Re: Regarding "git log" on "git series" metadata

[Josh Triplett <josh@joshtriplett.org>]

On Sat, Nov 05, 2016 at 09:50:07PM -0700, Jacob Keller wrote:
> On Sat, Nov 5, 2016 at 1:25 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> > On Sat, Nov 05, 2016 at 09:21:58PM +0100, Christian Couder wrote:
> >> On Sat, Nov 5, 2016 at 4:18 PM, Josh Triplett <josh@joshtriplett.org> wrote:
> >> > On Sat, Nov 05, 2016 at 01:45:27PM +0100, Christian Couder wrote:
> >> >> And with what Peff says above it looks like we will need ways
> >> >> configure and tweak commit reachability with gitlink/gitref anyway. So
> >> >> the point of gitref compared to gitlink would be that they just have a
> >> >> different reachability by default. But couldn't that be replaced by a
> >> >> default rule saying that when a gitlink is reached "this way or that
> >> >> way" then the commit reachability should be enforced, and otherwise it
> >> >> should not be?
> >> >
> >> > Any version of git unaware of that rule, though, would consider objects
> >> > only reachable by gitlink as unreachable and delete them, causing data
> >> > loss.  Likewise for a server not aware of that rule.  And a server
> >> > unaware of that rule would not supply those objects to a client pulling
> >> > such a branch.
> >>
> >> Yeah, so you would really need an up-to-date server and client to
> >> store the git-series data.
> >> But anyway if we create a gitref object, you would also need
> >> up-to-date servers and clients to make it work.
> >
> > Agreed, but gitrefs have the advantage of failing safe, rather than
> > failing with dataloss.
> >
> > - Josh Triplett
> 
> Isn't the "failing safe" only true if the client disconnects when a
> server doesn't advertise "i understand gitrefs"? So couldn't we, as
> part of the rules for reachability advertise a capability that does a
> similar thing and fails safe as well?

We could, but if we (or one of the many third-party git implementations)
miss a case, gitlinks+reachability may appear to work in many cases with
dataloss afterward, while gitrefs will fail early and not appear
functional.