Linus Torvalds <torvalds@xxxxxxxx> wrote:
>
>
> On Thu, 20 Apr 2006, Shawn Pearce wrote:
> >
> > So with 1.3.0.g56c1 "git repack -a -d -f" did worse:
> >
> > Total 46391, written 46391 (delta 6649), reused 39742 (delta 0)
> > 129M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
> >
> > I just tried -f on v1.2.3 and it did slightly better then before:
> >
> > Total 46391, written 46391 (delta 6847), reused 38012 (delta 0)
> > 59M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
Oddly enough repacking the v1.2.3 pack using 1.3.0.g56c1 created an
even smaller pack ("git-repack -a -d"):
Total 46391, written 46391 (delta 8253), reused 44985 (delta 6847)
49M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
and repacking again with "git-repack -a -d" chopped another 1M:
Total 46391, written 46391 (delta 8258), reused 46386 (delta 8253)
48M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pac
but then adding -f definately gives us the 2x explosion again:
Total 46391, written 46391 (delta 6649), reused 37894 (delta 0)
129M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
> Interesting. The bigger packs do generate fewer deltas, but they don't
> seem to be _that_ much fewer. And the deltas themselves certainly
> shouldn't be bigger.
>
> It almost sounds like there's a problem with choosing what to delta
> against, not necessarily a delta algorithm problem. Although that sounds a
> bit strange, because I wouldn't have thought we actually changed the
> packing algorithm noticeably since 1.2.3.
>
> Hmm. Doing "gitk v1.2.3.. -- pack-objects.c" shows that I was wrong. Junio
> did the "hash basename and direname a bit differently" thing, which would
> appear to change the "find objects to delta against" a lot. That could be
> it.
>
> You could try to revert that change:
>
> git revert eeef7135fed9b8784627c4c96e125241c06c65e1
>
> which needs a trivial manual fixup (remove the conflict entirely:
> everything between the "<<<<" and ">>>>>" lines should go), and see if
> that's it.
Whoa. I did that revert and fixup on top of 'next'. The pack
from "git-repack -a -d -f" is now even larger due to even less
delta reuse:
Total 46391, written 46391 (delta 5148), reused 39565 (delta 0)
171M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
> You can also try to see if
>
> git repack -a -d -f --window=50
>
> makes for a better pack (at the cost of a much slower repack). It makes
> git try more objects to delta against, and can thus hide a bad sort order.
With --window=50 on 'next' (without the revert'):
Total 46391, written 46391 (delta 6666), reused 39723 (delta 0)
129M pack-7f766f5af5547554bacb28c0294bd562589dc5e7.pack
For added measure I tried --window=100 and 500 with pretty much
the same result (slightly higher delta but still a 129M pack).
--
Shawn.
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