Calculate and plot cumulative distribution functions of the added, removed, and total changed lines of all non-merge commits in a Git repository.
Run commit-size-distribution.py with the path to a Git repository, specifying
either the --preview flag, a location to save the plot as a PNG, or both.
The sample directory contains a plot of Git's own commit size distribution, generated with:
./commit-size-distribution.py --max-size 2000 --mark-hours ../git/ sample/git.png
The --mark-hours option draws vertical lines at increments of 400 to
indicate how many hours the data point would take to review. In a famous study
of code review of a multi-million line Java application at Cisco Systems,
SmartBear found that
- defects discovered approaches zero at 400 lines of inspection;
- reviewing more than 400 lines of code per hour greatly reduces the number of defects found; and
- mental fatigue sets in after about 60 minutes of review.
The optimal rate of inspection will vary with language and context but 400 is a nice round number.
The --max-size option causes any data point in the respective graph above
the supplied value to be discarded. This is useful to indicate that commits
above a certain size are not realistically thoroughly reviewable, such as style
changes across an entire code base.
$ python3 -m venv venv
$ . venv/bin/activate
$ pip install -r requirements.txt