incubator-cassandra-user mailing list archives

Site index · List index
Message view « Date » · « Thread »
Top « Date » · « Thread »
From DE VITO Dominique <dominique.dev...@thalesgroup.com>
Subject RE: vnode and NetworkTopologyStrategy: not playing well together ?
Date Tue, 05 Aug 2014 15:57:18 GMT
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
Mime
View raw message