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From Michael Kjellman <mkjell...@barracuda.com>
Subject Re: num_tokens - virtual nodes
Date Fri, 04 Jan 2013 16:18:51 GMT
http://www.mail-archive.com/user@cassandra.apache.org/msg26528.html

From: Alain RODRIGUEZ <arodrime@gmail.com<mailto:arodrime@gmail.com>>
Reply-To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Date: Friday, January 4, 2013 6:00 AM
To: "user@cassandra.apache.org<mailto:user@cassandra.apache.org>" <user@cassandra.apache.org<mailto:user@cassandra.apache.org>>
Subject: num_tokens - virtual nodes

Hi,

I just discover the vnodes new feature described here: http://www.datastax.com/dev/blog/virtual-nodes-in-cassandra-1-2

In the post above, Brandon says "If you’d like to upgrade an installation to virtual nodes,
that’s possible too, but I’ll save that for a later post". Does this post now exist somewhere
?

From the cassandra.yaml:

# If you already have a cluster with 1 token per node, and wish to migrate to
# multiple tokens per node, see http://wiki.apache.org/cassandra/Operations
# num_tokens: 256

I see no reference to vnodes or num_tokens on this wiki.

So, how to switch from "physical" nodes to vnodes ?

This is useful only if your number of nodes is greater than the RF, right ?

Why 256 token by default ? Where this value come from ?

Is there more advantage / disadvantage of using vnodes that improving the internodes data
streaming by increasing the number of data sources ?

Alain

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