Re: git fetch origin $SHA1 doesn't work as often as it could

[Jeff King <peff@peff.net>]

On Wed, May 18, 2016 at 06:40:37PM -0400, JP Sugarbroad wrote:

> > I just fear that it is a wrong approach to solve the real issue and
> > instead make it worse by relieving the pressure from the project and
> > hosting site to configure their repository to support their users
> > properly.
> 
> Unfortunately I don't see the likes of github or bitbucket adding
> allow-reachable-sha1-in-want any time soon, as it is an expensive
> operation server-side.

I don't think it's _too_ bad, at least compared to some of the nastier
things one can convince the server side of a git fetch to do. It at
least looks at just the commits; the bad cases usually involve
traversing the whole object graph.

It's also something that's easily sped up with reachability bitmaps.

But I haven't done any real analysis on the kind of load it would cause.
So no promises, but I don't think it's outside the realm of possibility
for GitHub to enable, if it's something that would be useful to a lot of
people. I can't speak for Bitbucket. :)

-Peff