git-pisect - Parallel regression finder

git-pisect is an alternative to git bisect run that uses multiple concurrent tests to try to finish a bisect more quickly. It's experimental, but should work fine. Provides best results when run on repositories that have a test suite with the following qualities:

• Requires no input from a user
• Takes a long (for some definition of long, usually greater than a few seconds) to run
• Is safely parallelizable (ie. tests won't step on each others' feet regarding things like file or database access)
• Doesn't implement any parallelization itself (otherwise the parallelization that pisect provides is redundant)

Install

$ wget https://raw.githubusercontent.com/hoelzro/git-pisect/master/git-pisect
$ cpanm List::MoreUtils
$ cpanm Sys::Info # optional, used for CPU detection

Usage

$ git bisect start
$ git bisect bad 1234abc
$ git bisect good xyz0987
$ git pisect command [args]

git-pisect attempts to detect the number of CPUs you have and runs that many tests at once - you can specify the number of jobs to run with the PISECT_JOBS environment variable.

Explanation

I wrote up a blog post about why I wrote this tool, as well as how it works.

Dependencies

Requires the List::MoreUtils Perl module, and optionally the Sys::Info module if you want to automatically detect the number of jobs to run on non-Linux systems.

Caveats

This is kind of proof-of-concept and is experimental, so the following are things to keep in mind while playing with git-pisect:

• I have no idea how it'll handle a flapping test (eg. multiple good/bad boundaries); it should converge on a boundary of some kind, though.
• It won't work if the test suite needs input from STDIN.
• It won't work if the test suite isn't safe to run in a parallel environment.
• The output of tests is discarded - it would be preferable to log it somewhere.
• Skipping commits isn't implemented.
• The "number of steps" metric isn't accurate, since it currently uses the existing git-bisect machinery to print the progress report.