From: Robert Klemme <shortcutter@...>
Date: 2007-10-17T15:00:08+09:00
Subject: Re: Struct is slow

On 16.10.2007 19:05, Alex Fenton wrote:
> Wayne Magor wrote:
>> I have a script in which I was using a 2-element array where a struct
>> would be used in another language, so I decided to give the Ruby class
>> Struct a try.
>>
>> My script went from taking 2 seconds to taking 27 seconds from this
>> simple change!  
> 
> This doesn't sound likely, even if your script did nothing else but use 
> the Struct class. I'd look elsewhere for the source of slowness (try 
> running your script with -rprofile).
> 
> A quick benchmark suggests that Struct is somewhat slower to instantiate 
> (+100%), marginally slower to set values in (+33%), and the same speed 
> to fetch values from as an Array:
> 
> BENCHMARK:
> 
> require 'benchmark'
> 
> GC.disable
> Foo = Struct.new(:foo, :bar)
> 
> repetitions = 500_000
> 
> puts 'struct-init', Benchmark::measure {
>   repetitions.times { f = Foo.new('x', 666) }
> }
> 
> puts 'array-init', Benchmark::measure {
>   repetitions.times { f = ['x', 666] }
> }
> 
> puts 'struct-get', Benchmark::measure {
>   f = Foo.new('x', 666)
>   repetitions.times { g = f.foo }
> }
> 
> puts 'array-get', Benchmark::measure {
>   f = ['x', 666]
>   repetitions.times { g = f[0] }
> }
> 
> puts 'struct-set', Benchmark::measure {
>   f = Foo.new('x', 666)
>   repetitions.times { f.foo = 'y' }
> }
> 
> puts 'array-set', Benchmark::measure {
>   f = ['x', 666]
>   repetitions.times { f[0] = 'y' }
> }
> 
> 
> __END__
> 
> RESULTS (ruby 1.8.4 (2005-12-24) [i386-mswin32])
> 
> struct-init
>   1.359000   0.031000   1.390000 (  1.390000)
> array-init
>   0.563000   0.016000   0.579000 (  0.579000)
> struct-get
>   0.281000   0.000000   0.281000 (  0.281000)
> array-get
>   0.297000   0.000000   0.297000 (  0.297000)
> struct-set
>   0.422000   0.000000   0.422000 (  0.422000)
> array-set
>   0.281000   0.000000   0.281000 (  0.281000)

I'm not sure whether you are familiar with Benchmark#bmbm which does a 
rehearsal - personally I rather not switch off GC since in realistic 
situations GC time belongs into the mix.  But results are rather similar:

Robert@Babelfish2 /cygdrive/c/TEMP
$ ruby array-struct.rb
Rehearsal --------------------------------------------------
struct init      3.812000   0.000000   3.812000 (  3.923000)
array init       1.672000   0.000000   1.672000 (  1.709000)
struct get       0.437000   0.000000   0.437000 (  0.440000)
array get        0.485000   0.000000   0.485000 (  0.485000)
struct set       0.718000   0.000000   0.718000 (  0.716000)
array set        0.500000   0.000000   0.500000 (  0.510000)
----------------------------------------- total: 7.624000sec

                      user     system      total        real
struct init      3.891000   0.000000   3.891000 (  3.984000)
array init       1.640000   0.000000   1.640000 (  1.690000)
struct get       0.438000   0.000000   0.438000 (  0.450000)
array get        0.469000   0.000000   0.469000 (  0.469000)
struct set       0.703000   0.000000   0.703000 (  0.715000)
array set        0.484000   0.000000   0.484000 (  0.504000)

Robert@Babelfish2 /cygdrive/c/TEMP
$ cat array-struct.rb
require 'benchmark'

REP = 500_000

Foo = Struct.new :foo, :bar

data = "foo"
c1 = Foo.new data, data
c2 = [data, data]

Benchmark.bmbm 15 do |x|
   x.report 'struct init' do
     REP.times { Foo.new data, data }
   end

   x.report 'array init' do
     REP.times { [data, data] }
   end

   x.report 'struct get' do
     REP.times { c1.bar }
   end

   x.report 'array get' do
     REP.times { c2[1] }
   end

   x.report 'struct set' do
     REP.times { c1.bar = data }
   end

   x.report 'array set' do
     REP.times { c2[1] = data }
   end
end

Kind regards

	robert