Fix bugs in pre-init

The first thing a ra system does when it starts is run a pre-init
phase for each registered Ra server, mostly to recover the
ra_log_snapshot_state table. This apperas to have been broken
for along time and the ra_log_snapshot_table has not been populated
ahead of WAL / segment writer recovery. This was fine as this bit
was just an optimisation and never affected the workings of
the Ra infrastructure.

However since 5b7a265 it needs
this in order to avoid the segment writer crashing when it detects
a gap (caused by the WAL dropping entries lower than the current
snapshot).

This commit mostly fixes the pre-init process but also addresses
a potential race condition which still could cause the segment
writer to crash for the same reason.

src/ra_directory.erl

@@ -19,7 +19,8 @@
          pid_of/2,
          uid_of/2,
          overview/1,
-         list_registered/1
+         list_registered/1,
+         is_registered_uid/2
          ]).
 
 -export_type([
@@ -199,6 +200,13 @@ list_registered(System) when is_atom(System) ->
     Tbl = get_reverse(System),
     dets:select(Tbl, [{'_', [], ['$_']}]).
 
+-spec is_registered_uid(atom(), ra_uid()) -> boolean().
+is_registered_uid(System, UId)
+  when is_atom(System) andalso
+       is_binary(UId) ->
+    Tbl = get_reverse(System),
+    [] =/= dets:select(Tbl, [{{'_', UId}, [], ['$_']}]).
+
 get_name(#{directory := Tbl}) ->
     Tbl;
 get_name(System) when is_atom(System) ->

src/ra_log_pre_init.erl

@@ -22,6 +22,7 @@
 
 -record(state, {}).
 
+-define(ETSTBL, ra_log_snapshot_state).
 %%%===================================================================
 %%% API functions
 %%%===================================================================
@@ -40,7 +41,16 @@ init([System]) ->
     Regd = ra_directory:list_registered(System),
     ?INFO("ra system '~ts' running pre init for ~b registered servers",
           [System, length(Regd)]),
-    _ = [catch(pre_init(System, Name)) || {Name, _U} <- Regd],
+    _ = [begin
+             try pre_init(System, Name, UId) of
+                 ok -> ok
+             catch _:Err ->
+                       ?ERROR("pre_init failed in system ~s for UId ~ts with name ~ts"
+                              " This error may need manual intervention",
+                              [System, UId, Name]),
+                       throw({stop, {error, Err}})
+             end
+         end|| {Name, UId} <- Regd],
     {ok, #state{} , hibernate}.
 
 handle_call(_Request, _From, State) ->
@@ -63,8 +73,20 @@ code_change(_OldVsn, State, _Extra) ->
 %%% Internal functions
 %%%===================================================================
 
-pre_init(System, Name) ->
-    {ok, #{log_init_args := Log}} = ra_server_sup_sup:recover_config(System, Name),
-    _ = ra_log:pre_init(Log),
-    ok.
+pre_init(System, Name, UId) ->
+    case ets:lookup(?ETSTBL, UId) of
+        [{_, _}] ->
+            %% already initialised
+            ok;
+        [] ->
+            case ra_system:fetch(System) of
+                undefined ->
+                    {error, system_not_started};
+                SysCfg ->
+                    {ok, #{log_init_args := Log}} =
+                        ra_server_sup_sup:recover_config(System, Name),
+                    ok = ra_log:pre_init(Log#{system_config => SysCfg}),
+                    ok
+            end
+    end.
 

src/ra_log_segment_writer.erl

@@ -236,8 +236,8 @@ do_segment({ServerUId, StartIdx0, EndIdx, Tid},
             _ = clean_closed_mem_tables(System, ServerUId, Tid),
             ok;
         Segment0 ->
-            case append_to_segment(ServerUId, Tid, StartIdx0, EndIdx,
-                                   Segment0, State) of
+            case catch append_to_segment(ServerUId, Tid, StartIdx0, EndIdx,
+                                         Segment0, State) of
                 undefined ->
                     ?WARN("segment_writer: skipping segments for ~w as
                            directory ~ts disappeared whilst writing",
@@ -308,40 +308,57 @@ append_to_segment(_, _, StartIdx, EndIdx, Seg, Closed, _State)
   when StartIdx >= EndIdx ->
     {Seg, Closed};
 append_to_segment(UId, Tid, Idx, EndIdx, Seg0, Closed, State) ->
-    [{_, Term, Data0}] = ets:lookup(Tid, Idx),
-    Data = term_to_iovec(Data0),
-    DataSize = iolist_size(Data),
-    case ra_log_segment:append(Seg0, Idx, Term, {DataSize, Data}) of
-        {ok, Seg} ->
-            ok = counters:add(State#state.counter, ?C_ENTRIES, 1),
-            %% this isn't completely accurate as firstly the segment may not
-            %% have written it to disk and it doesn't include data written to
-            %% the segment index but is probably good enough to get comparative
-            %% data rates for different Ra components
-            ok = counters:add(State#state.counter, ?C_BYTES_WRITTEN, DataSize),
-            append_to_segment(UId, Tid, Idx+1, EndIdx, Seg, Closed, State);
-        {error, full} ->
-            % close and open a new segment
-            case open_successor_segment(Seg0, State#state.segment_conf) of
-                undefined ->
-                    %% a successor cannot be opened - this is most likely due
-                    %% to the directory having been deleted.
-                    %% clear close mem tables here
-                    _ = ets:delete(Tid),
-                    _ = clean_closed_mem_tables(State#state.system, UId, Tid),
-                    undefined;
-                Seg ->
-                    ok = counters:add(State#state.counter, ?C_SEGMENTS, 1),
-                    %% re-evaluate snapshot state for the server in case
-                    %% a snapshot has completed during segment flush
-                    StartIdx = start_index(UId, Idx),
-                    % recurse
-                    append_to_segment(UId, Tid, StartIdx, EndIdx, Seg,
-                                      [Seg0 | Closed], State)
+    case ets:lookup(Tid, Idx) of
+        [] ->
+            %% oh dear, an expected index was not found in the mem table.
+            ?WARN("segment_writer: missing index ~b in mem table ~s for uid ~s"
+                  "checking to see if UId has been unregistered",
+                  [Idx, Tid, UId]),
+            case ra_directory:is_registered_uid(State#state.system, UId) of
+                true ->
+                    ?ERROR("segment_writer: uid ~s is registered, exiting...",
+                           [UId]),
+                    exit({missing_index, UId, Idx});
+                false ->
+                    ?INFO("segment_writer: UId ~s was not registered, skipping",
+                          [UId]),
+                    throw(undefined)
             end;
-        {error, Posix} ->
-            FileName = ra_log_segment:filename(Seg0),
-            exit({segment_writer_append_error, FileName, Posix})
+        [{_, Term, Data0}] ->
+            Data = term_to_iovec(Data0),
+            DataSize = iolist_size(Data),
+            case ra_log_segment:append(Seg0, Idx, Term, {DataSize, Data}) of
+                {ok, Seg} ->
+                    ok = counters:add(State#state.counter, ?C_ENTRIES, 1),
+                    %% this isn't completely accurate as firstly the segment may not
+                    %% have written it to disk and it doesn't include data written to
+                    %% the segment index but is probably good enough to get comparative
+                    %% data rates for different Ra components
+                    ok = counters:add(State#state.counter, ?C_BYTES_WRITTEN, DataSize),
+                    append_to_segment(UId, Tid, Idx+1, EndIdx, Seg, Closed, State);
+                {error, full} ->
+                    % close and open a new segment
+                    case open_successor_segment(Seg0, State#state.segment_conf) of
+                        undefined ->
+                            %% a successor cannot be opened - this is most likely due
+                            %% to the directory having been deleted.
+                            %% clear close mem tables here
+                            _ = ets:delete(Tid),
+                            _ = clean_closed_mem_tables(State#state.system, UId, Tid),
+                            undefined;
+                        Seg ->
+                            ok = counters:add(State#state.counter, ?C_SEGMENTS, 1),
+                            %% re-evaluate snapshot state for the server in case
+                            %% a snapshot has completed during segment flush
+                            StartIdx = start_index(UId, Idx),
+                            % recurse
+                            append_to_segment(UId, Tid, StartIdx, EndIdx, Seg,
+                                              [Seg0 | Closed], State)
+                    end;
+                {error, Posix} ->
+                    FileName = ra_log_segment:filename(Seg0),
+                    exit({segment_writer_append_error, FileName, Posix})
+            end
     end.
 
 find_segment_files(Dir) ->

src/ra_server_proc.erl

@@ -1022,11 +1022,17 @@ terminate(Reason, StateName,
         ra_server:system_config(ServerState),
     UId = uid(State),
     Id = id(State),
-    _ = ra_server:terminate(ServerState, Reason),
     case Reason of
         {shutdown, delete} ->
             Parent = ra_directory:where_is_parent(Names, UId),
+            %% we need to unregister _before_ the log closes
+            %% in the ra_server:terminate/2 function
+            %% as we want the directory to be deleted
+            %% after the server is removed from the ra directory.
+            %% This is so that the segment writer can avoid
+            %% crashing if it detects a missing key
             catch ra_directory:unregister_name(Names, UId),
+            _ = ra_server:terminate(ServerState, Reason),
             catch ra_log_meta:delete_sync(MetaName, UId),
             catch ra_counters:delete(Id),
             Self = self(),
@@ -1044,9 +1050,9 @@ terminate(Reason, StateName,
                               end
                       end),
             ok;
-
-
-        _ -> ok
+        _ ->
+            _ = ra_server:terminate(ServerState, Reason),
+            ok
     end,
     catch ra_leaderboard:clear(ClusterName),
     _ = ets:delete(ra_metrics, MetricsKey),

test/ra_dbg_SUITE.erl

@@ -9,7 +9,6 @@
 -compile(nowarn_export_all).
 -compile(export_all).
 
--include_lib("common_test/include/ct.hrl").
 -include_lib("eunit/include/eunit.hrl").
 
 all() ->

test/ra_directory_SUITE.erl

@@ -72,6 +72,7 @@ basics(_Config) ->
     % registrations should always succeed - no negative test
     Self = ra_directory:where_is(?SYS, UId),
     UId = ra_directory:uid_of(?SYS, test1),
+    ?assert(ra_directory:is_registered_uid(?SYS, UId)),
     % ensure it can be read from another process
     _ = spawn_link(
           fun () ->
@@ -86,6 +87,7 @@ basics(_Config) ->
     undefined = ra_directory:name_of(?SYS, UId),
     undefined = ra_directory:cluster_name_of(?SYS, UId),
     undefined = ra_directory:uid_of(?SYS, test1),
+    ?assertNot(ra_directory:is_registered_uid(?SYS, UId)),
     ok.
 
 persistence(_Config) ->

test/ra_log_2_SUITE.erl

@@ -67,31 +67,38 @@ groups() ->
     ].
 
 init_per_suite(Config) ->
-    {ok, _} = ra:start([{data_dir, ?config(priv_dir, Config)},
-                        {segment_max_entries, 128}]),
     Config.
 
 end_per_suite(Config) ->
-    application:stop(ra),
     Config.
 
 init_per_group(G, Config) ->
-    [{access_pattern, G} | Config].
+    DataDir = filename:join(?config(priv_dir, Config), G),
+    [{access_pattern, G},
+     {work_dir, DataDir}
+     | Config].
 
 end_per_group(_, Config) ->
     Config.
 
 init_per_testcase(TestCase, Config) ->
+    ok = start_ra(Config),
     ra_env:configure_logger(logger),
-    PrivDir = ?config(priv_dir, Config),
+    DataDir = ?config(work_dir, Config),
     UId = <<(atom_to_binary(TestCase, utf8))/binary,
             (atom_to_binary(?config(access_pattern, Config)))/binary>>,
-    ra:start(),
     ok = ra_directory:register_name(default, UId, self(), undefined,
                                     TestCase, TestCase),
-    [{uid, UId}, {test_case, TestCase}, {wal_dir, PrivDir} | Config].
+    ServerConf = #{log_init_args => #{uid => UId}},
+
+    ok = ra_lib:make_dir(filename:join([DataDir, node(), UId])),
+    ok = ra_lib:write_file(filename:join([DataDir, node(), UId, "config"]),
+                           list_to_binary(io_lib:format("~p.", [ServerConf]))),
+
+    [{uid, UId}, {test_case, TestCase}, {wal_dir, DataDir} | Config].
 
 end_per_testcase(_, _Config) ->
+    application:stop(ra),
     ok.
 
 -define(N1, {n1, node()}).
@@ -429,13 +436,13 @@ written_event_after_snapshot(Config) ->
     ok.
 
 writes_lower_than_snapshot_index_are_dropped(Config) ->
+    logger:set_primary_config(level, debug),
     Log0 = ra_log_init(Config, #{min_snapshot_interval => 1}),
     Log1 = ra_log:append({1, 1, <<"one">>}, Log0),
     Log1b = deliver_all_log_events(ra_log:append({2, 1, <<"two">>}, Log1), 500),
     true = erlang:suspend_process(whereis(ra_log_wal)),
     Log2 = write_n(3, 500, 1, Log1b),
-    {Log3, _} = ra_log:update_release_cursor(100, #{}, 1,
-                                             <<"100">>, Log2),
+    {Log3, _} = ra_log:update_release_cursor(100, #{}, 1, <<"100">>, Log2),
     Log4 = deliver_all_log_events(Log3, 500),
 
     Overview = ra_log:overview(Log4),
@@ -473,8 +480,10 @@ writes_lower_than_snapshot_index_are_dropped(Config) ->
                    cache_size := 0,
                    cache_range := undefined,
                    last_written_index_term := {499, 1}}, OverviewAfter),
+    %% restart the app to test recovery with a "gappy" wal
+    application:stop(ra),
+    start_ra(Config),
     erlang:monitor(process, whereis(ra_log_segment_writer)),
-    exit(whereis(ra_log_wal), kill),
     receive
         {'DOWN', _, _, _, _} = D ->
             ct:fail("DOWN received ~p", [D])
@@ -589,7 +598,7 @@ recovery(Config) ->
     Log4 = assert_log_events(Log3, Pred, 2000),
     ra_log:close(Log4),
     application:stop(ra),
-    ra:start(),
+    start_ra(Config),
 
     Log5 = ra_log_init(Config),
     {20, 3} = ra_log:last_index_term(Log5),
@@ -610,7 +619,7 @@ recover_bigly(Config) ->
     Log2 = assert_log_events(Log1, Pred, 2000),
     ra_log:close(Log2),
     application:stop(ra),
-    ra:start(),
+    start_ra(Config),
     Log = ra_log_init(Config),
     {9999, 1} = ra_log:last_written(Log),
     {9999, 1} = ra_log:last_index_term(Log),
@@ -1150,21 +1159,23 @@ transient_writer_is_handled(Config) ->
     Self = self(),
     UId2 = <<(?config(uid, Config))/binary, "sub_proc">>,
     _Pid = spawn(fun () ->
-                         ra_directory:register_name(default, <<"sub_proc">>,
+                         ra_directory:register_name(default, UId2,
                                                     self(), undefined,
                                                     sub_proc, sub_proc),
                          Log0 = ra_log_init(Config, #{uid => UId2}),
                          Log1 = append_n(1, 10, 2, Log0),
                          % ignore events
                          Log2 = deliver_all_log_events(Log1, 500),
                          ra_log:close(Log2),
-                         Self ! done
+                         Self ! done,
+                         ok
                  end),
     receive done -> ok
     after 2000 -> exit(timeout)
     end,
-    ra:start(),
+    UId2 = ra_directory:unregister_name(default, UId2),
     _ = ra_log_init(Config),
+    ct:pal("~p", [ra_directory:list_registered(default)]),
     ok.
 
 open_segments_limit(Config) ->
@@ -1499,8 +1510,8 @@ meta(Idx, Term, Cluster) ->
       machine_version => 1}.
 
 create_snapshot_chunk(Config, #{index := Idx} = Meta, Context) ->
-    OthDir = filename:join(?config(priv_dir, Config), "snapshot_installation"),
-    CPDir = filename:join(?config(priv_dir, Config), "checkpoints"),
+    OthDir = filename:join(?config(work_dir, Config), "snapshot_installation"),
+    CPDir = filename:join(?config(work_dir, Config), "checkpoints"),
     ok = ra_lib:make_dir(OthDir),
     ok = ra_lib:make_dir(CPDir),
     Sn0 = ra_snapshot:init(<<"someotheruid_adsfasdf">>, ra_log_snapshot,
@@ -1538,3 +1549,8 @@ restart_wal() ->
     ok = supervisor:terminate_child(SupPid, ra_log_wal),
     {ok, _} = supervisor:restart_child(SupPid, ra_log_wal),
     ok.
+
+start_ra(Config) ->
+    {ok, _} = ra:start([{data_dir, ?config(work_dir, Config)},
+                        {segment_max_entries, 128}]),
+    ok.