"At the scale that Facebook operates, a lot of traditional
approaches to serving web content break down or simply aren't
practical. The challenge for Facebook's engineers has been to keep
the site up and running smoothly in spite of handling close to half
a billion active users. This article takes a look at some of the
software and techniques they use to accomplish that.
"Facebook's scaling challenge
"Before we get into the details, here are a few factoids to give
you an idea of the scaling challenge that Facebook has to deal
* Facebook serves 570 billion page views per month (according to
Google Ad Planner).
* There are more photos on Facebook than all other photo sites
combined (including sites like Flickr).
* More than 3 billion photos are uploaded every month.
* Facebook's systems serve 1.2 million photos per second. This
doesn't include the images served by Facebook's CDN."