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From Dan Feldman <hriunde...@gmail.com>
Subject Re: Cassandra read optimization
Date Thu, 19 Apr 2012 06:26:45 GMT
Hi Tyler and Aaron,

Thanks for your replies.

Tyler,
fetching scs using your pycassa script on our server takes ~7 s -
consistent with the times we've been seeing. Now, we aren't really experts
in Cassandra, but it seems that JNA is enabled by default for Cassandra >
1.0 according to Jeremy (
http://comments.gmane.org/gmane.comp.db.cassandra.user/21441). But in case
it isn't, how do you turn it on in 1.0.8?

I'm also setting MAX_HEAP_SIZE="2G" in cassandra-env.sh. I'm hoping that's
how you increase java heap size. I've tried "3G" as well, without any
increase in performance. It did however allow for taking larger slices.

Aaron,
we are not doing multi-threaded requests for now, but we'll give it a shot
in the next day or two and I'll let you know if there is any improvement

Thanks for your help!
Dan F.


On Wed, Apr 18, 2012 at 9:44 PM, Tyler Hobbs <tyler@datastax.com> wrote:

> I tested this out with a small pycassa script:
> https://gist.github.com/2418598
>
> On my not-very-impressive laptop, I can read 5000 of the super columns in
> 3 seconds (cold) or 1.5 (warm).  Reading in batches of 1000 super columns
> at a time gives much better performance; I definitely recommend going with
> a smaller batch size.
>
> Make sure that the timeout on your ConnectionPool isn't too low to handle
> a big request in pycassa.  If you turn on logging (as it is in the script I
> linked), you should be able to see if the request is timing out a couple of
> times before it succeeds.
>
> It might also be good to make sure that you've got JNA in place and your
> heap size is sufficient.
>
>
> On Wed, Apr 18, 2012 at 8:59 PM, Aaron Turner <synfinatic@gmail.com>wrote:
>
>> On Wed, Apr 18, 2012 at 5:00 PM, Dan Feldman <hriundel88@gmail.com>
>> wrote:
>> > Hi all,
>> >
>> > I'm trying to optimize moving data from Cassandra to HDFS using either
>> Ruby
>> > or Python client. Right now, I'm playing around on my staging server,
>> an 8
>> > GB single node machine. My data in Cassandra (1.0.8) consist of 2 rows
>> (for
>> > now) with ~150k super columns each (I know, I know - super columns are
>> bad).
>> > Every super column has ~25 columns totaling ~800 bytes per super column.
>> >
>> > I should also mention that currently the database is static - there are
>> no
>> > writes/updates, only reads.
>> >
>> > Anyways, in my python/ruby scripts, I'm taking slices of 5000
>> supercolumns
>> > long from a single row.  It takes 13 seconds with ruby and 8 seconds
>> with
>> > pycassa to get a single slice. Or, in other words, it's currently
>> reading at
>> > speeds of less than 500 kB per second. The speed seems to be linear
>> with the
>> > length of a slice (i.e. 6 seconds for 2500 scs for ruby). If I run
>> nodetool
>> > cfstats while my script is running, it tells me that my read latency on
>> the
>> > column family is ~300ms.
>> >
>> > I assume that this is not normal and thus was wondering what parameters
>> I
>> > could tweak to improve the performance.
>> >
>>
>> Is your client mult-threaded?  The single threaded performance of
>> Cassandra isn't at all impressive and it really is designed for
>> dealing with a lot of simultaneous requests.
>>
>>
>> --
>> 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"
>>
>
>
>
> --
> Tyler Hobbs
> DataStax <http://datastax.com/>
>
>

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