How to delete commits (and git branches) completely ?

[simonmichael]

Thank you for jj, which is awesome!

My question:

I'm cleaning up a repo (because jj log showed me that I have hundreds of stale old branches in it).

I have found jj better than git for finding old branches to delete.
Eg: jj log --no-graph -r 'bookmarks() ~ person(simon)'

And I've found that jj bookmark delete BOOKMARK also deletes the git branch.

But not the commits themselves, I think because they are still referenced by git refs created by jj like refs/jj/keep/HASH.
I'd like to cleanly delete those, so git (or jj) can garbage collect these commits.

I also tried jj abandoning them, which didn't help. Then I saw

To prevent GC from deleting commits that are still reachable from the operation log, the GitBackend stores a ref for each commit in the operation log in the refs/jj/keep/ namespace.

So do I need to jj op abandon all operations that mention them, as well ? It seems hard.

[martinvonz]

So do I need to jj op abandon all operations that mention them, as well ? It seems hard.

Yes, that's what you need to do. If you just deleted the branches, then you'll have to abandon most operations in your repo. jj op abandon ..@- will delete all operations before the current operation. Then follow that by jj util gc to remove the unused refs/jj/keep/ refs and run git gc (i.e. jj util gc does that for you).

[simonmichael]

Thanks @martinvonz! Losing all operation history of course sounds bad. Is there any way to see which operations reference those commits ? I didn't see an obvious one.

[simonmichael]

Found them this way!

for o in `jj op log --no-graph -T 'id.short()++"\n"'`; do echo $o:; jj op show $o | grep HASH; done

I had a hunch it would be the first "import git refs" operation, and it was. But also today's attempts to forget/delete the bookmark and then abandon the commit.

[simonmichael]

I tried abandoning all the ops listed by the above, which seemd successful; afterward, none were listed. On the other hand, the deleted git branches and commits were back. I deleted them again with git. I gc'd on both sides. I ended up abandoning all ops as Martin showed above. Perhaps I made mistakes, but I could not eradicate these commits. If someone else comes up with a successful procedure, I'd be glad to know it.

[yuja]

You'll have to use jj util gc --expire=now to delete jj/keep refs immediately.

Also note all predecessor commits are preserved. For example, old commits displayed in jj evolog -r <REVISIONS_SHOULD_BE_KEPT> won't be deleted even if old operations got abandoned.

[simonmichael]

Thank you, --expire=now (or --prune=now on the git side) was another important clue. And noted about evolog.

For the record, I got these stale branches cleaned out in this way:

1. Take advantage of jj to save a list of the branches to be deleted. Eg: jj log --no-graph -r 'bookmarks() ~ person(simon)' -T 'bookmarks++"\n"'
2. Give names to any unnamed heads created with jj: jj bookmark create ...
3. Discard jj state, in the simplest way: rm -rf .jj
4. Delete each branch with git: for b in ...; do git branch -D $b; done
5. Also delete the "keep" references created by jj: gsed -i '/\/keep\//d' .git/info/refs; gsed -i '/\/keep\//d' .git/packed-refs
6. Check one or two hashes to see if they're still referenced: rg SOMEHASH .git
7. If still mentioned in .git/logs/HEAD, that means the git reflog still references it. As with jj's operations log, the simplest way to fix that is discard the entire reflog: git reflog expire --expire=now --all.
   I'm not sure if a more surgical removal is feasible.
8. Now all references should be gone; discard the commits with: git gc --prune=now
9. And verify they're gone: git show SOMEHASH (should fail)
10. And finally bring back jj (starting fresh): jj git init --colocate

Bottom line, neither jj nor git give up data easily, even when you want them to !

And as #git pointed out, the easier way when you really want to clean up is:
clone the repo and transfer the branches you really want to keep.