[Monotone-devel] Re: FreeBSD's requirements for its future VCS

[Bruce Stephens]

Lapo Luchini <address@hidden> writes:

[...]

>> VCSFeatureObliterate: Obliterate functionality, to remove complete
>> content and history from the repository in the event of import
>> errors, policy decisions to remove content, etc
>
> kill_* commands can do that, but a local file sync is then needed to
> remove unused file content (a command to clean in the background while
> the server is active would be nice: afterall it could be read-only while
> scanning it all, locking the file for a few moments at the end, just to
> DELETE the extra rows)

But then the next time you sync, everything reappears.  And anyway,
you can only kill a leaf revision.

I think there's probably inspiration to be had in the page outlining
git's support for this,
<http://wikitest.freebsd.org/VCSFeatureObliterate>.  In that in a
distributed system you can't really be sure that all mirrors have
killed the data (for one thing you can't mess with the DVDs everyone
burned last week with their databases), but you can make it easier for
people to accept the decisions of someone they regard as upstream.

That is, obliterating a non-leaf revision is (in a handwaving sort of
way), like plucking all the descendents of the revision onto the
parent of the revision, then killing them all and killing the revision
itself.

And doing something or other so that syncing doesn't just revive them,
and so that everyone else syncing gets an opportunity to conveniently
move the revisions too (including transplanting any descendents that
they have that weren't in the original).

It all feels doable, but I suspect it'll involve some effort to be
realistically usable.  Probably valuable (for those relatively rare
occasions where you want it) for people other than FreeBSD.

[...]