[Top][All Lists]
[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]
Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin
From: |
Thomas Lord |
Subject: |
Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin |
Date: |
Mon, 6 Dec 2004 10:50:32 -0800 (PST) |
> From: "Stephen J. Turnbull" <address@hidden>
> 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.
Another point is that we have seen zero (`0') evidence that any
significant saving would arrive, under any real-world usage
conditions, from the use of binary deltas.
Suppose that magically, or whatever, all technical issues re merging
and so forth are resolved. You can now commit with changes to
binary files and those parts of those changesets will be
O(xdelta-result) in size.
We win a bullet point but....
Where's the convincing class of scenarios that show me, as project
maintainer, I should do what I can to raise the priority of
binary delta compression? Note that I am apt to evaluate costs
in dollars, not (directly) bytes and nanoseconds.
Who is editting these BLOB files that change in such reliably small
xdelta increments? What is it about the xdelta format that ensures
this (and, hence, how fragile is the situation)?
I have heard suggestions like "people editting sound files" but,
supposing that the on-disk format of such files is a compressed one,
is that really true?
It seems to me that the relationship of compression to binary files
reveals the implausibility that binary delta compression will be
significantly useful:
Programmers often use binary files for space compression. Many
forms of compression share the familiar chaotic property of formats
like `gzip': small changes to the "content" that generates the
compressed form generated global changes to the compressed form.
[[cartouche!
The better a job binary-file-format designers do at space
compression -- i.e., the more reason there is to have most
binary file formats *at all* -- /the less useful it is to
have generic binary delta compression in a revision control
systems!/
]]
Don't get me wrong: I can think of plenty of applications for
non-textual diffs. I just don't see any huge wins for generic
binary diffs. Does anyone else?
I hate it when people ask for features that don't make sense
but then it takes 3 years to figure out how to articulate why
the original request doesn't make sense. Don't you?
-t
- Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin, (continued)
- Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin, Stephen J. Turnbull, 2004/12/05
- Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin,
Thomas Lord <=
- [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Stefan Monnier, 2004/12/06
- Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin, Florian Weimer, 2004/12/06
- [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Stefan Monnier, 2004/12/06
- [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Charles Duffy, 2004/12/06
- Re: [Gnu-arch-users] Arch Versus CVS Versus Subversoin, Bruce Stephens, 2004/12/06
- [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Charles Duffy, 2004/12/06
- Re: [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Aaron Bentley, 2004/12/06
- Re: [Gnu-arch-users] Re: Arch Versus CVS Versus Subversoin, Bruce Stephens, 2004/12/06
- [Gnu-arch-users] Re: Re: Arch Versus CVS Versus Subversoin, Charles Duffy, 2004/12/06
- Re: [Gnu-arch-users] Re: Re: Arch Versus CVS Versus Subversoin, Bruce Stephens, 2004/12/06