Effective Code Reviews

Aug 18, 2024 – Filed as: Software⁷²

Software engineering research has identified¹ some techniques and rules of thumb for making code reviews more effective at identifying defects:

1. Limit code reviews to 1 hour or less.
   • After 60-90 minutes into a code review the ability to find further defects drops off dramatically due to focus fatigue.
   • If a code review in progress is dragging on past 1 hour, consider taking a break and continuing the remainder later in a “part 2”.
2. Limit code reviews to 400 lines of code or less.
   • Code reviews performed faster than 400-500 lines of code per hour show a dramatic drop in density of detected defects.
   • Combining that result with the earlier result that reviews lasting longer than 1 hour are problematic, we can conclude that no more than 400 lines of code should be reviewed in the same session.
3. Identify the most complex/risky/controversial changes to review first when there is the least focus fatigue.²
4. Link to related “context” (i.e. files, documentation, classes, etc) alongside the immediate changes of a code review, for a 15-30% increase in defect detection.
5. Self-review changes before posting them for external review, because 50% of defects can be found in a self-review at half the time cost of an external review.
6. An individual code review should be either asynchronous or synchronous but not both.
   • For a code review posted asynchronously, there is little gain in following up with an additional full synchronous review: Only an additional 4% of defects are likely to be found.