Re: [PATCH 4/4] core.abbrev: raise the default abbreviation to 12 hexdigits

From: SZEDER Gábor <szeder@ira.uka.de>
Date: Sep 29, 2016, 02:44 UTC
Message-ID: <20160929024400.22605-1-szeder@ira.uka.de>
In-Reply-To: <20160928233047.14313-5-gitster@pobox.com>

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> As Peff said, responding in a thread started by Linus's suggestion
> to raise the default abbreviation to 12 hexdigits:
> 
>     I actually think "12" might be sane for a long time. That's 48 bits of
>     sha1, so we'd expect a 50% change of a _single_ collision at 2^24, or 16

s/change/chance/

I know it's quoted, but still.

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>     million.  The biggest repository I know about (in number of objects) is
>     the one holding all of the objects for all of the forks of
>     torvalds/linux on GitHub. It's at about 15 million objects.
> 
>     Which _seems_ close, but remember that's the size where we expect to see
>     a single collision. They don't become common until much later (I didn't
>     compute an exact number, but Linus's 16x sounds about right). I know
>     that the growth of the kernel isn't really linear, but I think the need
>     to bump to "13" might not just be decades, but possibly a century or
>     more.
> 
>     So 12 seems reasonable, and the only downside for it (or for "13", for
>     that matter) is a few extra bytes. I dunno, maybe people will really
>     hate that, but I have a feeling these are mostly cut-and-pasted anyway.

I for one raise my hand in protest...

"few extra bytes" is not the only downside, and it's not at all about how many characters are copy-and-pasted. In my opinion it's much more important that this change wastes 5 columns worth of valuable screen real estate e.g. for 'git blame' or 'git log --oneline' in projects that don't need it and certainly won't ever need it.

Sure, users working on smaller repos are free to reset core.abbrev to its original value. I don't have any numbers, of course, but I suspect that there are many more smaller repos out there that this change will affect disadvantageously, than there are large repos for which it's beneficial.

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> And this does exactly that.
> 
> Keep the tests working by explicitly asking for the old 7 hexdigits
> setting in the fake system-wide configuration file used for tests.
> 
> Signed-off-by: Junio C Hamano <gitster@pobox.com>