Modern Update System

[Michael Schroeder]

On Tue, Nov 29, 2005 at 04:36:02PM +0000, David Woodhouse wrote:
> On Tue, 2005-11-29 at 16:01 +0000, Nigel Metheringham wrote:
> > How well does it work if you pull the rpm header (presumably thats
> > always needed for an update), build the payload using existing files on
> > the system (ie from the previous install) via cpio/minigzip, glue the 2
> > together and rsync that?
> 
> Badly. The compressed payload doesn't rsync well -- you have to
> decompress it if you want rsync to do anything other than just download
> it all again.
> 
> There were once some zlib patches which made zlib-compressed stuff
> slightly more rsync-friendly by deliberately discarding history and
> inserting sync points in the data stream, but they're not a patch on
> just rsyncing the _uncompressed_ version.

The problem is the rsync block size. To make rsync reuse data
a complete block has to be found in the new rpm. If you have
a rpm with contains lots of small files (like the kernel) that
all are slightly changed (because they contain the version number),
the rsync delta protocol won't help much.

Cheers,
  Michael.

-- 
Michael Schroeder                                   mls at suse.de
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