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  • 2 commits
  • 4 files changed
  • 1 contributor

Commits on Oct 14, 2026

  1. connected: negate alternate refs in deepening fetches too 

    The connectivity check spawned by check_connected() uses

  git rev-list --objects --stdin --not --all --quiet --alternate-refs

where 39b44ba (check_everything_connected: assume alternate ref
tips are valid, 2019-07-01) added "--alternate-refs" so that the walk
from the fetched tips stops at the refs of any alternate object store,
on the assumption that the alternate is already fully connected.

That only works because "--alternate-refs" comes after "--not".
cf1e7c0 (fetch-pack: write shallow, then check connectivity,
2018-07-02) drops "--not --all" for deepening fetches, since those
need to verify the whole chain up to the new shallow boundary rather
than stopping at refs we already had. For such fetches we therefore
run

  git --shallow-file ... rev-list --objects --stdin --quiet --alternate-refs

with the alternate's refs as positive revisions, and rev-list
enumerates every object reachable from them. Unless one of those refs
happens to lie inside the newly fetched shallow range, where the
grafts cut the walk short, that is the alternate's entire history.

This is slow for setups that attach a large alternate to a fresh
repository and then do a shallow fetch of a ref that is a few commits
ahead of the alternate, which is how CI runners share a clone of a
big repository between jobs. With a 7M-object alternate (a bare clone
of gitlab-org/gitlab), "git fetch --depth 1" transfers an empty pack
in under a second and the connectivity check then takes 227s. With
the alternate's refs negated the same rev-list finishes in 0.0s.

Pass "--not" in both cases, before the branch that adds "--all" for
non-deepening fetches, so that "--alternate-refs" is negated for
deepening fetches as well. Such a fetch still has to reach the new
shallow boundary from the fetched tips without stopping at our own
refs, which is what cf1e7c0 wanted. It stops at the alternate's
refs, as every other fetch already does. Move "--alternate-refs" up
next to "--all" so that the arguments that bound the walk are in one
place.

Add tests to t5618 that check the arguments of the rev-list child via
GIT_TRACE2_EVENT for a regular and for a deepening fetch. The result
of the check is the same either way for a complete alternate, so
there is no behavioural difference to assert on. The difference is
only in which objects are walked.

Helped-by: Patrick Steinhardt <ps@pks.im>
Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Igor Wiedler <iwiedler@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
    @igorwwwwwwwwwwwwwwwwwwww @gitster
    igorwwwwwwwwwwwwwwwwwwww authored and gitster committed Oct 14, 2026
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  2. odb: ignore refs of shallow and grafted alternates 

    odb_for_each_alternate_ref() reports the refs of every alternate
object store that is a repository. Its three callers use them as
commits whose history can be assumed to be present: "rev-list
--alternate-refs" (and through it the connectivity check after a
fetch), fetch-pack, which sends them as "have"s so that the server
does not resend what the alternate has, and receive-pack, which
advertises them as ".have".

That assumption does not hold for a shallow repository, whose refs
point at commits with no history behind them below its shallow
boundary, nor for a grafted one. A repository borrowing objects from
such an alternate does not see the alternate's shallow file, so the
history that is missing there is missing here as well. The fetch then
succeeds, the connectivity check stops at the alternate's refs, and
a later "git log" fails with "Could not read <oid>".

"git clone --reference" already rejects a shallow or grafted
reference repository for this reason, but nothing prevents such a
repository from being added via objects/info/alternates or
GIT_ALTERNATE_OBJECT_DIRECTORIES, or from being made shallow after
other repositories started borrowing from it.

Skip the refs of an alternate that has a "shallow" file or an
"info/grafts" file, the same checks clone uses. Its objects are still
available through the object store. Only its refs are no longer used
as a boundary.

Partial clones have the same problem for the objects they lack, but
detecting one requires reading the alternate's config, so this
patch does not handle them.

Helped-by: Junio C Hamano <gitster@pobox.com>
Signed-off-by: Igor Wiedler <iwiedler@gitlab.com>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
    @igorwwwwwwwwwwwwwwwwwwww @gitster
    igorwwwwwwwwwwwwwwwwwwww authored and gitster committed Oct 14, 2026
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    24e67bf View commit details
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