rpm delta compression (FYI)

[Jeff Johnson]

On Mar 1, 2006, at 7:27 AM, Neal Becker wrote:

> http://freshmeat.net/releases/221137/


Java ick. And SuSE's delta rpm's are way more complicated than  
necessary because
the deltafication is intertwined with rpmlib in the rpm file  
installer state machine. SuSE delta
rpm's are also violently incompatible with other rpm features like  
repackaging, and it's not
clear whether the significant amount of work to achieve  
interoperability is worth the effort.

Meanwhile, I stubbed my toe on vcdelta and hsadelta this past  
weekend. Both schemes have a compression analogue
that looks faster than zlib with nearly as good compression. In  
addition, both schemes would generalize nicely to deltafication
w/o changes to the rpm file installer.

Alas, xdelta3 appears to be the only open vcdelta implementation that  
I could find, and Josh's coding style makes
my head hurt a lot. The hsadelta from IBM may be encumbered by  
patents as well (vcdelta is patent free).

There's also gzib --rsyncable if anyone cares to attempt an rsync  
transport channel in smart. rpm payloads are rsync ready
these days, and bandwidth savings appear to be of order 35% or more w/ 
o the complexity of preparing SuSE delta rpm's.
Some of that work has been started with the FreshRPM's repositories.

The really hard problem with using delta transport is how to manage  
all possible deltas, which has nothing whatsoever
to do with what scheme is used for deltafication.

hth

73 de Jeff