Re: Heap requirement for Off-heap space

[Robert Coli]

On Fri, Oct 11, 2013 at 5:47 AM, Artur Kronenberg <
artur.kronenb...@openmarket.com> wrote:

> 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.
>

The row cache is only really useful in very specific cases involving very
small, hot, and uniform in size datasets. Many more people have shot
themselves in the foot by using it than have had great success.

The off-heap row cache also invalidates on UPDATE, which is significantly
different from what many people expect.


> Is there a formula that maps heap space to off-heap?


FWIW, I'd also like to know the answer to this question.

=Rob

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