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From aaron morton <aa...@thelastpickle.com>
Subject Re: Cassandra network latency & tuning
Date Thu, 21 Feb 2013 16:53:38 GMT
>  I would like to understand how we can capture network latencies between a 1GbE and 10GbE
for ex.
Cassandra reports two latencies.

The CF latencies reported by nodetool cfstats, nodetool cfhistograms and the CF MBeans cover
the local time it takes to read or write the data. This does not include any local wait times,
network latency or coordinator overhead. 

The Storage Proxy latency from nodetool proxyhistograms and the StorageProxy MBean is the
total latency for a request on a coordinator.

Under load, with a consistent workload,  the CF latency should not vary too much. While the
request latency can increase as wait time becomes more of an factor. 

Additionally streaming is throttled which you may want to increase, see the the yaml file.

   
> We will soon be adding SSD's and was wondering how Cassandra can utilize the 10GbE and
the SSD's and if there are specific tuning that is required.
You may want to increase both the concurrent_writes and reads in the yaml file to take advantage
of the extra IO. 
Same for the compaction settings, comments in the yaml file will help. 

With SSD and 10GbE you can easily hold more data on each node. Typically we advise 300GB to
500GB per node with HDD and 1GbE, because of the time repair and node replacement takes. With
SSD and 10GbE it will take less, and even less if you are using SSD. 

If you feel like being thorough add repair and node replacement (all under load) to your test
lineup. 

Hope that helps. 

-----------------
Aaron Morton
Freelance Cassandra Developer
New Zealand

@aaronmorton
http://www.thelastpickle.com

On 20/02/2013, at 1:44 PM, Brandon Walsh <brandon_90210_s@yahoo.com> wrote:

> I have a 5 node cluster and currently running ver 1.2. Prior to full scale deployment,
I'm running some benchmarks  using YCSB. From a hadoop cluster deployment we saw an excellent
improvement using higher speed networks. However Cassandra does not include network latencies
and I would like to understand how we can capture network latencies between a 1GbE and 10GbE
for ex. As of now all the graphs look the same. We will soon be adding SSD's and was wondering
how Cassandra can utilize the 10GbE and the SSD's and if there are specific tuning that is
required.


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