Aşağıdaki kodu var ve 5 kez Firefox Bu web sayfasını yüzümüz, sonra MySQL bana 5 bağlantılarını gösterdi. PDO Kılavuzu acorrding,

Persistent connections are not closed at the end of the script, but are cached and re-used when another script requests a connection using the same credentials. The persistent connection cache allows you to avoid the overhead of establishing a new connection every time a script needs to talk to a database, resulting in a faster web application.

I have used the same credentials, but the number of MYSQL connection keep increasing. Even trying to close connection with $db = null could not close the connections. What's wrong of my code?

<?php
try {
 $dbh = new PDO('mysql:host=127.0.0.1;dbname=lingtong', 'root', 'xxxxxx', array(PDO::ATTR_PERSISTENT => true));
 foreach ($dbh->query('SELECT * from agent') as $row) 
  print_r($row);
 $dbh = null;
} catch (PDOException $e) {
 print "Error! : " . $e->getMessage() . "<br/>";
 die();
}