As you know MonetDB is developed using mercurial. You can find the
official repository here. We use git-remote-hg, a local git repository
and some scripts to mirror MonetDB’s source code on github.
The github mirror stopped updating on June 12. This is something that
has happened in the past, when people by mistake made or pushed
commits directly on github. In these cases the fix was usually simple:
merge the commits from github into the local repository and push them
back to mercurial.
This time the issue was more serious. The first clue was that there
were no extra commits in github. The second and much more serious clue
was that mercurial was crashing when it was trying to get new commits
from upstream.
We tried running git gc and git hg gc <remote> as per the
instructions in git-remote-hg’s readme, because MonetDB’s mercurial
history is pretty large (about 75K commits in the default branch since
July 2000). This did help but we ended up with different SHA-1 hashes
for many commits in the last two years. In fact the first commit that
was different was one that was done on github and was back-ported to
mercurial.
We spent a lot of effort trying to reconcile the two histories but
ultimately we were not willing to push about 9K duplicate commits on
the default branch in the mercurial repository. The final fix is that
we force pushed the “correct” history to gitub. All the branches that
existed before this change are saved using the prefix old-history.
We are making some changes in order to avoid having the same problem
in the future. The most important is a policy change: commits directly
to github are no longer acceptable. This means that in case a commit
like that happens in the future and we are unable to update the
mirror, they will be discarded by force pushing the history from
mercurial.