I'm considering debdelta, which would manage efficient delta between deb files, for snapshot.debian.net to utilize disk space more efficiently.

I wrote short shell script using rdiff or xdelta and tried how much efficient delta can be generated. It also regenerate exact same deb file from base deb file and delta file.

For example:

 22473302 tetex-base_3.0-3_all.deb
 22473170 tetex-base_3.0-2_all.deb

delta between these 2 debs
   231706 t.rdiff
   184444 t.xdelta

   9055368 evolution_2.2.2-4_i386.deb
   9055634 evolution_2.2.2-3_i386.deb

delta between these 2 debs
    575034 e.rdiff
    341246 e.xdelta

  43838036 openoffice.org-bin_1.1.3-8_i386.deb
  43832154 openoffice.org-bin_1.1.3-9_i386.deb

delta between these 2 debs
   9984718 ooo.rdiff
   6728138 ooo.xdelta

  43879974 openoffice.org-bin_1.1.4-1_i386.deb
  43789874 openoffice.org-bin_1.1.4-2_i386.deb

delta between these 2 debs
  13645574 ooo4.rdiff
   8307308 ooo4.xdelta

Hmm, most case xdelta is better than rdiff. Anyway, I should rewrite the script more better, especially more robust. Current major issues is that it is too slow to process (both take delta and apply delta) so it would not be suitable to apply all deb files in snapshot.debian.net's pool.

By the way, while I was testing the script, I found https://wiki.ubuntu.com/APTPackageDeltas. Hmm, it does very similar way to take delta, but it would be somewhat different objective than mine. My script tries to generate the same deb as original deb (it may not be perfect yet though).

I also find another debdelta.