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author | Paul J. Davis <paul.joseph.davis@gmail.com> | 2017-02-24 12:55:37 -0600 |
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committer | Paul J. Davis <paul.joseph.davis@gmail.com> | 2017-04-21 10:41:30 -0500 |
commit | e4c3705def6021a6b801c0bc0ceaac4abbc7c0d8 (patch) | |
tree | 18f9348bb8d2ecd2c7b449db6997e56f5a7032dc | |
parent | 778738b1b61dbb559a0ecc2acdd8720a02cc7ec8 (diff) | |
download | couchdb-e4c3705def6021a6b801c0bc0ceaac4abbc7c0d8.tar.gz |
Fix stale shards cache
There's a race condition in mem3_shards that can result in having shards
in the cache for a database that's been deleted. This results in a
confused cluster that thinks a database exists until you attempt to open
it.
The fix is to ignore any cache insert requests that come from an older
version of the dbs db than mem3_shards cache knows about.
Big thanks to @jdoane for the identification and original patch.
COUCHDB-3376
-rw-r--r-- | src/mem3/src/mem3_shards.erl | 59 |
1 files changed, 48 insertions, 11 deletions
diff --git a/src/mem3/src/mem3_shards.erl b/src/mem3/src/mem3_shards.erl index c7f33c61f..ca5deaf45 100644 --- a/src/mem3/src/mem3_shards.erl +++ b/src/mem3/src/mem3_shards.erl @@ -27,7 +27,8 @@ -record(st, { max_size = 25000, cur_size = 0, - changes_pid + changes_pid, + update_seq }). -include_lib("mem3/include/mem3.hrl"). @@ -191,11 +192,12 @@ init([]) -> ets:new(?ATIMES, [ordered_set, protected, named_table]), ok = config:listen_for_changes(?MODULE, nil), SizeList = config:get("mem3", "shard_cache_size", "25000"), - {Pid, _} = spawn_monitor(fun() -> listen_for_changes(get_update_seq()) end), + UpdateSeq = get_update_seq(), {ok, #st{ max_size = list_to_integer(SizeList), cur_size = 0, - changes_pid = Pid + changes_pid = start_changes_listener(UpdateSeq), + update_seq = UpdateSeq }}. handle_call({set_max_size, Size}, _From, St) -> @@ -210,12 +212,28 @@ handle_cast({cache_hit, DbName}, St) -> couch_stats:increment_counter([mem3, shard_cache, hit]), cache_hit(DbName), {noreply, St}; -handle_cast({cache_insert, DbName, Shards}, St) -> +handle_cast({cache_insert, DbName, Shards, UpdateSeq}, St) -> couch_stats:increment_counter([mem3, shard_cache, miss]), - {noreply, cache_free(cache_insert(St, DbName, Shards))}; + % This comparison correctly uses the `<` operator + % and not `=<`. The easiest way to understand why is + % to think of when a _dbs db doesn't change. If it used + % `=<` it would be impossible to insert anything into + % the cache. + NewSt = case UpdateSeq < St#st.update_seq of + true -> St; + false -> cache_free(cache_insert(St, DbName, Shards)) + end, + {noreply, NewSt}; handle_cast({cache_remove, DbName}, St) -> couch_stats:increment_counter([mem3, shard_cache, eviction]), {noreply, cache_remove(St, DbName)}; +handle_cast({cache_insert_change, DbName, Shards, UpdateSeq}, St) -> + Msg = {cache_insert, DbName, Shards, UpdateSeq}, + {noreply, NewSt} = handle_cast(Msg, St), + {noreply, NewSt#st{update_seq = UpdateSeq}}; +handle_cast({cache_remove_change, DbName, UpdateSeq}, St) -> + {noreply, NewSt} = handle_cast({cache_remove, DbName}, St), + {noreply, NewSt#st{update_seq = UpdateSeq}}; handle_cast(_Msg, St) -> {noreply, St}. @@ -232,8 +250,9 @@ handle_info({'DOWN', _, _, Pid, Reason}, #st{changes_pid=Pid}=St) -> erlang:send_after(5000, self(), {start_listener, Seq}), {noreply, NewSt#st{changes_pid=undefined}}; handle_info({start_listener, Seq}, St) -> - {NewPid, _} = spawn_monitor(fun() -> listen_for_changes(Seq) end), - {noreply, St#st{changes_pid=NewPid}}; + {noreply, St#st{ + changes_pid = start_changes_listener(Seq) + }}; handle_info(restart_config_listener, State) -> ok = config:listen_for_changes(?MODULE, nil), {noreply, State}; @@ -249,6 +268,21 @@ code_change(_OldVsn, #st{}=St, _Extra) -> %% internal functions +start_changes_listener(SinceSeq) -> + Self = self(), + {Pid, _} = erlang:spawn_monitor(fun() -> + erlang:spawn_link(fun() -> + Ref = erlang:monitor(process, Self), + receive + {'DOWN', Ref, _, _, _} -> + ok + end, + exit(shutdown) + end), + listen_for_changes(SinceSeq) + end), + Pid. + fold_fun(#full_doc_info{}=FDI, _, Acc) -> DI = couch_doc:to_doc_info(FDI), fold_fun(DI, nil, Acc); @@ -287,10 +321,11 @@ changes_callback({stop, EndSeq}, _) -> exit({seq, EndSeq}); changes_callback({change, {Change}, _}, _) -> DbName = couch_util:get_value(<<"id">>, Change), + Seq = couch_util:get_value(<<"seq">>, Change), case DbName of <<"_design/", _/binary>> -> ok; _Else -> case mem3_util:is_deleted(Change) of true -> - gen_server:cast(?MODULE, {cache_remove, DbName}); + gen_server:cast(?MODULE, {cache_remove_change, DbName, Seq}); false -> case couch_util:get_value(doc, Change) of {error, Reason} -> @@ -298,13 +333,14 @@ changes_callback({change, {Change}, _}, _) -> [DbName, Reason]); {Doc} -> Shards = mem3_util:build_ordered_shards(DbName, Doc), - gen_server:cast(?MODULE, {cache_insert, DbName, Shards}), + Msg = {cache_insert_change, DbName, Shards, Seq}, + gen_server:cast(?MODULE, Msg), [create_if_missing(mem3:name(S)) || S <- Shards, mem3:node(S) =:= node()] end end end, - {ok, couch_util:get_value(<<"seq">>, Change)}; + {ok, Seq}; changes_callback(timeout, _) -> ok. @@ -320,8 +356,9 @@ load_shards_from_disk(DbName) when is_binary(DbName) -> load_shards_from_db(#db{} = ShardDb, DbName) -> case couch_db:open_doc(ShardDb, DbName, [ejson_body]) of {ok, #doc{body = {Props}}} -> + Seq = couch_db:get_update_seq(ShardDb), Shards = mem3_util:build_ordered_shards(DbName, Props), - gen_server:cast(?MODULE, {cache_insert, DbName, Shards}), + gen_server:cast(?MODULE, {cache_insert, DbName, Shards, Seq}), Shards; {not_found, _} -> erlang:error(database_does_not_exist, ?b2l(DbName)) |