apt-0.6.44 and incremental updates

Michael Vogt michael.vogt at ubuntu.com
Thu May 25 11:05:23 BST 2006

On Wed, May 24, 2006 at 12:59:29PM +0200, chantra wrote:
> Hi there,
Hi chantra,
> apt-0.6.44 has being release under debian/unstable, this new version of 
> apt does integrare incremental update and therefore minimize apt-get 
> update process time.
> I've released a .deb, you can get more information at: 
> http://www.debuntu.org/2006/05/23/56-apt-0-6-44-and-incremental-updates/
> So if you want to try it out, get it from there.
> I'm wondering if I should submit this package to revu or not (apt being 
> not much of a universe package), or should we simply wait for the apt 
> package maintener to compile it out.

There is no need to submit it to revu. We are aware of the incremental
update feature in apt. The apt--pdiff [1] branch (that the version in
debian uses) is not merged for ubuntu (yet) because:
a) we are late in the release cycle (obviously :) 
b) it needs archive support to generate diff files and a diffIndex 
c) it only works on indexfiles, not packages
d) its not entirely clear if it is the right solution for ubuntu

Let me explain the last point. Debian re-generates its Indexfiles
(Packages.gz, Sources.gz) once a day. Ubuntu 24 times a day (or even
up to 48 times a day). The incremental IndexFile updates work by
keeping a bunch of ed-style diffs around and a indexfile that keeps
track of what indexes are available. Apt looks at the current sha1 of
the indexfile and downloads the right patches and applies them. This
works very well for debian because you only have to keep a single diff
per day. For ubuntu it would mean that we would have to store ~24
diffs per day, resulting in a lot of small files on the servers and
pretty big indexfiles. 

We have a SoC student interessed it working on a different solution to
solve this problem. He expressed interesst to investigate a zsync
based solution (this came up before a couple of times and Paul Sladen
did some work [2] on it too). If we can get this idea working we would
be able to solve the incremental updates problem with a single
solution for both indexfiles and packages in a clean and elegant

[1] http://people.ubuntu.com/~mvo/bzr/apt/pdiff
[2] https://wiki.ubuntu.com/PaulSladen/Succinct
Linux is not The Answer. Yes is the answer. Linux is The Question. - Neo

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