[btilly]

I strongly prefer git merge over git rebase.

Using rebase results in a cleaner history and simplified workflow in many cases. However it also means that when you have a disaster, it can be truly unrecoverable. I hope you have an old backup because you told your source control system to scramble its history, and you don't have any good way to back it out later.

For those who don't know what I mean, the funny commit ids that git produces are a hash signifying the current state of the repository AND the complete history of how you got there. Every time you rebase you take the other repository, and its history, and then replay your new commits as happening now, one after the other. Now suppose that you rebased off of a repository. Then the repository is rebased by someone else. Now there is no way to merge your code back except to --force it. And that means that if your codebase is messed up, you're now screwed up with history screwed up and no good way to sort it out.

That result is impossible if you're using a merge based result. The cost is, though, that the history is accurately complicated. And the existence of a complex history is a huge problem for useful tools like git bisect.

[james_s_tayler]

I don't know. Since git uses content-based addressing, you can't actually alter any commit, only create new ones. And orphaned commits don't get garbage collected for like 30 days even if you explicitly tell git to clean things up. So, the original stuff will still be there. It might just not be obvious how to access it. Part of the commit is the reference to zero or more parent commit object ids. So, if you find the old commit, it still has it's history intact. `git log -g` is a handy command to see a composite git log that travels across branch changes.

I do get what you mean though. You effectively create new commits with an alternate view of history. I don't get quite why/how that causes a situation in which the code can't be merged? I don't rebase much, I prefer merging. Is there any resource that can explain why rebasing might be dangerous like that?

In general if branches diverge too far then you have difficulties merging no matter which strategy you use and sometimes if it diverges too far it just becomes hopeless. Mostly though if you are working in a team, commit daily and merging/rebasing frequently it should present fairly few problems.

I find I never run the actual command git bisect. I just do `git log --decorate --oneline --graph` and eyeball a good commit to start from and then basically do it by hand using commit messages to aid in making reasonable guesses as to where to try but following the basic binary search philosophy. Works well enough even with a complex history.

[btilly]

Here is an example of how to create a problem.

You rebase your private branch off of a shared master and pull in other people's commits. Someone else pushes out their rebased version using force. More commits are made on top of the other people's commits, including reversing some bad commits. You try to rebase off of the shared master.

In your last rebase, you are trying to replay all of the commits in your history that are not in the remote history. However git does not understand which local commits are from you and not pulled in on the previous rebase. It therefore tries to play them on top of the remote master if it can make sense of them. Which means that you bring back the reversed commits. You might find conflicts in code that you have not touched. You resolve them as best you may. And now you've got the definitive version of what happens, and no way with the screwed up history to figure out why it is going to go wrong. Then you force commit because that is how a rebase flow works..and everyone is screwed.

I agree on branches diverging too far. Merge early, merge often.

If you never run the command to git bisect, you should try it. What it's for is finding the random commit that recently broke a piece of functionality that nobody realized would break. Because nobody realized it, the log messages will say nothing useful. And you don't need to figure out where the change is - just write a test program for the breakage, run git bisect, and look at the offending commit.

[shandor]

> Then you force commit because that is how a rebase flow works

Absolutely not. Force pushing a shared master is probably the worst sin one can commit with git. I guess you already have come upon the 'why' of it.

A "Rebase workflow" works so that devs use rebase to 'move' their work on an updated master after a pull/remote update, resolve potential conflicts locally, and do a fast-forward push to origin/master. This also works on copying work between different feature branches just as well.

[james_s_tayler]

Ah OK. Hmm my policy is to always disable force push on master. Force pushing to master should never be allowed.

[Stratoscope]

> Since git uses content-based addressing, you can't actually alter any commit, only create new ones. And orphaned commits don't get garbage collected for like 30 days even if you explicitly tell git to clean things up. So, the original stuff will still be there. It might just not be obvious how to access it.

SmartGit does a splendid job with this. In the Log window where you see all your commits and how they are related to each other, there is a Recyclable Commits checkbox. Turn that on and everything in the reflog shows up in the log tree, just as if it were any ordinary commit. You can right click one of these commits and add a branch there, or do any of the other operations you can do in the commit log window.

Same thing for stashes. Did you know they are just commits too? I didn't, until I clicked one of the stash checkboxes in SmartGit. Then the stash showed up in the tree just like any other commit.

I don't understand why so many developers are resistant to the idea of using a powerful Git GUI like SmartGit. For me it is like having a superpower compared to the meager options the Git command line gives you.

Even if you like the command line, it's not like you have to choose one or the other. You can use SmartGit and the Git command line, whichever makes any task easier for you.

[jonahx]

Linus on rebase:

https://www.mail-archive.com/[e-mail]...

[333c]

I work on a small open source project. Our master branch is protected from force pushes, and I only use rebase on personal branches for features or bug fixes. It's very nice if I'm planning to merge several commits but I need to fix something in one or more of them.

I agree that rebasing should not happen in the main branch(es) of a repo.