Size calculations for off heap caching

[Todd Nine <to...@spidertracks.com>]

Hi guys,
  We've just built a K tree implementation in cassandra.  We're going
for relatively "wide" nodes in our tree to minimize our tree depth and
increase our search times.   Most of the links between parent/child
nodes are longs.  We're ready to start tuning the size of K so that our
most access paths in our tree will be row cached in Cassandra.  We're on
Cassandra 0.8.7, and I can't find any documentation regarding the actual
memory size of the off heap row cache.  Can someone explain how much
additional space will be used when caching rows?  For instance, if our
links between nodes are all Longs, and we have 100 children (cols), that
gives us 900 bytes with a 0 byte placeholder value.  What is the
additional overhead when using the off heap storage?

Thanks,
Todd

Re: Size calculations for off heap caching

[Chris Goffinet <cg...@chrisgoffinet.com>]

My best advice on this is, insert a bit of data into the tree, and then do a
heap dump to calculate the extra overhead. It's unfortunately more than you
would like from our testing.

On Tue, Oct 18, 2011 at 8:14 PM, Todd Nine <to...@spidertracks.com> wrote:

> **
> Hi guys,
>   We've just built a K tree implementation in cassandra.  We're going for
> relatively "wide" nodes in our tree to minimize our tree depth and increase
> our search times.   Most of the links between parent/child nodes are longs.
> We're ready to start tuning the size of K so that our most access paths in
> our tree will be row cached in Cassandra.  We're on Cassandra 0.8.7, and I
> can't find any documentation regarding the actual memory size of the off
> heap row cache.  Can someone explain how much additional space will be used
> when caching rows?  For instance, if our links between nodes are all Longs,
> and we have 100 children (cols), that gives us 900 bytes with a 0 byte
> placeholder value.  What is the additional overhead when using the off heap
> storage?
>
> Thanks,
> Todd
>