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From DuyHai Doan <doanduy...@gmail.com>
Subject RE: vnode and NetworkTopologyStrategy: not playing well together ?
Date Tue, 05 Aug 2014 18:07:24 GMT
The discussion about racks & NTS is also mentioned in this recent article :
planetcassandra.org/multi-data-center-replication-in-nosql-databases/

The last section may be of interest for you
Le 5 août 2014 18:14, "DE VITO Dominique" <dominique.devito@thalesgroup.com>
a écrit :

> > Jonathan wrote:
> >
> > Yes, if you have only 1 machine in a rack then your cluster will be
> imbalanced.  You're going to be able to dream up all sorts of weird failure
> cases when you choose a scenario like RF=2 & totally imbalanced network
> arch.
> >
> > Vnodes attempt to solve the problem of imbalanced rings by choosing so
> many tokens that it's improbable that the ring will be imbalanced.
>
> Storage/load distro = function(1st replica placement, other replica
> placement)
>
> vnode solves the balancing pb for 1st replica placement // so, yes, I
> agree with you, but for 1st replica placement only
>
> But NetworkTopologyStrategy (NTS) influences other (2+) replica placement
> => as NTS best behavior relies on token distro, and you have no control on
> tokens with vnodes, the best option I see with **vnode** is to use only one
> rack with NTS.
>
> Dominique
>
>
> -----Message d'origine-----
> De : jonathan.haddad@gmail.com [mailto:jonathan.haddad@gmail.com] De la
> part de Jonathan Haddad
> Envoyé : mardi 5 août 2014 18:04
> À : user@cassandra.apache.org
> Objet : Re: vnode and NetworkTopologyStrategy: not playing well together ?
>
> Yes, if you have only 1 machine in a rack then your cluster will be
> imbalanced.  You're going to be able to dream up all sorts of weird failure
> cases when you choose a scenario like RF=2 & totally imbalanced network
> arch.
>
> Vnodes attempt to solve the problem of imbalanced rings by choosing so
> many tokens that it's improbable that the ring will be imbalanced.
>
>
>
> On Tue, Aug 5, 2014 at 8:57 AM, DE VITO Dominique <
> dominique.devito@thalesgroup.com> wrote:
> > First, thanks for your answer.
> >
> >> This is incorrect.  Network Topology w/ Vnodes will be fine, assuming
> you've got RF= # of racks.
> >
> > IMHO, it's not a good enough condition.
> > Let's use an example with RF=2
> >
> > N1/rack_1   N2/rack_1   N3/rack_1   N4/rack_2
> >
> > Here, you have RF= # of racks
> > And due to NetworkTopologyStrategy, N4 will store *all* the cluster
> data, leading to a completely imbalanced cluster.
> >
> > IMHO, it happens when using nodes *or* vnodes.
> >
> > As well-balanced clusters with NetworkTopologyStrategy rely on carefully
> chosen token distribution/path along the ring *and* as tokens are
> randomly-generated with vnodes, my guess is that with vnodes and
> NetworkTopologyStrategy, it's better to define a single (logical) rack //
> due to "carefully chosen tokens" vs "randomly-generated token" clash.
> >
> > I don't see other options left.
> > Do you see other ones ?
> >
> > Regards,
> > Dominique
> >
> >
> >
> >
> > -----Message d'origine-----
> > De : jonathan.haddad@gmail.com [mailto:jonathan.haddad@gmail.com] De
> > la part de Jonathan Haddad Envoyé : mardi 5 août 2014 17:43 À :
> > user@cassandra.apache.org Objet : Re: vnode and
> > NetworkTopologyStrategy: not playing well together ?
> >
> > This is incorrect.  Network Topology w/ Vnodes will be fine, assuming
> you've got RF= # of racks.  For each token, replicas are chosen based on
> the strategy.  Essentially, you could have a wild imbalance in token
> ownership, but it wouldn't matter because the replicas would be distributed
> across the rest of the machines.
> >
> > http://www.datastax.com/documentation/cassandra/2.0/cassandra/architec
> > ture/architectureDataDistributeReplication_c.html
> >
> > On Tue, Aug 5, 2014 at 8:19 AM, DE VITO Dominique <
> dominique.devito@thalesgroup.com> wrote:
> >> Hi,
> >>
> >>
> >>
> >> My understanding is that NetworkTopologyStrategy does NOT play well
> >> with vnodes, due to:
> >>
> >> ·         Vnode => tokens are (usually) randomly generated (AFAIK)
> >>
> >> ·         NetworkTopologyStrategy => required carefully choosen tokens
> for
> >> all nodes in order to not to get a VERY unbalanced ring like in
> >> https://issues.apache.org/jira/browse/CASSANDRA-3810
> >>
> >>
> >>
> >> When playing with vnodes, is the recommendation to define one rack
> >> for the entire cluster ?
> >>
> >>
> >>
> >> Thanks.
> >>
> >>
> >>
> >> Regards,
> >>
> >> Dominique
> >>
> >>
> >>
> >>
> >
> >
> >
> > --
> > Jon Haddad
> > http://www.rustyrazorblade.com
> > skype: rustyrazorblade
>
>
>
> --
> Jon Haddad
> http://www.rustyrazorblade.com
> skype: rustyrazorblade
>

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