mysql_connect (localhost / 127.0.0.1) slow on Windows platform

I am using Windows 7, Apache 2, PHP 5, MySQL 5, all are on the same machine. I have found an interesting issue, I have the following code:

    $sql = "select * from user1";
    $conn = mysql_connect("localhost", "root", "xxxxxxxx");
    mysql_select_db("test1");
    mysql_query("set names utf8");
    $result = mysql_query($sql, $conn);
    while ($row = mysql_fetch_assoc($result)){
        foreach ($row as $key => $value){
            echo $key." => ".$value." || ";
        }
        echo "<br/>";
    }
    mysql_free_result($result);
    mysql_close($conn);

The running time for the above code is over 1 second.

When I use 127.0.0.1 instead of localhost, the running time is around 10 ms.

I tried to find the underlying reason on the internet, and this is the result:

I recently moved my development from XP to Windows 7 and found that webpages I had developed were taking 5 seconds long to load. This was unacceptable of course so I had to track down the problem. I eventually tracked down the offending function/method pdo::construct. I also found that mysql_connect was taking about 1 second to make a connection. After a little googling I found an explaination that php had issues with IPv6 and that you could fix the problem by either disabling IPv6 or switching to the ipaddress 127.0.0.1 when making your connection.

I wonder what the issue of IPv6 on PHP is, just want to get a deeper understaning. Thanks.