Re: Multiple fetches when unshallowing a shallow clone

From: Jason Paller-Rzepka <jasonpr@google.com>
Date: Dec 4, 2015, 21:38 UTC
Message-ID: <CACs8u9Qvqn4KDMKo+RHsQaf+dw+CGtWrOpoUJzaZAqD1rFRiuw@mail.gmail.com>
In-Reply-To: <20151204212712.GA22493@sigill.intra.peff.net>

It appears that it happens when the shallow history grows to include a commit that's pointed to by a previously unseen tag. For example, when I deepen a checkout of git to depth 8, I hit v2.5.2, and a second fetch takes place.

```
$ git clone --depth=1 http://github.com/git/git
Cloning into 'git'...
remote: Counting objects: 2925, done.
remote: Compressing objects: 100% (2602/2602), done.
remote: Total 2925 (delta 230), reused 2329 (delta 206), pack-reused 0
Receiving objects: 100% (2925/2925), 6.17 MiB | 0 bytes/s, done.
Resolving deltas: 100% (230/230), done.
Checking connectivity... done.
$ git -C git fetch --depth=8
remote: Counting objects: 858, done.
remote: Compressing objects: 100% (774/774), done.
remote: Total 858 (delta 793), reused 138 (delta 80), pack-reused 0
Receiving objects: 100% (858/858), 364.53 KiB | 0 bytes/s, done.
Resolving deltas: 100% (793/793), completed with 476 local objects.
remote: Counting objects: 1, done.
remote: Total 1 (delta 0), reused 1 (delta 0), pack-reused 0
Unpacking objects: 100% (1/1), done.
From http://github.com/git/git
 * [new tag]         v2.5.2     -> v2.5.2
$
```

But why would fetching a tag (or set of tags) merit a depth of zero? Doesn't depth 1 mean "give me the the objects, and none of their descendants"? Why use 0?

Thanks! Jason

On Fri, Dec 4, 2015 at 4:27 PM, Jeff King <peff@peff.net> wrote:

Show 48 quoted lines

> On Fri, Dec 04, 2015 at 12:46:59PM -0800, Stefan Beller wrote:
>
>> On Mon, Nov 30, 2015 at 11:35 AM, Jason Paller-Rzepka
>> <jasonpr@google.com> wrote:
>> > Hi all,
>> >
>> > Would anyone be willing to help me understand some shallow-clone
>> > behavior?  (I found a bug in Dulwich, and I'm looking for some context
>> > so I can determine how to fix it.)
>> >
>> > I learned that cgit sometimes performs two fetches for a `git fetch
>> > --unshallow`: one with depth 'infinity', and a subsequent one with
>> > depth zero.
>>
>> Is there a condition to trigger this 'sometimes' ?
>>
>> I just tried reproducing via
>> $ GIT_TRACE=1 git fetch --unshallow
>>
>> and could not see a second fetch, but only a
>> fetch-pack with --depth=2147483647
>
> This seems to reproduce consistently for me:
>
>   $ git clone --depth=1 git://github.com/git/git
>   Cloning into 'git'...
>   remote: Counting objects: 2925, done.
>   remote: Compressing objects: 100% (2602/2602), done.
>   remote: Total 2925 (delta 230), reused 2329 (delta 206), pack-reused 0
>   Receiving objects: 100% (2925/2925), 6.17 MiB | 10.80 MiB/s, done.
>   Resolving deltas: 100% (230/230), done.
>
>   $ cd git
>   $ git fetch --unshallow
>   remote: Counting objects: 185430, done.
>   remote: Compressing objects: 100% (46933/46933), done.
>   remote: Total 185430 (delta 140505), reused 181589 (delta 136694), pack-reused 0
>   Receiving objects: 100% (185430/185430), 52.80 MiB | 10.84 MiB/s, done.
>   Resolving deltas: 100% (140505/140505), completed with 1784 local objects.
>   remote: Counting objects: 579, done.
>   remote: Compressing objects: 100% (579/579), done.
>   remote: Total 579 (delta 0), reused 579 (delta 0), pack-reused 0
>   Receiving objects: 100% (579/579), 266.85 KiB | 0 bytes/s, done.
>   [... fetch output ...]
>
> That looks like two packs being received for the --unshallow case.
>
> -Peff