With small files (say, < 100MB) , I usually just load the whole thing in, and then get all the elements I'm interested in, and work on them - I find it easier than the stream interface. However, in your case, we might be stretching it unless you've got a 64-bit perl. So here's a stream example. Note that for your example, I just put the whole thing in "<something>..</something>" tags so it'd be valid XML.

use strict;
use warnings;
use XML::Twig;

my $twig = XML::Twig->new(
                          twig_handlers => {
                              offer => sub {
                                  printf("%s,%s,%s\n",
                                         $_->att('id'),
                                         $_->first_child('f1')->text()
+,
                                         $_->first_child('f2')->text()
+,
                                        );
                              }
                          }
                         );
$twig->parsefile('a.xml');
[download]

Hope that helps