Last year we invited David to work with us for a few days to add a generic interface to apt to call external solvers. After a few iterations, this patch finally landed in master and recently (about 3 months ago), in debian unstable.
[ David Kalnischkies ] * [ABI-Break] Implement EDSP in libapt-pkg so that all front-ends which use the internal resolver can now be used also with external ones as the usage is hidden in between the old API * provide two edsp solvers in apt-utils: - ‘dump’ to quickly output a complete scenario and - ‘apt’ to use the internal as an external resolver
Today the new version of apt-cudf was upload in unstable and with it the latest bug fixes that makes it ready for daily use. I’ve used it quite a lot myself to upgrade my machine and it seems working pretty well so far… The most important difference with the old version is the support for multi-arch enabled machines.
This marks an important milestone in our efforts to integrate external solvers, built using different technologies, directly into apt. From a user prospective, this means that (s)he will have the possibility to check if there exists a better (best ?) solution to an installation problem then what proposed by the internal apt solver. Moreover, even if apt-get gives very satisfactory answers, there are occasions where it fails miserably, leaving the user wondering how to unravel the complex web of dependencies to accomplish his task. Available cudf solvers in debian are at the moment : aspcud, mccs and packup.
From an architectural point of view this is accomplished by abstracting the installation problem via a simple textual protocol (EDSP) and using an external tool to do the heavy duty translation. Since all solvers now available in debian are not meant to be debian-specific, using them involve a two step translation. The EDSP protocol specification is for the moment “hidden” in the apt documentation. I hope to find a better place for it soon : it would be cool if other package managers as smart or cupt could add an implementation on EDSP in their code so to automatically benefit of this technology.
To make it happen, Apt first creates an EDSP file that is then handled to apt-cudf that takes care of the translation to cudf and back into EDSP that is then read back by apt. Apt-cudf is the bridge between edsp and the external solvers and takes care of doing the book keeping and to select the right optimization criteria.
Roberto recently wrote a very nice article explaining how to use apt-get with an external solver.
In a nutshell, if you want to try this out you just need to install apt-cudf, one external solver like aspcud from the university of Pasdam and then call apt-get using the —solver option (that is not yet documented #67442 ). For example :
apt-get install -s gnome --solver aspcud
This will install gnome while using the a optimization criteria that tries to minimizing the changes on the system. Various other optimization criteria for all apt-get default actions can be specified in the apt-cudf configuration file /etc/apt-cudf.conf
I hope the new release of apt-cudf make it into testing before the freeze. Time to test !!!