PHP armazenando em cache resultados sql

$filename = 'cache.txt';
if (filemtime($filename) < time()-24*3600) { //older than a day
  /*get your data*/
  file_put_contents($filename, serialize(array($getCategories, $getTags, [...])); //your data in a serialized form
} else {
  $data = unserialize(file_get_contents($filename));
  list($getCategories, $getTags, [...]) = $data;
}