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From Jonathan Ellis <jbel...@gmail.com>
Subject Re: Cassandra versus HBase performance study
Date Fri, 05 Feb 2010 22:59:01 GMT
On Fri, Feb 5, 2010 at 4:51 PM, Brian Frank Cooper
<cooperb@yahoo-inc.com> wrote:
> Yes, I had used the default 0.1.
>
> These boxes have 8 GB of RAM and I was giving 6 GB to the JVM (-Xmx). Does Cassandra
do a read caching of data? It seems from the text in storage.conf that keys cache fraction
refers only to indexing the keys, not caching the content. So I would imagine increasing the
keys cached fraction would decrease the memory used for data caching

0.5 doesn't do data caching (except what you get for free from the
OS).  0.6 will change this, but for 0.5 things are nice and simple. :)
 So a large heap can actually make things worse if it makes the GC
lazy and the OS can't use that to cache data.

If your data set is larger than 5GB on disk I would say give it
KeysCachedFraction of 0.2, 3GB JVM heap.  Otherwise 0.4 and 5GB.

-Jonathan

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