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

David Tweed [off-list ref] wrote:

On Mon, May 12, 2008 at 4:52 PM, Teemu Likonen [off-list ref] wrote:

quoted

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.

-- 
Shawn.