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From Aaron Turner <synfina...@gmail.com>
Subject Re: how can we get (a lot) more performance from cassandra
Date Thu, 17 May 2012 01:38:53 GMT
On Wed, May 16, 2012 at 12:59 PM, Yiming Sun <yiming.sun@gmail.com> wrote:
> Hello,
>
> I asked the question as a follow-up under a different thread, so I figure I
> should ask here instead in case the other one gets buried, and besides, I
> have a little more information.
>
> "We find the lack of performance disturbing" as we are only able to get
> about 3-4MB/sec read performance out of Cassandra.
>
> We are using cassandra as the backend for an IR repository of digital texts.
> It is a read-mostly repository with occasional writes.  Each row represents
> a book volume, and each column of a row represents a page of the volume.
>  Granted the data size is small -- the average size of a column text is
> 2-3KB, and each row has about 250 columns (varies quite a bit from one
> volume to another).
>
> Currently we are running a 3-node cluster, and will soon be upgraded to a
> 6-node setup.  Each node is a VM with 4 cores and 16GB of memory.  All VMs
> use SAN as disk storage.
>
> To retrieve a volume, a slice query is used via Hector that specifies the
> row key (the volume), and a list of column keys (pages), and the consistency
> level is set to ONE.  It is typical to retrieve multiple volumes per
> request.
>
> The read rate that I have been seeing is about 3-4 MB/sec, and that is
> reading the raw bytes... using string serializer the rate is even lower,
> about 2.2MB/sec.
>
> The server log shows the GC ParNew frequently gets longer than 200ms, often
> in the range of 4-5seconds.  But nowhere near 15 seconds (which is an
> indication that JVM heap is being swapped out).
>
> Currently we have not added JNA.  From a blog post, it seems JNA is able to
> increase the performance by 13%, and we are hoping to increase the
> performance by something more like 1300% (3-4 MB/sec is just disturbingly
> low).  And we are hesitant to disable swap entirely since one of the nodes
> is running a couple other services
>
> Do you have any suggestions on how we may boost the performance?  Thanks!

Have you tried using more threads on the client side?  Generally
speaking, when I need faster read/write performance I look for ways to
parallelize my requests and it scales pretty much linearly.


-- 
Aaron Turner
http://synfin.net/         Twitter: @synfinatic
http://tcpreplay.synfin.net/ - Pcap editing and replay tools for Unix & Windows
Those who would give up essential Liberty, to purchase a little temporary
Safety, deserve neither Liberty nor Safety.
    -- Benjamin Franklin
"carpe diem quam minimum credula postero"

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