nickva commented on a change in pull request #610: Optimize ddoc cache URL: https://github.com/apache/couchdb/pull/610#discussion_r126275438
########## File path: src/ddoc_cache/src/ddoc_cache_lru.erl ########## @@ -0,0 +1,309 @@ +% 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_lru). +-behaviour(gen_server). +-vsn(1). + + +-export([ + start_link/0, + open/1, + insert/2, + refresh/2 +]). + +-export([ + init/1, + terminate/2, + handle_call/3, + handle_cast/2, + handle_info/2, + code_change/3 +]). + +-export([ + handle_db_event/3 +]). + + +-include("ddoc_cache.hrl"). + + +-record(st, { + pids, % pid -> key + dbs, % dbname -> docid -> key -> pid + evictor +}). + + +start_link() -> + gen_server:start_link({local, ?MODULE}, ?MODULE, [], []). + + +open(Key) -> + try ets:lookup(?CACHE, Key) of + [] -> + lru_start(Key, true); + [#entry{pid = undefined}] -> + lru_start(Key, false); + [#entry{val = undefined, pid = Pid}] -> + couch_stats:increment_counter([ddoc_cache, miss]), + ddoc_cache_entry:open(Pid, Key); + [#entry{val = Val, pid = Pid}] -> + couch_stats:increment_counter([ddoc_cache, hit]), + ddoc_cache_entry:accessed(Pid), + {ok, Val} + catch _:_ -> + couch_stats:increment_counter([ddoc_cache, recovery]), + ddoc_cache_entry:recover(Key) + end. + + +insert(Key, Value) -> + case ets:lookup(?CACHE, Key) of + [] -> + gen_server:call(?MODULE, {start, Key, Value}, infinity); + [#entry{}] -> + ok + end. + + +refresh(DbName, DDocIds) -> + gen_server:cast(?MODULE, {refresh, DbName, DDocIds}). + + +init(_) -> + process_flag(trap_exit, true), + {ok, Pids} = khash:new(), + {ok, Dbs} = khash:new(), + {ok, Evictor} = couch_event:link_listener( + ?MODULE, handle_db_event, nil, [all_dbs] + ), + {ok, #st{ + pids = Pids, + dbs = Dbs, + evictor = Evictor + }}. + + +terminate(_Reason, St) -> + case is_pid(St#st.evictor) of + true -> catch exit(St#st.evictor, kill); + false -> ok + end, + ok. + + +handle_call({start, Key, Default}, _From, St) -> + #st{ + pids = Pids, + dbs = Dbs + } = St, + case ets:lookup(?CACHE, Key) of + [] -> + MaxSize = config:get_integer("ddoc_cache", "max_size", 1000), + CurSize = ets:info(?CACHE, size), + case trim(St, CurSize, max(0, MaxSize)) of + ok -> + true = ets:insert_new(?CACHE, #entry{key = Key}), + {ok, Pid} = ddoc_cache_entry:start_link(Key, Default), + true = ets:update_element(?CACHE, Key, {#entry.pid, Pid}), + ok = khash:put(Pids, Pid, Key), + store_key(Dbs, Key, Pid), + {reply, {ok, Pid}, St}; + full -> + ?EVENT(full, Key), + {reply, full, St} + end; + [#entry{pid = Pid}] -> + {reply, {ok, Pid}, St} + end; + +handle_call(Msg, _From, St) -> + {stop, {invalid_call, Msg}, {invalid_call, Msg}, St}. + + +handle_cast({evict, DbName}, St) -> + gen_server:abcast(mem3:nodes(), ?MODULE, {do_evict, DbName}), + {noreply, St}; + +handle_cast({refresh, DbName, DDocIds}, St) -> + gen_server:abcast(mem3:nodes(), ?MODULE, {do_refresh, DbName, DDocIds}), + {noreply, St}; + +handle_cast({do_evict, DbName}, St) -> + #st{ + dbs = Dbs + } = St, + ToRem = case khash:lookup(Dbs, DbName) of + {value, DDocIds} -> + AccOut = khash:fold(DDocIds, fun(_, Keys, Acc1) -> + khash:to_list(Keys) ++ Acc1 + end, []), + ?EVENT(evicted, DbName), + AccOut; + not_found -> + ?EVENT(evict_noop, DbName), + [] + end, + lists:foreach(fun({Key, Pid}) -> + remove_entry(St, Key, Pid) + end, ToRem), + khash:del(Dbs, DbName), + {noreply, St}; + +handle_cast({do_refresh, DbName, DDocIdList}, St) -> + #st{ + dbs = Dbs + } = St, + % We prepend no_ddocid to the DDocIdList below + % so that we refresh all custom and validation + % function entries which load data from all + % design documents. + case khash:lookup(Dbs, DbName) of + {value, DDocIds} -> + lists:foreach(fun(DDocId) -> + case khash:lookup(DDocIds, DDocId) of + {value, Keys} -> + khash:fold(Keys, fun(_, Pid, _) -> + ddoc_cache_entry:refresh(Pid) + end, nil); + not_found -> + ok + end + end, [no_ddocid | DDocIdList]); + not_found -> + ok + end, + {noreply, St}; + +handle_cast(Msg, St) -> + {stop, {invalid_cast, Msg}, St}. + + +handle_info({'EXIT', Pid, _Reason}, #st{evictor = Pid} = St) -> + ?EVENT(evictor_died, Pid), + {ok, Evictor} = couch_event:link_listener( Review comment: Any worry about event listeners re-spawning and crashing back to back? Remember seeing for config change listeners in other parts of the code we add a delay before restarting another one. I guess here we don't want to risk losing db events if we add any delay. ---------------------------------------------------------------- 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
