On Thu, 2005-12-29 at 17:17 +0100, Fredrik Lundh wrote:
>  Noam Raphael wrote:
>  
>  > I'm not saying that practically it must be used - I'm just saying that
>  > it can't be called a heuristic, and that it doesn't involve any "fancy
>  > overkill size hinting or history tracking". It actually means
>  > something like this:
>  > 1. If you want to insert and the table is full, resize the table to
>  > twice the current size.
>  > 2. If you delete and the number of elements turns out to be less than
>  > a quarter of the size of the table, resize the table to half of the
>  > current size.
>  
>  sure sounds like a heuristic algorithm to me... (as in "not guaranteed to
>  be optimal under all circumstances, even if it's probably quite good in all
>  practical cases")
>  
>  </F>

My problem with this heuristic is it doesn't work well for the
probably-fairly-common use-case of; fill it, empty it, fill it, empty
it, fill it...etc.

As Guido pointed out, if you do have a use-case where a container gets
very big, then shrinks and doesn't grow again, you can manually cleanup
by creating a new container and del'ing the old one. If the
implementation is changed to use this heuristic, there is no simple way
to avoid the re-allocs for this use-case... (don't empty, but fill with
None... ugh!).

My gut feeling is this heuristic will cause more pain than it would
gain...

-- 
Donovan Baarda <abo@[...].au> 
http://minkirri.apana.org.au/~abo/

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