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Re: package pool and big Packages.gz file

On 8 Jan 2001, Goswin Brederlow wrote:

>      > Apparently reversing the direction of rsync infringes on a
>      > patent.
> When I rsync a file, rsync starts ssh to connect to the remote host
> and starts rsync there in the reverse mode.

Not really, you have to use quite a different set of operations to do it
one way vs the other. The core computation is the same, mind you.
> Hmm, which patent anyway?

Don't know, I never heard back from Tridge on that.
> I don't need to get a filelisting, apt-get tells me the name. :)

You have missed the point, the presence of the ability to do file listings
prevents the adoption of rsync servers with high connection limits.

>      > Reversed checksums (with a detached checksum file) is something
>      > someone should implement for debian-cd. You calud even quite
>      > reasonably do that totally using HTTP and not run the risk of
>      > rsync load at all.
> At the moment the client calculates one roling checksum and md5sum per
> block.

I know how rsync works, and it uses MD4.

> Given a 650MB file, I don't want to know the hit/miss ratios for the
> roling checksum and the md5sum. Must be realy bad.

The ratio is supposed to only scale with block size, so it should be the
same for big files and small files (ignoring the increase in block size
with file size).  The amount of time expended doing this calculation is
not trivial however. 

For CD images the concern is of course available disk bandwidth, reversed
checksums eliminate that bottleneck.


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