Social Networking backend architecture

Question

Ideally, where would an application like Facebook store its \"Friends\" data? In a database table? in an xml file?

Answer 1

From Facebooks engineering page:

"Already, we are the second most-trafficked PHP site in the world (Yahoo is #1), and one of the largest MySQL installations anywhere, running thousands of databases."

and

"We've built a lightweight but powerful multi-language RPC framework that allows us to seamlessly and easily tie together subsystems written in any language, running on any platform. Facebook is built in PHP, C++, Perl, Python, Erlang, Java, and even a little bit of ML—and it all works together. * We are the largest user in the world of memcached, an open-source caching system. Originally developed by LiveJournal, we've since made so many scalability improvements and performance upgrades that we will be the primary contributor of features in the next major release. * We've created a custom-built search engine serving millions of queries a day, completely distributed and entirely in-memory, with real-time updates."