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

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.


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