One interesting thing which was mentioned is the fact that everything is build from source, without relying on binaries. This helps avoiding issues with dependencies becoming obsolete but still being used in other projects, an issue I indeed encountered a lot.
How is it technically possible? If I try the same thing in my company, even considering the huge gap between the scale of my company codebase and the scale of Google's one, it wouldn't be possible for two reasons:
The IDE (Visual Studio) will quickly become unresponsive, given that is suffers a lot at even small solutions containing, say, 50 projects.
Any static analysis would be crunched by the size of the whole codebase. For example code metrics or static checking of code contracts would hardly be possible (code contracts would probably take days or weeks).
With continuous integration, compiling would take a huge amount of time too and would crunch the servers as soon as a project with lots of dependencies is modified, requiring a large tree of projects to be recompiled.
How can a small company circumvent those issues and be able to:
Use the IDE without being affected by poor performance,
Compile the code after each commit without crunching the server, even when the consequences of a change require a large amount of the codebase to be recompiled?