Re: Why repository grows after "git gc"? / Purpose of *.keep files?

[Junio C Hamano <gitster@pobox.com>]

"Shawn O. Pearce" <spearce@spearce.org> writes:

> David Tweed <david.tweed@gmail.com> wrote:
>> On Mon, May 12, 2008 at 4:52 PM, Teemu Likonen <tlikonen@iki.fi> wrote:
>> > Teemu Likonen wrote (2008-05-12 15:29 +0300):
>> > Probably a crazy idea: What if "gc --aggressive" first removed *.keep
>> > files and after packing and garbage-collecting and whatever it does it
>> > would add a .keep file for the newly created pack?
>> 
>> My understanding is that the repacking with -a redoes the computation
>> to repack ALL the objects in every pack and loose objects,
>
> No.  -a means repack all objects in all packs which do not have a
> .keep on them.  Without -a we only repack loose objects.
>
>> whereas
>> what would be preferred is to try to delta new objects (loose and
>> packed) against the existing .keep pack (extending it with the new
>> objects) but not trying to re-deltify objects in the .keep pack.
>
> We cannot do that.  Deltas in pack A may not reference base objects
> in pack B.  This is a simplification rule that prevents us from
> needing to worry about damaging a pack when we repack and delete
> another pack.
>
>> This
>> is because .keep files are primarily for those who are cloning onto a
>> machine that isn't powerful (maybe even a laptop/palmtop) but who are
>> cloning from a powerful server, so that you wouldn't necessarily want
>> to apply your strategy unconditionally.
>
> Yes, sort of.  We use .keep for two reasons:
>
>   - As a "lock file" to prevent a pack that was just created by a
>     git-fetch or git-recieve-pack from being deleted by a concurrent
>     git-repack before the objects it contains are linked into the
>     refs space and thus considered reachable;
>
>   - As a way to avoid _huge_ packs (say >1G) that would take a lot
>     of disk IO just to copy with 100% delta reuse from an old pack
>     to a new pack each time the user runs git-gc.
>
> I think git-clone marking a 150M linux-2.6 pack with .keep is wrong;
> most users working with the linux-2.6 sources have sufficient
> hardware to deal with the disk IO required to copy that with 100%
> delta reuse.  But I have a repository at day-job with a 600M pack,
> that's starting to head into the realm where git-gc while running
> on battery on a laptop would prefer to have that .keep.

Perhaps clone can decide to keep the .keep file depending on the size of
the pack then?