How to delete the old history after running git filter-branch?

Question

Suppose I have such tree:

... -- a -- b -- c -- d -- ...
             \
              e -- a -- k

and I want it become just

... -- a -- b -- c -- d -- ...

I know how to attach branch name to "e". I know that what I'm going to do will change history, and this is bad. Also I guess I need to use something like rebase or filter-branch. But how exactly - I'm lost.

Ok. Situation is following: I have rather big tree now (like this)

                 s -- p -- r   
                /
a -- b -- c -- d -- e --- g -- w
           \               \
            t -- p -- l     y -- k

but in my one of first commits (like to "b" for ex.) I added binary files, which makes whole repo very heavy. So I decided to take them away. I did it with filter-branch. And Now I have 2 long branches of commits identical to each other starting from second commit.

                 s -- p -- r   
                /
a -- b -- c -- d -- e --- g -- w
      \    \               \
       \    t -- p -- l     y -- k
        \
         \             s'-- p'-- r'  
          \           /
           b'-- c'-- d'-- e'--- g'-- w'
                 \               \
                  t'-- p'-- l'    y'-- k'

where b' is commit without binary file in it. So I can't do merge. I don't want this whole tree to be in history duplicated so.

Answer 1

After importing a Subversion repository with multiple years of history, I ran into a similar problem with bloat from lots of binary assets. In git: shrinking Subversion import, I describe trimming my git repo from 4.5 GiB to around 100 MiB.

Assuming you want to delete from all commits the files removed in “Delete media files” (6fe87d), you can adapt the approach from my blog post to your repo:

$ git filter-branch -d /dev/shm/git --index-filter \
  "git rm --cached -f --ignore-unmatch media/Optika.1.3.?.*; \
   git rm --cached -f --ignore-unmatch media/lens.svg; \
   git rm --cached -f --ignore-unmatch media/lens_simulation.swf; \
   git rm --cached -f --ignore-unmatch media/v.html" \
  --tag-name-filter cat --prune-empty -- --all

Your github repo doesn't have any tags, but I include a tag-name filter in case you have private tags.

The git filter-branch documentation covers the --prune-empty option.

--prune-empty
Some kinds of filters will generate empty commits that leave the tree untouched. This switch allows git-filter-branch to ignore such commits …

Using this option means your rewritten history will not contain a “Delete media files” commit because it no longer affects the tree. The media files are never created in the new history.

At this point, you'll see duplication in your repository due to another documented behavior.

The original refs, if different from the rewritten ones, will be stored in the namespace refs/original/.

If you're happy with the newly rewritten history, then delete the backup copies.

$ git for-each-ref --format="%(refname)" refs/original/ | \
  xargs -n 1 git update-ref -d

Git is vigilant about protecting your work, so even after all this intentional rewriting and deleting the reflog is keeping the old commits alive. Purge them with a sequence of two commands:

$ git reflog expire --verbose --expire=0 --all
$ git gc --prune=0

Now your local repository is ready, but you need to push the updates to GitHub. You could do them one at a time. For a local branch, say master, you'd run

$ git push -f origin master

Say you don't have a local issue5 branch any more. Your clone still has a ref called origin/issue5 that tracks where it is in your GitHub repository. Running git filter-branch modifies all the origin refs too, so you can update GitHub without a branch.

$ git push -f origin origin/issue5:issue5

If all your local branches match their respective commits on the GitHub side (i.e., no unpushed commits), then you can perform a bulk update.

$ git for-each-ref --format="%(refname)" refs/remotes/origin/ | \
  grep -v 'HEAD$' | perl -pe 's,^refs/remotes/origin/,,' | \
  xargs -n 1 -I '{}' git push -f origin 'refs/remotes/origin/{}:{}'

The output of the first stage is a list of refnames:

$ git for-each-ref --format="%(refname)" refs/remotes/origin/
refs/remotes/origin/HEAD
refs/remotes/origin/issue2
refs/remotes/origin/issue3
refs/remotes/origin/issue5
refs/remotes/origin/master
refs/remotes/origin/section_merge
refs/remotes/origin/side-media-icons
refs/remotes/origin/side-pane-splitter
refs/remotes/origin/side-popup
refs/remotes/origin/v2

We don't want the HEAD pseudo-ref and remove it with grep -v. For the rest, we use Perl to strip off the refs/remotes/origin/ prefix and for each one run a command of the form

$ git push -f origin refs/remotes/origin/BRANCH:BRANCH