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Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin

From: Andrew Suffield
Subject: Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin
Date: Mon, 6 Dec 2004 01:57:22 +0000
User-agent: Mutt/1.5.6+20040907i

On Sun, Dec 05, 2004 at 07:27:37PM -0600, John A Meinel wrote:
> Andrew Suffield wrote:
> >On Sun, Dec 05, 2004 at 02:59:32PM -0600, John A Meinel wrote:
> >
> >>Arch does not support binary diff in the subversion sense.
> >
> >
> >Nonsense, it works just fine.
> >
> No. In subversion, if you have a binary file, and you make changes, it 
> only stores the changes to the file. (something like xdelta). So if you 
> have a binary file that is 100k long, and you append 10k to it, the 
> changeset that is stored in the archive is only ~10k in size. (I think 
> the same is true if you modify only 10k of the file.)
> However, with arch, if a file is declared binary and it is considered to 
> be changed, then a completely new copy of the file is added to the 
> repository. Actually, I just checked, and 2 new copies are added to the 
> repository, the old version, and the new one.

Yes, arch supports binary diffs in exactly the same sense as subversion.

It doesn't do delta compression on them. That's irrelevant.

xdelta is not a diff. It's delta compression. That's even in the *name*.

> This is most definitely NOT what the original poster was meaning by 
> "binary diff".

You mean they were out of their tree and using the wrong names for
things? You'll never get anywhere like that. "$foo diff" is an
operation which generates the input to "$foo patch", such that:

patch(A, diff(A, B)) == B, where A and B are of type $foo

That's the definition.

> >Compression is not related in any way.
> >
> compression is not binary diff. True. But the reason people want binary 
> diff is so that when you have your 10MB Word document, and you change 2 
> lines in it, when you do the commit it doesn't have to upload 10MB of 
> data.

No, the reason people want binary diffs is so that they can have
binary files stored in revision control. That's what it means and
that's what it does.

  .''`.  ** Debian GNU/Linux ** | Andrew Suffield
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