[tarantool-patches] Re: [PATCH v2 7/7] relay: join new replicas off read view

[Vladimir Davydov]

On Tue, Aug 20, 2019 at 02:53:33PM +0300, Konstantin Osipov wrote:
> * Vladimir Davydov <vdavydov.dev at gmail.com> [19/08/20 11:22]:
> > > > Historically, we join a new replica off the last checkpoint. As a
> > > > result, we must always keep the last memtx snapshot and all vinyl data
> > > > files corresponding to it. Actually, there's no need to use the last
> > > > checkpoint for joining a replica. Instead we can use the current read
> > > > view as both memtx and vinyl support it. This should speed up the
> > > > process of joining a new replica, because we don't need to replay all
> > > > xlogs written after the last checkpoint, only those that are accumulated
> > > > while we are relaying the current read view. This should also allow us
> > > > to avoid creating a snapshot file on bootstrap, because the only reason
> > > > why we need it is allowing joining replicas. Besides, this is a step
> > > > towards decoupling the vinyl metadata log from checkpointing in
> > > > particular and from xlogs in general.
> > > > 
> > > 
> > > How does this work given relay_* functions are running in a relay thread? 
> > 
> > Those functions don't run in a relay thread. Just like in case of index
> > build, we open and use iterators in the tx thread.
> 
> Then they shouldn't be prefixed relay_*, this is confusing.

Well, yeah, kinda. OTOH they do relay data to a replica that's why I
named them relay_something :-/ Also, those functions live in relay.cc,
which is consistent with the relay_ prefix.

If not relay_, what prefix do you think we should use then? join_?
May be, we should also move those functions to a separate file? join.c?