From: Shawn O. Pearce <spearce@spearce.org>
Date: Tue, 03 Apr 2007 17:21:23 GMT
Subject: Re: Distribution of longest common hash prefixes
Message-ID: <20070403172123.GD27706@spearce.org>
In-Reply-To: <867istcrhr.fsf@blue.stonehenge.com>

"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.