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%% This Source Code Form is subject to the terms of the Mozilla Public
%% License, v. 2.0. If a copy of the MPL was not distributed with this
%% file, You can obtain one at https://mozilla.org/MPL/2.0/.
%%
%% Copyright (c) 2010-2020 VMware, Inc. or its affiliates. All rights reserved.
%%
-module(rabbit_mirror_queue_mode_exactly).
-include("rabbit.hrl").
-behaviour(rabbit_mirror_queue_mode).
-export([description/0, suggested_queue_nodes/5, validate_policy/1]).
-rabbit_boot_step({?MODULE,
[{description, "mirror mode exactly"},
{mfa, {rabbit_registry, register,
[ha_mode, <<"exactly">>, ?MODULE]}},
{requires, rabbit_registry},
{enables, kernel_ready}]}).
description() ->
[{description, <<"Mirror queue to a specified number of nodes">>}].
%% When we need to add nodes, we randomise our candidate list as a
%% crude form of load-balancing. TODO it would also be nice to
%% randomise the list of ones to remove when we have too many - we
%% would have to take account of synchronisation though.
suggested_queue_nodes(Count, MNode, SNodes, _SSNodes, Poss) ->
SCount = Count - 1,
{MNode, case SCount > length(SNodes) of
true -> Cand = shuffle((Poss -- [MNode]) -- SNodes),
SNodes ++ lists:sublist(Cand, SCount - length(SNodes));
false -> lists:sublist(SNodes, SCount)
end}.
shuffle(L) ->
{_, L1} = lists:unzip(lists:keysort(1, [{rand:uniform(), N} || N <- L])),
L1.
validate_policy(N) when is_integer(N) andalso N > 0 ->
ok;
validate_policy(Params) ->
{error, "ha-mode=\"exactly\" takes an integer, ~p given", [Params]}.
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