// chooses a set of random ids. This set does not contain a fixed number of elements but they are around 20
$params = ['n' => $num_records, 'c' => $count, 'dc' => ($count * 2 < 20) ? 20 : $count * 2];
$results = DB::connection('mysql.huge_table')->select('SELECT id FROM atoms_in_universe WHERE RAND() * :n < :dc ORDER BY RAND() LIMIT 0,:c', $params);