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From Tim Wintle <timwin...@gmail.com>
Subject Re: Provisioning/Configuration Question
Date Sat, 01 Mar 2014 19:02:27 GMT
137GB would fairly easily fit in core memory on a single node these days:
so it seems a very low amount for a 27 node cluster..

Off the top of my head: would 99th percentile latency be improved by using
replication factor 5, assuming you are doing quorum operations..

Sent from my phone
On 1 Mar 2014 14:33, "William Katsak" <wkatsak@cs.rutgers.edu> wrote:

> Hello,
>
> I am doing some academic work with Cassandra 1.1.6 (I am on an older
> version because of a bunch of implemented modifications that have been
> in the works for a while), and I am wondering if the list can help me
> resolve some questions I have.
>
> I am running a cluster of 27 nodes with the following configuration:
>
> Intel Atom (2 core) @ 1.8 GHz
> 4 GB RAM
> 250 GB HDD
> 64 GB SSD
> Gigabit Ethernet
>
> With this cluster size, I currently have loaded 135 GB of data
> (replicated * 3), giving me data of ~15 GB per node. I am using Leveled
> Compaction with a 5mb SSTable size. Commitlog is in HDD, data is on SSD.
>
> My workload is YCSB/uniform distribution/75% read-25% write.
>
> My questions are:
>
> - Is this a reasonable data size for this hardware?
>
> - What should be compaction throughput be set to?  I am targeting a 99th
> percentile latency SLA, and it seems that compaction throughput greatly
> affects the 99th percentile latency. The guideline seems to be 16-32x
> insertion rate, but this slows down the 99th percentile time dramatically.
> In addition, there seems to be a feedback loop where if you insert faster,
> you need more compaction, but if you had more compaction, you can't insert
> as fast. What is best practice on this?
>
> - What is a reasonable operation throughput to expect from this
> configuration?
>
> Sorry for the info dump, but I have been fighting with this for a while
> now. I've tried to read everything I can about tuning and provisioning,
> but continue to have an issue where I can find a load rate that hits my
> 99th percentile SLA on average, but have large latency spikes that don't
> seem to match a pattern.
>
> Thanks in advance for any advice you can give, even if it is just "go
> read this document".
>
> Sincerely,
>
> Bill Katsak
> Ph.D. Student
> Rutgers University
>

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