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From Yiming Sun <yiming....@gmail.com>
Subject Re: how can we get (a lot) more performance from cassandra
Date Wed, 16 May 2012 20:26:38 GMT
Ah, never thought I would be quoting Luke's "No, that's not true... that's
impossible~~" here...  sigh.

But seriously, thanks Mike.  Instead of using memcached, would it help to
turn on row cache?

An even more philosophical question:  what would be a better choice for
read-heavy loads?  a major part of the reason we went for Cassandra was to
not deal with millions of small files, but we completely overlooked the
assumed workload.  Thanks!

-- Y.



On Wed, May 16, 2012 at 4:07 PM, Mike Peters <cassandra@softwareprojects.com
> wrote:

>  Hi Yiming,
>
> Cassandra is optimized for write-heavy environments.
>
> If you have a read-heavy application, you shouldn't be running your reads
> through Cassandra.
>
> On the bright side - Cassandra read throughput will remain consistent,
> regardless of your volume.  But you are going to have to "wrap" your reads
> with memcache (or redis), so that the bulk of your reads can be served from
> memory.
>
>
> Thanks,
> Mike Peters
>
>
> On 5/16/2012 3:59 PM, Yiming Sun 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!
>
>  -- Y.
>
>
>
>

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