Github user banjiewen commented on a diff in the pull request:
https://github.com/apache/couchdb-mem3/pull/19#discussion_r59493169
--- Diff: src/mem3_sync_event_listener.erl ---
@@ -51,35 +68,136 @@ handle_event(NodesDb, updated, #state{nodes = NodesDb}
= St) ->
Nodes = mem3:nodes(),
Live = nodes(),
[mem3_sync:push(NodesDb, N) || N <- Nodes, lists:member(N, Live)],
- {ok, St};
+ maybe_push_shards(St);
handle_event(ShardsDb, updated, #state{shards = ShardsDb} = St) ->
mem3_sync:push(ShardsDb, mem3_sync:find_next_node()),
- {ok, St};
+ maybe_push_shards(St);
handle_event(UsersDb, updated, #state{users = UsersDb} = St) ->
mem3_sync:push(UsersDb, mem3_sync:find_next_node()),
- {ok, St};
+ maybe_push_shards(St);
handle_event(<<"shards/", _/binary>> = ShardName, updated, St) ->
- try mem3:shards(mem3:dbname(ShardName)) of
- Shards ->
- Targets = [S || #shard{node=N, name=Name} = S <- Shards,
- N =/= node(), Name =:= ShardName],
- Live = nodes(),
- [mem3_sync:push(ShardName,N) || #shard{node=N} <- Targets,
- lists:member(N, Live)]
- catch error:database_does_not_exist ->
- ok
- end,
- {ok, St};
+ Buckets = bucket_shard(ShardName, St#state.buckets),
+ maybe_push_shards(St#state{buckets=Buckets});
handle_event(<<"shards/", _:18/binary, _/binary>> = ShardName, deleted,
St) ->
mem3_sync:remove_shard(ShardName),
- {ok, St};
+ maybe_push_shards(St);
handle_event(_DbName, _Event, St) ->
- {ok, St}.
+ maybe_push_shards(St).
+handle_cast({set_frequency, Frequency}, St) ->
+ #state{delay = Delay, buckets = Buckets0} = St,
+ Buckets1 = rebucket_shards(Delay, Frequency, Buckets0),
+ maybe_push_shards(St#state{frequency=Frequency, buckets=Buckets1});
+handle_cast({set_delay, Delay}, St) ->
+ #state{frequency = Frequency, buckets = Buckets0} = St,
+ Buckets1 = rebucket_shards(Delay, Frequency, Buckets0),
+ maybe_push_shards(St#state{delay=Delay, buckets=Buckets1});
handle_cast(Msg, St) ->
couch_log:notice("unexpected cast to mem3_sync_event_listener: ~p",
[Msg]),
- {ok, St}.
+ maybe_push_shards(St).
+handle_info(timeout, St) ->
+ maybe_push_shards(St);
handle_info(Msg, St) ->
couch_log:notice("unexpected info to mem3_sync_event_listener: ~p",
[Msg]),
+ maybe_push_shards(St).
+
+handle_config_change("mem3", "sync_delay", Delay0, _, St) ->
+ try list_to_integer(Delay0) of
+ Delay1 ->
+ couch_event_listener:cast(
+ ?MODULE,
+ {set_delay, Delay1}
+ )
+ catch error:badarg ->
+ couch_log:warning(
+ "ignoring bad value for mem3.sync_delay: ~p",
+ [Delay0]
+ )
+ end,
+ {ok, St};
+handle_config_change("mem3", "sync_frequency", Frequency0, _, St) ->
+ try list_to_integer(Frequency0) of
+ Frequency1 ->
+ couch_event_listener:cast(
+ ?MODULE,
+ {set_frequency, Frequency1}
+ )
+ catch error:badarg ->
+ couch_log:warning(
+ "ignoring bad value for mem3.sync_frequency: ~p",
+ [Frequency0]
+ )
+ end,
+ {ok, St};
+handle_config_change(_, _, _, _, St) ->
{ok, St}.
+
+handle_config_terminate(_, stop, _) -> ok;
+handle_config_terminate(_Server, _Reason, St) ->
+ Fun = fun() ->
+ timer:sleep(5000),
+ config:listen_for_changes(?MODULE, St)
+ end,
+ spawn(Fun).
+
+bucket_shard(ShardName, [B|Bs]=Buckets0) ->
+ case waiting(ShardName, Buckets0) of
+ true -> Buckets0;
+ false -> [sets:add_element(ShardName, B)|Bs]
+ end.
--- End diff --
I'm not sure that's quite the right analysis - given the fixed-rate flow of
sets through the bucket list any database updated more frequently than
`mem3.sync_frequency` is on average equally likely to result in nine
`is_element` checks as it is to result in one (or three, etc).
Assuming that's true, then keeping the newest bucket at the head would be
preferable given its high mutation rates - we only need to split off the last
element once every `mem3.sync_frequency` milliseconds, but may mutate the head
much more frequently in a cluster with a great number of active databases.
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