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Subject: Re: how large can a cluster over the WAN be?
From: John Lewis <lewilists@gmail.com>
In-Reply-To: <AANLkTikPqEdkBDdqb5CwvkZUdiKpDUd96nKVMNdMTSME@mail.gmail.com>
Date: Tue, 8 Mar 2011 09:25:27 -0800
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To: user@cassandra.apache.org

Thanks for the reply, I realize my question was rather nebulous as I =
consider this proposed deployment to be rather nebulous as well. Any bit =
of information and a direction on which sections of documentation are =
relevant helps this challenge become less nebulous over time. I will do =
some reading on the topics you have provided.

Thanks again
Lewis

On Mar 7, 2011, at 11:52 PM, Robert Coli wrote:

> On Mon, Mar 7, 2011 at 11:32 AM, John Lewis <lewilists@gmail.com> =
wrote:
>> When you say decent latency and throughput what numbers do you =
consider decent? I know throughput would be highly dependent on the =
quantity of kb shoved through the pipe so I would expect throughput =
needs would be highly dependent on the data actually in cassandra.
>=20
> As you say, throughput needed is dependent on Cassandra payload size,
> but also (in 0.7) read repair percentage. Cassandra is a large
> consumer of network traffic relative to the amount of data serviced to
> clients due to background repair processes like read repair and manual
> AES repair. There are obviously scenarios where you might saturate the
> WAN link given large enough nodes or numbers of nodes per datacenter..
>=20
> When I am talking about latency, my experience is with WAN latency
> under 100ms and without DynamicEndpointSnitch. I suspect that within
> an order of magnitude of that latency, with or without DES, is likely
> to be fine for many use cases. There are a few tunables  which might
> be appropriate to increase when operating in more than two datacenters
> with greater possible latency between any two as well as replication
> strategies and consistency levels which offer certain latency
> behavior. As always, simulating your actual workload is likely to give
> you the most relevant information as to the impact of inter-cassandra
> latency on your application. :)
>=20
> =3DRob