Hi, Using fewer vnodes means you'll have a higher chance of hot spots in your cluster. Hot spots in Cassandra are nodes that, by random chance, are responsible for a higher percentage of the token space than others. This means they will receive more data and also more traffic/load than other nodes in the cluster.
CASSANDRA-7032 goes a long way towards addresses this issue by allocating vnode tokens more intelligently, rather than just randomly assigning them. If you're using a version of Cassandra that contains this feature (3.0+), you can use a smaller number of vnodes in your cluster. A high number of vnodes won't affect performance for most Cassandra workloads, but if you're running tasks that need to do token-range scans (such as Spark), there is usually a significant performance hit. If you're on C* 3.0+ and are using Spark (or similar workloads - cassandra lucene index plugin is also affected) then I'd recommend using fewer vnodes - 16 would be ok. You'll probably still see some variance in token-space ownership between nodes, but the trade-off for better Spark performance will likely be worth it. Justin On Wed, 12 Jul 2017 at 00:34 ZAIDI, ASAD A <az1...@att.com> wrote: > Hi Folks, > > > > Pardon me if I’m missing something obvious. I’m still using > apache-cassandra 2.2 and planning for upgrade to 3.x. > > I came across this jira [ > https://issues.apache.org/jira/browse/CASSANDRA-7032] that suggests > reducing num_token may improve general performance of Cassandra like > having num_token=16 instead of 256 may help! > > > > Can you please suggests if having less num_token would provide real > performance benefits or if it comes with any downsides that we should also > consider? I’ll much appreciate your insights. > > > > Thank you > > Asad > -- *Justin Cameron*Senior Software Engineer <https://www.instaclustr.com/> This email has been sent on behalf of Instaclustr Pty. Limited (Australia) and Instaclustr Inc (USA). This email and any attachments may contain confidential and legally privileged information. If you are not the intended recipient, do not copy or disclose its content, but please reply to this email immediately and highlight the error to the sender and then immediately delete the message.
