davisp commented on a change in pull request #610: Optimize ddoc cache
URL: https://github.com/apache/couchdb/pull/610#discussion_r123763744
##########
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:
Right. I was only focused on the worst case we've seen where we have very
little load on ddoc_cache and were still hitting the thundering herd (because
of the TTL expiration). I'll contemplate the mem3 approach but if memory serves
that requires us to change our hard limit on cache size to a soft limit.
Granted that's not a huge issue but its something to think about.
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