To: gnu-arch-users@gnu.org
Subject: Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin
References: <20041205000613.PNEI7152.lakermmtao09.cox.net@nonerjsnum1tkq>
	<26E1F314-4654-11D9-AD55-000A957659CC@spy.net>
	<20041205023828.GA11443@suffields.me.uk>
Organization: The XEmacs Project
From: "Stephen J. Turnbull" <stephen@xemacs.org>
Date: Mon, 06 Dec 2004 12:16:40 +0900
In-Reply-To: <20041205023828.GA11443@suffields.me.uk> (Andrew Suffield's
	message of "Sun, 5 Dec 2004 02:38:28 +0000")
Message-ID: <87pt1o9kvb.fsf@tleepslib.sk.tsukuba.ac.jp>
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>>>>> "Andrew" == Andrew Suffield <asuffield@debian.org> writes:

    >> There has been discussion of binary diffs a while back, but I
    >> don't remember quite what came out of it.

    Andrew> Arch already has the only kind of binary diff that is
    Andrew> possible.  It would be possible to compress the changesets
    Andrew> better [...].

True, but not a very helpful way to express it.

Summary: "binary" files are not readable by humans or programs, so you
can't expect their "diffs" to be either.  The only thing a "binary"
diff is useful for is exact patching, ie, replacing an exact copy of
the "old" file with an exact copy of the "new" file.  Arch implements
this by storing a copy of each.  If the old file in the target
workspace is identical to the old file in the archive, then it is
replaced with the new file by using "cp" (or the equivalent) rather
than "patch" or the xdelta equivalent.  Thus, archives are larger than
theoretically necessary, but Arch does implement binary diffing and
patching as accurately as is possible.

I hope I didn't spoil your day, Andrew.  ;-)

-- 
Institute of Policy and Planning Sciences     http://turnbull.sk.tsukuba.ac.jp
University of Tsukuba                    Tennodai 1-1-1 Tsukuba 305-8573 JAPAN
               Ask not how you can "do" free software business;
              ask what your business can "do for" free software.


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