[marssaxman]

How often do you find that command useful?

In ~18 years of git use, I have never needed it, but I see it mentioned often as an important reason to handle commits in some certain way. I wonder what accounts for the difference.

[arp242]

I used it a few weeks ago to track down a weird regression/bug in Firefox. A few years ago I used it to track down a regression in Wine.

That's probably the most important case: large complex codebases with lots of changes where "wtf is going on" isn't so obvious from just the code.

I've never used it for any of my personal projects or even at my dayjob, because they've much smaller with far fewer changes (relatively speaking).

[ajb]

It's useful when the codebase is difficult to debug directly. Eg, your users have a bug that maybe appears on specific hardware, which the developers don't have. The users can't be expected to comprehend the code base enough to debug, but bisect is a mechanical process that they are capable of.

Having said that, bisect is also an O(log N) method and it's useful where otherwise you might end up spending O(N) time debugging something. I have myself split a configuration change into many stupidly-small commits (locally, without the intention to push that) purely so I could run bisect instead of manually reviewing the change to figure out which part broke stuff.

[sam_bristow]

Git bisect is one of those tools that - once you learn how to use it effetively - fundamentally changes how you think about your git repos. I have had people tell me that a clean git history isn't worth the effort but once they really grok what you can do with that solid foundation really come around.

One case where git bisect really saved me was when we discovered a really subtle bug in an embedded project I was working on. I was able to write a 20 line shell script that built the code, flashed the device, ran 100 iterations of a check, and do some basic stats. I left the bisect chugging away over the weekend and came back to an innocuous-looking commit from 6 months earlier. We could've spent weeks trying to find the root cause without it.

[8note]

whats N here?

[ajb]

In the case of git bisect, the number of commits. In the alternate case, it depends what debugging strategy you decided to use.

[vlovich123]

I think it’s not that you couldn’t have used it but because you discount it it wasn’t something you reached for. If you flip the script as something that’s out there and explicitly look for opportunities to use it it’s there. Alternatively, you don’t structure your commits carefully and thus git bisect for you is a mess that would pull up a giant amount of code anyway.

Heck, I used it yesterday because I had a PR where I was cleaning things in the C++ build system where things stopped working in CI in weird ways I couldn’t figure out but was fine locally. I used bisect locally to figure out which commits to test. You just have to think that a blind bisect search is going to be more effective than trying to spot check the commits that are a problem (and for tricky bugs this is often the case because your intuition can mislead you).

I’ve also used it to find weird performance regressions I couldn’t figure out.

[rcxdude]

Occasionally, but when it's useful, it's very useful. But generally only if most commits are buildable and roughly functional, otherwise it becomes a big pain (as does any manual process of finding what change introduced a regression).

[SoftTalker]

Same. I've only done bisect debugging a few times. I'm almost always able to use more traditional debugging especially if I have a good idea about where the bug must be from behavior.

Bisects are good when the bug is reproducible, you have a "this used to work and now it doesnt" situatiuon, and the code base is too big or too unfamiliar for you to have a good intuition about where to look. You can pretty quickly get to the commit where the bug first appears, and then look at what changed in that commit.

[overfeed]

How do you trace the origin of breaking changes, especially those arising from integration problems? For fairly busy codebases (>10 commits per day), and a certain subset of regressions, bisect is invaluable in finding the root cause. you can always do it the "hard way", so it's not the only way

[marssaxman]

I don't really ever find myself having to do that. I guess it's been a long time since I worked in an environment which did not use an "only merge to main after passing CI" workflow, and back then we weren't using git, anyway.

There was one git-using startup I worked for which had a merge-recklessly development style, and there was one occasion when I could have used `git bisect` to disprove my coworker's accusation that I had thoughtlessly broken the build (it was him, actually, and, yuck - what a toxic work environment!), but the commit in question was like HEAD~3 so it would probably have taken me longer to use git bisect than to just test it by hand.

[mb7733]

> I don't really ever find myself having to do that. I guess it's been a long time since I worked in an environment which did not use an "only merge to main after passing CI" workflow, and back then we weren't using git, anyway.

You _never_ have bugs that slip through the test suite? That is extremely impressive / borderline impossible. Even highly tested gold-standard projects like SQLite see bugs in production.

And once you find a regression that wasn't covered by your test suite, the fastest way to find where it originated is often git bisect.

[Dylan16807]

Bugs that slip through the test suite and it's important to trace the origin and it requires building more than a couple best-guess versions to find it. And even then, if it wastes an hour or two once in a blue moon that's not a big motivator for workflow changes.

You're skeptical of a far stronger claim than the one they actually made.

[sfink]

Performance regressions often match all of those constraints, at least in an active project.

[overfeed]

> I guess it's been a long time since I worked in an environment which did not use an "only merge to main after passing CI"

It's the same for me, but some integration bugs still escape the notice of unit tests. Examples from memory: a specific subset users being thrown into an endless redirect due to a cookie rename that wasn't propagated across all sub-systems on the backend, multiple instances of run-time errors that resulted from dependency version mismatches (dynamic loading), and a new notification banner element covering critical UI elements on an infrequently used page - effectively conflicting CSS position. In all these cases, the CI tests were passing, but passing tests don't mean your software is working as expected in all cases.

[sampullman]

I also find git bisect to be useful, but very rarely and never for personal projets.

In the cases you mentioned, robust e2e and integration tests would ideally be able to catch the bugs. And for the UI issue in particular, I wouldn't think to track down the commit that caused it, but just fix it and move on.

[turbocon]

Honestly if you haven't ever used got bisect I'd say you're missing out on a very powerful tool. To be able to, without any knowledge of the code base, isolate down to the exact commit that introduced a big is incredibly powerful

[hombre_fatal]

A coworker taught me how to use it long ago, else I would never have known it was there to reach for.

And the few times I've reached for it, I was really thankful it was there.

[chrishill89]

I’ve just used it two times in the last few months. One was to track down a commit which triggered a bug I found in Git. I wouldn’t be able to troubleshoot it myself. And I couldn’t send the whole repository because it’s not OSS. But with a script to reproduce the bug and half an hour I was able to find the problematic change.

I also tried to make a minimal reproduction but wasn’t able to.

[Thorrez]

I don't use git much. But at my job, where we use mercurial, where the unit of work is commit, I use bisect frequently. When one of our automated tests starts failing, I can run bisect and easily find the commit that caused it.

[isleyaardvark]

Often enough that I am truly shocked to hear someone say they have never needed it.

[matkoniecz]

I used it multiple times to track down which commit introduced confusing bug.

[spooneybarger]

I personally bisect regularly to find when issues were introduced.