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From Alain RODRIGUEZ <arodr...@gmail.com>
Subject num_tokens - virtual nodes
Date Fri, 04 Jan 2013 14:00:08 GMT
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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