When I joined Google last June, I discovered a new world: tons of new acronyms or project code names to learn about, but also a particular environment for your source code. At Google, engineers work on a huge monolithic source code repository comprising of: 

• 1 billion files
• 9 million source files
• 2 billion lines of code
• 35 million commits
• 86 terabytes of content
• 45 thousands of commits every day.

Rachel Potvin, who’s an engineering manager at Google, wrote an article for ACM about how Google handles such a huge repository, as well as the tools and practices around that. Wired also covered the topic in their article “Google is 2 billion lines of code and it’s all in one place”. And Rachel also presented this topic at the @Scale conference.