Re: Git wire protocol v2 fails fetching shallow changes with `pack has XXX unresolved deltas` on large repos with lots of tags Inbox x

From: Jonathan Tan <jonathantanmy@google.com>
Date: Oct 13, 2018, 00:43 UTC
Message-ID: <20181013004356.257709-1-jonathantanmy@google.com>
In-Reply-To: <CAGY-PBgsG-T3JY=awszwGMpFx+jDx-a1FcV0s6vR067bSqgZaA@mail.gmail.com>

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> On large repositories with lots of tags - git wire protocol v2 fails
> to fetch shallow changes, it fails with error `pack has XXX unresolved
> deltas`. Unfortunately I didn't find easy way to reproduce it except
> cloning+fetching chromium repository, the way jenkins does.
> Reproduction steps:

[snip]

Thanks for your bug report and reproduction steps. I managed to reproduce your issue and took a look.

The main issue seems to be that with v2, upload-pack doesn't pass "--shallow X" to pack-objects (the write_one_shallow() callback is never called, even if I change the "if (shallow_nr)" to "if (1)"), so pack-objects probably doesn't know that some objects cannot be used as delta bases. (With v0, write_one_shallow() is indeed called.) The issue probably lies in how v0 and v2 handle client-provided shallows differently.

There also seems to be another issue in that negotiation occurs differently in these 2 protocols - I see the full list of "have" lines being sent in the final request to the server in v0, but a very limited list in v2. This might be because of the ref prefix limiting in v2, but I haven't fully investigated it.

I'll look some more into this.