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Re: Apt and rsync... I know...



On Sun 18 Jan 2004 4:47 am, Goswin von Brederlow wrote:
> Andreas Metzler <ametzler@downhill.at.eu.org> writes:
> > Goswin von Brederlow <brederlo@informatik.uni-tuebingen.de> wrote:
> > > Doug Holland <meldroc@frii.com> writes:
> >
> > [...]
> >
> > >> because it hogs I/O and CPU cycles on the Debian servers.  That's a
> > >> valid reason, but surely there are ways around it.
> > >
> > > Its called cnysr and I asked for supporting it i think over a year
> > > ago, never got a reply.
> > >
> > > cnysr (rsync backwards you might have noticed) reverses the roles the
> > > client and server play in rsync. Instead of the client sending a
> > > blockwise checksum to the server the server send them, either
> > > calculated on the fly or from a precalculated file. The client then
> > > checks what blocks it needs and requests those. The blockwise
> > > checksums are (depending on the block size, assuming 1K) about 2% of
> > > the file.
> >
> > [...]
> >
> > Hmm. Iirc in almost every discussion about apt+rsync the existence of
> > a rsync-like algorthm with reversed sides (client doing the expensive
> > calculation) hascome up and was always said to be patent-encumbered.
> >                cu andreas
>
> I know of no such patent and rumors of such one in US don't realy
> intrest me (not being in the US and all).
>
> The algorithm used to find blocks that need to be downloaded is
> identical to rsync, just the method of fetching them (i.e. the client
> requesting instead of the server pushing) is reversed. If cnysr falls
> under any patent then rsync should too.
>
> MfG
>         Goswin

I'm all for this.  If there's a patent on the rsync/cnysr algorithms, they can 
most likely be invalidated with prior art, and any company that wants to push 
the matter would end up looking like SCO.

And I do believe that the gzip packages already have the -rsyncable option 
built into them.

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