Howto remove unused objects from a git repsitory?

Question

I accidentally added, committed and pushed a huge binary file with my very latest commit to a Git repository.

How can I make Git remove the object(s) that was/were created for that commit so my .git directory shrinks to a sane size again?

Edit: Thanks for your answers; I tried several solutions. None worked. For example the one from GitHub removed the files from the history, but the .git directory size hasn't decreased:

$ BADFILES=$(find test_data -type f -exec echo -n "'{}' " \;)

$ git filter-branch --index-filter "git rm -rf --cached --ignore-unmatch $BADFILES" HEAD
Rewrite 14ed3f41474f0a2f624a440e5a106c2768edb67b (66/66)
rm 'test_data/images/001.jpg'
[...snip...]
rm 'test_data/images/281.jpg'
Ref 'refs/heads/master' was rewritten

$ git log -p # looks nice

$ rm -rf .git/refs/original/
$ git reflog expire --all
$ git gc --aggressive --prune
Counting objects: 625, done.
Delta compression using up to 2 threads.
Compressing objects: 100% (598/598), done.
Writing objects: 100% (625/625), done.
Total 625 (delta 351), reused 0 (delta 0)

$ du -hs .git
174M    .git
$ # still 175 MB :-(

Answer 1

This guide on removing sensitive data can apply, using the same method. You'll be rewriting history to remove that file from every revision it was present in. This is destructive and will cause repo conflicts with any other checkouts, so warn any collaborators first.

If you want to keep the binary available in the repo for other people, then there's no real way to do what you want. It's pretty much all or none.

Answer 2

Your git reflog expire --all is incorrect. It removes reflog entries that are older than the expire time, which defaults to 90 days. Use git reflog expire --all --expire=now.

My answer to a similar question deals with the problem of really scrubbing unused objects from a repository.