(Please keep me CC'd, I'm not subscribed to the list) Hi folks,
I previously mentioned this on the IRC channel, but Axel asked me to put my question in an e-mail, so here it is. I've been running into some problems with the aptitude problem resolver. Most recently it would not seem to find a solution for doing a full-upgrade on my system, but regularly I find that it first offers to remove a lot of packages, and only later offers the better solution of just upgrading a few packages. In an attempt to see if I could diagnose and perhaps improve this behaviour, I dove into the documenation. However, it seems that the user manual [1] mostly talks about using the interface, but is missing a general introduction on how the resolver works to generate solutions, introducing concepts like cost, score, and (even without details) would help reasoning about what the resolver is doing and why. The manual does talk about cost [2] and customizing things with hints [3], but without the general introduction it is hard to understand how these mechanisms fit in the whole. Also, while searching for solutions the UI shows a count of open/closed/conflict/deferred, which are also not explained in the manual. One particular confusion is that the configuration reference [4] shows various options that influence the "Score" of package versions, but none of the other documentation talks about this score, so I'm puzzled as to how it is used. It would seem sensible to use the score as part of the cost, but it seems that none of the "basic cost components" listed [2] would refer to this score. Perhaps the cost is used to evaluate a complete solution and the score is used to direct the search by scoring individual steps? I tried turning on debug info through Aptitude::CmdLine::Resolver-Debug and Aptitude::CmdLine::Resolver-Dump, mostly discovering that I did not know enough about the process to understand the output (also, it seems to me that Resolver-Debug is *very* verbose, and that a less verbose output showing only considered solutions and their cost/score might be useful). Is there perhaps some "internal" documentation about the resolver that I missed? I tried looking through the source code (in particular problemresolver.h [5]), which has some overview of the concepts involved, but does not seem to document the process itself. Gr. Matthijs [1]: https://www.debian.org/doc/manuals/aptitude/ch02s03.en.html [2]: https://www.debian.org/doc/manuals/aptitude/ch02s03s04.en.html [3]: https://www.debian.org/doc/manuals/aptitude/ch02s03s05.en.html [4]: https://www.debian.org/doc/manuals/aptitude/ch02s05s05.en.html [5]: https://anonscm.debian.org/cgit/aptitude/aptitude.git/tree/src/generic/problemresolver/problemresolver.h
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