Modern code reviews in open-source projects: Which problems do they fix?

Moritz Beller, Alberto Bacchelli, Andy Zaidman, Elmar Juergens

Research output: Chapter in Book/Conference proceedings/Edited volumeConference contributionScientificpeer-review

164 Citations (Scopus)
147 Downloads (Pure)


Code review is the manual assessment of source code by humans, mainly intended to identify defects and quality problems. Modern Code Review (MCR), a lightweight variant of the code inspections investigated since the 1970s, prevails today both in industry and open-source software (OSS) systems. The objective of this paper is to increase our understanding of the practical benefits that the MCR process produces on reviewed source code. To that end, we empirically explore the problems fixed through MCR in OSS systems. We manually classified over 1,400 changes taking place in reviewed code from two OSS projects into a validated categorization scheme. Surprisingly, results show that the types of changes due to the MCR process in OSS are strikingly similar to those in the industry and academic systems from literature, featuring the similar 75:25 ratio of maintainability-related to functional problems. We also reveal that 7-35% of review comments are discarded and that 10-22% of the changes are not triggered by an explicit review comment. Patterns emerged in the review data; we investigated them revealing the technical factors that influence the number of changes due to the MCR process. We found that bug-fixing tasks lead to fewer changes and tasks with more altered files and a higher code churn have more changes. Contrary to intuition, the person of the reviewer had no impact on the number of changes. Copyright is held by the author/owner(s). Publication rights licensed to ACM.

Original languageEnglish
Title of host publicationProceedings of the 11th Working Conference on Mining Software Repositories
PublisherAssociation for Computing Machinery (ACM)
Number of pages10
ISBN (Electronic)9781450328630
Publication statusPublished - 31 May 2014
Event11th International Working Conference on Mining Software Repositories, MSR 2014 - Hyderabad, India
Duration: 31 May 20141 Jun 2014


Conference11th International Working Conference on Mining Software Repositories, MSR 2014


  • Code review
  • Defects
  • Open source software


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