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From Brian Fitzpatrick <>
Subject Re: Sizing a Cassandra cluster
Date Thu, 24 Mar 2011 13:27:08 GMT
Thanks for the tips on the replication factor.  Any thoughts on the
number of nodes in a cluster to support an RF=3 with a workload of 400
ops/sec (4-8K sized rows, 50/50 read/write)?  Based on the "sweet
spot" hardware referenced in the wiki (8-core, 16-32GB RAM), what kink
of ops/sec could I reasonably expect from each node.  Just looking for
a range to make some educated guesses.


On Wed, Mar 23, 2011 at 9:04 PM, aaron morton <> wrote:
> It really does depend on what your workload is like, and in the end will
> involve a certain amount of fudge factor.
> provides some guidance.
> can be used to get a
> rough idea of the memory requirements. Note that secondary indexes are also
> CF's with the same memory settings as the parent.
> With RF3 you can lose afford to lose one replica for a key a token range and
> still be available (Assuming Quorum CL). With RF 5 you can lose 2 replicas
> and still be available for the keys in the range.
> I'm been careful to say "lose X replicas" because the other nodes in the
> cluster don't count when considering an operation for a key. Two examples, 9
> node cluster with RF3. If you lose nodes 2 and 3 and they are replicas for
> node 1, Quorum operations on keys in the range for node 1 will fail (ranges
> for 2 and 3 will be ok). If you lose nodes 2 and 5 Quorum operations will
> succeed for all keys.
> RF 3 is reasonable starting point for some redundancy, RF 5 is more. After
> that it's Web Scale (tm).
> Hope that helps
> Aaron
> On 24 Mar 2011, at 04:04, Brian Fitzpatrick wrote:
> I'm going through the process of specing out the hardware for a
> Cassandra cluster. The relevant specs:
> - Support 460 operations/sec (50/50 read/write workload). Row size
> ranges from 4 to 8K.
> - Support 29 million objects for the first year
> - Support 365 GB storage for the first year, based on Cassandra tests
> (data + index + overhead * replication factor of 3)
> I'm looking for advice on the node size for this cluster, recommended
> RAM per node, and whether RF=3 seems to be a good choice for general
> availability and resistance to failure.
> I've looked at the YCSB benchmark paper and through the archives of
> this email list looking for pointers.  I haven't found any general
> guidelines on recommended cluster size to support X operations/sec
> with Y data size at RF factor of Z, that I could extrapolate from.
> Any and all recommendations appreciated.
> Thanks,
> Brian

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