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ra_server_proc.erl
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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) 2017-2023 Broadcom. All Rights Reserved. The term Broadcom refers to Broadcom Inc. and/or its subsidiaries.
%%
%% @hidden
-module(ra_server_proc).
-behaviour(gen_statem).
-compile({inline, [handle_raft_state/3]}).
-include("ra.hrl").
-include("ra_server.hrl").
%% State functions
-export([
post_init/3,
recover/3,
recovered/3,
leader/3,
pre_vote/3,
candidate/3,
follower/3,
receive_snapshot/3,
await_condition/3,
terminating_leader/3,
terminating_follower/3
]).
%% gen_statem callbacks
-export([
init/1,
format_status/1,
handle_event/4,
terminate/3,
code_change/4,
callback_mode/0
]).
%% API
-export([start_link/1,
command/3,
cast_command/2,
cast_command/3,
query/5,
state_query/3,
local_state_query/3,
trigger_election/2,
ping/2,
log_fold/4,
transfer_leadership/3,
force_shrink_members_to_current_member/1
]).
-export([send_rpc/3]).
-ifdef(TEST).
-export([leader_call/3,
local_call/3]).
-endif.
-define(DEFAULT_BROADCAST_TIME, 100).
-define(DEFAULT_ELECTION_MULT, 5).
-define(TICK_INTERVAL_MS, 1000).
-define(DEFAULT_AWAIT_CONDITION_TIMEOUT, 30000).
%% Utilisation average calculations are all in μs.
-define(INSTALL_SNAP_RPC_TIMEOUT, 120 * 1000).
-define(HANDLE_EFFECTS(Effects, EvtType, State0),
handle_effects(?FUNCTION_NAME, Effects, EvtType, State0)).
-type query_fun() :: ra:query_fun().
-type query_options() :: #{condition => ra:query_condition()}.
-type ra_command() :: {ra_server:command_type(), term(),
ra_server:command_reply_mode()}.
-type ra_leader_call_ret(Result) :: {ok, Result, Leader::ra_server_id()} |
{error, term()} |
{timeout, ra_server_id()}.
-type ra_local_call_ret(Result) :: {ok, Result, LocalServer::ra_server_id()} |
{error, term()} |
{timeout, ra_server_id()}.
-type ra_cmd_ret() :: ra_leader_call_ret(term()).
-type gen_statem_start_ret() :: {ok, pid()} | ignore | {error, term()}.
%% ra_event types
-type ra_event_reject_detail() :: {not_leader, Leader :: option(ra_server_id()),
ra_server:command_correlation()}.
-type ra_event_body() ::
% used for notifying senders of the ultimate fate of their command
% sent using ra:pipeline_command/3|4
{applied, [{ra_server:command_correlation(), Reply :: term()}]} |
{rejected, ra_event_reject_detail()} |
% used to send message side-effects emitted by the state machine
{machine, term()}.
-type ra_event() :: {ra_event, Sender :: ra_server_id(), ra_event_body()}.
%% the Sender is the ra process that emitted the ra_event.
-type server_loc() :: ra_server_id() | [ra_server_id()].
-export_type([ra_leader_call_ret/1,
ra_local_call_ret/1,
ra_cmd_ret/0,
safe_call_ret/1,
ra_event_reject_detail/0,
ra_event/0,
ra_event_body/0,
query_options/0]).
%% the ra server proc keeps monitors on behalf of different components
%% the state machine, log and server code. The tag is used to determine
%% which component to dispatch the down to
-record(conf, {log_id :: unicode:chardata(),
name :: atom(),
cluster_name :: term(),
broadcast_time = ?DEFAULT_BROADCAST_TIME :: non_neg_integer(),
tick_timeout :: non_neg_integer(),
await_condition_timeout :: non_neg_integer(),
ra_event_formatter :: undefined | {module(), atom(), [term()]},
flush_commands_size = ?FLUSH_COMMANDS_SIZE :: non_neg_integer(),
snapshot_chunk_size = ?DEFAULT_SNAPSHOT_CHUNK_SIZE :: non_neg_integer(),
receive_snapshot_timeout = ?DEFAULT_RECEIVE_SNAPSHOT_TIMEOUT :: non_neg_integer(),
install_snap_rpc_timeout :: non_neg_integer(),
aten_poll_interval = 1000 :: non_neg_integer(),
counter :: undefined | counters:counters_ref()
}).
-record(state, {conf :: #conf{},
server_state :: ra_server:ra_server_state(),
monitors = ra_monitors:init() :: ra_monitors:state(),
pending_commands = [] :: [{{pid(), any()}, term()}],
leader_monitor :: reference() | undefined,
leader_last_seen :: integer() | undefined,
low_priority_commands :: ra_ets_queue:state(),
election_timeout_set = false :: boolean(),
%% the log index last time gc was forced
pending_notifys = #{} :: #{pid() => [term()]},
pending_queries = [] :: [{ra:query_condition(),
gen_statem:from(),
query_fun()}]
}).
%%%===================================================================
%%% API
%%%===================================================================
-spec start_link(ra_server:ra_server_config()) -> gen_statem_start_ret().
start_link(Config = #{id := Id}) ->
Name = ra_lib:ra_server_id_to_local_name(Id),
gen_statem:start_link({local, Name}, ?MODULE, Config, []).
-spec command(server_loc(), ra_command(), timeout()) ->
ra_cmd_ret().
command(ServerLoc, Cmd, Timeout) ->
leader_call(ServerLoc, {command, normal, Cmd}, Timeout).
-spec cast_command(ra_server_id(), ra_command()) -> ok.
cast_command(ServerId, Cmd) ->
gen_statem:cast(ServerId, {command, low, Cmd}).
-spec cast_command(ra_server_id(), ra_server:command_priority(), ra_command()) -> ok.
cast_command(ServerId, Priority, Cmd) ->
gen_statem:cast(ServerId, {command, Priority, Cmd}).
-spec query(server_loc(), query_fun(),
local | consistent | leader,
query_options(),
timeout()) ->
ra_server_proc:ra_leader_call_ret({ra_idxterm(), Reply :: term()})
| ra_server_proc:ra_leader_call_ret(Reply :: term())
| {ok, {ra_idxterm(), Reply :: term()}, not_known}.
query(ServerLoc, QueryFun, local, Options, Timeout)
when map_size(Options) =:= 0 ->
statem_call(ServerLoc, {local_query, QueryFun}, Timeout);
query(ServerLoc, QueryFun, local, Options, Timeout) ->
statem_call(ServerLoc, {local_query, QueryFun, Options}, Timeout);
query(ServerLoc, QueryFun, leader, Options, Timeout)
when map_size(Options) =:= 0 ->
leader_call(ServerLoc, {local_query, QueryFun}, Timeout);
query(ServerLoc, QueryFun, leader, Options, Timeout) ->
leader_call(ServerLoc, {local_query, QueryFun, Options}, Timeout);
query(ServerLoc, QueryFun, consistent, _Options, Timeout) ->
leader_call(ServerLoc, {consistent_query, QueryFun}, Timeout).
-spec log_fold(ra_server_id(), fun(), term(), integer()) -> term().
log_fold(ServerId, Fun, InitialState, Timeout) ->
gen_statem:call(ServerId, {log_fold, Fun, InitialState}, Timeout).
%% used to query the raft state rather than the machine state
-spec state_query(server_loc(),
all |
overview |
voters |
members |
members_info |
initial_members |
machine, timeout()) ->
ra_leader_call_ret(term()).
state_query(ServerLoc, Spec, Timeout) ->
leader_call(ServerLoc, {state_query, Spec}, Timeout).
-spec local_state_query(server_loc(),
all |
overview |
voters |
members |
members_info |
initial_members |
machine, timeout()) ->
ra_local_call_ret(term()).
local_state_query(ServerLoc, Spec, Timeout) ->
local_call(ServerLoc, {state_query, Spec}, Timeout).
-spec trigger_election(ra_server_id(), timeout()) -> ok.
trigger_election(ServerId, Timeout) ->
gen_statem:call(ServerId, trigger_election, Timeout).
-spec transfer_leadership(ra_server_id(), ra_server_id(), timeout()) ->
ok | already_leader | {error, term()} | {timeout, ra_server_id()}.
transfer_leadership(ServerId, TargetServerId, Timeout) ->
leader_call(ServerId, {transfer_leadership, TargetServerId}, Timeout).
-spec force_shrink_members_to_current_member(ra_server_id()) -> ok.
force_shrink_members_to_current_member(ServerId) ->
gen_statem_safe_call(ServerId, force_member_change, 5000).
-spec ping(ra_server_id(), timeout()) -> safe_call_ret({pong, states()}).
ping(ServerId, Timeout) ->
gen_statem_safe_call(ServerId, ping, Timeout).
leader_call(ServerLoc, Msg, Timeout) ->
statem_call(ServerLoc, {leader_call, Msg}, Timeout).
local_call(ServerLoc, Msg, Timeout) ->
statem_call(ServerLoc, {local_call, Msg}, Timeout).
statem_call(ServerIds, Msg, Timeout)
when is_list(ServerIds) ->
multi_statem_call(ServerIds, Msg, [], Timeout);
statem_call(ServerId, Msg, Timeout) ->
case gen_statem_safe_call(ServerId, Msg, Timeout) of
{redirect, Leader} ->
statem_call(Leader, Msg, Timeout);
{wrap_reply, Reply} ->
{ok, Reply, ServerId};
{error, _} = E ->
E;
timeout ->
{timeout, ServerId};
Reply ->
Reply
end.
multi_statem_call([ServerId | ServerIds], Msg, Errs, Timeout) ->
case statem_call(ServerId, Msg, Timeout) of
{Tag, Info} = E
when Tag == timeout orelse
(Tag == error andalso
(Info == noproc orelse
Info == nodedown orelse
Info == shutdown orelse
Info == system_not_started)) ->
%% these are the retryable errors, any others we consider
%% genuine errors that a retry will not fix
case ServerIds of
[] ->
{error, {no_more_servers_to_try, [E | Errs]}};
_ ->
multi_statem_call(ServerIds, Msg, [E | Errs], Timeout)
end;
Reply ->
Reply
end.
%%%===================================================================
%%% gen_statem callbacks
%%%===================================================================
init(#{reply_to := ReplyTo} = Config) ->
%% we have a reply to key, perform init async
{ok, post_init, maps:remove(reply_to, Config),
[{next_event, internal, {go, ReplyTo}}]};
init(Config) ->
%% no reply_to key, must have been started by an older node run synchronous
%% init
State = do_init(Config),
{ok, recover, State, [{next_event, cast, go}]}.
do_init(#{id := Id,
cluster_name := ClusterName} = Config0) ->
Key = ra_lib:ra_server_id_to_local_name(Id),
true = ets:insert(ra_state, {Key, init, unknown}),
process_flag(trap_exit, true),
Config = #{counter := Counter,
system_config := SysConf} = maps:merge(config_defaults(Id),
Config0),
MsgQData = maps:get(message_queue_data, SysConf, off_heap),
MinBinVheapSize = maps:get(server_min_bin_vheap_size, SysConf,
?MIN_BIN_VHEAP_SIZE),
MinHeapSize = maps:get(server_min_heap_size, SysConf, ?MIN_BIN_VHEAP_SIZE),
process_flag(message_queue_data, MsgQData),
process_flag(min_bin_vheap_size, MinBinVheapSize),
process_flag(min_heap_size, MinHeapSize),
#{cluster := Cluster} = ServerState = ra_server:init(Config),
LogId = ra_server:log_id(ServerState),
UId = ra_server:uid(ServerState),
% ensure ra_directory has the new pid
#{names := Names} = SysConf,
ok = ra_directory:register_name(Names, UId, self(),
maps:get(parent, Config, undefined), Key,
ClusterName),
% ensure each relevant erlang node is connected
PeerNodes = [PeerNode ||
{_, PeerNode} <- maps:keys(maps:remove(Id, Cluster))],
case PeerNodes -- nodes() of
[] ->
%% all peer nodes are connected
ok;
DisconnectedNodes ->
%% as most messages are sent using noconnect we explicitly attempt to
%% connect to all relevant nodes
_ = spawn(fun () ->
[net_kernel:connect_node(N)
|| N <- DisconnectedNodes]
end),
ok
end,
TickTime = maps:get(tick_timeout, Config),
InstallSnapRpcTimeout = maps:get(install_snap_rpc_timeout, Config),
AwaitCondTimeout = maps:get(await_condition_timeout, Config),
RaEventFormatterMFA = maps:get(ra_event_formatter, Config, undefined),
FlushCommandsSize = maps:get(low_priority_commands_flush_size, SysConf,
?FLUSH_COMMANDS_SIZE),
SnapshotChunkSize = maps:get(snapshot_chunk_size, SysConf,
?DEFAULT_SNAPSHOT_CHUNK_SIZE),
ReceiveSnapshotTimeout = maps:get(receive_snapshot_timeout, SysConf,
?DEFAULT_RECEIVE_SNAPSHOT_TIMEOUT),
AtenPollInt = application:get_env(aten, poll_interval, 1000),
State = #state{conf = #conf{log_id = LogId,
cluster_name = ClusterName,
name = Key,
tick_timeout = TickTime,
await_condition_timeout = AwaitCondTimeout,
ra_event_formatter = RaEventFormatterMFA,
flush_commands_size = FlushCommandsSize,
snapshot_chunk_size = SnapshotChunkSize,
install_snap_rpc_timeout = InstallSnapRpcTimeout,
receive_snapshot_timeout = ReceiveSnapshotTimeout,
aten_poll_interval = AtenPollInt,
counter = Counter},
low_priority_commands = ra_ets_queue:new(),
server_state = ServerState},
ok = net_kernel:monitor_nodes(true, [nodedown_reason]),
State.
%% callback mode
callback_mode() -> [state_functions, state_enter].
%%%===================================================================
%%% State functions
%%%===================================================================
post_init(enter, _OldState, State) ->
{keep_state, State, []};
post_init(internal, {go, {ReplyToRef, ReplyToPid}}, Config) ->
State = do_init(Config),
ReplyToPid ! {ReplyToRef, ok},
{next_state, recover, State, [{next_event, internal, go}]}.
recover(enter, OldState, State0) ->
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
{keep_state, State, Actions};
recover(internal, go, State = #state{server_state = ServerState0}) ->
ServerState = ra_server:recover(ServerState0),
incr_counter(State#state.conf, ?C_RA_SRV_GCS, 1),
%% we have to issue the next_event here so that the recovered state is
%% only passed through very briefly
next_state(recovered, State#state{server_state = ServerState},
[{next_event, internal, next}]);
recover(_, _, State) ->
% all other events need to be postponed until we can return
% `next_event` from init
{keep_state, State, {postpone, true}}.
%% this is a passthrough state to allow state machines to emit node local
%% effects post recovery
recovered(enter, OldState, State0) ->
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
ok = record_cluster_change(State),
{keep_state, State, Actions};
recovered(internal, next, #state{server_state = ServerState} = State) ->
true = erlang:garbage_collect(),
_ = ets:insert(ra_metrics, ra_server:metrics(ServerState)),
next_state(follower, State, set_tick_timer(State, [])).
leader(enter, OldState, #state{low_priority_commands = Delayed0} = State0) ->
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
Delayed = case OldState of
await_condition ->
%% if we're returning from await_condition we may still
%% have valid delayed commands to schedule
schedule_command_flush(Delayed0),
Delayed0;
_ ->
%% for any other state it is best to just reset the
%% delayed commands
ra_ets_queue:reset(Delayed0)
end,
ok = record_cluster_change(State),
{keep_state, State#state{leader_last_seen = undefined,
pending_notifys = #{},
low_priority_commands = Delayed,
election_timeout_set = false}, Actions};
leader(EventType, {leader_call, Msg}, State) ->
% no need to redirect
leader(EventType, Msg, State);
leader(EventType, {local_call, Msg}, State) ->
leader(EventType, Msg, State);
leader(EventType, {leader_cast, Msg}, State) ->
leader(EventType, Msg, State);
leader(EventType, {command, normal, {CmdType, Data, ReplyMode}},
#state{conf = Conf} = State0) ->
case validate_reply_mode(ReplyMode) of
ok ->
%% normal priority commands are written immediately
Cmd = make_command(CmdType, EventType, Data, ReplyMode),
{NextState, State1, Effects} = handle_leader({command, Cmd}, State0),
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
case NextState of
leader ->
{keep_state, State, Actions};
_ ->
next_state(NextState, State, Actions)
end;
Error ->
ok = incr_counter(Conf, ?C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, 1),
case EventType of
{call, From} ->
{keep_state, State0, [{reply, From, Error}]};
_ ->
{keep_state, State0, []}
end
end;
leader(EventType, {command, low, {CmdType, Data, ReplyMode}},
#state{conf = Conf,
low_priority_commands = Delayed} = State0) ->
case validate_reply_mode(ReplyMode) of
ok ->
%% cache the low priority command until the flush_commands message
%% arrives
Cmd = make_command(CmdType, EventType, Data, ReplyMode),
%% if there are no prior delayed commands
%% (and thus no action queued to do so)
%% queue a state timeout to flush them
%% We use a cast to ourselves instead of a zero timeout as we want
%% to get onto the back of the erlang mailbox not just the current
%% gen_statem event buffer.
case ra_ets_queue:len(Delayed) of
0 ->
ok = gen_statem:cast(self(), flush_commands);
_ ->
ok
end,
State = State0#state{low_priority_commands =
ra_ets_queue:in(Cmd, Delayed)},
{keep_state, State, []};
Error ->
ok = incr_counter(Conf, ?C_RA_SRV_INVALID_REPLY_MODE_COMMANDS, 1),
case EventType of
{call, From} ->
{keep_state, State0, [{reply, From, Error}]};
_ ->
{keep_state, State0, []}
end
end;
leader(EventType, {aux_command, Cmd}, State0) ->
{_, ServerState, Effects} = ra_server:handle_aux(?FUNCTION_NAME, EventType,
Cmd, State0#state.server_state),
{State, Actions} =
?HANDLE_EFFECTS(Effects, EventType,
State0#state{server_state = ServerState}),
{keep_state, State#state{server_state = ServerState}, Actions};
leader(EventType, flush_commands,
#state{conf = #conf{flush_commands_size = Size},
low_priority_commands = Delayed0} = State0) ->
{Commands, Delayed} = ra_ets_queue:take(Size, Delayed0),
%% write a batch of delayed commands
{NextState, State1, Effects} = handle_leader({commands, Commands}, State0),
State2 = State1#state{low_priority_commands = Delayed},
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State2),
case NextState of
leader ->
schedule_command_flush(Delayed),
{keep_state, State#state{low_priority_commands = Delayed}, Actions};
_ ->
next_state(NextState, State, Actions)
end;
leader({call, _From} = EventType, {local_query, QueryFun}, State) ->
leader(EventType, {local_query, QueryFun, #{}}, State);
leader({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(leader, From, QueryFun, Options, State);
leader({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
leader({call, From}, {consistent_query, QueryFun},
#state{conf = Conf,
server_state = ServerState0} = State0) ->
{leader, ServerState1, Effects} =
ra_server:handle_leader({consistent_query, From, QueryFun},
ServerState0),
incr_counter(Conf, ?C_RA_SRV_CONSISTENT_QUERIES, 1),
{State1, Actions} =
?HANDLE_EFFECTS(Effects, {call, From},
State0#state{server_state = ServerState1}),
{keep_state, State1, Actions};
leader({call, From}, ping, State) ->
{keep_state, State, [{reply, From, {pong, leader}}]};
leader(info, {node_event, _Node, _Evt}, State) ->
{keep_state, State, []};
leader(info, {'DOWN', _MRef, process, Pid, Info}, State0) ->
handle_process_down(Pid, Info, ?FUNCTION_NAME, State0);
leader(info, {Status, Node, InfoList}, State0)
when Status =:= nodedown orelse
Status =:= nodeup ->
handle_node_status_change(Node, Status, InfoList, ?FUNCTION_NAME, State0);
leader(info, {update_peer, PeerId, Update}, State0) ->
State = update_peer(PeerId, Update, State0),
{keep_state, State, []};
leader(_, tick_timeout, State0) ->
{State1, RpcEffs} = make_rpcs(State0),
ServerState0 = State1#state.server_state,
Effects = ra_server:tick(ServerState0),
ServerState = ra_server:log_tick(ServerState0),
{State2, Actions} = ?HANDLE_EFFECTS(RpcEffs ++ Effects ++ [{aux, tick}],
cast, State1#state{server_state = ServerState}),
%% try sending any pending applied notifications again
State = send_applied_notifications(State2, #{}),
{keep_state, handle_tick_metrics(State),
set_tick_timer(State, Actions)};
leader({timeout, Name}, machine_timeout, State0) ->
% the machine timer timed out, add a timeout message
Cmd = make_command('$usr', cast, {timeout, Name}, noreply),
{leader, State1, Effects} = handle_leader({command, Cmd}, State0),
{State, Actions} = ?HANDLE_EFFECTS(Effects, cast, State1),
{keep_state, State, Actions};
leader({call, From}, trigger_election, State) ->
{keep_state, State, [{reply, From, ok}]};
leader({call, From}, {log_fold, Fun, Term}, State) ->
fold_log(From, Fun, Term, State);
leader(EventType, Msg, State0) ->
case handle_leader(Msg, State0) of
{leader, State1, Effects1} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects1, EventType, State1),
{keep_state, State, Actions};
{stop, State1, Effects} ->
% interact before shutting down in case followers need
% to know about the new commit index
{State, _Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
{stop, normal, State};
{delete_and_terminate, State1, Effects} ->
{State2, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
State = send_rpcs(State2),
case ra_server:is_fully_replicated(State#state.server_state) of
true ->
{stop, {shutdown, delete}, State};
false ->
next_state(terminating_leader, State, Actions)
end;
{await_condition, State1, Effects1} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects1, EventType, State1),
?DEBUG_IF(is_command(Msg), "~ts: postponing ~0P",
[log_id(State0), Msg, 10]),
next_state(await_condition, State,
[{postpone, is_command(Msg)} | Actions]);
{NextState, State1, Effects1} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects1, EventType, State1),
next_state(NextState, State, Actions)
end.
candidate(enter, OldState, State0) ->
{State1, Actions0} = handle_enter(?FUNCTION_NAME, OldState, State0),
{State, Actions} = maybe_set_election_timeout(short, State1, Actions0),
{keep_state, State, Actions};
candidate({call, From}, {leader_call, Msg},
#state{pending_commands = Pending} = State) ->
{keep_state, State#state{pending_commands = [{From, Msg} | Pending]}};
candidate(EventType, {local_call, Msg}, State) ->
candidate(EventType, Msg, State);
candidate(cast, {command, _Priority,
{_CmdType, _Data, {notify, Corr, Pid}}},
State) ->
_ = reject_command(Pid, Corr, State),
{keep_state, State, []};
candidate({call, _From} = EventType, {local_query, QueryFun}, State) ->
candidate(EventType, {local_query, QueryFun, #{}}, State);
candidate({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(candidate, From, QueryFun, Options, State);
candidate({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
candidate({call, From}, ping, State) ->
{keep_state, State, [{reply, From, {pong, candidate}}]};
candidate(info, {node_event, _Node, _Evt}, State) ->
{keep_state, State};
candidate(_, tick_timeout, State0) ->
State = maybe_persist_last_applied(State0),
{keep_state, handle_tick_metrics(State), set_tick_timer(State, [])};
candidate({call, From}, trigger_election, State) ->
{keep_state, State, [{reply, From, ok}]};
candidate(EventType, Msg, State0) ->
case handle_candidate(Msg, State0) of
{candidate, State1, Effects} ->
{State2, Actions0} = ?HANDLE_EFFECTS(Effects, EventType, State1),
{State, Actions} = maybe_set_election_timeout(medium, State2, Actions0),
{keep_state, State, Actions};
{follower, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(follower, State, Actions);
{leader, State1, Effects} ->
{State, Actions0} = ?HANDLE_EFFECTS(Effects, EventType, State1),
%% reset the tick timer to avoid it triggering early after a leader
%% change
Actions = set_tick_timer(State, Actions0),
next_state(leader, State, Actions)
end.
pre_vote(enter, OldState, #state{leader_monitor = MRef} = State0) ->
_ = stop_monitor(MRef),
{State1, Actions0} = handle_enter(?FUNCTION_NAME, OldState, State0),
{State, Actions} = maybe_set_election_timeout(long, State1, Actions0),
{keep_state, State#state{leader_monitor = undefined}, Actions};
pre_vote({call, From}, {leader_call, Msg},
State = #state{pending_commands = Pending}) ->
{keep_state, State#state{pending_commands = [{From, Msg} | Pending]}};
pre_vote(EventType, {local_call, Msg}, State) ->
pre_vote(EventType, Msg, State);
pre_vote(cast, {command, _Priority,
{_CmdType, _Data, {notify, Corr, Pid}}},
State) ->
_ = reject_command(Pid, Corr, State),
{keep_state, State, []};
pre_vote({call, _From} = EventType, {local_query, QueryFun}, State) ->
pre_vote(EventType, {local_query, QueryFun, #{}}, State);
pre_vote({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(pre_vote, From, QueryFun, Options, State);
pre_vote({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
pre_vote({call, From}, ping, State) ->
{keep_state, State, [{reply, From, {pong, pre_vote}}]};
pre_vote(info, {node_event, _Node, _Evt}, State) ->
{keep_state, State};
pre_vote(info, {Status, Node, InfoList}, State0)
when Status =:= nodedown orelse Status =:= nodeup ->
handle_node_status_change(Node, Status, InfoList, ?FUNCTION_NAME, State0);
pre_vote(info, {'DOWN', _MRef, process, Pid, Info}, State0) ->
handle_process_down(Pid, Info, ?FUNCTION_NAME, State0);
pre_vote(_, tick_timeout, State0) ->
State = maybe_persist_last_applied(State0),
{keep_state, handle_tick_metrics(State), set_tick_timer(State, [])};
pre_vote({call, From}, trigger_election, State) ->
{keep_state, State, [{reply, From, ok}]};
pre_vote(EventType, Msg, State0) ->
case handle_pre_vote(Msg, State0) of
{pre_vote, State1, Effects} ->
{State2, Actions0} = ?HANDLE_EFFECTS(Effects, EventType, State1),
{State, Actions} = maybe_set_election_timeout(long, State2, Actions0),
{keep_state, State, Actions};
{follower, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(follower, State, Actions);
{candidate, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(candidate, State, Actions)
end.
follower(enter, OldState, #state{low_priority_commands = Delayed,
server_state = ServerState} = State0) ->
%% New cluster starts should be coordinated and elections triggered
%% explicitly hence if this is a new one we wait here.
%% Else we set an election timer
%% Set the timeout length based on the previous state
TimeoutLen = case OldState of
recovered -> short;
_ -> long
end,
{State1, Actions0} = handle_enter(?FUNCTION_NAME, OldState, State0),
{State, Actions} = case ra_server:is_new(ServerState) of
true ->
{State1, Actions0};
false ->
?DEBUG("~ts: is not new, setting "
"election timeout.",
[log_id(State0)]),
maybe_set_election_timeout(TimeoutLen, State1,
Actions0)
end,
Monitors = ra_monitors:remove_all(machine, State#state.monitors),
{keep_state, State#state{low_priority_commands = ra_ets_queue:reset(Delayed),
monitors = Monitors}, Actions};
follower({call, From}, {leader_call, Msg}, State) ->
maybe_redirect(From, Msg, State);
follower(EventType, {local_call, Msg}, State) ->
follower(EventType, Msg, State);
follower(_, {command, Priority, {_CmdType, Data, noreply}},
State) ->
% forward to leader
case leader_id(State) of
undefined ->
?WARN("~ts: leader cast - leader not known. "
"Command is dropped.", [log_id(State)]),
{keep_state, State, []};
LeaderId ->
?DEBUG("~ts: follower leader cast - redirecting to ~w ",
[log_id(State), LeaderId]),
ok = ra:pipeline_command(LeaderId, Data, no_correlation, Priority),
{keep_state, State, []}
end;
follower(cast, {command, _Priority,
{_CmdType, _Data, {notify, Corr, Pid}}},
State) ->
_ = reject_command(Pid, Corr, State),
{keep_state, State, []};
follower({call, _From} = EventType, {local_query, QueryFun}, State) ->
follower(EventType, {local_query, QueryFun, #{}}, State);
follower({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(follower, From, QueryFun, Options, State);
follower({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
follower(EventType, {aux_command, Cmd}, State0) ->
{_, ServerState, Effects} = ra_server:handle_aux(?FUNCTION_NAME, EventType, Cmd,
State0#state.server_state),
{State, Actions} =
?HANDLE_EFFECTS(Effects, EventType,
State0#state{server_state = ServerState}),
{keep_state, State#state{server_state = ServerState}, Actions};
follower({call, From}, trigger_election, State) ->
?DEBUG("~ts: election triggered by ~w", [log_id(State), element(1, From)]),
{keep_state, State, [{reply, From, ok},
{next_event, cast, election_timeout}]};
follower({call, From}, ping, State) ->
{keep_state, State, [{reply, From, {pong, follower}}]};
follower(info, {'DOWN', MRef, process, _Pid, Info},
#state{leader_monitor = MRef} = State0) ->
?INFO("~ts: Leader monitor down with ~W, setting election timeout",
[log_id(State0), Info, 8]),
%% If the DOWN reason is something else than `noconnection', we know that
%% the leader process is really gone. We want to clear the leader ID we
%% know at this point, while a new election is running.
%%
%% This is to make sure that `follower_leader_change()' won't create a
%% useless monitor and more importantly, it won't redirect pending
%% commands to that old leader. This would cause the commands callers to
%% get a `noproc' error or a timeout.
State1 = case Info of
noconnection ->
State0;
_ ->
clear_leader_id(State0)
end,
TimeoutLen = case Info of
noconnection ->
short;
_ ->
%% if it isn't a network related error
%% set the shortest timeout
really_short
end,
{State, Actions} = maybe_set_election_timeout(TimeoutLen, State1, []),
{keep_state, State#state{leader_monitor = undefined}, Actions};
follower(info, {'DOWN', _MRef, process, Pid, Info}, State0) ->
handle_process_down(Pid, Info, ?FUNCTION_NAME, State0);
follower(info, {node_event, Node, down}, State0) ->
case leader_id(State0) of
{_, Node} ->
?DEBUG("~ts: Leader node ~w may be down, setting pre-vote timeout",
[log_id(State0), Node]),
{State, Actions} = maybe_set_election_timeout(long, State0, []),
{keep_state, State, Actions};
_ ->
{keep_state, State0, []}
end;
follower(info, {node_event, Node, up}, State) ->
case leader_id(State) of
{_, Node} when State#state.election_timeout_set ->
?DEBUG("~ts: Leader node ~w is back up, cancelling pre-vote timeout",
[log_id(State), Node]),
{keep_state,
State#state{election_timeout_set = false},
[{state_timeout, infinity, election_timeout}]};
_ ->
{keep_state, State, []}
end;
follower(info, {Status, Node, InfoList}, State0)
when Status =:= nodedown orelse Status =:= nodeup ->
handle_node_status_change(Node, Status, InfoList, ?FUNCTION_NAME, State0);
follower(_, tick_timeout, #state{server_state = ServerState0} = State0) ->
ServerState = ra_server:log_tick(ServerState0),
{State, Actions} = ?HANDLE_EFFECTS([{aux, tick}], cast,
State0#state{server_state = ServerState}),
{keep_state, handle_tick_metrics(State),
set_tick_timer(State, Actions)};
follower({call, From}, {log_fold, Fun, Term}, State) ->
fold_log(From, Fun, Term, State);
follower(EventType, Msg, #state{conf = #conf{name = Name},
server_state = SS0} = State0) ->
case handle_follower(Msg, State0) of
{follower, State1, Effects} ->
{State2, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
State = #state{server_state = SS} = follower_leader_change(State0, State2),
Membership0 = ra_server:get_membership(SS0),
case ra_server:get_membership(SS) of
Membership0 ->
ok;
Membership ->
true = ets:update_element(ra_state, Name, {3, Membership})
end,
{keep_state, State, Actions};
{pre_vote, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(pre_vote, State, Actions);
{await_condition, State1, Effects} ->
{State2, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
State = follower_leader_change(State0, State2),
next_state(await_condition, State, Actions);
{receive_snapshot, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(receive_snapshot, State, Actions);
{delete_and_terminate, State1, Effects} ->
{State, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
next_state(terminating_follower, State, Actions)
end.
%% TODO: handle leader down abort snapshot and revert to follower
receive_snapshot(enter, OldState, State0 = #state{conf = Conf}) ->
#conf{receive_snapshot_timeout = ReceiveSnapshotTimeout} = Conf,
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
{keep_state, State,
[{state_timeout, ReceiveSnapshotTimeout, receive_snapshot_timeout}
| Actions]};
receive_snapshot(_, tick_timeout, State0) ->
{keep_state, State0, set_tick_timer(State0, [])};
receive_snapshot({call, From}, {leader_call, Msg}, State) ->
maybe_redirect(From, Msg, State);
receive_snapshot(EventType, {local_call, Msg}, State) ->
receive_snapshot(EventType, Msg, State);
receive_snapshot({call, _From} = EventType, {local_query, QueryFun}, State) ->
receive_snapshot(EventType, {local_query, QueryFun, #{}}, State);
receive_snapshot({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(
receive_snapshot, From, QueryFun, Options, State);
receive_snapshot({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
receive_snapshot(EventType, Msg, State0) ->
case handle_receive_snapshot(Msg, State0) of
{receive_snapshot, State1, Effects} ->
{#state{conf = Conf} = State, Actions} =
?HANDLE_EFFECTS(Effects, EventType, State1),
#conf{receive_snapshot_timeout = ReceiveSnapshotTimeout} = Conf,
{keep_state, State,
[{state_timeout, ReceiveSnapshotTimeout,
receive_snapshot_timeout} | Actions]};
{follower, State1, Effects} ->
{State2, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
State = follower_leader_change(State0, State2),
next_state(follower, State, Actions)
end.
terminating_leader(enter, OldState, State0) ->
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
{keep_state, State, Actions};
terminating_leader(_EvtType, {command, _, _}, State0) ->
% do not process any further commands
{keep_state, State0, []};
terminating_leader(EvtType, Msg, State0) ->
LogName = log_id(State0),
?DEBUG("~ts: terminating leader received ~W", [LogName, Msg, 10]),
{State, Actions} = case leader(EvtType, Msg, State0) of
{next_state, terminating_leader, S, A} ->
{S, A};
{keep_state, S, A} ->
{S, A};
{stop, {shutdown, delete}, S} ->
{S, []}
end,
NS = State#state.server_state,
case ra_server:is_fully_replicated(NS) of
true ->
{stop, {shutdown, delete}, State};
false ->
?DEBUG("~ts: is not fully replicated after ~W",
[LogName, Msg, 7]),
{keep_state, send_rpcs(State), Actions}
end.
terminating_follower(enter, OldState, State0) ->
{State, Actions} = handle_enter(?FUNCTION_NAME, OldState, State0),
{keep_state, State, Actions};
terminating_follower(EvtType, Msg, State0) ->
% only process ra_log_events
LogName = log_id(State0),
?DEBUG("~ts: terminating follower received ~W", [LogName, Msg, 10]),
{State, Actions} = case follower(EvtType, Msg, State0) of
{next_state, terminating_follower, S, A} ->
{S, A};
{next_state, NextState, S, A} ->
?DEBUG("~ts: terminating follower requested state '~s'"
" - remaining in current state",
[LogName, NextState]),
{S, A};
{keep_state, S, A} ->
{S, A}
end,
case ra_server:is_fully_persisted(State#state.server_state) of
true ->
{stop, {shutdown, delete}, State};
false ->
?DEBUG("~ts: is not fully persisted after ~W",
[log_id(State), Msg, 7]),
{keep_state, State, Actions}
end.
await_condition(enter, OldState, #state{conf = Conf,
server_state = ServerState} = State0) ->
{State, Actions0} = handle_enter(?FUNCTION_NAME, OldState, State0),
Timeout = ra_server:get_condition_timeout(ServerState,
Conf#conf.await_condition_timeout),
Actions = [{state_timeout, Timeout, await_condition_timeout} | Actions0],
{keep_state, State, Actions};
await_condition({call, From}, {leader_call, Msg}, State) ->
maybe_redirect(From, Msg, State);
await_condition(EventType, {local_call, Msg}, State) ->
await_condition(EventType, Msg, State);
await_condition({call, _From} = EventType, {local_query, QueryFun}, State) ->
await_condition(EventType, {local_query, QueryFun, #{}}, State);
await_condition({call, From}, {local_query, QueryFun, Options}, State) ->
perform_or_delay_local_query(
await_condition, From, QueryFun, Options, State);
await_condition({call, From}, {state_query, Spec}, State) ->
Reply = {ok, do_state_query(Spec, State), id(State)},
{keep_state, State, [{reply, From, Reply}]};
await_condition(EventType, {aux_command, Cmd}, State0) ->
{_, ServerState, Effects} = ra_server:handle_aux(?FUNCTION_NAME, EventType,
Cmd, State0#state.server_state),
{State, Actions} =
?HANDLE_EFFECTS(Effects, EventType,
State0#state{server_state = ServerState}),
{keep_state, State#state{server_state = ServerState}, Actions};
await_condition({call, From}, ping, State) ->
{keep_state, State, [{reply, From, {pong, await_condition}}]};
await_condition({call, From}, trigger_election, State) ->
{keep_state, State, [{reply, From, ok},
{next_event, cast, election_timeout}]};
await_condition(info, {'DOWN', MRef, process, _Pid, _Info},
State = #state{leader_monitor = MRef}) ->
?INFO("~ts: await_condition - Leader monitor down. Entering follower state.",
[log_id(State)]),
next_state(follower, State#state{leader_monitor = undefined}, []);
await_condition(info, {'DOWN', _MRef, process, Pid, Info}, State0) ->
handle_process_down(Pid, Info, ?FUNCTION_NAME, State0);
await_condition(info, {node_event, Node, down}, State) ->
case leader_id(State) of
{_, Node} ->
?WARN("~ts: await_condition - Leader node ~w might be down."
" Re-entering follower state.",
[log_id(State), Node]),
next_state(follower, State, []);
_ ->
{keep_state, State}
end;
await_condition(info, {Status, Node, InfoList}, State0)
when Status =:= nodedown orelse Status =:= nodeup ->
handle_node_status_change(Node, Status, InfoList, ?FUNCTION_NAME, State0);
await_condition(_, tick_timeout, State0) ->
{State, Actions} = ?HANDLE_EFFECTS([{aux, tick}], cast, State0),
{keep_state, State, set_tick_timer(State, Actions)};
await_condition(EventType, Msg, State0) ->
case handle_await_condition(Msg, State0) of
{follower, State1, Effects} ->
{State2, Actions} = ?HANDLE_EFFECTS(Effects, EventType, State1),
State = follower_leader_change(State0, State2),
next_state(follower, State, Actions);