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% Licensed under the Apache License, Version 2.0 (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.apache.org/licenses/LICENSE-2.0
%
% Unless required by applicable law or agreed to in writing, software
% distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
% WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
% License for the specific language governing permissions and limitations under
% the License.
% Maintain cluster membership and stability notifications for replications.
% On changes to cluster membership, broadcast events to `replication` gen_event.
% Listeners will get `{cluster, stable}` or `{cluster, unstable}` events.
%
% Cluster stability is defined as "there have been no nodes added or removed in
% last `QuietPeriod` seconds". QuietPeriod value is configurable. To ensure a
% speedier startup, during initialization there is a shorter StartupPeriod
% in effect (also configurable).
%
% This module is also in charge of calculating ownership of replications based
% on where their _replicator db documents shards live.
-module(couch_replicator_clustering).
-behaviour(gen_server).
-behaviour(config_listener).
-behaviour(mem3_cluster).
-export([
start_link/0
]).
-export([
init/1,
terminate/2,
handle_call/3,
handle_info/2,
handle_cast/2,
code_change/3
]).
-export([
owner/2,
owner/3,
is_stable/0,
link_cluster_event_listener/3
]).
% config_listener callbacks
-export([
handle_config_change/5,
handle_config_terminate/3
]).
% mem3_cluster callbacks
-export([
cluster_stable/1,
cluster_unstable/1
]).
-include_lib("couch/include/couch_db.hrl").
-include_lib("mem3/include/mem3.hrl").
-define(DEFAULT_QUIET_PERIOD, 60). % seconds
-define(DEFAULT_START_PERIOD, 5). % seconds
-define(RELISTEN_DELAY, 5000).
-record(state, {
mem3_cluster_pid :: pid(),
cluster_stable :: boolean()
}).
-spec start_link() -> {ok, pid()} | ignore | {error, term()}.
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
% owner/2 function computes ownership for a {DbName, DocId} tuple
% `unstable` if cluster is considered to be unstable i.e. it has changed
% recently, or returns node() which of the owner.
%
-spec owner(Dbname :: binary(), DocId :: binary()) -> node() | unstable.
owner(<<"shards/", _/binary>> = DbName, DocId) ->
case is_stable() of
false ->
unstable;
true ->
owner_int(DbName, DocId)
end;
owner(_DbName, _DocId) ->
node().
% Direct calculation of node membership. This is the algorithm part. It
% doesn't read the shard map, just picks owner based on a hash.
-spec owner(binary(), binary(), [node()]) -> node().
owner(DbName, DocId, Nodes) ->
hd(mem3_util:rotate_list({DbName, DocId}, lists:usort(Nodes))).
-spec is_stable() -> true | false.
is_stable() ->
gen_server:call(?MODULE, is_stable).
-spec link_cluster_event_listener(atom(), atom(), list()) -> pid().
link_cluster_event_listener(Mod, Fun, Args)
when is_atom(Mod), is_atom(Fun), is_list(Args) ->
CallbackFun =
fun(Event = {cluster, _}) -> erlang:apply(Mod, Fun, Args ++ [Event]);
(_) -> ok
end,
{ok, Pid} = couch_replicator_notifier:start_link(CallbackFun),
Pid.
% Mem3 cluster callbacks
cluster_unstable(Server) ->
couch_replicator_notifier:notify({cluster, unstable}),
couch_stats:update_gauge([couch_replicator, cluster_is_stable], 0),
couch_log:notice("~s : cluster unstable", [?MODULE]),
gen_server:cast(Server, cluster_unstable),
Server.
cluster_stable(Server) ->
couch_replicator_notifier:notify({cluster, stable}),
couch_stats:update_gauge([couch_replicator, cluster_is_stable], 1),
couch_log:notice("~s : cluster stable", [?MODULE]),
gen_server:cast(Server, cluster_stable),
Server.
% gen_server callbacks
init([]) ->
ok = config:listen_for_changes(?MODULE, nil),
Period = abs(config:get_integer("replicator", "cluster_quiet_period",
?DEFAULT_QUIET_PERIOD)),
StartPeriod = abs(config:get_integer("replicator", "cluster_start_period",
?DEFAULT_START_PERIOD)),
couch_stats:update_gauge([couch_replicator, cluster_is_stable], 0),
{ok, Mem3Cluster} = mem3_cluster:start_link(?MODULE, self(), StartPeriod,
Period),
{ok, #state{mem3_cluster_pid = Mem3Cluster, cluster_stable = false}}.
terminate(_Reason, _State) ->
ok.
handle_call(is_stable, _From, #state{cluster_stable = IsStable} = State) ->
{reply, IsStable, State}.
handle_cast({set_period, Period}, #state{mem3_cluster_pid = Pid} = State) ->
ok = mem3_cluster:set_period(Pid, Period),
{noreply, State};
handle_cast(cluster_stable, State) ->
{noreply, State#state{cluster_stable = true}};
handle_cast(cluster_unstable, State) ->
{noreply, State#state{cluster_stable = false}}.
handle_info(restart_config_listener, State) ->
ok = config:listen_for_changes(?MODULE, nil),
{noreply, State}.
code_change(_OldVsn, State, _Extra) ->
{ok, State}.
%% Internal functions
handle_config_change("replicator", "cluster_quiet_period", V, _, S) ->
ok = gen_server:cast(?MODULE, {set_period, list_to_integer(V)}),
{ok, S};
handle_config_change(_, _, _, _, S) ->
{ok, S}.
handle_config_terminate(_, stop, _) -> ok;
handle_config_terminate(_S, _R, _St) ->
Pid = whereis(?MODULE),
erlang:send_after(?RELISTEN_DELAY, Pid, restart_config_listener).
-spec owner_int(binary(), binary()) -> node().
owner_int(ShardName, DocId) ->
DbName = mem3:dbname(ShardName),
Live = [node() | nodes()],
Shards = mem3:shards(DbName, DocId),
Nodes = [N || #shard{node=N} <- Shards, lists:member(N, Live)],
owner(DbName, DocId, Nodes).
|
