my $twig= XML::Twig->new( twig_roots => { Hit_num => \&hit_num } );
$twig->parsefile( $file);

sub hit_num
  { my( $t, $hit_num)= @_;
    # do stuff with the hit_num

    # $t->purge will free the memory if you don't need 
    # to keep the hit_num around

  }