Re: [PATCH 2/2] fetch-pack: do not check links for partial fetch

From: Jonathan Tan <jonathantanmy@google.com>
Date: Mar 14, 2018, 22:24 UTC
Message-ID: <20180314152429.df14adfb49b028e2e2a9001a@google.com>
In-Reply-To: <xmqqwoyexqy4.fsf@gitster-ct.c.googlers.com>

On Wed, 14 Mar 2018 14:55:31 -0700 Junio C Hamano <gitster@pobox.com> wrote:

Show 13 quoted lines

> Jonathan Tan <jonathantanmy@google.com> writes:
> 
> > When doing a partial clone or fetch with transfer.fsckobjects=1, use the
> > --fsck-objects instead of the --strict flag when invoking index-pack so
> > that links are not checked, only objects. This is because incomplete
> > links are expected when doing a partial clone or fetch.
> 
> It is expected that _some_ links are missing, but this makes me
> wonder if we can do better than disabling the connectivity check
> altogether.  Does "git fetch" lack sufficient information to attempt
> the connectivity check, and when (and only when) it hits a broken
> link, see if that is because the connectivity check traversal is
> crossing a "partial" fetch boundary, or something along that line?

Our only definition (currently) for the "partial" fetch boundary is whether an object in a promisor packfile (a packfile obtained from the promisor remote) references it, so I think that checking for crossing a "partial" fetch boundary does not add anything. This is because by that definition, any missing links observed from objects newly fetched from the promisor remote cross a "partial" fetch boundary (since all objects fetched in this way "promise" all objects that they refer to).

But it is true that we might be able to do better in checking, for example, that a packfile fetched using a blob size limit contains all referenced trees (that is, only blobs are allowed to be missing).