hi,
i am trying to note down the discussion on crimson we have in this morning:
1. osdmap cache: there are two approaches,
* C/S mode: shard#0 will act as the server. we could follow the model
of config proxy. say, let shard#0 be the mini server, and when a
certain shard, shard#n for instance, gets a new osdmap, it will inform
shard#0, by submitting following message to shard#0:
future<foreign_ptr<osdmap_ref>> add(foreign_ptr<osdmap_ref>&& map);
and here are two cases here,
1) shad#0 already has a copy of map of map->epoch. in this case, it
will just return its own copy of osdmap as a foreign_ptr. shard#n will
throw the `map` away, and keep the returned foreign_ptr<> instead in
its local map<epoch_t, foreign_ptr<osdmap_ref>>. but for returning a
proper *foreign_ptr<>*, we need to delegate this request to the one
who actually *owns* the osdmap.
2) shard#0 does not has the map yet. it will add the new osdmap to
its map<epoch_t, foreign_ptr<osdmap_ref>>, and return
foreign_ptr<osdmap_ref>. shard#n can tell if it actually owns the
returned map by checking get_owner_shard().
* symmetric model: everyone is the client and everyone is the server.
when shard#n gets an osdmap of epoch m, which it does not possess yet,
it will keep it in a map<epoch_t, lw_shared_ptr<> after querying all
shards for a map of epoch m, and nobody replies with a non-null
foreign_ptr<>. when shard#n needs the osdmap of epoch m, it sends the
following message to all its peer shards in parallel:
future<foreign_ptr<osdmap_ref>> get(epoch_t epoch).
in both mode, we might want to avoid refcounting foreign_ptr<>
locally. and only delete it when we trimming this certain osdmap.
2. regarding to the interface between bluestore (objectstore) and the
rest part of osd, we could have something like:
seastar::future<RetVal> ObjectStore::submit_transaction(Transaction&& txn)
3. the CephContext in ObjectStore, we need a *copy* of the ConfigValue
which is registered as an observer which is updated by config proxy in
Seastar world. so we don't need to worry about reading a dirty option
being updated by a Seastar thread.
--
Regards
Kefu Chai
