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From Ivan Kelly <iv...@apache.org>
Subject Re: Odd Number of Nodes spread across 3 Datacenter
Date Tue, 11 Aug 2015 11:17:14 GMT
It's a floor, yes. So for 3 you need 2, 5 needs 3, 7 needs 4 etc.

On Tue, Aug 11, 2015 at 1:07 PM Kaushal Shriyan <kaushalshriyan@gmail.com>
wrote:

> Hi,
>
> While referring to
>
> http://whilefalse.blogspot.com.es/2012/12/building-global-highly-available.html
> and the description "ZooKeeper requires a majority (n/2 + 1) of servers to
> be available and able to communicate with each other in order to form a
> quorum" I suppose it is floor function and not ceiling function while
> referring to
> https://en.wikipedia.org/wiki/Floor_and_ceiling_functions#Examples. Please
> correct me if i am understanding it wrong?
>
> Regards,
>
> Kaushal
>
> On Tue, 11 Aug 2015 at 14:31 Flavio Junqueira <fpj@apache.org> wrote:
>
> > I don't think there is a straightforward answer to the question, but here
> > is some insight.
> >
> > If you use 3 servers with 3 data centers, you'll have one server per DC,
> > which means that upon a crash, the clients in some data center will have
> to
> > go remotely for reads.
> >
> > With 5 servers, at least one DC will have at most one server, which is a
> > bit better, but the DC with one server will have the problem that with
> the
> > one server crashing, the clients will need to go remotely for reads.
> >
> > 7 or 9 are better options, since you can have multiple nodes per DC to
> > serve local read traffic.
> >
> > I have used 5-7 per DC with flexible quorums in a system I worked on.
> >
> > -Flavio
> >
> > > On 11 Aug 2015, at 08:47, Kaushal Shriyan <kaushalshriyan@gmail.com>
> > wrote:
> > >
> > > Hi,
> > >
> > > I have a very basic question of setting up Zookeeper ensemble across 3
> > > Datacenter. Since zookeeper quorum is based on odd number of nodes for
> > > Leader election. What would be the ideal odd number of nodes spread
> > across
> > > 3 Datacenter is it 3 or 5 or 7 or 9? if either of DC1 or DC2 or DC3 is
> > not
> > > reachable or degraded?
> > >
> > > DC1 meaning Datacenter 1
> > > DC2 meaning Datacenter 2
> > > DC3 meaning Datacenter 3
> > >
> > > Any help will be highly appreciable.
> > >
> > > Regards,
> > >
> > > Kaushal
> >
> >
>

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