cassandra component on heap or off heap.

A summary of the components in cassandra that store offheap.

cassandra 1.2 and later use offheap for
bloom filter
compression offset map
row cache

cassandra 2.0 and later use offheap for
bloom filter
compression offset map
partition summary
index samples
row cache

Remember , off heap is not equal as non heap. Off-heap means the object is stored non in java heap allocated to the jvm, that is the native memory.

For example in the Bloom filter.

public static IAllocator newOffHeapAllocator(String offheap_allocator) throws ConfigurationException
{
if (!offheap_allocator.contains("."))
offheap_allocator = "org.apache.cassandra.io.util." + offheap_allocator;
return FBUtilities.construct(offheap_allocator, "off-heap allocator");
}

As you can see, if you want to determine if the object is stored on heap or offheap, you can to read into the code. I tried to inspect cassandra 2.0.2 using jconsole, it only show total usage of onheap or offheap. The cassandra community suggest it is better to read NEWS.txt or their blog to read the latest change if the component move on or off heap.

http://www.datastax.com/documentation/cassandra/2.0/webhelp/cassandra/operations/ops_tune_jvm_c.html
https://groups.google.com/forum/#!topic/nosql-databases/kFHS6QfZDuE
http://www.yourkit.com/docs/kb/sizes.jsp