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From Jeremy Jongsma <jer...@barchart.com>
Subject Re: vnode and NetworkTopologyStrategy: not playing well together ?
Date Tue, 05 Aug 2014 16:00:50 GMT
If your nodes are not actually evenly distributed across physical racks for
redundancy, don't use multiple racks.


On Tue, Aug 5, 2014 at 10:57 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/architecture/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
>

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