won't this line:  $results{$pid} = $data;

turn this:
$VAR1 = {
         ‘id_1’ => {     
                  'thing_1' => {
                            'a' => 1,
                            'b' => 4.5,
                            'c' => 1200
                                                }
                   'thing_2' => {
                            'a' => 0,
                            'b' => 3.2,
                            'c' => 100
                                                }
                }
          ‘id_2’ => {
                    'thing_1' => {
                            'a' => 1,
                            'b' => 4.5,
                            'c' => 1200
                                                }
                     'thing_2' => {
                            'a' => 0,
                            'b' => 3.2,
                            'c' => 100
                                                }
                }
}

Into something much more complex since each child is forked on the list of things, and then loops through a list of 1 million id's.