Re: [BUG] Lazy fetch in partial clone fails with "not our ref" since 5946a564 (odb/source: make read_object_info() pluggable)

[Patrick Steinhardt <ps@pks.im>]

On Wed, Nov 04, 2026 at 12:56:53PM +0100, Patrick Ohly wrote:
> Kristofer Karlsson <krka@spotify.com> writes:
> 
> > On Tue, 3 Nov 2026 at 14:31, Patrick Ohly <patrick.ohly@intel.com> wrote:
> >>
> >> Hello,
> >>
> >> "git merge" in a blobless partial clone fails with "not our ref" while
> >> lazily fetching a missing object. This started to occur today in the
> >> Kubernetes CI, completely breaking the merging of PRs. We should have
> >> been using git 2.54.0, the affected version, for a few days at least
> >> without issues, so it can't be ruled out that this is at least partly
> >> caused by a change on the GitHub side. We are about to revert to git
> >> 2.52.0 to unblock the Kubernetes project.
> >>
> >> [...]
> >>
> >> I bisected v2.52.0 (good) to v2.54.0 (bad). The first bad commit is:
> >>
> >> 5946a564cddc0bf471f27ae4c3fe205441e3ef65
> >> odb/source: make `read_object_info()` function pluggable
> >>
> >> The parent, 3bc3177ad7 ( 2.53.0.185.g3bc3177ad7 ), is good.
> >
> > Thanks for the detailed report.  I think I have found the cause: I
> > can reproduce the failure with your steps and make it go away with a
> > small change to the loose object cache.
> 
> Any idea why this suddenly started to occur?
> 
> We were using 2.54.0 for several days without issues prior to the
> failure. For example,
> https://storage.googleapis.com/kubernetes-ci-logs/pr-logs/pull/batch/pull-kubernetes-cmd/2117551425255903232/clone-log.txt
> merged several different PRs for
> https://prow.k8s.io/view/gs/kubernetes-ci-logs/pr-logs/pull/batch/pull-kubernetes-cmd/2117551425255903232
> using
> us-docker.pkg.dev/k8s-infra-prow/images/clonerefs:v20261028-c06373a3e
> as environment. It contains 2.54.0.

The issue here depends on the actual objects IDs that you're merging.
You need to merge at least one object with the same first two hex
characters into a newly written object that same first two characters.
If so, you can trigger a stale loose object cache that makes Git think
that the object does not exist locally, and it then tries to fetch it
from the promisor remote.

I've sent a fix for this bug via [1]. Thanks!

Patrick

[1]: <20261104-pks-odb-loose-stale-cache-v1-0-a00d5cdb5e7d@pks.im>