[Nix-dev] Re: Proposal for hydra with librsync

[Jeff Johnson]

On May 11, 2010, at 10:03 AM, Ludovic Courtès wrote:

> Hi,
> 
> Jeff Johnson <n3npq at mac.com> writes:
> 
>>>> librsync is a zombie project. which is a shame, Martin Pool is a
>>>> really smart guy, just that the rsync protocol is patent encumbered
>>>> many years now.
>>> 
>>> I did not know about the patent problems.
>>> 
>> 
>> The issues are quite old. But in 1998 it was known that ~87%
>> of the bandwidth needed for displaying web pages could be saved
>> with an rsync-like protocol implemented in browsers. You would
>> think that saving 87% of the bandwidth used displaying web pages
>> would be a useful implementation. The implementation has never
>> happened because of the patent. Sadly the patent has never
>> produced a useful product afaik.
> 
> I didn’t about the issue, but I found a summary:
> 
>  http://ozlabs.org/~rusty/rproxy.html
> 

Yep, that's the issue, and that post was the most recent public
description (that I'm aware of) of the patent issues involved.

(aside)
Note that there are other problems associated with rproxy, such as
there are only so many protocols that one can rationally multiplex over
HTTP on port 80 and so adding an additional protcol like rproxy on port 80 as well
as all the others is, well, a bit naively engineered for a workable proposal.
But I digress ...

The deltafication associated with rproxy is/was dead-on soundly engineered.

> There’s a transcription of a talk by Tridgell where he briefly mentions
> the patent issue:
> 
>  http://olstrans.sourceforge.net/release/OLS2000-rsync/OLS2000-rsync.html
> 

(aside)
BTW, there's also a compression scheme from Tridgell
based on rsync concepts that is likely soundly engineered
as well. I've forgotten the name, looked briefly a couple years back,
but never botherd to use (because of vanishingly small deployment).
I can/will dig out some details if necessary.

73 de Jeff