An example of why you should use Memcached and cache in general

index.php

<?php

// database host
$host = '127.0.0.1';
// database name
$db   = 'cache';
// database user
$user = 'homestead';
// the easiest password in the world
$pass = 'secret';
// database charset - which is optional
$charset = 'utf8';

// we forge the database connection string
$dsn = "mysql:host=$host;dbname=$db;charset=$charset";
// and we prepare some default values for our PDO object
$opt = [
    PDO::ATTR_ERRMODE            => PDO::ERRMODE_EXCEPTION,
    PDO::ATTR_DEFAULT_FETCH_MODE => PDO::FETCH_ASSOC,
    PDO::ATTR_EMULATE_PREPARES   => false,
];
// we instanciate our PDO Object
$pdo = new PDO($dsn, $user, $pass, $opt);

// Getting a Memcached instance
$memcached = new Memcached;
// Try to get a connection to the Memecached Server
$memcached->addServer('localhost', 11211) or die ("Could not connect");

// Try to get the variables from the cache
$cache_result = $memcached->get('nodes_list');
$cache_title = $memcached->get('complex_title');

// Create a SELECT Query with useless conditions just to make it run slow 
$sqlQuery = "SELECT * FROM node WHERE type = 'page' AND created < NOW() + INTERVAL 120 DAY AND nid IN (SELECT nid FROM node WHERE created < NOW() + INTERVAL 120 DAY)";

// We check if we have our values in the cache before we go with the normal 
if($cache_result && $cache_title) {
  // Second User Request
  // we get the results from the cache
  $arr = $cache_result;
  $title = $cache_title;
}
else
{
  // First User Request 
  // we execute the query
  $select = $pdo->prepare($sqlQuery)->execute();
  // we fetch the data
  $arr = $select->fetchAll();
  // and we store it in the cache
  $memcached->set('nodes_list', $arr);

  // same for the function's result
  $complex_title = get_complex_title();
  $memcached->set('complex_title', $complex_title, 30);
}

// Result
// We display the very complex title
print '<h2>' . $cache_title . '</h2>';
// we then iterate over the query result to display 
foreach($arr as $row)
{
  // we print the data contained in the row
  print '<p>' . $row['nid'] . ' - ' . $row['title'] . ' - ' . $row['type'] . '</p>';
}

// the mega complicated function which return the complicated title
function get_complex_title() {
    sleep(2);
    return 'It is not as complicated as it seems';
}


?>