Using zsync for .deb downloads: initial benchmark results

[Tim Webster]

debdeltas look quite quite good
And I would rather ubuntu and debian used the same infrastructure.





On Wed, Jul 15, 2009 at 2:52 AM, John McCabe-Dansted<gmatht at gmail.com> wrote:
> On Wed, Jul 15, 2009 at 12:19 AM, Lars Wirzenius<lars at ubuntu.com> wrote:
>> Before I continue working on this, I'd like to have some feedback on
>> this: is a 25% reduction in download sizes worthwhile to pursue? It
>> would seem to require changing dpkg to call the external gzip binary to
>> use --rsyncable, rather than use the internal zlib library.
>
> I think a better solution would be to fix zsync so it can look inside
> ar files. In principle all this requires is adding an offset to every
> http request so we can use the zsync look-inside, but the zsync source
> code doesn't have this make a clear distinction between the http
> offset and the local offset. We could try asking the author to add
> this capability.
>
>> What do other people think?
>
> My opinion is that deb deltas are more useful. The average size was
> only 11% of the original, according to
>  http://tonelli.sns.it/pub/mennucc1/debdelta/run/tests/README
> This is similar to my experiences
>
> The disadvantage of debdeltas is that they take more space than .zsync files.
>
>> PS. I've fully automated my benchmark, and am happy to share the
>> scripts. If anyone wants to play with them, drop me a note, and I'll set
>> up a public bzr branch. You'll need fast access to a mirror, since they
>> download snapshots of hardy-security and the corresponding packages from
>> hardy, for a total of about three gigabytes.
>
> So if we were using n->n+1 debdeltas, we would need ~300MB of extra
> packages for Hardy? This seems reasonable given that we can delete old
> packages, omit unimportant packages etc.
>
> FYI, the debdelta in Ubuntu cannot handle lzma packages, and gives a
> cryptic 'debdelta failed  :   <type 'exceptions.AssertionError'>'
> error if it comes across them. However it seems easy to add this
> functionality to debdelta.
>
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