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From Sam Overton <>
Subject Re: RFC: Cassandra Virtual Nodes
Date Tue, 20 Mar 2012 15:37:13 GMT
On 19 March 2012 23:41, Peter Schuller <> wrote:
>>> Using this ring bucket in the CRUSH topology, (with the hash function
>>> being the identity function) would give the exact same distribution
>>> properties as the virtual node strategy that I suggested previously,
>>> but of course with much better topology awareness.
>> I will have to re-read your orignal post. I seem to have missed something :)
> I did, and I may or may not understand what you mean.
> Are you comparing vnodes + hashing, with CRUSH + pre-partitioning by
> hash + identity hash as you traverse down the topology tree?

Yes. I was just trying to illustrate that it's not necessary to have
CRUSH doing the partitioning and placement of primary replicas. The
same functionality can be achieved by having logically separate
placement (a ring with virtual nodes) and a replication strategy which
implements the CRUSH algorithm for replica placement. I think you
agreed with this further down your previous reply anyway, perhaps I
was just being too verbose :)

The reason I'm trying to make that distinction is because it will be
less work than wholesale replacing the entire distribution logic in
Cassandra with CRUSH. I'm not sure if that's exactly what your design
is suggesting?

Sam Overton
Acunu | | @acunu

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