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From David Brower <david.bro...@oracle.com>
Subject Re: Leader elections between 2 nodes.
Date Thu, 10 May 2018 20:36:57 GMT
Without quorum, the client has no idea how current the read data may 
be.   It might be from a replica that is hours/days/weeks out of data.   
Sometimes this won't matter, sometimes it will be a critical failing.

-dB


On 5/9/2018 6:40 PM, Prasanth Mathialagan wrote:
> For reads, is Quorum necessary? Reads are served from local the local
> replica, right?
>
> On Wed, May 9, 2018 at 8:29 AM, Jordan Zimmerman <jordan@jordanzimmerman.com
>> wrote:
>> A quorum means (n/2)+1 - In a 3 node cluster that is 2. So, if 2 servers
>> are up you can achieve quorum.
>>
>>> we need odd
>>> numbers in order to form a quorum
>> The "odd" in this formula refers to the number of configured servers not
>> how many are running at a given time. That's the reasoning for quorum in
>> the first place. Quorum I/O ensures that a majority of nodes is referenced
>> for reads or writes (in ZooKeeper writes are what matter for quorum).
>>
>> -Jordan
>>
>>> On May 9, 2018, at 10:26 AM, Kaushal Shriyan <kaushalshriyan@gmail.com>
>> wrote:
>>> Hi,
>>>
>>> In a ensemble of 3 nodes with 1 leader and 2 followers, if the leader
>> goes
>>> down then two servers can elect a leader among themselves. But we need
>> odd
>>> numbers in order to form a quorum. I am confused. Please correct me if i
>> am
>>> understanding it wrong.
>>>
>>> Any help will be highly appreciable
>>>
>>> Best Regards,
>>>
>>> Kaushal
>>


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