Does Using Bazel Help Speed Up Continuous Integration Builds?

TL;DR

This study investigates whether Bazel accelerates CI builds by analyzing 383 projects, revealing significant speedups with parallel and incremental builds, and offering practical guidance for developers to optimize Bazel usage.

Contribution

It provides empirical evidence on Bazel's performance benefits in CI environments and compares its effectiveness with traditional build tools like Maven.

Findings

Median speedup of 2.00x to 12.80x with parallel builds at increasing degrees of parallelism.

Incremental builds achieve median speedups of around 4.2x to 4.7x for long-build projects.

Approximately 31% of Bazel projects do not utilize Bazel in CI, indicating room for optimization.

Abstract

A long continuous integration (CI) build forces developers to wait for CI feedback before starting subsequent development activities, leading to time wasted. In addition to a variety of build scheduling and test selection heuristics studied in the past, new artifact-based build technologies like Bazel have built-in support for advanced performance optimizations such as parallel build and incremental build (caching of build results). However, little is known about the extent to which new build technologies like Bazel deliver on their promised benefits, especially for long-build duration projects. In this study, we collected 383 Bazel projects from GitHub, then studied their parallel and incremental build usage of Bazel in 4 popular CI services, and compared the results with Maven projects. We conducted 3,500 experiments on 383 Bazel projects and analyzed the build logs of a subset of 70 buildable projects to evaluate the performance impact of Bazel's parallel builds. Additionally, we performed 102,232 experiments on the 70 buildable projects' last 100 commits to evaluate Bazel's incremental build performance. Our results show that 31.23% of Bazel projects adopt a CI service but do not use Bazel in the CI service, while for those who do use Bazel in CI, 27.76% of them use other tools to facilitate Bazel's execution. Compared to sequential builds, the median speedups for long-build duration projects are 2.00x, 3.84x, 7.36x, and 12.80x, at parallelism degrees 2, 4, 8, and 16, respectively, even though, compared to a clean build, applying incremental build achieves a median speedup of 4.22x (with a build system tool-independent CI cache) and 4.71x (with a build system tool-specific cache) for long-build duration projects. Our results provide guidance for developers to improve the usage of Bazel in their projects.