What happens to a git branch after delete if it was not merged?

Question

I have a small repo with a master and an experimental branch for trying out some new features. I decided not to implement those features on the master.

What happens to the commits of the experimental branch when I delete that branch using git push origin --delete <branchName>? Will git keep some non accessible remnants? If I remember well I have tags on that branch and it is uploaded to github. Will this cause any problem?

edit:

I checked with gitk --all as suggested, the commit graph looks like this:

What I want to remove the babel branch with all of its commits, and I don't want it to be restorable. Is this possible?

Answer 1

Deleting a branch will only do that: Delete the branch. Since a branch is just a reference to a commit, only that reference is gone. The commit is still there.

Similar to programming languages, Git has a garbage collection which will eventually remove commit objects which are no longer referenced. So if that branch was the only pointer to that commit, you will effectively lose access to it, and it will be deleted “soon”.

If you have other references, that includes other branches, tags, and commits that indirectly reference that commit (i.e. for which that commit is a parent), then the commit is still referenced and it will not be deleted.

So if you want to get rid of a commit, you would need to remove all references to that commit. If you want to delete the branch, and there are other things referencing a commit from that branch, then that is not a problem and will not cause problems: It is desired behavior that the commit is then kept so the other things don’t break.

Answer 2

What happens to the commits of the experimental branch when I delete that branch using git push origin --delete <branchName> ?

The specific branch will be deleted in your local and your remote repository. I might not be possible to restore it again.

Will git keep some non accessible remnants?

According to this answer https://stackoverflow.com/a/4674570/1654730, it might be possible to restore the branch with the help of the reflog.

If I remember well I have tags on that branch and it is uploaded to github. Will this cause any problem?

This should not cause any problems. If you have tags on that branch you can still access the tags and create a new branch based on them.

Answer 3

Yes, git will keep some non-accessible remnants - at least to begin with. Commits that can't be accessed from existing branches or tags are called dangling commits. See this question for example: Git: what is a dangling commit/blob and where do they come from?

If you created tags on the branch and pushed those tags to GitHub, then the tags will still exist in your local repository, so commits accessible from those tags won't ever be deleted.

You could use for example gitk --all to show all branches and tags in your local repository, and if you see tags that were on the old branch that you have now deleted, you could delete each tag as well, using

git tag -d TAG-NAME

to delete the tag locally, and also delete the tag from GitHub using:

git push origin :refs/tags/TAG-NAME

Non-accessible commits are eventually removed when git performs garbage collection in the repository. As mentioned in the other Stack Overflow question, there's more information about this in the Maintenance and Data Recovery section on git-scm.com.