nickva commented on a change in pull request #610: Optimize ddoc cache URL: https://github.com/apache/couchdb/pull/610#discussion_r126020189
########## File path: src/ddoc_cache/src/ddoc_cache_lru.erl ########## @@ -0,0 +1,311 @@ +% 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 + size, + 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, + size = 0, + 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, + size = CurSize + } = St, + case ets:lookup(?CACHE, Key) of + [] -> + MaxSize = config:get_integer("ddoc_cache", "max_size", 1000), + case trim(St, CurSize, max(0, MaxSize)) of + {ok, N} -> + 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#st{size = CurSize - N + 1}}; + 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(Key, 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( + ?MODULE, handle_db_event, nil, [all_dbs] + ), + {noreply, St#st{evictor=Evictor}}; + +handle_info({'EXIT', Pid, normal}, St) -> + % This clause handles when an entry starts + % up but encounters an error or uncacheable + % response from its recover call. + #st{ + pids = Pids + } = St, + {value, Key} = khash:lookup(Pids, Pid), + khash:del(Pids, Pid), + remove_key(St, Key), + {noreply, St}; + +handle_info(Msg, St) -> + {stop, {invalid_info, Msg}, St}. + + +code_change(_OldVsn, St, _Extra) -> + {ok, St}. + + +handle_db_event(ShardDbName, created, St) -> + gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}), + {ok, St}; + +handle_db_event(ShardDbName, deleted, St) -> + gen_server:cast(?MODULE, {evict, mem3:dbname(ShardDbName)}), + {ok, St}; + +handle_db_event(_DbName, _Event, St) -> + {ok, St}. + + +lru_start(Key, DoInsert) -> + case gen_server:call(?MODULE, {start, Key, undefined}, infinity) of + {ok, Pid} -> + couch_stats:increment_counter([ddoc_cache, miss]), + Resp = ddoc_cache_entry:open(Pid, Key), + if not DoInsert -> ok; true -> + ddoc_cache_entry:insert(Key, Resp) + end, + Resp; + full -> + couch_stats:increment_counter([ddoc_cache, recovery]), + ddoc_cache_entry:recover(Key) + end. + + +trim(_, _, 0) -> + full; + +trim(_St, CurSize, MaxSize) when CurSize < MaxSize -> + {ok, 0}; + +trim(St, CurSize, MaxSize) when CurSize >= MaxSize -> Review comment: The result of trim is one of `full`, `{ok, 1}`, `{ok, 0}` what about the case when an operator adjusts max value at runtime? Wouldn't we want to remove enough entries to make the new constraint take effect. handle_call for `start` is already generalized to handle {ok, N} result so it would be a just a foreach or a list comprehension here. ---------------------------------------------------------------- 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
