Rebalance quorum queues

[#166551605]

1 files changed, 109 insertions, 0 deletions

diff --git a/src/rabbit_quorum_queue.erl b/src/rabbit_quorum_queue.erl
index b4118b96ac..4fe9c4cbf3 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([rebalance/2]).
 
 %%-include_lib("rabbit_common/include/rabbit.hrl").
 -include_lib("rabbit.hrl").
@@ -847,6 +848,114 @@ grow(Node, VhostSpec, QueueSpec, Strategy) ->
         is_match(amqqueue:get_vhost(Q), VhostSpec) andalso
         is_match(get_resource_name(amqqueue:get_name(Q)), QueueSpec) ].
 
+-spec rebalance(binary(), binary()) -> {ok, [{node(), pos_integer()}]}.
+rebalance(VhostSpec, QueueSpec) ->
+    Running = rabbit_mnesia:cluster_nodes(running),
+    NumRunning = length(Running),
+    ToRebalance = [Q || Q <- rabbit_amqqueue:list(),
+                        amqqueue:get_type(Q) == ?MODULE,
+                        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).
+
+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 ->
+            {RaName, _} = Pid = amqqueue:get_pid(Q),
+            Name = amqqueue:get_name(Q),
+            Members = get_nodes(Q) -- [N],
+            case Members of
+                [] ->
+                    {not_migrated, update_not_migrated_queue(N, Queue, Queues, ByNode)};
+                _ ->
+                    [{Length, Destination} | _] = sort_by_number_of_queues(Members, ByNode),
+                    rabbit_log:warning("Migrating quorum queue ~p from node ~p with ~p queues to node ~p with ~p queues",
+                               [Name, N, length(All), Destination, Length]),
+                    case ra:transfer_leadership(Pid, {RaName, Destination}) of
+                        ok ->
+                            {_, _, {_, NewNode}} = ra:members(Pid),
+                            rabbit_log:warning("Quorum queue ~p migrated to ~p", [Name, NewNode]),
+                            {migrated, update_migrated_queue(NewNode, N, Queue, Queues, ByNode)};
+                        already_leader ->
+                            rabbit_log:warning("Quorum queue ~p in ~p is already a leader",
+                                               [Name, Destination]),
+                            {not_migrated, update_not_migrated_queue(N, Queue, Queues, ByNode)};
+                        {error, Reason} ->
+                            rabbit_log:warning("Error migrating quorum queue ~p: ~p", [Name, Reason]),
+                            {not_migrated, update_not_migrated_queue(N, Queue, Queues, ByNode)};
+                        {timeout, _} ->
+                            %% TODO should we retry once?
+                            rabbit_log:warning("Timeout migrating quorum queue ~p: ~p", [Name]),
+                            {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) ->
+                                 maps:update_with(amqqueue:qnode(Q),
+                                                  fun(L) -> [{log_entries(Q), Q, false} | L] end,
+                                                  [{log_entries(Q), Q, false}], Acc)
+                         end, #{}, Queues),
+    maps:map(fun(_K, V) -> lists:keysort(1, V) end, ByNode).
+
+log_entries(Q) ->
+    Name = amqqueue:get_name(Q),
+    case ets:lookup(ra_metrics, Name) of
+        [] -> 0;
+        [{_, _, SnapIdx, _, _, LastIdx, _}] -> LastIdx - SnapIdx
+    end.
+
 get_resource_name(#resource{name  = Name}) ->
     Name.