Cheaper and dirtier way to code a cache:
<?php
$cache_file = 'URI to cache file';
$cache_life = '120'; //caching time, in seconds
$filemtime = @filemtime($cache_file); // returns FALSE if file does not exist
if (!$filemtime or (time() - $filemtime >= $cache_life)){
 ob_start();
 resource_consuming_function();
 file_put_contents($cache_file,ob_get_flush());
}else{
 readfile($cache_file);
}
?>