use XML::Twig;

# at most one div will be loaded in memory
  my $twig=XML::Twig->new(   
    twig_handlers => 
    { channel => sub { 
        my( $node )= @_;
        my( $id )= $node->{'att'}->{id};
        my( $chan )= $node->{'att'}->{chan};
        my( $sign )= $node->text;
        say qq(UPDATE channel SET channum="$chan",xmltvid="$id" WHERE callsign="$sign");
  
        $node->purge;
      },
    },
  );
  $twig->parsefile( 'my_big.xml');