Merge pull request #2106 from rabbitmq/rebalance-all-queues

Rebalance all queues

3 files changed, 184 insertions, 0 deletions

diff --git a/src/rabbit_amqqueue.erl b/src/rabbit_amqqueue.erl
index f740aa7c06..e4c262ad79 100644
--- a/src/rabbit_amqqueue.erl
+++ b/src/rabbit_amqqueue.erl
@@ -53,6 +53,8 @@
 -export([pid_of/1, pid_of/2]).
 -export([mark_local_durable_queues_stopped/1]).
 
+-export([rebalance/3]).
+
 %% internal
 -export([internal_declare/2, internal_delete/2, run_backing_queue/3,
          set_ram_duration_target/2, set_maximum_since_use/2,
@@ -484,6 +486,120 @@ not_found_or_absent_dirty(Name) ->
         {ok, Q}            -> {absent, Q, nodedown}
     end.
 
+-spec rebalance('all' | 'quorum' | 'classic', binary(), binary()) ->
+                       {ok, [{node(), pos_integer()}]}.
+rebalance(Type, VhostSpec, QueueSpec) ->
+    Running = rabbit_mnesia:cluster_nodes(running),
+    NumRunning = length(Running),
+    ToRebalance = [Q || Q <- rabbit_amqqueue:list(),
+                        filter_per_type(Type, Q),
+                        is_replicated(Q),
+                        is_match(amqqueue:get_vhost(Q), VhostSpec) andalso
+                            is_match(get_resource_name(amqqueue:get_name(Q)), QueueSpec)],
+    NumToRebalance = length(ToRebalance),
+    ByNode = group_by_node(ToRebalance),
+    Rem = case (NumToRebalance rem NumRunning) of
+              0 -> 0;
+              _ -> 1
+          end,
+    MaxQueuesDesired = (NumToRebalance div NumRunning) + Rem,
+    iterative_rebalance(ByNode, MaxQueuesDesired).
+
+filter_per_type(all, _) ->
+    true;
+filter_per_type(quorum, Q) ->
+    ?amqqueue_is_quorum(Q);
+filter_per_type(classic, Q) ->
+    ?amqqueue_is_classic(Q).
+
+rebalance_module(Q) when ?amqqueue_is_quorum(Q) ->
+    rabbit_quorum_queue;
+rebalance_module(Q) when ?amqqueue_is_classic(Q) ->
+    rabbit_mirror_queue_misc.
+
+get_resource_name(#resource{name  = Name}) ->
+    Name.
+
+is_match(Subj, E) ->
+   nomatch /= re:run(Subj, E).
+
+iterative_rebalance(ByNode, MaxQueuesDesired) ->
+    case maybe_migrate(ByNode, MaxQueuesDesired) of
+        {ok, Summary} ->
+            rabbit_log:warning("Nothing to do, all balanced"),
+            {ok, Summary};
+        {migrated, Other} ->
+            iterative_rebalance(Other, MaxQueuesDesired);
+        {not_migrated, Other} ->
+            iterative_rebalance(Other, MaxQueuesDesired)
+    end.
+
+maybe_migrate(ByNode, MaxQueuesDesired) ->
+    maybe_migrate(ByNode, MaxQueuesDesired, maps:keys(ByNode)).
+
+maybe_migrate(ByNode, _, []) ->
+    {ok, maps:fold(fun(K, V, Acc) ->
+                           [{K, length(V)} | Acc]
+                   end, [], ByNode)};
+maybe_migrate(ByNode, MaxQueuesDesired, [N | Nodes]) ->
+    case maps:get(N, ByNode, []) of
+        [{_, Q, false} = Queue | Queues] = All when length(All) > MaxQueuesDesired ->
+            Name = amqqueue:get_name(Q),
+            Module = rebalance_module(Q),
+            OtherNodes = Module:get_replicas(Q) -- [N],
+            case OtherNodes of
+                [] ->
+                    {not_migrated, update_not_migrated_queue(N, Queue, Queues, ByNode)};
+                _ ->
+                    [{Length, Destination} | _] = sort_by_number_of_queues(OtherNodes, ByNode),
+                    rabbit_log:warning("Migrating queue ~p from node ~p with ~p queues to node ~p with ~p queues",
+                                       [Name, N, length(All), Destination, Length]),
+                    case Module:transfer_leadership(Q, Destination) of
+                        {migrated, NewNode} ->
+                            rabbit_log:warning("Queue ~p migrated to ~p", [Name, NewNode]),
+                            {migrated, update_migrated_queue(Destination, N, Queue, Queues, ByNode)};
+                        {not_migrated, Reason} ->
+                            rabbit_log:warning("Error migrating queue ~p: ~p", [Name, Reason]),
+                            {not_migrated, update_not_migrated_queue(N, Queue, Queues, ByNode)}
+                    end
+            end;
+        [{_, _, true} | _] = All when length(All) > MaxQueuesDesired ->
+            rabbit_log:warning("Node ~p contains ~p queues, but all have already migrated. "
+                               "Do nothing", [N, length(All)]),
+            maybe_migrate(ByNode, MaxQueuesDesired, Nodes);
+        All ->
+            rabbit_log:warning("Node ~p only contains ~p queues, do nothing",
+                               [N, length(All)]),
+            maybe_migrate(ByNode, MaxQueuesDesired, Nodes)
+    end.
+
+update_not_migrated_queue(N, {Entries, Q, _}, Queues, ByNode) ->
+    maps:update(N, Queues ++ [{Entries, Q, true}], ByNode).
+
+update_migrated_queue(NewNode, OldNode, {Entries, Q, _}, Queues, ByNode) ->
+    maps:update_with(NewNode,
+                     fun(L) -> L ++ [{Entries, Q, true}] end,
+                     [{Entries, Q, true}], maps:update(OldNode, Queues, ByNode)).
+
+sort_by_number_of_queues(Nodes, ByNode) ->
+    lists:keysort(1,
+                  lists:map(fun(Node) ->
+                                    {num_queues(Node, ByNode), Node}
+                            end, Nodes)).
+
+num_queues(Node, ByNode) ->
+    length(maps:get(Node, ByNode, [])).
+
+group_by_node(Queues) ->
+    ByNode = lists:foldl(fun(Q, Acc) ->
+                                 Module = rebalance_module(Q),
+                                 Length = Module:queue_length(Q),
+                                 maps:update_with(amqqueue:qnode(Q),
+                                                   fun(L) -> [{Length, Q, false} | L] end,
+                                                  [{Length, Q, false}], Acc)
+                         end, #{}, Queues),
+    maps:map(fun(_K, V) -> lists:keysort(1, V) end, ByNode).
+
 -spec with(name(),
            qfun(A),
            fun((not_found_or_absent()) -> rabbit_types:channel_exit())) ->
diff --git a/src/rabbit_mirror_queue_misc.erl b/src/rabbit_mirror_queue_misc.erl
index f63f417b93..c1ae96b02f 100644
--- a/src/rabbit_mirror_queue_misc.erl
+++ b/src/rabbit_mirror_queue_misc.erl
@@ -28,6 +28,8 @@
 
 -export([sync_queue/1, cancel_sync_queue/1]).
 
+-export([transfer_leadership/2, queue_length/1, get_replicas/1]).
+
 %% for testing only
 -export([module/1]).
 
@@ -535,6 +537,46 @@ update_mirrors(Q) when ?is_amqqueue(Q) ->
     maybe_auto_sync(Q),
     ok.
 
+queue_length(Q) ->
+    [{messages, M}] = rabbit_amqqueue:info(Q, [messages]),
+    M.
+
+get_replicas(Q) ->
+    {MNode, SNodes} = suggested_queue_nodes(Q),
+    [MNode] ++ SNodes.
+
+transfer_leadership(Q, Destination) ->
+    QName = amqqueue:get_name(Q),
+    {OldMNode, OldSNodes, _} = actual_queue_nodes(Q),
+    OldNodes = [OldMNode | OldSNodes],
+    add_mirrors(QName, [Destination] -- OldNodes, async),
+    drop_mirrors(QName, OldNodes -- [Destination]),
+    {Result, NewQ} = wait_for_new_master(QName, Destination),
+    update_mirrors(NewQ),
+    Result.
+
+wait_for_new_master(QName, Destination) ->
+    wait_for_new_master(QName, Destination, 100).
+
+wait_for_new_master(QName, _, 0) ->
+    {ok, Q} = rabbit_amqqueue:lookup(QName),
+    {{not_migrated, ""}, Q};
+wait_for_new_master(QName, Destination, N) ->
+    {ok, Q} = rabbit_amqqueue:lookup(QName),
+    case amqqueue:get_pid(Q) of
+        none ->
+            timer:sleep(100),
+            wait_for_new_master(QName, Destination, N - 1);
+        Pid ->
+            case node(Pid) of
+                Destination ->
+                    {{migrated, Destination}, Q};
+                _ ->
+                    timer:sleep(100),
+                    wait_for_new_master(QName, Destination, N - 1)
+            end
+    end.
+
 %% The arrival of a newly synced slave may cause the master to die if
 %% the policy does not want the master but it has been kept alive
 %% because there were no synced slaves.
diff --git a/src/rabbit_quorum_queue.erl b/src/rabbit_quorum_queue.erl
index b4118b96ac..4f8c129291 100644
--- a/src/rabbit_quorum_queue.erl
+++ b/src/rabbit_quorum_queue.erl
@@ -39,6 +39,7 @@
 -export([cleanup_data_dir/0]).
 -export([shrink_all/1,
          grow/4]).
+-export([transfer_leadership/2, get_replicas/1, queue_length/1]).
 
 %%-include_lib("rabbit_common/include/rabbit.hrl").
 -include_lib("rabbit.hrl").
@@ -847,6 +848,31 @@ grow(Node, VhostSpec, QueueSpec, Strategy) ->
         is_match(amqqueue:get_vhost(Q), VhostSpec) andalso
         is_match(get_resource_name(amqqueue:get_name(Q)), QueueSpec) ].
 
+transfer_leadership(Q, Destination) ->
+    {RaName, _} = Pid = amqqueue:get_pid(Q),
+    case ra:transfer_leadership(Pid, {RaName, Destination}) of
+        ok ->
+            {_, _, {_, NewNode}} = ra:members(Pid),
+            {migrated, NewNode};
+        already_leader ->
+            {not_migrated, already_leader};
+        {error, Reason} ->
+            {not_migrated, Reason};
+        {timeout, _} ->
+            %% TODO should we retry once?
+            {not_migrated, timeout}
+    end.
+
+queue_length(Q) ->
+    Name = amqqueue:get_name(Q),
+    case ets:lookup(ra_metrics, Name) of
+        [] -> 0;
+        [{_, _, SnapIdx, _, _, LastIdx, _}] -> LastIdx - SnapIdx
+    end.
+
+get_replicas(Q) ->
+    get_nodes(Q).
+
 get_resource_name(#resource{name  = Name}) ->
     Name.