nickva commented on a change in pull request #610: Optimize ddoc cache URL: https://github.com/apache/couchdb/pull/610#discussion_r126275240
########## File path: src/ddoc_cache/src/ddoc_cache_entry.erl ########## @@ -0,0 +1,332 @@ +% 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(ddoc_cache_entry). +-behaviour(gen_server). + + +-export([ + dbname/1, + ddocid/1, + recover/1, + insert/2, + + start_link/2, + shutdown/1, + open/2, + accessed/1, + refresh/1 +]). + +-export([ + init/1, + terminate/2, + handle_call/3, + handle_cast/2, + handle_info/2, + code_change/3 +]). + +-export([ + do_open/1 +]). + + +-include("ddoc_cache.hrl"). + + +-record(st, { + key, + val, + opener, + waiters, + ts, + accessed +}). + + +dbname({Mod, Arg}) -> + Mod:dbname(Arg). + + +ddocid({Mod, Arg}) -> + Mod:ddocid(Arg). + + +recover({Mod, Arg}) -> + Mod:recover(Arg). + + +insert({Mod, Arg}, Value) -> + Mod:insert(Arg, Value). + + +start_link(Key, Default) -> + Pid = proc_lib:spawn_link(?MODULE, init, [{Key, Default}]), + {ok, Pid}. + + +shutdown(Pid) -> + ok = gen_server:call(Pid, shutdown). + + +open(Pid, Key) -> + try + Resp = gen_server:call(Pid, open), + case Resp of + {open_ok, Val} -> + Val; + {open_error, {T, R, S}} -> + erlang:raise(T, R, S) + end + catch exit:_ -> + % Its possible that this process was evicted just + % before we tried talking to it. Just fallback + % to a standard recovery + recover(Key) + end. + + +accessed(Pid) -> + gen_server:cast(Pid, accessed). + + +refresh(Pid) -> + gen_server:cast(Pid, force_refresh). + + +init({Key, undefined}) -> + true = ets:update_element(?CACHE, Key, {#entry.pid, self()}), + St = #st{ + key = Key, + opener = spawn_opener(Key), + waiters = [], + accessed = 1 + }, + ?EVENT(started, Key), + gen_server:enter_loop(?MODULE, [], St); + +init({Key, Default}) -> + Updates = [ + {#entry.val, Default}, + {#entry.pid, self()} + ], + NewTs = os:timestamp(), + true = ets:update_element(?CACHE, Key, Updates), + true = ets:insert(?LRU, {{NewTs, Key, self()}}), + St = #st{ + key = Key, + val = {open_ok, {ok, Default}}, + opener = start_timer(), + waiters = undefined, + ts = NewTs, + accessed = 1 + }, + ?EVENT(default_started, Key), + gen_server:enter_loop(?MODULE, [], St). + + +terminate(_Reason, St) -> + #st{ + key = Key, + opener = Pid, + ts = Ts + } = St, + % We may have already deleted our cache entry + % during shutdown + Pattern = #entry{key = Key, pid = self(), _ = '_'}, + CacheMSpec = [{Pattern, [], [true]}], + true = ets:select_delete(?CACHE, CacheMSpec) < 2, + % We may have already deleted our LRU entry + % during shutdown + if Ts == undefined -> ok; true -> + LruMSpec = [{{{Ts, Key, self()}}, [], [true]}], + true = ets:select_delete(?LRU, LruMSpec) < 2 + end, + % Blow away any current opener if it exists + if not is_pid(Pid) -> ok; true -> + catch exit(Pid, kill) + end, + ok. + + +handle_call(open, From, #st{val = undefined} = St) -> + NewSt = St#st{ + waiters = [From | St#st.waiters] + }, + {noreply, NewSt}; + +handle_call(open, _From, St) -> + {reply, St#st.val, St}; + +handle_call(shutdown, _From, St) -> + remove_from_cache(St), + {stop, normal, ok, St}; + +handle_call(Msg, _From, St) -> + {stop, {bad_call, Msg}, {bad_call, Msg}, St}. + + +handle_cast(accessed, St) -> Review comment: Running the `ddoc_cache_speed` test with 1500 to 2000 workers saw that cache entry processes had `accessed` messages backed up in their queues (300-1000) messages. They seemed to be in a steady state so they didn't seem to increase much. But if that's something we'd want to mitigate, we could something like not calling update_lru on every accessed message. So for example on each update_lru call put a 'last_update_timestamp' in the process dictionary or state and only update again if last update was more than 1 second old. That way in most cases `accessed` cast handler will just drain the messages and get back to waiting for more message to prevent messages from accumulating. ---------------------------------------------------------------- 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
