"Joseph McDonald" <joe / vpop.net> wrote in message
news:eTp17.43890$AM.956429 / e420r-sjo3.usenetserver.com...
>
> Hi,
>
> Just wondering if there is a trick to speed up the following:
>
> % cat junk.rb
> a = Hash.new
> for i in 0..1000000
>   a[i] = "joe"
> end
>
> for i in 0..1000000
>   data = a[i]
> end
>
> /usr/bin/time ./junk.rb
> 34.55user 0.19system 0:34.73elapsed 100%CPU (0avgtext+0avgdata
0maxresident)k
> 0inputs+0outputs (232major+11360minor)pagefaults 0swaps
>
>
> If I do a GC.disable it gets much better:
>
> /usr/bin/time ./junk.rb
> 5.02user 0.13system 0:05.14elapsed 100%CPU (0avgtext+0avgdata
0maxresident)k
> 0inputs+0outputs (228major+12371minor)pagefaults 0swaps
>
> I have tried the above with both 1.6.4 and 1.7.1 with generational
> GC patch, results are about the same.
>
> Should we just make sure that we turn off GC when doing something like
> above?
>
> python is about 4 seconds for the same thing and perl is 5.1 seconds.

Hmm. I'm not familiar with Ruby's Hash class implementation.

However, in a language like Smalltalk one can provide a "hint" as to the
number of elements the hash (aka <Dictionary>) object will contain. This
allows it to pre-allocate enough space, so it does not have to keep getting
grown and rehashed. Second, growth is typically performed in powers of two
rounded up to the nearest prime number (to improve the likelyhood of a good
hashing distribution).

A given hashed collection object (or a subclass) may be customized to change
the default resize (add/remove) growth/shrink policy characteristics or
algorithm.

For comparison, when I ran the above snippet in SmallScript (QKS Smalltalk),
it took:

     0.556 seconds to build the hash.

     0.869 seconds to both build the hash and then query it (which is
                   what the provided snippet appears to do).

SmallScript GC is fully enabled.

I don't know what machine the original poster was using for the Ruby run.

My machine used for this run is a 1.2GHz AMD TBird. Assuming that the
original poster was running on a 500MHz machine then a comparable
SmallScript run would take about 2-seconds.

--
-- Dave S. [ http://www.smallscript.net ]

>
> thanks,
> -joe
>
>