Distribution Development: Package Rebuilds

I wondered several times in the past why Novell/SUSE people eg in Novell Open Audio interviews presented our internal autobuild system as something special. The relevant feature here is that both the legacy autobuild as well the new openSUSE Build Service have the functionality to rebuild all dependent packages everytime after a change. A new compiler version, a newly enabled security check, or an innocent looking change to a library can break larger parts of the distribution. openSUSE Factory gets completely rebuilt every few days, and the same happens for older maintained products a bit more infrequently. It's an easy way to discover regressions and to prevent an inconsistent distribution so I couldn't imagine a distribution being created without such "feature".

Today I read the comment section of this story where a user writes that Mandriva "2007.1 Spring failed to rebuild all python defendant rpms after upgrading the core python install to 2.5" and that the official Mandriva comment was along the line of "Well you don't expect us to rebuild every package in the distro against each other for every release, can you?". Hard to believe, or? Adam Williamson of Mandriva jumped into the discussion with "For 2008, we (well, it was about 90% me...) rebuilt the entirety of /main, which had never been done before. For 2008.1 I'm hoping to get /contrib done too. But it would be nice to have an automated rebuild of everything". So Mandriva doesn't manage to get its packages rebuilt once during a whole release cycle while SUSE does it every few days!?

Most strange quote of Adam: "we already have a buildsystem that does everything useful that the openSUSE system does". Really? :-)

How does the Debian/Ubuntu build system work? How does Fedora's Koji build the distribution?

Update: Really a coincidence, Novell Open Audio is bringing a new episode about autobuild/build service just today.