Re: [PATCH 2/2] index-pack: prefetch missing REF_DELTA bases

> When fetching, the client sends "have" commit IDs indicating that the
> server does not need to send any object referenced by those commits,
> reducing network I/O. When the client is a partial clone, the client
> still sends "have"s in this way, even if it does not have every object
> referenced by a commit it sent as "have".
>
> If a server omits such an object, it is fine: the client could lazily
> fetch that object before this fetch, and it can still do so after.
>
> The issue is when the server sends a thin pack containing an object that
> is a REF_DELTA against such a missing object: index-pack fails to fix
> the thin pack. When support for lazily fetching missing objects was
> added in 8b4c0103a9 ("sha1_file: support lazily fetching missing
> objects", 2017-12-08), support in index-pack was turned off in the
> belief that it accesses the repo only to do hash collision checks.
> However, this is not true: it also needs to access the repo to resolve
> REF_DELTA bases.

> Signed-off-by: Jonathan Tan <jonathantanmy@google.com>
> ---
>  builtin/index-pack.c     | 26 +++++++++++++++--
>  t/t5616-partial-clone.sh | 61 ++++++++++++++++++++++++++++++++++++++++
>  2 files changed, 85 insertions(+), 2 deletions(-)