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Zookeeper, mail # dev - How zab avoid split-brain problem?


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cheetah 2011-08-30, 07:23
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RE: How zab avoid split-brain problem?
Alexander Shraer 2011-08-30, 19:21
Hi Peter,

It's the second option. The servers don't know if the leader failed or
was partitioned from them. So each group of 3 servers in your scenario
can't distinguish the situation from another scenario where none of the servers
failed but these 3 servers are partitioned from the other 4. To prevent a split brain
in an asynchronous network a leader must have the support of a quorum.

Alex

> -----Original Message-----
> From: cheetah [mailto:[EMAIL PROTECTED]]
> Sent: Tuesday, August 30, 2011 12:23 AM
> To: [EMAIL PROTECTED]
> Subject: How zab avoid split-brain problem?
>
> Hi folks,
>     I am reading the zab paper, but a bit confusing how zab handle
> split
> brain problem.
>     Suppose there are A, B, C, D, E, F and G seven servers, now A is
> the
> leader. When A dies and at the same time, B,C,D are isolated from E, F
> and
> G.
>      In this case, will Zab continue working like this: if B>C>D and
> E>F>G,
> so the two groups are both voting and electing B and E as their leaders
> separately. Thus, there is a split brain problem.
>      Or Zookeeper just stop working, because there were original 7
> servers,
> after 1 failure, a new leader still expects to have a quorum of 3
> servers
> voting for it as the leader. And because the two groups are separate
> from
> each other, no leader can be elected out.
>
>       If it is the first case, Zookeeper will have a split brain
> problem,
> which probably is not the case. But in the second case, a 7-node
> Zookeeper
> service can only handle a node failure and a network partition failure.
>
>      Am I understanding wrongly? Looking forward to your insights.
>
> Thanks,
> Peter
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cheetah 2011-08-30, 22:36
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Alexander Shraer 2011-08-30, 23:04