Noticed that in one of my git-annex repositories, git-annex was spending a full second at startup checking all the git-annex branches from remotes to see if they contained changes that needed to be merged in. So, I added a cache of recently merged branches to avoid that. I remember considering this optimisation years ago; don't know why I didn't do it then. Not every day that I can speed up git-annex so much!
git annex log --all show location log changes for all keys.
This was tricky to get right and fast.