Subject: Re: [External Mail]Re: Partial-clone cause big performance impact on server

From: Derrick Stolee <[email-masked]>
Date: Wed, 17 Aug 2022 09:41:10 -0400

On 8/17/2022 6:22 AM, 程洋 wrote:
> But I still think the protocol still should tell the server which ref
> the blob is reachable.
> Because it would be really hard to implement any kind of ACL

I think this idea has merit on its face, but it wouldn't really solve the
problem since the reachability query would still need to be done, just
from a smaller set of references at first. If we were able to say "this
blob can be found at path X at commit Y" then the server could do a
commit-reachability query and a path traversal, which should be a lot
faster.

However, it would be extremely difficult to plumb into the partial clone
machinery. At the point where Git realizes it is missing a promisor
object, that code is very generic and removed from any kind of walk from a
reference. That is further complicated by the fact that the walk is
probably from a local reference, which can be entirely different from the
remote reference.

> But git is surely designed for open sources community. It makes senses
> this request will be rejected.

We try to keep all kinds of users in mind, so the fact that this applies
to not-completely-open repositories is not a blocker.

One possible hurdle is the fact that this branch-level security is a
feature of Gerrit, not a feature of Git itself. Optimizing Git to that
special case that Git does not itself support is less valuable to the Git
project itself.

My personal take is that the technical complexity required to make this
faster paired with the limited scope means that this feature would have a
difficult time getting accepted into the Git project. Perhaps a motivated
contributor will find ways to overcome these obstacles and find other
interesting applications that benefit a larger portion of Git users.

That's just my expectation. I'd be happy to read any patches that try to
solve this problem.

Thanks,
-Stolee