Move faster, wait less: Improving code review time at Meta

What this post added

This post details Meta's efforts to improve code review time by introducing and refining several tools and processes. It introduces the 'Time In Review' metric (P75) as a key indicator of developer satisfaction and productivity, and 'Eyeball Time' as a guardrail metric. It describes the development and impact of 'Next Reviewable Diff,' a feature that uses ML to queue up relevant diffs for reviewers, leading to a 17% increase in review actions per day. It also explains improvements to the reviewer recommendation system, incorporating work hour awareness and file ownership, which resulted in a 1.5% increase in diffs reviewed within 24 hours and improved recommendation accuracy. Finally, it introduces 'Stale Diff Nudgebot,' which uses targeted pings to expedite reviews for slow-moving diffs, reducing average 'Time In Review' by 7% and the proportion of diffs waiting longer than three days by 12%.