How do git grafts and replace differ? (Are grafts now deprecated?)

Question

There are very few Q&A's on git grafts versus replace. The search [git] +grafts +replace only found two that felt relevant of the 5. what-are-git-info-grafts-for and git-what-is-a-graftcommit-or-a-graft-id. There is also a note on git.wiki.kernel.org:GraftPoint

Are grafts now completely overtaken by the replace and filter-branch, or do they still needed for some special corner cases (and backward compatibility) ?

In general, how do they differ (e.g. which are transported between repos), and how are they generically the same? I've seen that Linus doesn't appear to care about grafts at present in the discussion on commit generation numbers (of the max parents back to any root variety) "Grafts are already unreliable."

EDIT: more info found.
A search of www.kernel.org/pub/software/scm/git/docs for graft only found 3 results:

1. git-filter-branch(1),
2. v1.5.4.7/git-filter-branch(1),
3. v1.5.0.7/git-svn(1).

A slightly broader search found RelNotes/1.6.5.txt which contains:

• refs/replace/ hierarchy is designed to be usable as a replacement of the "grafts" mechanism, with the added advantage that it can be transferred across repositories.

Unfortunately, the gitrepository-layout(5) isn't yet up to date with the refs/replace/ repository layout info (and notes), nor any deprecation note of info/grafts.

This gets closer to supporting what I was thinking but I'd welcome any confirmation or clarification.

Answer 1

In the same discussion about Commit Generation Number that you mention, Jakub Narębski does confirm that grafts are more aproblem than a solution:

grafts are so horrible hack that I would be not against turning off generation numbers if they are used.
In the case of replace objects you need both non-replaced and replaced DAG generation numbers.
[...] Grafts are non-transferable, and if you use them to cull rather than add history they are unsafe against garbage collection... I think.

(publishing has always been taken care of with git filter-branch, as illustrated by this 2008 thread on grafts workflow.)

The difference between grafts and git replace is best illustrated by this SO question "Setting git parent pointer to a different parent", and the comments of (Jakub's again) answer.

It does include the reference to Git1.6.5

From what I understand (from GraftPoints), git replace has superseded git grafts (assuming you have git 1.6.5 or later)

(Jakub:)

• if you want to rewrite history then grafts + git-filter-branch (or interactive rebase, or fast-export + e.g. reposurgeon) is the way to do it.
• If you want/need to preserve history, then git-replace is far superior to graft