Re: warning: no common commits - slow pull

[Junio C Hamano <gitster@pobox.com>]

Len Brown <lenb@kernel.org> writes:

> A couple of hours ago I pulled my reference copy of Linux tree,
> which brought the tip here:
>
> commit 7cf712db6087342e5e7e259d3883a7b5ac3212d1
> Merge: 58a14ee... 30ddb15...
> Author: Linus Torvalds <torvalds@woody.linux-foundation.org>
> Date:   Sun Feb 10 12:03:57 2008 -0800
>
>     Merge git://git.kernel.org/pub/scm/linux/kernel/git/davem/net-2.6
>
> Then, 10 minutes ago I did a pull to bring the head here:
>
> commit 19af35546de68c872dcb687613e0902a602cb20e
> Author: Linus Torvalds <torvalds@woody.linux-foundation.org>
> Date:   Sun Feb 10 14:18:14 2008 -0800
>
>     Linux 2.6.25-rc1
>
> But this second pull seems to have re-downloaded 172MB,
> when it should have only needed the last few commits.
>
> thanks,

Thanks.  This is very puzzling.

> [lenb@d975xbx2 linus (master)]$ git pull
> remote: Counting objects: 447, done.
> remote: Compressing objects: 100% (39/39), done.
> remote: Total 328 (delta 291), reused 325 (delta 289)

This part looks quite sane.

	$ git rev-list --objects ^7cf712d v2.6.25-rc1^0 | wc -l
	328

> Receiving objects: 100% (328/328), 60.81 KiB, done.
> Resolving deltas: 100% (291/291), completed with 97 local objects.

and the number of received objects exactly match.

> warning: no common commits

This is however very unexpected.  The sequence internally should
be doing the equivalent of:

  - fetch the objects to complete the branches we track
    (i.e. what the above "rev-list" that fetches to complete the
    commit pointed by the v2.6.25-rc1 tag based on your earlier
    tip 7cf712d);

  - store the tip (19af355 = v2.6.25-rc1^0) to the tracking
    branch;

  - run another "git fetch" to retrieve objects to complete the
    v2.6.25-rc1 tag itself, based on our available refs (which
    includes the commit 19af355).

which should result in transferring only one object, which would
say something like:

    From git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
       7cf712d..19af355  master     -> linus
    remote: Counting objects: 1, done.
    remote: Total 1 (delta 0), reused 0 (delta 0)
    Unpacking objects: 100% (1/1), done.
    From git://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux-2.6
     * [new tag]         v2.6.25-rc1 -> v2.6.25-rc1
    Updating 7cf712d..19af355

We would need a bit more digging to reproduce it, as I do not
seem to be able to.