How to permanently delete a commit from Git's history?

Question

How can I permanently delete a commit from Git's history?

One of the developers on the team has accidentally committed a 200 MB file and pushed it to our Git server. It was deleted a few days later but the history is there. Our code files are only about 75 MB, and we have 4 branches. Due to the 200 MB file commit, the history is preserved and the size of our project folder (specifically the hidden .git folder) has ballooned to close to 700 MB. How do I permanently delete the two check-ins (commit of the huge file, delete of the huge file) from git as if it never happened? I'm using `TortoiseGit if that matters.

Answer 1

Delete the file from a checkout

Github has a useful page how to permanently delete file(s) from a repository, in brief:

$ git filter-branch --force --index-filter \
  'git rm --cached --ignore-unmatch 200MB-filename' \
  --prune-empty --tag-name-filter cat -- --all
$ git push --all -f

That would remove the file from all branches. Then to recover the space locally:

$ rm -rf .git/refs/original/
$ git reflog expire --expire=now --all
$ git gc --prune=now

Recovering space on the git server

Force pushing does not remove any commits/objects on the remote server. If you don't want to wait for git to clean up itself, you can run it explicitly on the server:

$ ssh git server
$ cd /my/project/repo.git
$ git gc --prune=now

Compare the size of the repo before and after - ensure that it is the size you expect. If at any time in the future it reverts to the larger size - someone has pushed the deleted commits back into the repository (need to do all steps again).

Teammates

If there are other developers using this repository - they will need to clean up their checkouts. Otherwise when they pull from the repository and push their changes they will add back the deleted file as it's still in their local history. There are two ways to avoid that:

1. Clone again
2. fetch and reset

The first is very simple, the second means one of two things:

User has no local commits

$ git fetch
$ git reset origin/master -hard

That would make any local checkout exactly match the remote

User does have local commits

$ git fetch
$ git rebase -i origin/master

The user needs to make sure they don't have any local commits referencing the delete file - or they'll add it back to the repository.

User cleanup

Then (optionally, because git won't push unreferenced commits to the server) recover space, and everyone has a consistent slimmer repository state:

$ rm -rf .git/refs/original/
$ git reflog expire --expire=now --all
$ git gc --prune=now