Re: RFC: reverse history tree, for faster & background clones

On vr, 2015-06-12 at 13:39 +0200, Andres G. Aragoneses wrote:

On 12/06/15 13:33, Dennis Kaarsemaker wrote:

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On vr, 2015-06-12 at 13:26 +0200, Andres G. Aragoneses wrote:

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AFAIU git stores the contents of a repo as a sequence of patches in the
.git metadata folder.

It does not, it stores full snapshots of files.

In bare repos too?

Yes. A bare repo is nothing more than the .git dir of a non-bare repo
with the core.bare variable set to True :)

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1. `git clone --depth 1` would be way faster, and without the need of
on-demand compressing of packfiles in the server side, correct me if I'm
wrong?

You're wrong due to the misunderstanding of how git works :)

Thanks for pointing this out, do you mind giving me a link of some docs 
where I can correct my knowledge about this?

http://git-scm.com/book/en/v2/Git-Internals-Git-Objects should help.

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2. `git clone` would be able to allow a "fast operation, complete in the
background" mode that would allow you to download the first snapshot of
the repo very quickly, so that the user would be able to start working
on his working directory very quickly, while a "background job" keeps
retreiving the history data in the background.

This could actually be a good thing, and can be emulated now with git
clone --depth=1 and subsequent fetches in the background to deepen the
history. I can see some value in clone doing this by itself, first doing
a depth=1 fetch, then launching itself into the background, giving you a
worktree to play with earlier.

You're right, didn't think about the feature that converts a --depth=1 
repo to a normal one. Then a patch that would create a --progressive 
flag (for instance, didn't think of a better name yet) for the `clone` 
command would actually be trivial to create, I assume, because it would 
just use `depth=1` and then retrieve the rest of the history in the 
background, right?

A naive implementation that does just clone --depth=1 and then fetch
--unshallow would probably not be too hard, no. But whether that would
be the 'right' way of implementing it, I wouldn't know.

-- 
Dennis Kaarsemaker
http://www.kaarsemaker.net