Group versus Individual Review Requests: Tradeoffs in Speed and Quality at Mozilla Firefox

TL;DR

This study analyzes how group versus individual review requests impact review speed and quality in Mozilla Firefox, finding group reviews enhance quality and offer other benefits without significantly affecting review velocity.

Contribution

It provides the first empirical comparison of group and individual review requests, highlighting their effects on review quality and workflow in a large-scale open-source project.

Findings

Group reviews are associated with higher review quality.

Group reviews have negligible impact on review velocity.

Practitioner insights highlight benefits like balanced workload and training.

Abstract

The speed at which code changes are integrated into the software codebase, also referred to as code review velocity, is a prevalent industry metric for improved throughput and developer satisfaction. While prior studies have explored factors influencing review velocity, the role of the review assignment process, particularly the `group review request', is unclear. In group review requests, available on platforms like Phabricator, GitHub, and Bitbucket, a code change is assigned to a reviewer group, allowing any member to review it, unlike individual review assignments to specific reviewers. Drawing parallels with shared task queues in Management Sciences, this study examines the effects of group versus individual review requests on velocity and quality. We investigate approximately 66,000 revisions in the Mozilla Firefox project, combining statistical modeling with practitioner views from a focus group discussion. Our study associates group reviews with improved review quality, characterized by fewer regressions, while having a negligible association with review velocity. Additional perceived benefits include balanced work distribution and training opportunities for new reviewers.