Fixing Regressions with bisect

A quick introduction to using bisect to find regressions. This was written with Mercurial in mind, but applies equally well to git.

Delivered February 2011 for BBYOpen.

Canonical URL: http://luke.francl.org/talks/fixing-regressions-with-bisect/

Transcript

1. Fixing regressions with bisect Luke Francl
 BBYOpen
2. Your current branch is a series of commits 720 719 718 717 4 3 2 1 ...
3. Some where in that series is a regression... 720 719 718 717 4 3 2 1 ...
4. but where? 720 719 718 717 4 3 2 1 ...
5. bisect to the rescue!
6. linear search O(n)
   worst case: 9 changesets 720 719 718 717 716 715 714 713 712 711 Working Known Bug
7. binary search O(log(n))
   worst case: 4 changesets 720 719 718 717 716 715 714 713 712 711 Known Bug Working
8. binary search O(log(n))
   worst case: 4 changesets 720 719 718 717 716 715 714 713 712 711 Known Bug Working Bad
9. binary search O(log(n))
   worst case: 4 changesets 720 719 718 717 716 715 714 713 712 711 Known Bug Working Bad
10. 720 719 718 717 716 715 714 713 712 711 Known Bug Working Bad Bad binary search O(log(n))
    worst case: 4 changesets
11. 720 719 718 717 716 715 714 713 712 711 Known Bug Working Bad Bad binary search O(log(n))
    worst case: 4 changesets
12. 720 719 718 717 716 715 714 713 712 711 Known Bug Working Bad Bad Good binary search O(log(n))
    worst case: 4 changesets
13. 720 719 718 717 716 715 714 713 712 711 Known Bug Working BUG! Good binary search O(log(n))
    worst case: 4 changesets Bad
15. Lines of code examined Debug Page hg bisect HTML 270 22 JavaScript 400 4 CSS 1,000 6 Total 1,670 32
16. Use your tools!