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.dev...@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.had...@gmail.com [mailto:jonathan.had...@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.dev...@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.had...@gmail.com [mailto:jonathan.had...@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.dev...@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 >
