup0(Component, Key, rabbit_misc:const(not_found)) of
+        not_found -> not_found;
+        Params    -> Params#runtime_parameters.value
+    end.
+
+value(Component, Key, Default) ->
+    Params = lookup0(Component, Key,
+                     fun () -> lookup_missing(Component, Key, Default) end),
+    Params#runtime_parameters.value.
+
+lookup0(Component, Key, DefaultFun) ->
+    case mnesia:dirty_read(?TABLE, {Component, Key}) of
+        []  -> DefaultFun();
+        [R] -> R
+    end.
+
+lookup_missing(Component, Key, Default) ->
+    rabbit_misc:execute_mnesia_transaction(
+      fun () ->
+              case mnesia:read(?TABLE, {Component, Key}, read) of
+                  []  -> Record = c(Component, Key, Default),
+                         mnesia:write(?TABLE, Record, write),
+                         Record;
+                  [R] -> R
+              end
+      end).
+
+c(Component, Key, Default) -> #runtime_parameters{key = {Component, Key},
+                                                  value = Default}.
+
+p(#runtime_parameters{key = {Component, Key}, value = Value}) ->
+    [{component, Component},
+     {key,       Key},
+     {value,     Value}].
+
+info_keys() -> [component, key, value].
+
+%%---------------------------------------------------------------------------
+
+lookup_component(Component) ->
+    case rabbit_registry:lookup_module(
+           runtime_parameter, list_to_atom(binary_to_list(Component))) of
+        {error, not_found} -> {errors,
+                               [{"component ~s not found", [Component]}]};
+        {ok, Module}       -> {ok, Module}
+    end.
+
+parse(Src0) ->
+    Src1 = string:strip(Src0),
+    Src = case lists:reverse(Src1) of
+              [$. |_] -> Src1;
+              _       -> Src1 ++ "."
+          end,
+    case erl_scan:string(Src) of
+        {ok, Scanned, _} ->
+            case erl_parse:parse_term(Scanned) of
+                {ok, Parsed} ->
+                    {ok, Parsed};
+                {error, E} ->
+                    {errors,
+                     [{"Could not parse value: ~s", [format_parse_error(E)]}]}
+            end;
+        {error, E, _} ->
+            {errors, [{"Could not scan value: ~s", [format_parse_error(E)]}]}
+    end.
+
+format_parse_error({_Line, Mod, Err}) ->
+    lists:flatten(Mod:format_error(Err)).
+
+format(Term) ->
+    list_to_binary(rabbit_misc:format("~p", [Term])).
+
+%%---------------------------------------------------------------------------
+
+%% We will want to be able to biject these to JSON. So we have some
+%% generic restrictions on what we consider acceptable.
+validate(Proplist = [T | _]) when is_tuple(T) -> validate_proplist(Proplist);
+validate(L) when is_list(L)                   -> validate_list(L);
+validate(T) when is_tuple(T)                  -> {error, "tuple: ~p", [T]};
+validate(B) when is_boolean(B)                -> ok;
+validate(null)                                -> ok;
+validate(A) when is_atom(A)                   -> {error, "atom: ~p", [A]};
+validate(N) when is_number(N)                 -> ok;
+validate(B) when is_binary(B)                 -> ok;
+validate(B) when is_bitstring(B)              -> {error, "bitstring: ~p", [B]}.
+
+validate_list(L) -> [validate(I) || I <- L].
+validate_proplist(L) -> [vp(I) || I <- L].
+
+vp({K, V}) when is_binary(K) -> validate(V);
+vp({K, _V})                  -> {error, "bad key: ~p", [K]};
+vp(H)                        -> {error, "not two tuple: ~p", [H]}.
+
+flatten_errors(L) ->
+    case [{F, A} || I <- lists:flatten([L]), {error, F, A} <- [I]] of
+        [] -> ok;
+        E  -> {errors, E}
+    end.
diff --git a/src/rabbit_runtime_parameters_test.erl b/src/rabbit_runtime_parameters_test.erl
new file mode 100644
index 00000000..f23b3227
--- /dev/null
+++ b/src/rabbit_runtime_parameters_test.erl
@@ -0,0 +1,38 @@
+%% The contents of this file are subject to the Mozilla Public License
+%% Version 1.1 (the "License"); you may not use this file except in
+%% compliance with the License. You may obtain a copy of the License
+%% at http://www.mozilla.org/MPL/
+%%
+%% Software distributed under the License is distributed on an "AS IS"
+%% basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See
+%% the License for the specific language governing rights and
+%% limitations under the License.
+%%
+%% The Original Code is RabbitMQ.
+%%
+%% The Initial Developer of the Original Code is VMware, Inc.
+%% Copyright (c) 2007-2012 VMware, Inc.  All rights reserved.
+%%
+
+-module(rabbit_runtime_parameters_test).
+-behaviour(rabbit_runtime_parameter).
+
+-export([validate/3, validate_clear/2, notify/3, notify_clear/2]).
+-export([register/0, unregister/0]).
+
+register() ->
+    rabbit_registry:register(runtime_parameter, <<"test">>, ?MODULE).
+
+unregister() ->
+    rabbit_registry:unregister(runtime_parameter, <<"test">>).
+
+validate(<<"test">>, <<"good">>,  _Term)      -> ok;
+validate(<<"test">>, <<"maybe">>, <<"good">>) -> ok;
+validate(<<"test">>, _, _)                    -> {error, "meh", []}.
+
+validate_clear(<<"test">>, <<"good">>)  -> ok;
+validate_clear(<<"test">>, <<"maybe">>) -> ok;
+validate_clear(<<"test">>, _)           -> {error, "meh", []}.
+
+notify(_, _, _) -> ok.
+notify_clear(_, _) -> ok.
diff --git a/src/rabbit_tests.erl b/src/rabbit_tests.erl
index 04ee6ef2..96b5fa38 100644
--- a/src/rabbit_tests.erl
+++ b/src/rabbit_tests.erl
@@ -53,6 +53,7 @@ all_tests() ->
     passed = test_option_parser(),
     passed = test_cluster_management(),
     passed = test_user_management(),
+    passed = test_runtime_parameters(),
     passed = test_server_status(),
     passed = test_confirms(),
     passed = maybe_run_cluster_dependent_tests(),
@@ -1097,6 +1098,38 @@ test_user_management() ->
 
     passed.
 
+test_runtime_parameters() ->
+    rabbit_runtime_parameters_test:register(),
+    Good = fun(L) -> ok                = control_action(set_parameter, L) end,
+    Bad  = fun(L) -> {error_string, _} = control_action(set_parameter, L) end,
+
+    %% Acceptable for bijection
+    Good(["test", "good", "<<\"ignore\">>"]),
+    Good(["test", "good", "123"]),
+    Good(["test", "good", "true"]),
+    Good(["test", "good", "false"]),
+    Good(["test", "good", "null"]),
+    Good(["test", "good", "[{<<\"key\">>, <<\"value\">>}]"]),
+
+    %% Various forms of fail due to non-bijectability
+    Bad(["test", "good", "atom"]),
+    Bad(["test", "good", "{tuple, foo}"]),
+    Bad(["test", "good", "[{<<\"key\">>, <<\"value\">>, 1}]"]),
+    Bad(["test", "good", "[{key, <<\"value\">>}]"]),
+
+    %% Test actual validation hook
+    Good(["test", "maybe", "<<\"good\">>"]),
+    Bad(["test", "maybe", "<<\"bad\">>"]),
+
+    ok = control_action(list_parameters, []),
+
+    ok = control_action(clear_parameter, ["test", "good"]),
+    ok = control_action(clear_parameter, ["test", "maybe"]),
+    {error_string, _} =
+        control_action(clear_parameter, ["test", "neverexisted"]),
+    rabbit_runtime_parameters_test:unregister(),
+    passed.
+
 test_server_status() ->
     %% create a few things so there is some useful information to list
     Writer = spawn(fun () -> receive shutdown -> ok end end),
diff --git a/src/rabbit_upgrade_functions.erl b/src/rabbit_upgrade_functions.erl
index 9f2535bd..485ccc5f 100644
--- a/src/rabbit_upgrade_functions.erl
+++ b/src/rabbit_upgrade_functions.erl
@@ -36,6 +36,7 @@
 -rabbit_upgrade({exchange_scratch,      mnesia, [trace_exchanges]}).
 -rabbit_upgrade({mirrored_supervisor,   mnesia, []}).
 -rabbit_upgrade({topic_trie_node,       mnesia, []}).
+-rabbit_upgrade({runtime_parameters,    mnesia, []}).
 
 %% -------------------------------------------------------------------
 
@@ -56,6 +57,7 @@
 -spec(exchange_scratch/0      :: () -> 'ok').
 -spec(mirrored_supervisor/0   :: () -> 'ok').
 -spec(topic_trie_node/0       :: () -> 'ok').
+-spec(runtime_parameters/0    :: () -> 'ok').
 
 -endif.
 
@@ -185,6 +187,12 @@ topic_trie_node() ->
             {attributes, [trie_node, edge_count, binding_count]},
             {type, ordered_set}]).
 
+runtime_parameters() ->
+    create(rabbit_runtime_parameters,
+           [{record_name, runtime_parameters},
+            {attributes, [key, value]},
+            {disc_copies, [node()]}]).
+
 %%--------------------------------------------------------------------
 
 transform(TableName, Fun, FieldList) ->
diff --git a/src/rabbit_variable_queue.erl b/src/rabbit_variable_queue.erl
index 209e5252..dafb3f2e 100644
--- a/src/rabbit_variable_queue.erl
+++ b/src/rabbit_variable_queue.erl
@@ -323,7 +323,6 @@
 
 -type(timestamp() :: {non_neg_integer(), non_neg_integer(), non_neg_integer()}).
 -type(seq_id()  :: non_neg_integer()).
--type(ack()     :: seq_id()).
 
 -type(rates() :: #rates { egress      :: {timestamp(), non_neg_integer()},
                           ingress     :: {timestamp(), non_neg_integer()},
@@ -335,6 +334,13 @@
                           count        :: non_neg_integer(),
                           end_seq_id   :: non_neg_integer() }).
 
+%% The compiler (rightfully) complains that ack() and state() are
+%% unused. For this reason we duplicate a -spec from
+%% rabbit_backing_queue with the only intent being to remove
+%% warnings. The problem here is that we can't parameterise the BQ
+%% behaviour by these two types as we would like to. We still leave
+%% these here for documentation purposes.
+-type(ack() :: seq_id()).
 -type(state() :: #vqstate {
              q1                    :: ?QUEUE:?QUEUE(),
              q2                    :: ?QUEUE:?QUEUE(),
@@ -368,6 +374,8 @@
              ack_out_counter       :: non_neg_integer(),
              ack_in_counter        :: non_neg_integer(),
              ack_rates             :: rates() }).
+%% Duplicated from rabbit_backing_queue
+-spec(ack/2 :: ([ack()], state()) -> {[rabbit_guid:guid()], state()}).
 
 -spec(multiple_routing_keys/0 :: () -> 'ok').
 
diff --git a/src/supervisor2.erl b/src/supervisor2.erl
index f1b74878..3d3623d7 100644
--- a/src/supervisor2.erl
+++ b/src/supervisor2.erl
@@ -411,6 +411,8 @@ handle_call({start_child, EArgs}, _From, State) when ?is_simple(State) ->
     #child{mfa = {M, F, A}} = hd(State#state.children),
     Args = A ++ EArgs,
     case do_start_child_i(M, F, Args) of
+        {ok, undefined} ->
+            {reply, {ok, undefined}, State};
 	{ok, Pid} ->
 	    NState = State#state{dynamics = 
 				 ?DICT:store(Pid, Args, State#state.dynamics)},
@@ -743,6 +745,8 @@ restart(Strategy, Child, State, Restart)
     #child{mfa = {M, F, A}} = Child,
     Dynamics = ?DICT:erase(Child#child.pid, State#state.dynamics),
     case do_start_child_i(M, F, A) of
+        {ok, undefined} ->
+            {ok, State};
 	{ok, Pid} ->
 	    NState = State#state{dynamics = ?DICT:store(Pid, A, Dynamics)},
 	    {ok, NState};