How Scalable Are PHP Web Applications?

Java developers and enthusiasts often keep repeating how Java is scalable, and look down on how PHP is just 'scripting' that does not scale.Well, we know we have a few big sites running Drupal, which of course uses the LAMP stack. Sites like The Onion, NowPublic, OurMedia, SavannahNow and others I forgot about.But, outside of Drupal, there are really larger sites that use PHP and MySQL.Here are some of them:

• Yahoo uses PHP almost everywhere, and gets an enormous amount of traffic. Read Michael Radwin PHP at Yahoo talk.
• Flickr. Cal Henderson, the lead developer for Flickr has a workshop on scalability using PHP and MySQL. He also wrote a O'Reilly book, Building Scalable Web Site, the Flickr way, on that experience.
• Digg. A very large user contributed news site that gets 200 million page views per month. This article on Digg PHP's Scalabiliy and Performance goes into details on how Digg managed to scale.

There is also a somewhat dated article on the PHP scalability myth.