[GitHub] [couchdb] davisp commented on a change in pull request #2637: Index auto-updater

[GitBox <gi...@apache.org>]

davisp commented on a change in pull request #2637: Index auto-updater
URL: https://github.com/apache/couchdb/pull/2637#discussion_r389860648
 
 

 ##########
 File path: src/fabric/src/fabric2_index.erl
 ##########
 @@ -0,0 +1,228 @@
+% 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.
+
+-module(fabric2_index).
+
+
+-behaviour(gen_server).
+
+
+-export([
+    register_index/1,
+
+    db_updated/1,
+
+    start_link/0,
+
+    init/1,
+    terminate/2,
+    handle_call/3,
+    handle_cast/2,
+    handle_info/2,
+    code_change/3
+]).
+
+
+-include_lib("couch/include/couch_db.hrl").
+
+
+-callback build_indices(Db :: map(), DDocs :: list(#doc{})) ->
+    [{ok, JobId::binary()} | {error, any()}].
+
+
+-define(SHARDS, 32).
+-define(DEFAULT_DELAY_MSEC, 60000).
+-define(DEFAULT_RESOLUTION_MSEC, 10000).
+
+
+register_index(Mod) when is_atom(Mod) ->
+    Indices = lists:usort([Mod | registrations()]),
+    application:set_env(fabric, indices, Indices).
+
+
+db_updated(DbName) when is_binary(DbName) ->
+    Table = table(erlang:phash2(DbName) rem ?SHARDS),
+    ets:insert_new(Table, {DbName, now_msec()}).
+
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+
+init(_) ->
+    lists:foreach(fun(T) ->
+        spawn_link(fun() -> process_loop(T) end)
+    end, create_tables()),
+    {ok, nil}.
+
+
+terminate(_M, _St) ->
+    ok.
+
+
+handle_call(Msg, _From, St) ->
+    {stop, {bad_call, Msg}, {bad_call, Msg}, St}.
+
+
+handle_cast(Msg, St) ->
+    {stop, {bad_cast, Msg}, St}.
+
+
+handle_info(Msg, St) ->
+    {stop, {bad_info, Msg}, St}.
+
+
+code_change(_OldVsn, St, _Extra) ->
+    {ok, St}.
+
+
+create_tables() ->
+    Opts = [
+        named_table,
+        public,
+        {write_concurrency, true},
+        {read_concurrency, true}
+    ],
+    Tables = [table(N) || N <- lists:seq(0, ?SHARDS - 1)],
+    [ets:new(T, Opts) || T <- Tables].
+
+
+table(Id) when is_integer(Id), Id >= 0 andalso Id < ?SHARDS ->
+    list_to_atom("fabric2_index_" ++ integer_to_list(Id)).
+
+
+process_loop(Table) ->
+    % In some cases we'd want to monitor the parent process and exit if it
+    % exits `normal` since links won't trigger then. However our parent never
+    % exists `normal`. When supervisor shuts it down, it will do it with a
+    % `shutdown` signal. Then the `process_loop` also never exits `normal` so
+    % there is no need to monitor it from the parent.
 
 Review comment:
   I remember asking about this, but I'm not sure its important enough to keep a long comment about something we're not doing that's more Erlang system knowledge.

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