On May 9, 2008, at 9:33 PM, Andres Valloud wrote:
> Reinout Heeck wrote:
>> Valloud, Andres wrote:
>>
>>> Hmmm... I think what is going on is that clustering is not letting
>>> the
>>> dictionary do its job quickly.
>>>
>> Yes, it surprised me that this case was not fixed in the hashing
>> overhaul.
>>
>>
>>
>
> For all hash functions there will be datasets that cause them to
> behave
> badly. This cannot be avoided.
>
>> I had hoped these [value judgment] days would be over...
Heh :-)
What I meant there was the days of worrying about clustered values.
More generally, before the hashing overhaul I had run into three
problems repeatedly:
1) Poor performance of hashed collections holding strings.
2) Poor performance of hashed collections holding clustered integer
values.
3) Poor abstraction of hash combination 'for dummies' leading to poor
#hash implementations on domain objects.
An earlier conversation we had extinguished my hopes for any solution
to 3) in the overhaul but I had fully expected both 1) and 2) to be
resolved by the redesign. Now I get the impression only 1) has been
addressed adequately.
You seem to be dismissing 2) as being a special case that needs not
perform with the base collection implementations. Since this is a
value judgment we can keep debating this, instead I can provide you a
simple datapoint: my shop would be relieved when 2) is addressed.
I had a quick look (for the first time) at the hash analysis tool in
order to measure performance of some hashed collection access
patterns. I only found quality assessments of #hash implementations
for integer based values but no benchmark tool to measure run time of
collection accesses - it seems this is not supported. Is there some
other tool I need to load in order to measure the performance of
hashed collections?
Thanks for your suggestions regarding Point>>hash, I'll experiment
with them when I'm back at work (bank holiday here today).
Cheers,
Reinout
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