Re: RFC: Design and code of partial clones (now, missing commits and trees OK)

Jonathan Tan [off-list ref] writes:

For those interested in partial clones and/or missing objects in repos,
I've updated my original partialclone patches to not require an explicit
list of promises. Fetch/clone still only permits exclusion of blobs, but
the infrastructure is there for a local repo to support missing trees
and commits as well.
...
Demo
====

Obtain a repository.

    $ make prefix=$HOME/local install
    $ cd $HOME/tmp
    $ git clone https://github.com/git/git

Make it advertise the new feature and allow requests for arbitrary blobs.

    $ git -C git config uploadpack.advertiseblobmaxbytes 1
    $ git -C git config uploadpack.allowanysha1inwant 1

Perform the partial clone and check that it is indeed smaller. Specify
"file://" in order to test the partial clone mechanism. (If not, Git will
perform a local clone, which unselectively copies every object.)

    $ git clone --blob-max-bytes=100000 "file://$(pwd)/git" git2
    $ git clone "file://$(pwd)/git" git3
    $ du -sh git2 git3
    116M	git2
    129M	git3

Observe that the new repo is automatically configured to fetch missing objects
from the original repo. Subsequent fetches will also be partial.

    $ cat git2/.git/config
    [core]
    	repositoryformatversion = 1
    	filemode = true
    	bare = false
    	logallrefupdates = true
    [remote "origin"]
    	url = [snip]
    	fetch = +refs/heads/*:refs/remotes/origin/*
    	blobmaxbytes = 100000
    [extensions]
    	partialclone = origin
    [branch "master"]
    	remote = origin
    	merge = refs/heads/master

The above sequence of events make quite a lot of sense.  And the
following description of how it is designed (snipped) is clear
enough (at least to me) to allow me to say that I quite like it.