Subject: Re: [PATCH 0/2] receive-pack: use advertised reference tips to inform connectivity check

From: Taylor Blau <[email-masked]>
Date: Mon, 31 Oct 2022 21:30:26 -0400

On Fri, Oct 28, 2022 at 04:42:19PM +0200, Patrick Steinhardt wrote:
> this patch series improves the connectivity check done by stateful
> git-receive-pack(1) to only consider references as reachable that have
> been advertised to the client. This has two advantages:

A third advantage which I didn't see mentioned here is that we have a
better chance of being helped by reachability bitmaps here. Because we
aren't likely to cover hidden references with bitmaps, we would be
paying a significant cost to build up a complete picture of what's
reachable from --all.

That will inevitably involve a lot of traversing from unbitmapped
reference tips (i.e. the hidden ones) down to either a random bitmap
sprinkled throughout history, or the root of that line of history.

But if we limited the negated side of our connectivity check to just the
non-hidden references, then we will likely end up with more full bitmap
coverage of those tips, without having to do any additional traversal.

So that is definitely something worth experimenting with.

Thanks,
Taylor