Heap requirement for Off-heap space

[Artur Kronenberg]

Hi,

I was playing around with cassandra off-heap options. I configured 3 GB 
off-heap for my row cache and 2 GB Heap space for cassandra. After 
running a bunch of load tests against it I saw the cache warm up. Doing 
a jmap histogram I noticed a lot of offHeapkey objects. At that point my 
row cache was only 500 MB big. So I got worried on how this will affect 
Heap space when I manage to fill the entire off-heap.

Is there a formular that maps heap space to off-heap? Or more 
spicifically how much heap space does it require to manage 3 GB off-heap 
space?

thanks!

artur