iilyak commented on a change in pull request #470: Scheduling Replicator URL: https://github.com/apache/couchdb/pull/470#discussion_r112509678
########## File path: src/couch_replicator/src/couch_replicator_clustering.erl ########## @@ -0,0 +1,235 @@ +% 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). + +-export([ + start_link/0 +]). + +-export([ + init/1, + terminate/2, + handle_call/3, + handle_info/2, + handle_cast/2, + code_change/3 +]). + +-export([ + owner/2, + is_stable/0, + link_cluster_event_listener/3 +]). + +% config_listener callbacks +-export([ + handle_config_change/5, + handle_config_terminate/3 +]). + +-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, { + start_time :: erlang:timestamp(), + last_change :: erlang:timestamp(), + period = ?DEFAULT_QUIET_PERIOD :: non_neg_integer(), + start_period = ?DEFAULT_START_PERIOD :: non_neg_integer(), + timer :: reference() +}). + + +-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(). + + +-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. + + +% gen_server callbacks + +init([]) -> + net_kernel:monitor_nodes(true), + 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_log:debug("Initialized clustering gen_server ~w", [self()]), + couch_stats:update_gauge([couch_replicator, cluster_is_stable], 0), + {ok, #state{ + start_time = os:timestamp(), + last_change = os:timestamp(), + period = Period, + start_period = StartPeriod, + timer = new_timer(StartPeriod) + }}. + + +terminate(_Reason, _State) -> + ok. + + +handle_call(is_stable, _From, State) -> + {reply, is_stable(State), State}. + + +handle_cast({set_period, QuietPeriod}, State) when Review comment: I think we need the same guard in `handle_config_change`. Alternatively you can add catch all `handle_cast` clause where you would log what happen. ---------------------------------------------------------------- This is an automated message from the Apache Git Service. To respond to the message, please log on GitHub and use the URL above to go to the specific comment. For queries about this service, please contact Infrastructure at: us...@infra.apache.org With regards, Apache Git Services
