Theoretical analysis of git bisect

Julien Courtiel (1) , Paul Dorbec (1) , Romain Lecoq (1)

1 Equipe AMACC - Laboratoire GREYC - UMR6072

In this paper, we consider the problem of finding a regression in a version control system (VCS), such as Git. The set of versions is modelled by a Directed Acyclic Graph (DAG) where vertices represent versions of the software, and arcs are the changes between different versions. We assume that somewhere in the DAG, a bug was introduced, which persists in all of its subsequent versions. It is possible to query a vertex to check whether the corresponding version carries the bug. Given a DAG and a bugged vertex, the Regression Search Problem consists in finding the first vertex containing the bug in a minimum number of queries in the worst-case scenario. This problem is known to be NP-hard. We study the algorithm used in Git to address this problem, known as git bisect. We prove that in a general setting, git bisect can use an exponentially larger number of queries than an optimal algorithm. We also consider the restriction where all vertices have indegree at most 2 (i.e. where merges are made between at most two branches at a time in the VCS), and prove that in this case, git bisect is a 1/log(3/2)-approximation algorithm, and that this bound is tight. We also provide a better approximation algorithm for this case.

Domains: Computer Science [cs]; Computational Complexity [cs.CC]; Data Structures and Algorithms [cs.DS]

Julien Courtiel, Paul Dorbec, Romain Lecoq. Theoretical analysis of git bisect. 15th LATIN American Symposium 2022: Theoretical Informatics, Nov 2022, Guanajuato, Mexico. pp.157-171, ⟨10.1007/978-3-031-20624-5_10⟩. ⟨hal-03431454v2⟩