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Garbage Collection in Git

plutov profile image Alex Pliutau ・1 min read

git-gc

To understand git garbage collector, we need to understand how branches work. Branches are just pointers to commits that move whenever a new commit is created.

Any time you do git commit --amend or git rebase a new commit object is created. But what happens to the old one? Old commit objects stick around in the datastore. The reason you don’t see them is because there are no pointers to them.

In addition, the git reflog stores a list of the previous branch pointers. In other words, even if you delete a branch, the reflog still shows it.

You will lose your old objects only when you run a git gc, which repacks the repository into a more efficient structure. Some git commands may automatically run git gc.

So, you just did a git reset --hard HEAD^ and threw out your last commit. Well, it turns out you really did need those changes. When you do a reset, the commit you threw out goes to a dangling state. It’s still in Git’s datastore, waiting for the next git gc execution to clean it up. So unless you’ve ran a git gc since you removed it, you can find it.

git fsck command will show your commits in dangling state.

Original article in my blog

Discussion

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Andy Zhao (he/him)

Woah, another tool to fix my mistakes via git. Git continues to blow my mind. Definitely going to use the dangling state in the future, but hopefully not too many times...

Think you would appreciate this article @maestromac .

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Mac Siri

Wow, wish I knew this sooner since I reset --hard pretty often. Thanks for sharing!