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From Maciej Smoleński <jezd...@gmail.com>
Subject Re: Ensuring there is at most one master
Date Mon, 02 Dec 2013 14:41:03 GMT
This problem is discussed here:


On 12/2/13, Neha Narkhede <neha.narkhede@gmail.com> wrote:
>>> At this time there are two masters - old in part B, and new in part A.
> After the network partition, there shouldn't be a leader in part B since it
> is a minority and will not be able to form a quorum.
> Thanks,
> Neha
> On Tue, Nov 26, 2013 at 6:34 AM, Maciej Smoleński <jezdnia@gmail.com>
> wrote:
>> Hi,
>> ZooKeeper is an excellent system. The problem with ensuring only one
>> master among clients bothers me.
>> Lets have a look at the situation when network partition happen: there
>> is part A (majority), and part B (minority).
>> Lets assume that before network partition happened the master was
>> connected to part B.
>> After the network partition, part A will elect new ZooKeeper leader,
>> and there will be new master elected among clients connected to part
>> A.
>> At this time there are two masters - old in part B, and new in part A.
>> The only solution I can think about to this problem, is to ensure that
>> the new master is inactive for some time - to ensure that the old
>> master in this time will detect that it is not connected to ZooKeeper
>> quorum, and will deactivate itself as a master.
>> This solution assumes that timers on these machines work correctly.
>> Is it possible to ensure only one master using ZooKeeper without
>> timing assumptions ?
>> Thanks,
>> Maciej

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