chewbranca commented on a change in pull request #610: Optimize ddoc cache
URL: https://github.com/apache/couchdb/pull/610#discussion_r123589451
##########
File path: src/ddoc_cache/src/ddoc_cache_opener.erl
##########
@@ -32,195 +32,96 @@
]).
-export([
- open_doc/2,
- open_doc/3,
- open_validation_funs/1,
- evict_docs/2,
- lookup/1,
- match_newest/1,
- recover_doc/2,
- recover_doc/3,
- recover_validation_funs/1
+ open/1
]).
--export([
- handle_db_event/3
-]).
--export([
- fetch_doc_data/1
-]).
-
--define(CACHE, ddoc_cache_lru).
--define(OPENING, ddoc_cache_opening).
--type dbname() :: iodata().
--type docid() :: iodata().
--type doc_hash() :: <<_:128>>.
--type revision() :: {pos_integer(), doc_hash()}.
+-include("ddoc_cache.hrl").
--record(opener, {
- key,
- pid,
- clients
-}).
-record(st, {
- db_ddocs,
- evictor
+ db_ddocs
}).
start_link() ->
gen_server:start_link({local, ?MODULE}, ?MODULE, [], []).
--spec open_doc(dbname(), docid()) -> {ok, #doc{}}.
-open_doc(DbName, DocId) ->
- Resp = gen_server:call(?MODULE, {open, {DbName, DocId}}, infinity),
- handle_open_response(Resp).
--spec open_doc(dbname(), docid(), revision()) -> {ok, #doc{}}.
-open_doc(DbName, DocId, Rev) ->
- Resp = gen_server:call(?MODULE, {open, {DbName, DocId, Rev}}, infinity),
- handle_open_response(Resp).
-
--spec open_validation_funs(dbname()) -> {ok, [fun()]}.
-open_validation_funs(DbName) ->
- Resp = gen_server:call(?MODULE, {open, {DbName, validation_funs}},
infinity),
- handle_open_response(Resp).
-
--spec evict_docs(dbname(), [docid()]) -> ok.
-evict_docs(DbName, DocIds) ->
- gen_server:cast(?MODULE, {evict, DbName, DocIds}).
-
-lookup(Key) ->
- try ets_lru:lookup_d(?CACHE, Key) of
- {ok, _} = Resp ->
- Resp;
- _ ->
- missing
- catch
- error:badarg ->
- recover
- end.
-
-match_newest(Key) ->
- try ets_lru:match_object(?CACHE, Key, '_') of
+open(Key) ->
+ try ets:lookup(?CACHE, Key) of
[] ->
- missing;
- Docs ->
- Sorted = lists:sort(
- fun (#doc{deleted=DelL, revs=L}, #doc{deleted=DelR, revs=R}) ->
- {not DelL, L} > {not DelR, R}
- end, Docs),
- {ok, hd(Sorted)}
- catch
- error:badarg ->
- recover
+ couch_stats:increment_counter([ddoc_cache, miss]),
+ Resp = gen_server:call(?MODULE, {open, Key}, infinity),
Review comment:
We're falling back on the same pattern here of sending an open message on
every cache miss. We've seen this to be problematic in the existing ddoc_cache,
and I think this is an important issue to solve here. Is there a reason you
think sticking with this approach is the proper way forward? It seems like
we'll still be susceptible to thundering herd problems when there is not an
entry in the cache.
Would it make sense to use the opener pattern you used recently in
mem3_shards?
https://github.com/apache/couchdb/commit/b71677f593fb62e590f37c2cbb5bb851bd12c11c
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