Working with an off-the-shelf shopping cart usually requires a little bit of patience. Scaling an e-commerce site does have its share of problems. There is a LOT of interactivity that needs to be implemented. This can be things along the lines of generating targeted ads, sending email or charging a credit card.

To charge a credit card, the ecommerce software will usually take the credit card information from the end user, put it into some form of web service request and the request is submitted to a remote system. While that web service request is taking place the process handling PHP is unable to take additional require requests to serve regular pages.

There has been a lot of talk over the past several years about the difference between performance and scalability. Never mind that the difference between the two will probably not really affect most developers. Never mind that the “difference between performance and scalability” argument is often used when someone’s code performs poorly and their best argument is “Yeah, but my code scales”. Yeah, sure it does.