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.

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From: Ramesh Natarajan <>
Date: Mon, 3 Oct 2011 21:47:08 -0500
To: <>
Subject: Cassandra JVM heap size

I was reading an article @ 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? 



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.