git-annex/doc/bugs/making_annex-merge_try_a_fast-forward.mdwn

While merging the git-annex branch, annex-merge does not end up in a fast-forward even when it would be possible.
But as sometimes annex-merge takes time, it would probably be worth it
(but maybe I miss something with my workflow...).

> I don't think a fast-forward will make things much faster.
> 
> git-annex needs its index file to be updated to reflect the merge.
> With the union merge it does now, this can be accomplished by using
> `git-diff-index` to efficiently get a list of files that have changed,
> and only merge those changes into the index with `git-update-index`.
> Then the index gets committed, generating the merge.
> 
> To fast-forward, it would just reset the git-annex branch to the new
> head of the remote it's merging to. But then the index needs to be
> updated to reflect this new head too. To do that needs the same method
> described above, essentially (with the difference that it can replace
> files in the index with the version from the git-annex branch, rather
> than merging in the changes... but only if the index is known to be
> already committed and have no other changes, which would require both
> an attempt to commit it first, and
> locking). 
> 
> So will take basically the same amount of time, except
> it would not need to commit the index at the end of the merge. The
> most expensive work is the `git-diff-index` and `git-update-index`,
> which are not avoided.
> 
> Although, perhaps fast-forward merge would use slightly
> less space. --[[Joey]]