Deb binary diffs?

Justin Dugger jldugger at
Fri Jan 16 23:00:36 GMT 2009

As noted in the discussion, Debian packages tend to have terrible
deltas.  One change can propagate a long ways in gzip.  The Rsync
author proposed a fix in like 2000 to reset the window regularly, to
limit the scope of changes at a price of a few percent compression.
Ultimately, rsync is a CPU intensive process on what I'm told is an
already overloaded server. xdelta without gzip hacks would effectively
double the size of the archive needed to support this proposal.

An interesting solution is zsync, which uses standard HTTP and does
all processing locally.  But even here, we need packages to be just a
bit different than it is, or you wind up paying the rsync CPU overhead
just to download the whole archive.  Zsync is smart enough to look
inside compressed archives, but doesn't know about the .deb format.
Using the command option --rsyncable should be a temporary workaround,
and the consequences are outlined in the gzip manpage.

Some initial work and analysis is already in the wiki.  . I too would be interested to hear
anything new on the subject.

Justin Dugger

On Wed, Jan 14, 2009 at 8:53 AM, Steven Harms <thisdyingdream at> wrote:
> I noticed that with Fedora 11, they want to enable Presto / Yum by
> default so that only the deltas of binary files are downloaded by
> default.  I believe zypper also downloads just the delta rpms for
> their updates also.  Is there anything planned for Jaunty that will
> implement a similar feature?
> I found but I didn't see if
> this has been implemented or will be.
> Thanks,
> Steven Harms
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