[GitHub] [couchdb] iilyak commented on a change in pull request #2060: CouchDB map indexes on FDB

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

iilyak commented on a change in pull request #2060: CouchDB map indexes on FDB
URL: https://github.com/apache/couchdb/pull/2060#discussion_r307720331
 
 

 ##########
 File path: src/couch_views/src/couch_views_server.erl
 ##########
 @@ -0,0 +1,101 @@
+% 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(couch_views_server).
+
+
+-behaviour(gen_server).
+
+
+-export([
+    start_link/0
+]).
+
+
+-export([
+    init/1,
+    terminate/2,
+    handle_call/3,
+    handle_cast/2,
+    handle_info/2,
+    code_change/3
+]).
+
+
+-define(MAX_WORKERS, 100).
+
+
+start_link() ->
+    gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
+
+
+init(_) ->
+    process_flag(trap_exit, true),
+    couch_views_jobs:set_timeout(),
+    State = #{
+        workers => [],
+        num_workers => num_workers()
+    },
+    {ok, spawn_workers(State)}.
+
+
+terminate(_, _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({'EXIT', Pid, Reason}, State) ->
+    #{workers := Workers} = State,
+    case Workers -- [Pid] of
+        Workers ->
+            LogMsg = "~p : unknown process ~p exited with ~p",
+            couch_log:error(LogMsg, [?MODULE, Pid, Reason]),
+            {stop, {unknown_pid_exit, Pid}, State};
+        NewWorkers ->
+            if Reason == normal -> ok; true ->
+                LogMsg = "~p : indexer process ~p exited with ~p",
+                couch_log:error(LogMsg, [?MODULE, Pid, Reason])
+            end,
+            {noreply, spawn_workers(State#{workers := NewWorkers})}
+    end;
+
+handle_info(Msg, St) ->
+    {stop, {bad_info, Msg}, St}.
+
+
+code_change(_OldVsn, St, _Extra) ->
+    {ok, St}.
+
+
+spawn_workers(State) ->
 
 Review comment:
   Not a huge concern if MAX_WORKERS would always be 100. However if we ever want to increase number of them (after performance evaluation) we might need to rewrite this function. The `length(Workers) < NumWorkers` is slow part. The opportunities for rewrite are:
   - use map to hold workers (this would also speed up `case Workers -- [Pid] of` on line 65)
   - write this function as:
   ```
   spawn_workers(#{workers = Workers, num_workers = NumWorkers} = State) -> 
     HowManyToSpawn = NumWorkers - length(Workers),
     spawn_workers(State, HowManyToSpawn).
   spawn_workers(State, 0) -> 
     State;
   spawn_workers(State, HowManyToSpawn) ->
      ...
      spawn_workers(State, HowManyToSpawn - 1).
   ```
   
   Feel free to ignore since for list of 100 it is a questionable optimization.

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