Bus-Factor

One developer. 161 files. The highest churn rate in the entire repository. This is not a startup with three engineers and no processes. This is MongoDB — one of the most widely used, most professionally maintained open-source codebases in the world. Thousands of contributors. Years of accumulated engineering discipline. And still: a single person holds exclusive knowledge of 161 files in a module that changes more than any other. Why MongoDB? We chose MongoDB deliberately. Not because it is a cautionary tale, but because it is the opposite: a project that does almost everything right. Structured contribution guidelines, active code review, long-term maintainers. If knowledge risk shows up here, it shows up everywhere. ...

Three months’ notice sounds like enough time. It isn’t. Not for the files nobody else has ever touched. Not for the modules where one person made every decision for the last two years. You discover those files during the handover. Or after it. We call it a knowledge transfer problem. It isn’t one. It’s a visibility problem. What bus factor actually means The term comes from a thought experiment: how many people on your team would need to be hit by a bus before the project is in serious trouble? ...