From mboxrd@z Thu Jan  1 00:00:00 1970
From: "Shawn O. Pearce" <spearce@spearce.org>
Subject: Re: Distribution of longest common hash prefixes
Date: Tue, 3 Apr 2007 13:21:23 -0400
Message-ID: <20070403172123.GD27706@spearce.org>
References: <20070402145857.GA13293@bohr.gbar.dtu.dk> <Pine.LNX.4.64.0704020817250.6730@woody.linux-foundation.org> <86bqi6kae7.fsf@blue.stonehenge.com> <Pine.LNX.4.64.0704020938470.6730@woody.linux-foundation.org> <86y7laitlz.fsf@blue.stonehenge.com> <86r6r2isva.fsf@blue.stonehenge.com> <m3r6r1jsmq.fsf@lugabout.jhcloos.org> <867istcrhr.fsf@blue.stonehenge.com>
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Cc: James Cloos <cloos@jhcloos.com>, git@vger.kernel.org,
	Linus Torvalds <torvalds@linux-foundation.org>,
	Peter Eriksen <s022018@student.dtu.dk>
To: "Randal L. Schwartz" <merlyn@stonehenge.com>
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"Randal L. Schwartz" <merlyn@stonehenge.com> wrote:
> >>>>> "James" == James Cloos <cloos@jhcloos.com> writes:
> 
> James> With that version the kernel gives:
> 
> James> 0: 
> James> 1: 
> James> 2: 
> James> 3: 565
> James> 4: 288450
> James> 5: 139080
> James> 6: 10699
> James> 7: 700
> James> 8: 32
> James> 9: 2
> 
> Fascinating.  So you can spell out *any* commit in linux-2.6.git with
> 10 hex chars.  What do we need 40 for, again? :)

Well, the other thing is those 2 commits at 9 bytes probably were
not that way a year ago.  One of those might have only needed 8,
and the other is newer, so now you need 9.

What the above tells me is that 8 is almost a safe default for our
abbreviations, but isn't safe enough, as there are collisions past 8.

-- 
Shawn.