From: Eleanor McHugh <eleanor@...>
Date: 2008-06-27T17:36:39+09:00
Subject: Re: Performance improvement possible?

On 27 Jun 2008, at 07:55, Philip Rhoades wrote:
> Eleanor McHugh wrote:
>> I'm surprised at the behaviour you're seeing so I ran a quick  
>> benchmark on what I believe to be an equivalent array handling  
>> problem with my laptop (OS X, Ruby 1.8.6-p111, Core 2 Duo 2GHz, 2GB  
>> RAM):
>> require 'benchmark'
>> include Benchmark
>> bm(6) do |y|
>>   y.report("appending") { x = []; (1..20000000).each { |i| x << i } }
>>   y.report("nested creation") { x = Array.new(1000)  
>> { Array.new(1000) { Array.new(20, 0) } } }
>>   y.report("unrolling") { x.flatten.flatten.length }
>> end
>>                        user     system      total        real
>> appending        7.350000   0.100000   7.450000 (  7.685458)
>> nested creation    0.850000   0.000000   0.850000 (  0.851341)
>> unrolling        15.240000   0.280000  15.520000 ( 20.927189)
>> which in each case is manipulating an array of 20,000,000 elements.  
>> This would be equivalent to processing 32000 files where each  
>> contained 625 occurrences of the 'k=' tag.
>
> I haven't used BM yet but I can't see how doing a benchmark on an  
> array helps?  When I had an array it was slow, when I ditched the  
> array it was fast?

Your experience runs counter to all of my experience, both in terms of  
several years of Ruby hacking and more generally in working on  
performance-optimisation for large data manipulation problems.  
Therefore being of a curious disposition I'd love to figure out why :)


Ellie

Eleanor McHugh
Games With Brains
http://slides.games-with-brains.net
----
raise ArgumentError unless @reality.responds_to? :reason