From: Jeff King <peff@peff.net>
Date: Fri, 26 Dec 2025 04:45:07 GMT
Subject: Re: Slow git pack-refs --all
Message-ID: <20251226044507.GA1971832@coredump.intra.peff.net>
In-Reply-To: <aU3K9lGbHw68Vv5U@fruit.crustytoothpaste.net>

On Thu, Dec 25, 2025 at 11:38:30PM +0000, brian m. carlson wrote:

> I think this is from `should_pack_ref`:
> 
>     /* Do not pack broken refs: */
>     if (!ref_resolves_to_object(ref->name, refs->base.repo, ref->oid, ref->flags))
>     	return 0;
> 
> So Git is going to need to verify that the object at least exists.  I
> don't know why we would need to _open_ them, however.  Perhaps someone
> else has ideas.

The packed-refs file stores tag-peeling information. So pack-refs opens
the object for any newly written ref via peel_object(), which has to at
least read the header to get the type. That call happens via
write_with_updates() in packed-backend.c.

  If we wanted to be really pedantic, anything in refs/heads/ should not
  point to a non-commit and thus should never need to be peeled. I'm not
  sure if we want to embed that assumption in this code path, though
  (nor would it necessarily help Martin's case if the refs are not in
  refs/heads anyway).

-Peff