Re: Keeping unreachable objects in a separate pack instead of loose?

[Jeff King <peff@peff.net>]

On Mon, Jun 11, 2012 at 10:44:39PM +0200, Hallvard Breien Furuseth wrote:

> >OK, so that 4.5 is at least a respectable percentage of the total
> >repo
> >size. I suspect it may be worse for small repos in that sense, (...)
> 
> 'git gc' gave a 3100% increase with my example:
> 
>     $ git clone --bare --branch linux-overhaul-20010122 \
>         git://git.savannah.gnu.org/config.git
>     $ cd config.git/
>     $ git tag -d `git tag`; git branch -D master
>     $ du -s objects
>     624     objects
>     $ git gc
>     $ du -s objects
>     19840   objects
> 
> Basically: Clone/fetch a repo, keep a small part of it, drop the
> rest, and gc.  Gc explodes all the objects you no longer want.

I would argue that this is not a very interesting case in the first
place, since the right thing to do is use "clone --single-branch"[1] to
void transferring all of those objects in the first place.

But there are plenty of variant cases, where you are not just deleting
all of the refs, but rather doing some manipulation of the branches,
diffing them to make sure it is safe to drop some bits, running
filter-branch, etc. And it would be nice to make those cases more
efficient.

-Peff

[1] It looks like "--single-branch" does not actually work, and still
    fetches master. I think this is a bug in the implementation of
    single-branch (it looks like it fetches HEAD unconditionally).
    +cc Duy.