I don't know why such an amount of memory is used (I can only assume XML::Simple gets very confused), but I do know how to deal with it.

Using Data::Dumper I noticed that $books is not a hashref, but a listref. Replacing the foreach with:

foreach my $book (@$books) {
    print "$book->{'asin'} \n";
}
[download]

solves the problem.

Hope this helps, -gjb-