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From: Konstantin Osipov via Tarantool-patches <tarantool-patches@dev.tarantool.org>
To: Vladislav Shpilevoy <v.shpilevoy@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org
Subject: Re: [Tarantool-patches] [PATCH 1/2] replication: introduce ballot.can_be_leader
Date: Tue, 20 Jul 2021 23:18:19 +0300
Message-ID: <20210720201819.GA71287@starling> (raw)
In-Reply-To: <5cee0ccb-9c87-701c-96e7-2bee12ccc365@tarantool.org>

* Vladislav Shpilevoy <v.shpilevoy@tarantool.org> [21/07/20 23:06]:
> >>>
> >>> Imagine there are nodes A, B, C, D, E.

^^^ 

> >>> A is a leader, E is a voter which can not become a leader.
> >>>
> >>> Imagine A's log index is 5, B = 4, C = 3, D = 2, E = 5.
> >>>
> >>> The majority's log index is 4, so entry 4 is committed. A dies, B
> >>> is partitioned away. The cluster is stuck, because neither C nor B
> >>> can get a quorum (3 votes).
> >>
> >> But how is it different from the real Raft? In normal Raft I can say
> >> E simply is too slow to make any actions. It is just stuck or died.
> >> The cluster will be stuck then, yes. Not much you can do here.
> > 
> > In a real raft:
> > - liveness is guaranteed if quorum is present; this guarantee here
> >   is not held
> > - you never sacrifice safety for liveness; you never lose
> >   committed entries if quorum is present; and you never lose it
> >   unnoticed! here you can lose a committed entry and not notice
> >   it.
> 
> Please, show me an example. The example above only shows that the
> election might stop if there are issues with the quorum. And this
> will happen regardless of whether I have voter role or not. In normal
> Raft you can kill 3/5 nodes and nothing will work too.

What is not clear with the example above? In it, I kill 2 out of
5, not 3 out of 5. And no, in Raft "nothing will work" is not
correct. The system will not be live, but will be safe.

-- 
Konstantin Osipov, Moscow, Russia

  reply	other threads:[~2021-07-20 20:18 UTC|newest]

Thread overview: 23+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-07-15 23:49 [Tarantool-patches] [PATCH 0/2] Bootstrap voter Vladislav Shpilevoy via Tarantool-patches
2021-07-15 23:49 ` [Tarantool-patches] [PATCH 1/2] replication: introduce ballot.can_be_leader Vladislav Shpilevoy via Tarantool-patches
2021-07-16 10:59   ` Serge Petrenko via Tarantool-patches
2021-07-18 17:00     ` Vladislav Shpilevoy via Tarantool-patches
2021-07-19  9:11       ` Sergey Petrenko via Tarantool-patches
2021-07-16 14:29   ` Konstantin Osipov via Tarantool-patches
2021-07-18 17:00     ` Vladislav Shpilevoy via Tarantool-patches
2021-07-19  9:12       ` Konstantin Osipov via Tarantool-patches
2021-07-19 22:06         ` Vladislav Shpilevoy via Tarantool-patches
2021-07-20  8:49           ` Konstantin Osipov via Tarantool-patches
2021-07-20 20:02             ` Vladislav Shpilevoy via Tarantool-patches
2021-07-20 20:18               ` Konstantin Osipov via Tarantool-patches [this message]
2021-07-20 21:16         ` Cyrill Gorcunov via Tarantool-patches
2021-07-20 23:20           ` Konstantin Osipov via Tarantool-patches
2021-07-21 18:51             ` Cyrill Gorcunov via Tarantool-patches
2021-07-21 21:43             ` Vladislav Shpilevoy via Tarantool-patches
2021-07-15 23:49 ` [Tarantool-patches] [PATCH 2/2] election: during bootstrap prefer candidates Vladislav Shpilevoy via Tarantool-patches
2021-07-16 11:30   ` Serge Petrenko via Tarantool-patches
2021-07-18 17:00     ` Vladislav Shpilevoy via Tarantool-patches
2021-07-16 14:27 ` [Tarantool-patches] [PATCH 0/2] Bootstrap voter Konstantin Osipov via Tarantool-patches
2021-07-18 17:00   ` Vladislav Shpilevoy via Tarantool-patches
2021-07-19  9:13     ` Konstantin Osipov via Tarantool-patches
2021-07-19 22:04       ` Vladislav Shpilevoy via Tarantool-patches

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