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From Yiming Sun <yiming....@gmail.com>
Subject Re: Cassandra read throughput with little/no caching.
Date Fri, 28 Dec 2012 14:02:34 GMT
James, sorry I was out for a few days.  Yes, if the row cache doesn't give
a good hit rate then it should be disabled.

Is there any chance to increase the VM configuration specs?  I couldn't
pinpoint in exactly which message you mentioned the VMs are 2GB mem and 2
cores, which is a bit meager.  Also is it possible to batch the writes
together?

-- Y.


On Mon, Dec 24, 2012 at 7:28 AM, James Masson <james.masson@opigram.com>wrote:

>
>
> On 21/12/12 17:56, Yiming Sun wrote:
>
>> James, you could experiment with Row cache, with off-heap JNA cache, and
>> see if it helps.  My own experience with row cache was not good, and the
>> OS cache seemed to be most useful, but in my case, our data space was
>> big, over 10TB.  Your sequential access pattern certainly doesn't play
>> well with LRU, but giving the small data space you have, you may be able
>> to fit the data from one column family entirely into the row cache.
>>
>>
>>
> I've done some experimenting today with JNA/row cache. Extra 500Mb of
> heap, 300Mb row cache, latest JNA, set caching=ALL in the schema for all
> column families in this keyspace.
>
> Getting average 5% row cache hit rate - no increase in cassandra
> throughput, and increased disk read I/O, basically because I've sacrificed
> Linux disk cache for the cassandra row-cache.
>
> Load average was 4 (2cpu boxes) for the duration of the cycle, where it
> was about 2 before, basically because of the disk I/O I think.
>
> So, I think I'll disable row caching again...
>
> James M
>

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