From: Serge Petrenko via Tarantool-patches <tarantool-patches@dev.tarantool.org> To: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>, gorcunov@gmail.com Cc: tarantool-patches@dev.tarantool.org Subject: Re: [Tarantool-patches] [PATCH 5/7] replication: send latest effective promote in initial join Date: Fri, 18 Jun 2021 00:00:18 +0300 [thread overview] Message-ID: <3a61c787-8a92-0191-1565-118915adbfcc@tarantool.org> (raw) In-Reply-To: <76d19171-2257-35e3-8f07-b1f0323c728f@tarantool.org> 16.06.2021 00:00, Vladislav Shpilevoy пишет: > Thanks for working on this! > > Hm. The patch makes me think why don't we send the Raft > checkpoint on join too? > > Otherwise it might happen that a replica joined, didn't > get the most actual Raft term yet, then the leader died, > and the replica would start elections with term 1. Even if > the latest term was 1000. > > Nothing critical, Raft will probably work, but it could > be an "optimization"? Also it would be consistent with the > libmo state - send all the snapshot data on join. I tried to implement such a patch, but faced the following problem: Unfortunately, we don't have information about replica's version during join, so I can only send raft state based on term > 1. Also, while writing a commit message I understood that this patch doesn't help much. Even if a node joins, but doesn't subscribe to the leader, it will still subscribe to someone else and receive the latest Raft state. After all, our doc states full-mesh is required for Raft to work, so we'll have someone else to subscribe to and receive Raft state from for sure. The patch's small and simple but I think it's not needed. I've made a tiny amendment to this commit though, please find the diff below. > Btw, the limbo state contains a term. And it means > that after join, but before subscribe, the limbo's term > is bigger than raft's term. Even though in the comments > of the limbo we say: > > * It means the limbo's term might be smaller than the raft term, while > * there are ongoing elections, or the leader is already known and this > * instance hasn't read its PROMOTE request yet. During other times the > * limbo and raft are in sync and the terms are the same. > > which means the limbo term should be always <= raft term. > Can this break something? Is it possible to make a test confirming > that we can't send the limbo state before the raft state? I don't think this could break anything. Limbo and Raft terms are not that interconnected now. ================================ diff --git a/src/box/relay.cc b/src/box/relay.cc index 289dea0f3..e05b53d5d 100644 --- a/src/box/relay.cc +++ b/src/box/relay.cc @@ -408,12 +408,17 @@ relay_initial_join(int fd, uint64_t sync, struct vclock *vclock) row.sync = sync; coio_write_xrow(&relay->io, &row); - /* Send out the latest limbo state. */ - char body[XROW_SYNCHRO_BODY_LEN_MAX]; - xrow_encode_synchro(&row, body, &req); - row.replica_id = req.replica_id; - row.sync = sync; - coio_write_xrow(&relay->io, &row); + /* + * Send out the latest limbo state. Don't do that when limbo is unused, + * let the old instances join without trouble. + */ + if (req.replica_id != REPLICA_ID_NIL) { + char body[XROW_SYNCHRO_BODY_LEN_MAX]; + xrow_encode_synchro(&row, body, &req); + row.replica_id = req.replica_id; + row.sync = sync; + coio_write_xrow(&relay->io, &row); + } /* Send read view to the replica. */ engine_join_xc(&ctx, &relay->stream); ================================ -- Serge Petrenko
next prev parent reply other threads:[~2021-06-17 21:02 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2021-06-10 13:32 [Tarantool-patches] [PATCH 0/7] forbid implicit limbo ownership transition Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 1/7] replication: always send raft state to subscribers Serge Petrenko via Tarantool-patches 2021-06-10 16:47 ` Cyrill Gorcunov via Tarantool-patches 2021-06-11 8:43 ` Serge Petrenko via Tarantool-patches 2021-06-11 8:44 ` Cyrill Gorcunov via Tarantool-patches 2021-06-15 20:53 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 2/7] replication: forbid implicit limbo owner transition Serge Petrenko via Tarantool-patches 2021-06-15 20:55 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches 2021-06-18 22:49 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-21 10:13 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 3/7] txn_limbo: fix promote term filtering Serge Petrenko via Tarantool-patches 2021-06-15 20:57 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches 2021-06-18 22:49 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-21 8:55 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 4/7] txn_limbo: persist the latest effective promote in snapshot Serge Petrenko via Tarantool-patches 2021-06-15 20:59 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 5/7] replication: send latest effective promote in initial join Serge Petrenko via Tarantool-patches 2021-06-15 21:00 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches [this message] 2021-06-18 22:52 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-21 10:12 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 6/7] box: introduce `box.ctl.demote` Serge Petrenko via Tarantool-patches 2021-06-18 22:52 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-21 14:56 ` Serge Petrenko via Tarantool-patches 2021-06-10 13:32 ` [Tarantool-patches] [PATCH 7/7] box: make promote/demote always bump the term Serge Petrenko via Tarantool-patches 2021-06-15 21:00 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-17 21:00 ` Serge Petrenko via Tarantool-patches 2021-06-18 22:53 ` Vladislav Shpilevoy via Tarantool-patches 2021-06-21 15:02 ` Serge Petrenko via Tarantool-patches 2021-06-15 20:53 ` [Tarantool-patches] [PATCH 0/7] forbid implicit limbo ownership transition Vladislav Shpilevoy via Tarantool-patches
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