Hi,
I'm pretty new to the list (and riak) so please forgive my ignorance but I
didn't manage to find a public bugtracker for riak. Hence I'm posting my
problem here. (Bitbucket and Internet Explorer(using it not by choice) do not
mix well. So that might be the problem why I didn't find it).
I've tried to use riak_kv_multi_backend with one of the backends being the
riak_kv_bitcask_backend. This does not seem to work with riak-0.11.0. I checked
tip as well, and I do not think it would work either. The problem boils to
these few lines (code snippets from tip):
riak_kv_vnode:
handle_info({Mod, Msg}, StateName, #state { mod = Mod } = StateData) ->
Mod:handle_info(StateData#state.modstate, Msg),
{next_state, StateName, StateData, ?TIMEOUT}.
riak_kv_bitcask_backend:
start(Partition, _Config) ->
%% Schedule sync (if necessary)
case application:get_env(bitcask, sync_strategy) of
{ok, {seconds, Seconds}} ->
SyncIntervalMs = timer:seconds(Seconds),
erlang:send_after(SyncIntervalMs, self(),
{?MODULE, {sync, SyncIntervalMs}});
_ -> ok end,
%% Schedule merge checks
erlang:send_after(?MERGE_CHECK_INTERVAL, self(), {?MODULE, merge_check}),
riak_kv_multi_backend:
handle_info(State, Msg) ->
F = fun(_Name, Module, SubState) ->
Module:handle_info(SubState, Msg)
end, [F(X) || X <- State#state.backends],
ok.
If riak_kv_multi_backend is configured in riak_kv_vnode the state's mod is
riak_kv_multi_backend but the messages scheduled in riak_kv_bitcask_backend are
going to have riak_kv_bitcask_backend as their Mod tag.
With my limited understanding about the rest of the sytem it seems to me that
adding this case to riak_kv_vnode would fix the problem:
handle_info({Mod, Msg}, StateName, #state { mod = riak_kv_multi_backend } =
StateData) ->
riak_kv_multi_backend:handle_info(StateData#state.modstate, Msg),
{next_state, StateName, StateData, ?TIMEOUT};
It is a bit wasteful because all the configured backends will get called with
this message, but it is the best I can think of without leaking too much
information about the specific backends into the generic code.
Modifying the handle_info case would work as well however one check would need
to disappear:
handle_info({_ModTag, Msg}, StateName, #state { mod = Mod } = StateData) ->
Mod:handle_info(StateData#state.modstate, Msg),
{next_state, StateName, StateData, ?TIMEOUT}.
There are a plethora of other ways to fix this like passing the Mod tag to
riak_kv_multi_backend so that it can filter based on it (this is probably my
favourite as it is not wasteful and there aren't many code changes needed
either):
riak_kv_vnode:
handle_info({Mod, Msg}, StateName, #state { mod = riak_kv_multi_backend } =
StateData) ->
riak_kv_multi_backend:handle_info(StateData#state.modstate, {Mod, Msg}),
{next_state, StateName, StateData, ?TIMEOUT};
riak_kv_multi_backend:
handle_info(State, {Mod, Msg}) ->
F = fun(_Name, Module, SubState) ->
Module:handle_info(SubState, Msg)
end, [F(X) || X = {_, Module, _} <- State#state.backends, Module =:=
Mod],
ok.
Code is not tested, but should compile. :)
Regards,
Tamas
--
Tamas Nagy
Erlang Solutions Ltd.
http://www.erlang-solutions.com
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