generate_xml.rb

require 'rubygems'
require 'builder'

def xml_proc
  Proc.new do |b|
    b.node do |b|
      2500.times {b.inner_node "some fake data"}
    end
  end
end

File.open('short_sample.xml', 'w') do |file|
  b = Builder::XmlMarkup.new(:target => file, :indent => 2)
  b.nodes {|b| xml_proc.call(b)}
end

File.open('long_sample.xml', 'w') do |file|
  b = Builder::XmlMarkup.new(:target => file, :indent => 2)
  b.nodes {|b| 1000.times { xml_proc.call(b) } }
end

long_sample_test.rb

require 'rubygems'
gem 'libxml-ruby', '>= 1.1.3'
require 'xml/libxml'

def parse
  x = XML::Reader.file('long_sample.xml', :options => XML::Parser::Options::NOBLANKS)
  
  x.next # <nodes>
  x.read # first <node>
  
  begin
    x.expand
    GC.start
  end while x.next != 0
  
  x.close
end

parse

short_sample_test.rb

require 'rubygems'
gem 'libxml-ruby', '>= 1.1.3'
require 'xml/libxml'

def parse
  x = XML::Reader.file('short_sample.xml', :options => XML::Parser::Options::NOBLANKS)
  
  x.next # <nodes>
  x.read # first <node>
  
  begin
    x.expand
    GC.start
  end while x.next != 0
  
  x.close
end

1000.times {parse}