davisp commented on a change in pull request #610: Optimize ddoc cache URL: https://github.com/apache/couchdb/pull/610#discussion_r123763380
########## File path: src/ddoc_cache/src/ddoc_cache_lru.erl ########## @@ -0,0 +1,316 @@ +% 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, + + insert/2, + accessed/1, + update/2, + remove/1, + 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, { + atimes, % key -> time + dbs, % dbname -> docid -> key -> [] + time, + evictor +}). + + +start_link() -> + gen_server:start_link({local, ?MODULE}, ?MODULE, [], []). + + +insert(Key, Val) -> + gen_server:call(?MODULE, {insert, Key, Val}). + + +accessed(Key) -> + gen_server:cast(?MODULE, {accessed, Key}). + + +update(Key, Val) -> + gen_server:call(?MODULE, {update, Key, Val}). + + +remove(Key) -> + gen_server:call(?MODULE, {remove, Key}). + + +refresh(DbName, DDocIds) -> + gen_server:cast(?MODULE, {refresh, DbName, DDocIds}). + + +init(_) -> + process_flag(trap_exit, true), + {ok, ATimes} = khash:new(), + {ok, Dbs} = khash:new(), + {ok, Evictor} = couch_event:link_listener( + ?MODULE, handle_db_event, nil, [all_dbs] + ), + {ok, #st{ + atimes = ATimes, + dbs = Dbs, + time = 0, + evictor = Evictor + }}. + + +terminate(_Reason, St) -> + case is_pid(St#st.evictor) of + true -> exit(St#st.evictor, kill); + false -> ok + end, + ok. + + +handle_call({insert, Key, Val}, _From, St) -> + #st{ + atimes = ATimes, + dbs = Dbs, + time = Time + } = St, + NewTime = Time + 1, + NewSt = St#st{time = NewTime}, + Pid = ddoc_cache_refresher:spawn_link(Key, ?REFRESH_TIMEOUT), + true = ets:insert(?CACHE, #entry{key = Key, val = Val, pid = Pid}), + true = ets:insert(?LRU, {NewTime, Key}), + ok = khash:put(ATimes, Key, NewTime), + store_key(Dbs, Key), + trim(NewSt), + ?EVENT(inserted, {Key, Val}), + {reply, ok, NewSt}; + +handle_call({update, Key, Val}, _From, St) -> + #st{ + atimes = ATimes + } = St, + case khash:lookup(ATimes, Key) of + {value, _} -> + ets:update_element(?CACHE, Key, {#entry.val, Val}), + ?EVENT(updated, {Key, Val}), + {reply, ok, St}; + not_found -> + {reply, evicted, St} + end; + +handle_call({remove, Key}, _From, St) -> + #st{ + atimes = ATimes, + dbs = Dbs + } = St, + case khash:lookup(ATimes, Key) of + {value, ATime} -> + [#entry{pid = Pid}] = ets:lookup(?CACHE, Key), + ddoc_cache_refresher:stop(Pid), + remove_key(St, Key, ATime), + + DbName = ddoc_cache_entry:dbname(Key), + DDocId = ddoc_cache_entry:ddocid(Key), + {value, DDocIds} = khash:lookup(Dbs, DbName), + {value, Keys} = khash:lookup(DDocIds, DDocId), + ok = khash:del(Keys, Key), + case khash:size(Keys) of + 0 -> khash:del(DDocIds, DDocId); + _ -> ok + end, + case khash:size(DDocIds) of + 0 -> khash:del(Dbs, DDocId); + _ -> ok + end, + + ?EVENT(removed, Key); + not_found -> + ok + end, + {reply, ok, St}; + +handle_call(Msg, _From, St) -> + {stop, {invalid_call, Msg}, {invalid_call, Msg}, St}. + + +handle_cast({accessed, Key}, St) -> + #st{ + atimes = ATimes, + time = Time + } = St, + NewTime = Time + 1, + case khash:lookup(ATimes, Key) of + {value, OldTime} -> + [#entry{pid = Pid}] = ets:lookup(?CACHE, Key), + true = is_process_alive(Pid), + true = ets:delete(?LRU, OldTime), + true = ets:insert(?LRU, {NewTime, Key}), + ok = khash:put(ATimes, Key, NewTime), + ?EVENT(accessed, Key); + not_found -> + % Likely a client read from the cache while an + % eviction message was in our mailbox + ok + end, + {noreply, 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, + case khash:lookup(Dbs, DbName) of + {value, DDocIds} -> + khash:fold(DDocIds, fun(_, Keys, _) -> + khash:fold(Keys, fun(Key, _, _) -> + [#entry{pid = Pid}] = ets:lookup(?CACHE, Key), + ddoc_cache_refresher:stop(Pid), + remove_key(St, Key) + end, nil) + end, nil), + khash:del(Dbs, DbName), + ?EVENT(evicted, DbName); + not_found -> + ?EVENT(evict_noop, DbName), + ok + end, + {noreply, St}; + +handle_cast({do_refresh, DbName, DDocIdList}, St) -> + #st{ + dbs = Dbs + } = St, + case khash:lookup(Dbs, DbName) of + {value, DDocIds} -> + lists:foreach(fun(DDocId) -> + case khash:lookup(DDocIds, DDocId) of + {value, Keys} -> + khash:fold(Keys, fun(Key, _, _) -> + [#entry{pid = Pid}] = ets:lookup(?CACHE, Key), + ddoc_cache_refresher: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( + ?MODULE, handle_db_event, nil, [all_dbs] + ), + {noreply, St#st{evictor=Evictor}}; + +handle_info(Msg, St) -> + {stop, {invalid_info, Msg}, St}. Review comment: Same as before this is asserting that the cache entries are behaving as expected. Each entry has exactly one refresher pid that lives for as long as the cache entry. We don't want more than one and we especially don't want zero. When we close an entry we unlink and stop the refresher so we should never see an unknown 'EXIT' message. ---------------------------------------------------------------- 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: [email protected] With regards, Apache Git Services
