Started in a dorm room four years ago, the social networking site Facebook now claims to be the fourth most-trafficked site in the world. Ninety million active users pound on 10,000 servers every day, uploading millions and millions of pieces of information in a given month. For example, "friends," who socialize in 21 languages, add 500 million photos per month.

At last count, Facebook stored 6.6 billion photos total, more than any other photo site. Roughly 400,000 developers and entrepreneurs have built 25,000 applications for the platform and about 140 new applications are added per day. (For more on Facebook’s application user interface appeal, see Why Microsoft Should Bring a Facebook-like Look to SharePoint and Web 2.0: Companies Gain Competitive Edge with Social Networking Tools).

Overall there are 25 terabytes of cached data available to help Facebook’s 2,000 databases serve up user requests.

Yeah, the infrastructure fairly boils over with activity and Jonathan Heiliger is the lucky VP of technical operations who gets to stir the pot. Heiliger, who has run technology for several start-ups and advised venture capitalist firm Sequoia Capital, also directed site engineering for Wal-Mart’s website. He joined Facebook in October 2007 to oversee its technology set-up, which many of its 600+ employees tinker with continuously. Whew! It’s a good thing Heiliger lists as an interest (on his LinkedIn profile!) "anything 24 x 7."

CIO Senior Editor Kim S. Nash recently interviewed Heiliger to talk about his work at Facebook.

CIO.com: You’ve done a lot of startups in the past. What lessons from that experience do you bring to Facebook?

Jonathan Heiliger: The decisions you make early on tend to leave a lasting impression. It’s difficult to change the way a startup is started. One of the challenges or opportunities that drew me here was going from a purely engineering-driven culture—writing software for users [for] sharing information—to now operating this truly large infrastructure. Those are two very different things. [Early on] you make tradeoffs in IT to speed development that often can lead to disaster later when you have to operate five years later.

Jonathan Heiliger, Facebook's VP of technical operations

What was the first thing you wanted to accomplish when you got to Facebook?

Heiliger: I spent the first three months coming up to speed. It was the longest coming-up-to-speed process I’d been through because most of my prior experience was at much younger companies. When I joined Facebook, there were 300 employees. [In the past] typically, I was among the first 10 employees. I knew where the bodies were buried, what cultural challenges there were. At Facebook, I had to figure it out.