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From Dominic Letz <>
Subject Re: Adding more nodes causes performance problem
Date Mon, 09 Feb 2015 15:37:54 GMT
Can you copy and example of your read and write queries? Are they both
degrading in the same way performance wise?

On Mon, Feb 9, 2015 at 8:39 PM, Laing, Michael <>

> Use token-awareness so you don't have as much coordinator overhead.
> ml
> On Mon, Feb 9, 2015 at 5:32 AM, Marcelo Valle (BLOOMBERG/ LONDON) <
>> wrote:
>> AFAIK, if you were using RF 3 in a 3 node cluster, so all your nodes had
>> all your data.
>> When the number of nodes started to grow, this assumption stopped being
>> true.
>> I think Cassandra will scale linearly from 9 nodes on, but comparing a
>> situation where all your nodes hold all your data is not really fair, as in
>> this situation Cassandra will behave as a database with two more replicas,
>> for reads.
>> I can be wrong, but this is my call.
>> From:
>> Subject: Re:Adding more nodes causes performance problem
>> I have a cluster with 3 nodes, the only keyspace is with replication
>> factor of 3,
>> the application read/write UUID-keyed data. I use CQL (casssandra-python),
>> most writes are done by execute_async, most read are done with consistency
>> level of ONE, overall performance in this setup is better than I expected.
>> Then I test 6-nodes cluster and 9-nodes. The performance (both read and
>> write) was getting worse and worse. Roughly speaking, 6-nodes is about 2~3
>> times slower than 3-nodes, and 9-nodes is about 5~6 times slower than
>> 3-nodes. All tests were done with same data set, same test program, same
>> client machines, for multiple times. I'm running Cassandra 2.1.2 with
>> default
>> configuration.
>> What I observed, is that with 6-nodes and 9-nodes, the Cassandra servers
>> were doing OK with IO, but CPU utilization was about 60%~70% higher than
>> 3-nodes.
>> I'd like to get suggestion how to troubleshoot this, as this is totally
>> against
>> what I read, that Cassandra is scaled linearly.

Dominic Letz
Director of R&D
Exosite <>

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