GIt: Removed several files from repository with BFG and there are enormous commit diffs

Question

I recently removed several large files from a repository using BFG --delete-files , and the output appeared to be what I expected. The correct files and sizes were reported as deleted from the repo and the local size reflects these removals.

However, when I upload and compare to master, it reports that there is a huge difference and it affects several hundred commits. I'm not sure what to make of this or how to understand it; it is too much to go through. I understand removing the files will restructure the repo, but how can I be sure what was intended actually happened in the diff?

Answer 1

It depends on the nature of the diff seen in all those files.

For instance, if they are EOL differences (end-of-lines), that could means the BFG commit-rewritten process was done locally with a config core.autocrlf which might have change eol for all the files (in addition of removing some of them).
Once pushed, all the other files would be shown as "different".

Answer 2

It's caused by java -jar bfg.war --delete-files filename will delete the the specified file from the whole commit histories for all branches, but you only push one branch to remote .

Assume the commit history as below before using BFG to delete files as below:

…---A---B---C---D  master, origin/master
         \
          E---F  mybranch, origin/mybranch

When you compare master branch with mybranch , the related commits are C , D , E and F .

And assume the delete-files is test.txt , and it only exist in commit B and E . When you execute

java -jar bfg.war --delete-files test.txt

The commit history will be:

…---A---B'---C'---D'  master, origin/master
         \
          E'---F'  mybranch, origin/mybranch

Note: it rewrite the commits not only for local branches ( master and mybranch ), but also re-point the tracking branches ( origin/master and origin/mybranch ).

If you do git fetch after that, you will find the local branches with their tracking branches are diverged:

        E---F    origin/mybranch
       /
      B---C---D  origin/master
     /     
…---A---B'---C'---D'  master
         \
          E'---F'  mybranch

While if you only force push mybranch to remote repo (not force push master branch), the commit history on remote repo will be:

      B---C---D  master
     /     
…---A---B'---E'---F'  mybranch

So when you compare mybranch with master branch again, the relate commits will contains B , C , D , B' , E' and F' .

And if you also force push local master btanch to remote, the count of related commits should be the same when you compared when using BFG.