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From Julian Perry <ju...@limitless.co.uk>
Subject Re: Help needed to understand zookeeper in solrcloud
Date Thu, 05 Mar 2015 08:29:16 GMT

I start out with 5 zk's.  All good.

One zk fails - I'm left with four.  Are they guaranteed
to split 4/0 or 3/1 - because if they split 2/2 I'm screwed,
right?

Surely to start with 5 zk's (or in fact any odd number - it
could be 21 even), and from a single failure you drop to an
even number - then there is the danger of NOT getting quorum.

So ... I can only assume that there is a mechanism in place
inside zk to guarantee this cannot happen, right?

--
Cheers
Jules.


On 05/03/2015 06:47, svante karlsson wrote:
> Yes, as long as it is three (the majority of 5) or more.
>
> This is why there is no point of having a 4 node cluster. This would also
> require 3 nodes for majority thus giving it the fault tolerance of a 3 node
> cluster but slower and more expensive.
>
>
>
> 2015-03-05 7:41 GMT+01:00 Aman Tandon <amantandon.10@gmail.com>:
>
>> Thanks svante.
>>
>> What if in the cluster of 5 zookeeper only 1 zookeeper goes down, will
>> zookeeper election can occur with 4 / even number of zookeepers alive?
>>
>> With Regards
>> Aman Tandon
>>
>> On Tue, Mar 3, 2015 at 6:35 PM, svante karlsson <saka@csi.se> wrote:
>>
>>> synchronous update of state and a requirement of more than half the
>>> zookeepers alive (and in sync) this makes it impossible to have a "split
>>> brain" situation ie when you partition a network and get let's say 3
>> alive
>>> on one side and 2 on the other.
>>>
>>> In this case the 2 node networks stops serving request since it's not in
>>> majority.
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> 2015-03-03 13:15 GMT+01:00 Aman Tandon <amantandon.10@gmail.com>:
>>>
>>>> But how they handle the failure?
>>>>
>>>> With Regards
>>>> Aman Tandon
>>>>
>>>> On Tue, Mar 3, 2015 at 5:17 PM, O. Klein <klein@octoweb.nl> wrote:
>>>>
>>>>> Zookeeper requires a majority of servers to be available. For
>> example:
>>>> Five
>>>>> machines ZooKeeper can handle the failure of two machines. That's why
>>> odd
>>>>> numbers are recommended.

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