From: Nicolas Pitre <nico@cam.org>
Date: Wed, 14 May 2008 05:33:53 +0000 (-0400)
Subject: let pack-objects do the writing of unreachable objects as loose objects
X-Git-Tag: v1.5.6-rc0~22^2~1
X-Git-Url: https://git.lorimer.id.au/gitweb.git/diff_plain/ca11b212eb3e31d6fee12e9974c67dc774c1bc7c?hp=ca11b212eb3e31d6fee12e9974c67dc774c1bc7c

let pack-objects do the writing of unreachable objects as loose objects

Commit ccc1297226b184c40459e9d373cc9eebfb7bd898 changed the behavior
of 'git repack -A' so unreachable objects are stored as loose objects.
However it did so in a naive and inn efficient way by making packs
about to be deleted inaccessible and feeding their content through
'git unpack-objects'.  While this works, there are major flaws with
this approach:

- It is unacceptably sloooooooooooooow.

In the Linux kernel repository with no actual unreachable objects,
doing 'git repack -A -d' before:

real    2m33.220s
user    2m21.675s
sys     0m3.510s

And with this change:

real    0m36.849s
user    0m24.365s
sys     0m1.950s

For reference, here's the timing for 'git repack -a -d':

real    0m35.816s
user    0m22.571s
sys     0m2.011s

This is explained by the fact that 'git unpack-objects' was used to
unpack _every_ objects even if (almost) 100% of them were thrown away.

- There is a black out period.

Between the removal of the .idx file for the redundant pack and the
completion of its unpacking, the unreachable objects become completely
unaccessible.  This is not a big issue as we're talking about unreachable
objects, but some consistency is always good.

- There is no way to easily set a sensible mtime for the newly created
unreachable loose objects.

So, while having a command called "pack-objects" to perform object
unpacking looks really odd, this is probably the best compromize to be
able to solve the above issues in an efficient way.

Signed-off-by: Nicolas Pitre <nico@cam.org>
Signed-off-by: Junio C Hamano <gitster@pobox.com>
---