Re: [RFC] shallow clone

[Johannes Schindelin <Johannes.Schindelin@gmx.de>]

Hi,

On Sun, 29 Jan 2006, Junio C Hamano wrote:

> Strategy
> --------
> 
> We have `info/grafts` mechanism to fake parent information for
> commit objects.  Using this facility, we could roughly do:
> 
> . Download the full tree for v2.6.14 commit and store its
>   objects locally.

On first read, I mistook "tree" for "commit"...

> . Set up `info/grafts` to lie to the local git that Linux kernel
>   history began at v2.6.14 version.

Maybe also record this in .git/config, so that you can

- disallow fetching from this repo, and
- easily extend the shallow copy to a larger shallow one, or a full one.

> . Run `git fetch git://.../linux-2.6 master`, with a local ref
>   pointing at v2.6.14 commit, to pretend that we have everything
>   up to v2.6.14 to `upload-pack` running on the other end.

How about refs/tags/start_shallow?

> . Update the `origin` branch with the master commit object name
>   we just fetched from Linus.
> 
> Design
> ------
>
> [...]
>
> Another functionality we would need is to tell `upload-pack` to
> use `info/grafts` of downloader's choice.  With this, after
> fetching the objects for v2.6.14 commit, the downloader can set
> up its own grafts file to cauterize the development history at
> v2.6.14, and tell the `upload-pack` to pretend the kernel
> history starts at that commit, while sending the tip of Linus'
> development track to us.

Why not just start another fetch? Then, "have <refs/tags/start_shallow>" 
would be sent, and upload-pack does the right thing?

If you absolutely want to get only one pack, which then is stored as-is, 
upload-pack could start two rev-list processes: one for the tree and one 
for all the rest.

> [...]
> 
> [NOTE]
> Most likely this is not directly run by the user but is run as
> the first command invoked by the shallow clone script.

Better make it an option to git-clone

> 4. `upload-pack` notices this is a single commit request, and
>    sends an ACK if it can satisfy the request (or a NAK if it
>    can't, e.g. it does not have the asked commit).  Instead of
>    doing the usual `get_common_commits` followed by
>    `create_pack_file`, it does:
> 
> 	$ git rev-list -n1 --objects $commit | git pack-object

Here it could say

(git rev-list -n1 --objects $commit_since; git rev-list --objects 
	^$commit_since $commit) | git pack-object

If the former is still needed (e.g. for git-tar-remote-tree), we could 
distinguish "single <ref>" and "shallow <ref>" commands.

> [...]
> 
> The second phase of the shallow clone is to fetch the history
> since v2.6.14 to the tip.

As I outlined above, I don't see the need for this.

Ciao,
Dscho