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From Edward Capriolo <>
Subject Re: RFC: Cassandra Virtual Nodes
Date Thu, 22 Mar 2012 00:41:33 GMT
I just see vnodes as a way to make the problem smaller and by making the
problem smaller the overall system is more agile. Aka rather then 1 node
streaming 100 gb the 4 nodes stream 25gb. Moves by hand are not so bad
because the take 1/4th the time.

The most simple vnode implementation is vmware.  Just make sure that 3 vm
nodes consecutive nodes so not end up on the same host. This is wasteful
because we have 4 jvms.

I envision vnodes as Cassandra master being a shared cache,memtables, and
manager for what we today consider a Cassandra  instance. Makes it simple
to think about.

On Wednesday, March 21, 2012, Peter Schuller <>
>> Software wise it is the same deal. Each node streams off only disk 4
>> to the new node.
> I think an implication on software is that if you want to make
> specific selections of partitions to move, you are effectively
> incompatible with deterministically generating the mapping of
> partition to responsible node. I.e., it probably means the vnode
> information must be kept as state. It is probably difficult to
> reconcile with balancing solutions like consistent hashing/crush/etc.
> --
> / Peter Schuller (@scode,

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