yum differential updates

[David Timms]

Jesse Keating wrote:
> On Mon, 2006-04-10 at 14:44 +0300, Filip Tsachev wrote:
>> I know SuSe implemented some sort of delta updates (I only read news
>> back then), why not for rpm? 
> 
> SuSE can do something like this as I do believe they run all the
> mirrors.  Since Fedora is open and we allow redistribution, we have no
> control over the majority of the mirrors that carry our bits.  This
> means that mirrors could be Unix, could be Windows, could be Linux,
> could be OSX, could be anything.  Delta RPMS require the server to have
> some infrastructure in place to produce them on the fly, OR they have to
> carry deltas from every possible entry point.  This could easily
> increase the amount of data a mirror would have to carry by an order of
> magnitude.  Not very cool when we're already at multiple gigabites just
> for each Core release.
> 
> I have yet to see a proposal for doing Delta rpm like actions that
> wouldn't cause extreme pain to the mirroring system, which we are very
> dependent on.
I haven't tried this but I thought I might: from my reading of the rsync 
protocol, it can efficiently sync two identically named files, even when 
the data moves around within the file. This is done by taking a rolling 
hash and comparing at each end.

An rpm update for say FC5, would be very likely to have very small 
changes - ie bug fixes, but since compiles would otherwise be the same I 
imagine it would be a good candidate for efficient rsyncing.

I was thinking that the changes for even openoffice, or the kernel might 
not be so great even between major release eg FC4 to FC5. Some rpm might 
hardly change eg docs and tzdata, or the language packs for openoffice 
or kde etc.

DaveT.