Re: [Tarantool-patches] [PATCH 1/3] raft: send state to new subscribers if Raft worked

["Alexander V. Tikhonov" <avtikhon@tarantool.org>]

Hi Vlad, thanks that you dropped the patch and created the new issue.
Without the patch testing of the test fixed. Check your branch rebased
in my branch:

https://gitlab.com/tarantool/tarantool/-/pipelines/206144990

On Wed, Oct 21, 2020 at 11:41:52PM +0200, Vladislav Shpilevoy wrote:
> Hi! Thanks for the review!
> 
> >> diff --git a/src/box/box.cc b/src/box/box.cc
> >> index 18568df3b..86daaf626 100644
> >> --- a/src/box/box.cc
> >> +++ b/src/box/box.cc
> >>   @@ -2154,13 +2155,14 @@ box_process_subscribe(struct ev_io *io, struct xrow_header *header)
> >>            tt_uuid_str(&replica_uuid), sio_socketname(io->fd));
> >>       say_info("remote vclock %s local vclock %s",
> >>            vclock_to_string(&replica_clock), vclock_to_string(&vclock));
> >> -    if (raft_is_enabled()) {
> >> +    if (replica_version_id >= version_id(2, 6, 0)) {
> > 
> > Why don't you use 'raft_was_used()` here together with version check?
> 
> It stops making sense. Its purpose was not to send anything while there can be
> old versions. Assuming that in this case Raft was never enabled. After we
> start checking subscriber's version, we can send Raft always when it is
> supported.
> 
> > I've just understood we should also check for relay version in relay_push_raft(), shouldn't we?
> 
> Perhaps, yeah.
> 
> The patch is dropped from the patchset, and has forked into a new issue:
> https://github.com/tarantool/tarantool/issues/5438
> 
> Main reason is that the patch breaks the tests. The problem is that when
> Raft is enabled and delivered to a subscriber, it bumps its local LSN. But
> after that the subscriber may get XlogGapError from master, if some of
> master logs were deleted. And the follower won't be able to auto-rejoin, because
> local LSN is > 0 already - Raft wrote something to WAL.
> 
> That breaks replication/replica_rejoin.test.lua. Not sure what to do with
> that yet. Auto-rejoin in a cluster with election is not so vital I think, so
> we can work on it in the next release. And for now not to send anything
> when Raft is off. It is bearable.