Re: Xdelta and CVS

[David H. Thornley]

Maarten de Boer wrote:
> 
> Hello,
> 
> Obviously, storing all revisions entirely will not be very
> efficient. The data is pretty straigthforward, and the
> differences between versions could be extracted very well
> with Xdelta. So Xdelta integration in CVS seems to be the
> solution.
> 
Could be.

> The webpage
> http://www.cvshome.org/cyclic/gallery/xdelta-dev.html
> looks very optimistic, so I was surprised to find out that
> I could hardly find any other references to Xdelta and CVS,
> let alone a patch or (starting) implementation.
> 
The page you have mentioned is a set of suggestions for people
who might have the interest, ability, and time to work on
integration of CVS and Xdelta, not a description of any work
going on.  In order for this implementation to appear, somebody's
going to have to do it, and from the tone of the page it's going
to be some outside volunteer.  If you have the interest, ability,
and time, you could do it.  (I'm not sure I have the interest,
and I know very well I don't have the time.)

Note that the page listed three projects of increasing order
of size, and using Xdelta to reduce repository size would
apparently fall under the third project.

> I am well aware of the fact, that CVS has not been designed
> to deal with large binary files, and that some people would
> consider it undesirable to add such functionality. I think
> it is worth the try though. As this is an important issue
> for our project, I can spend some time on this.
> 
CVS uses diff in different ways.  One is to keep the revision 
history files relatively small, and one is to merge changes.
I looked at the web pages to see if there was some Xdelta
correspondence to diff3, and apparently I'd have to go to
Sourceforge, which is down at the moment.  If Xdelta can
create binary diffs and apply them to other files, in order
to merge changes, and these merges result in something
useful enough times to make the capability worth having, then
it would seem to me to be an extension of the CVS philosophy.

It would still mean changing the RCS format, and that may be
a problem.  If Xdelta provides its own archive file format,
it is unlikely to be compatible with RCS, and it would be
necessary (at the very least) to have some means of telling
CVS what sort of file it was to access.  Ideally, it would
make it possible to version the file type, which is not
currently possible.

-- 
David H. Thornley                          Software Engineer
at CES International, Inc.:  address@hidden or (763)-694-2556
at home: (612)-623-0552 or address@hidden or
http://www.visi.com/~thornley/david/