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Re: Proposal: A new approach to differential debs




On Sun, Aug 13, 2017 at 12:38:56PM +0300, Adrian Bunk wrote:
> On Sat, Aug 12, 2017 at 02:16:21PM -0400, Julian Andres Klode wrote:
> >...
> > I think delta debs are generally a thing we should aim to have,
> >...
> 
> It sounds like something that would have been a cool feature 20 years
> ago when I was downloading Debian updates over an analog modem.
> 
> Today the required effort, infrastructure and added complexity would
> IMHO not be worth it for a potential few percent of bandwidth decrease.
> 
> > The .diff.tar member contains patches to apply to individual
> > files of the old package. No idea about specific algorithm
> > to choose here, yet.
> >...
> 
> Do you really want to ship *patches*, and not just copies of all
> changed files?
> 
> Patching binaries to a new upstream version doesn't sound to me like 
> something that would make sense.

bsdiff was specifically invented for patching binaries. See the
evaluation I posted a (few) hour(s) ago. It's used succesfully by
FreeBSD, Chrome, Android, Apple App Store, and other places.

Chrome switched to courgette meanwhile, which basically just 
disassembles the code and unifies offsets before passing it
to bsdiff.

Especially for security and stable updates, as opposed to new
(major) upstream versions it makes a substantial difference
(93% savings for the firefox 55.0-1 to 55.0-2 release, from 38
 MB down to 2.4).

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