Re: RFC: Separate commit identification from Merkle hashing

From: Eric S. Raymond <esr@thyrsus.com>
Date: May 21, 2019, 03:31 UTC
Message-ID: <20190521033153.GA2909@thyrsus.com>
In-Reply-To: <20190521025813.GA175422@google.com>

Jonathan Nieder <jrnieder@gmail.com>:

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> > I think it's a weakness, though, that most of it is written as though it
> > assumes only one hash transition will be necessary.  (This is me thinking
> > on long timescales again.)
> 
> Hm, can you point to what part of the doc suggested that?  Best to make
> the text clearer, to avoid confusing the next person.

I will reread it with an editorial eye and try to come up with concrete suggestions, perhaps a patch. My relative ignorance should actually be helpful here.

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> >                                    The same technique (probably the
> > same code!) could be used to map the otherwise uninterpreted
> > commit-IDs I'm proposing to lookup keys.
> 
> No, since Git relies on commit IDs for integrity checking.  The hash
> function transition described in that document relies on
> round-tripping ability for the duration of the transition.

I do not quite understand this comment yet. But I don't think it matters that I don't, and I will by the time I write any code. I expect the worst case is that the separated IDs require a different lookup table from the hashes, but will resolve at the same speed.

-- 
		<a href="http://www.catb.org/~esr/">Eric S. Raymond</a>