Re: Borrowing objects from nearby repositories

From: Junio C Hamano <gitster@pobox.com>
Date: Mar 28, 2014, 17:02 UTC
Message-ID: <xmqq8urucl3s.fsf@gitster.dls.corp.google.com>
In-Reply-To: <8030ADEA-B11F-47E8-AFE7-8F46E861F560@kellerfarm.com>

Andrew Keller <andrew@kellerfarm.com> writes:

Show 5 quoted lines

> Okay, so to re-frame my idea, like you said, the goal is to find a user-
> friendly way for the user to tell git-clone to set up the alternates file
> (or perhaps just use the --alternates parameter), and run a repack,
> and disconnect the alternate.  And yet, we still want to be able to use
> --reference on its own, because there are existing use cases for that.

Here are a few possible action items that came out of this discussion:

 1. Introduce a new "--borrow" option to "git clone".

    The updates to the SYNOPSIS section may go like this:

    -'git clone' [--reference <repository>] ...other options...
    +'git clone' [[--reference|--borrow] <repository>] ...other options...

    The new option can be used instead of "--reference" and they
    will be mutually incompatible.  The first implementation of the
    "--borrow" option would do the following:

      (1) run the same "git clone" with the same command line but
          replacing "--borrow" with "--reference"; if this fails, exit
          with the same failure.

      (2) in the resulting repository, run "git repack -a -d"; if this
          fails, remove the entire directory the first step created,
          and exit with failure.

      (3) remove .git/objects/info/alternates from the resulting
          repository and exit with success.

    and it may be acceptable as the final implementation as well.

 2. Make "git repack" safer for the users of "clone --reference" who
    want to keep sharing objects from the original.

    - Introduce the "repack.local" configuration variable that can
      be set to either true or false.  Missing variable defaults to
      "false".

    - A "repack" that is run without "-l" option on the command line
      will pretend as if it was given "-l" from the command line if
      "repack.local" is set to "true".  Add "repack --no-local"
      option to countermand this configuration variable from the
      command line.

    - Teach "git clone --reference" (but not "git clone --borrow")
      to set "repack.local = true" in the configuration of the
      resulting repository.