From mboxrd@z Thu Jan  1 00:00:00 1970
From: Junio C Hamano <gitster@pobox.com>
Subject: Re: git gc & deleted branches
Date: Fri, 09 May 2008 15:33:41 -0700
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Cc: Brandon Casey <casey@nrlssc.navy.mil>,
	Geert Bosch <bosch@adacore.com>, Jeff King <peff@peff.net>,
	git@vger.kernel.org
To: Nicolas Pitre <nico@cam.org>
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Nicolas Pitre <nico@cam.org> writes:

> On Fri, 9 May 2008, Brandon Casey wrote:
>
>> Unreferenced objects are sometimes used by other repositories which have
>> this repository listed as an alternate. So it may not be a good idea to
>> make the unreferenced objects inaccessible.
>
> Nah.  If this is really the case then you shouldn't be running gc at all 
> in the first place.

True.

I think the true motivation behind --keep-unreachable is not about the
shared object store (aka "alternates") but about races between gc and
push (or fetch).  Before push (or fetch) finishes and updates refs, the
new objects they create would be dangling _and_ the objects these dangling
objects refer to may be packed but unreferenced.  Repacking unreferenced
packed objects was a way to avoid losing them.