Andreas wrote:
> Stephen,
> 
> > You may not be hitting the IdDict scaling wall in the 30 
> second test.
> 
> There is no IDdict scaling wall here - the tallies show that 
> WeakValueDictionary is used which does not use identity (but rather
> equality) on its keys. Therfore the only scaling issue that 
> could come up would be LargeInts #hash value and making this 
> spread more is trivial.

Ah...right.  I didn't even notice that.  In the short test, the
id->object map is the bottleneck (rather than the object->id map or the
object->object change tracking dictionary).
 
> > To make the 30 second test faster, I would figure out ways 
> of reducing 
> > the number of calls to the LargeInteger comparison.
> 
> For example by using IDDicts?! ;-)))

Except that wouldn't work for LargeInteger keys.  If you used an IdDict,
you would need some way of canonicalizing the oids...which still means
using the LargeInteger comparison in this case.  

I would start by trying trying to minimize the additions and removals if
possible.  Then, I might consider using something other than
LargeIntegers as keys (would ByteArrays offer a faster
comparison?...there aren't any tests (like smallness, negativeness, etc)
involved in comparing ByteArrays).  Finally, I would think about going
one step further and reify the oid itself and canonicalize those into a
WeakSet (similar to Symbols).  I would make the oid hold its target
directly (eliminating the need for a Dictionary to map oid->object).
Then, I could figure out ways to make the other two IdDict's
(object->oid and object->old_object) scale better.

- Stephen