From mboxrd@z Thu Jan  1 00:00:00 1970
From: Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: "git reflog expire --all" very slow
Date: Mon, 30 Mar 2009 22:50:17 -0700 (PDT)
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On Mon, 30 Mar 2009, Linus Torvalds wrote:
> 
> If I do
> 
> 	mark_reachable(cb.ref_commit, 0);

Ok, I think I got it.

You had

	mark_reachable(cb.ref_commit, cmd->expire_unreachable);

but we care about the commits that are younger than 'expire_total' (older 
than that, and they are pruned unconditionally), but older than 
'expire_unreachable' (younger than that and the date doesn't matter).

So making it do

	mark_reachable(cb.ref_commit, cmd->expire_total);

marks the right parts reachable. Not the whole tree, but also not just the 
commits we're not going to expire regardless.

With that change, it's all basically instantaneous. We don't need to 
traverse the whole kernel history, and with that change to your patch, I 
get

	[torvalds@nehalem linux]$ time ~/git/git reflog expire --all

	real	0m1.715s
	user	0m1.676s
	sys	0m0.040s

which is still slower than I'd wish for, but is a whole lot faster than 
over half a minute.

		Linus