Someone has just talked about the heap size in this mail list, says that bigger heap size will result into a longer GC phase, that could probably be one of the reason not using larger heap size.

But I have really heard of some others using Cassandra with some 60 gigabytes of heap size.

從我的 BlackBerry® 無線裝置


From: Ramesh Natarajan <ramesh25@gmail.com>
Date: Mon, 3 Oct 2011 21:47:08 -0500
To: <user@cassandra.apache.org>
ReplyTo: user@cassandra.apache.org
Subject: Cassandra JVM heap size

I was reading an article @ http://www.acunu.com/products/choosing-cassandra/ and it mentions cassandra cannot benefit from more than 8GB allocated to JVM heap.  Is this true?  Are these cassandra installations with larger heap sizes? We are planning to have a cluster of 6 nodes with each node running with about 100 GB or so RAM. Will this be a problem? 

thanks
Ramesh

from http://www.acunu.com/products/choosing-cassandra/

Memory Ceiling

Cassandra typically cannot benefit from more than 8GB of RAM allocated to the Java heap, imposing a hard limit on data size. Taking advantage of big servers with lots of memory or many disks is no problem for Acunu. Thereʼs no memory ceiling for Acunu and as a result, no data ceiling either. Need to use larger servers? Go ahead.