Re: Reducing the cost of garbage collecting small arrays

On Thu, Jun 23, 2011 at 12:31 AM, Jan-Willem Maessen wrote:

On Wed, Jun 22, 2011 at 12:33 PM, Johan Tibell wrote:

...

Hi,

Now when we can efficiently copy small arrays I've gone back to benchmarking/optimizing my hash array mapped trie data structure. The data structure's performance depends on how efficiently we can allocate/collect/copy Array#s and MutableArrays#s of size <=32. Speeding up copying helped quite a bit, but the HAMT is still slower than a Patricia tree for inserts.

Is 5 the optimal number of bits to slice off at a time (ie the best fanout)?  It sounds like node copy cost on insert argues for a slightly narrower fanout.  You'll be evacuating / scanning more words total, but new nodes may equate to less scanning overall (especially if this is running long enough to have some nodes get tenure).

I'm experimenting with this. 6 is far too much, making inserts 4-5x slower. 4 doesn't seem to improve things much (which is a bit counter-intuitive given that 6 made things so much work), but I need to experiment some more. Cheers, Johan