<hedley.finger@myob.com> wrote in message
news:OF46900C46.01D83CFA-ONCA257265.0079A08E-CA257265.007A08D8@myob.com.au..
.
> Andy, Sebastian:
>
> > cheap copies
>
> For the unwashed, unwary, and unclued, what is a "cheap copy"?
> I've shied away from Subversion because I understood this term to
> mean that versions, tags, and branches all represent complete copies
> of every file, with successive changes creating a new file. Some older
> systems store a base file with deltas and admin data so that when a
> particular version is retrieved, the file is edited to remove irrelevant
> deltas.
>
> If Subversion uses copies, won't a project consisting of thousands of
> files rapidly eat up your disk quota. No doubt this information is in The
> Book but I couldn't find it.
Conceptually, each copy operation creates another instance of the original
files, that can be accessed at the new location. Similarly, each revision
holds a new copy of all files modified in that revision.
However, behind the scenes Subversion ensures that only the changes (deltas)
are stored for each change/copy. This means that copying a file uses up a
constant and very very small amount of space, regardless of the size of the
file.
You will see the same size increase if you make a million copies of a 0 byte
file or a 20GB file within your repository, and in both cases this increase
will be relatively small.
I believe SVN also uses compression to reduce the size requirements even
further (though don't quote me on that!).
- Mark Clements
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Received on Tue Jan 16 23:29:34 2007