Re: git-clone --single-branch clones objects outside of branch

From: Jeff King <peff@peff.net>
Date: Jan 27, 2020, 05:55 UTC
Message-ID: <20200127055509.GA12108@coredump.intra.peff.net>
In-Reply-To: <CAOTb1wfoMf338VPRYcjAv+EaMYQxKJ=kP6-qMykG-LfxPrWuag@mail.gmail.com>

On Sun, Jan 26, 2020 at 04:39:52AM -0800, Chris Jerdonek wrote:

Show 9 quoted lines

> However, when I attempted this with a local repo, I found that objects
> located only in branches other than the branch I specified are also
> cloned. Also, this is true even if the remote repo has only loose
> objects (i.e. no pack files). So it doesn't appear to be doing this
> only to avoid creating new files.
> 
> In contrast, git-fetch behaves as expected (including locally).
> git-fetch appears to fetch only objects in the given branch, when a
> branch is specified.

This is the expected outcome, because in your example you're cloning on the local filesystem. By default that enables some optimizations, one of which is to hard-link the object files into the destination repository. That avoids the cost of copying and re-hashing them (which a normal cross-system clone would do). And it even avoids traversing the objects to find which are necessary, instead just hard-linking everything.

So with:

> git clone --branch master --single-branch repo1 repo3

You should be able to see with "git for-each-ref" in repo3 that you only got the "master" branch, but not "dev". But those extra objects are available to you, because of the hard-links.

If you do:

  git clone --branch master --single-branch --no-local repo1 repo4

then repo4 will not have the objects (we really will send a packfile across a pipe, just as we would across the network for a cross-system clone).

> cd repo2
> git init
> git remote add other file:///<path-to-repo1>
> git fetch other master

This one behaves as you expected because git-fetch does not perform the same optimizations (it wouldn't make as much sense there, as generally in a fetch we already have most of the objects from the other side anyway, so hard-linking would just give us duplicates).

-Peff