On Wed, Apr 10, 2002 at 10:25:22AM +1000, Martijn van Oosterhout wrote:
> On Tue, Apr 09, 2002 at 05:02:34PM +0200, Michael Bramer wrote:
> > you propose to add 'some' diff files for all files on ftp-master.d.o?
> >
> > With rsync we need only one rsync-checksum file per normal file and
> > all apt's need only download the neededs parts.
> >
> > You get the point?
>
> With the standard rsync algorithm, the rsync checksum files would actually
> be 8 times larger than the original file (you need to store the checksum
> for each possible block in the file).
I don't see that the checksum file is larger than the origanl file. If
the checksum file is larger, we will have more bytes to download... This
was not the goal.
> What you are suggesting is that the server store checksums for precalculated
> blocks on the server. This would be 4 bytes per 1k in the original file or
> so. The transaction proceeds as follows:
>
> 1. Client asks for checksum list off server
> 2. Client calculates checksums for local file
> 3. Client compares list of server with list of client
> 4. Client downloads changed regions.
Yes, this is the way..
> Note, this is not the rsync algorithm, but the one that is possibly
> patented.
maybe I don't understand the rsync algorithm...
IMHO the rsync algorithm is:
1.) Computer beta splits file B in blocks.
2.) calculate two checksums
a.) weak ``rolling'' 32-bit checksum
b.) md5sum
3.) Computer B send this to computer A.
4.) Computer A search in file A for parts with the same checksums from
file B
5.) Computer A request unmatch blocks from computer B and
build the file B.
I get this from /usr/share/doc/rsync/tech_report.tex.gz
right?
The _only_ difference is: precalculate the checksums on computer B
Or maybe store the calculated checksums in a /var/cache/rsync/ cache
dir.
sorry, I know that partentes don't have any logic, but this is the same
algorithm, only with some cache. Comments?
Gruss
Grisu
--
Michael Bramer - a Debian Linux Developer http://www.debsupport.de
PGP: finger grisu@db.debian.org -- Linux Sysadmin -- Use Debian Linux
"Nicht geschehene Taten ziehen oft einen erstaunlichen Mangel an Folgen
nach sich." -- S.J. Lec
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