An Exploratory Study of Performance Regression Introducing Code Changes

Performance is an important aspect of software quality. In fact, large software systems failures are often due to performance issues rather than functional bugs. One of the most important performance issues is performance regression. Examples of performance regressions are response time degradation and increased resource utilization. Although performance regressions are not all bugs, they often have a direct impact on users' experience of the system. Due to the possible large impact of performance regressions, prior research proposes various automated approaches that detect performance regressions. However, the detection of performance regressions is conducted after the fact, i.e., after the system is built and deployed in the field or dedicated performance testing environments. On the other hand, there exists rich software quality research that examines the impact of code changes on software quality; while a majority of prior findings do not use performance regression as a sign of software quality degradation. In this paper, we perform an exploratory study on the source code changes that introduce performance regressions. We conduct a statistically rigorous performance evaluation on 1,126 commits from ten releases of Hadoop and 135 commits from five releases of RxJava. In particular, we repetitively run tests and performance micro-benchmarks for each commit while measuring response time, CPU usage, Memory usage and I/O traffic. We identify performance regressions in each test or performance micro-benchmark if there exists statistically significant degradation with medium or large effect sizes, in any performance metric. We find that performance regressions widely exist during the development of both subject systems. By manually examining the issue reports that are associated with the identified performance regression introducing commits, we find that the majority of the performance regressions are introduced while fixing other bugs. In addition, we identify six root-causes of performance regressions. 12.5% of the examined performance regressions can be avoided or their impact may be reduced during development. Our findings highlight the need for performance assurance activities during development. Developers should address avoidable performance regressions and be aware of the impact of unavoidable performance regressions.