Re: [Bug] data loss with cyclic alternates

[Jeff King <peff@peff.net>]

On Fri, Jul 11, 2014 at 06:01:46PM +0000, Keller, Jacob E wrote:

> > Yeah, don't do that.  A thinks "eh, the other guy must have it" and
> > B thinks the same.  In general, do not prune or gc a repository
> > other repositories borrow from, even if there is no cycle, because
> > the borrowee does not know anythning about objects that it itself no
> > longer needs but are still needed by its borrowers.
> > 
> 
> Doesn't gc get run automatically at some points? Is the automatic gc run
> setup to avoid this problem?

No, the automatic gc doesn't avoid this. It can't in the general case,
as the parent repository does not know how many or which children are
pointed to it as an alternate. And the borrowing repository does not
even need to have write permission to the parent, so it cannot write a
backpointer.

If people are using alternates, they should probably turn off gc.auto in
the borrowee (it doesn't seem unreasonable to me to do so automatically
via "clone -s" in cases where we can write to the alternates repo, and
to issue a warning otherwise).

-Peff