Purging old git history

I have recently come across a situation where I had to purge git history. A friend of mine has created a repository on top of CPython for good reasons. However after we decided to move CPython out of his library, in which case we wouldn't need the old history anymore.

So I had set out to do that. It was way more complicated than I expected. Purging the history is quite easy, you basically follow this stackoverflow post. You create a grafts file with the corresponding commit and use filter-branch.

Be careful though, this "tutorial" will delete your old history permanently. It will keep the history starting from the commit you make a graft from. Yes: Make a backup!

$ du -sh .git
121M    .git
$ # Removing the origin just to make sure no reference is kept.
$ git remote rm origin
$ echo 21581f18dc98b69c0dad8863d70a0ce7842ce4fe > .git/info/grafts
$ git filter-branch -- --all
Rewrite 4352ea1fb4b0dfa5d28ad26ce6b9e042b126bd60 (8/8)
Ref 'refs/heads/master' was rewritten
$ rm .git/info/grafts
$ du -sh .git
121M    .git

However, the repository size is quite big, still. It's basically the same as in the beginning. Git doesn't just delete old files that don't have a reference anymore (you have to actually tell it to do that). There are mechanisms to keep your repository clean (automatic git gc after a while, but still we want a clean repository, now).

$ git update-ref -d refs/original/refs/heads/master
$ git reflog expire --expire=now --all
$ git gc --prune=now --aggressive
$ du -sh .git
164K    .git

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