[Aptitude-devel] Bug#632125: aptitude fails to resolve dependencies for safe-upgrade

[Manuel A. Fernandez Montecelo]

2015-09-22 20:40 GMT+01:00 Grześ Andruszkiewicz <gandrusz at gmail.com>:
> Hi,
>
> This problem occurs every time a new stable Debian is released. As a
> workaround I always have to do aptitude dist-upgrade at some point (after
> upgrading selected packages in a safe way).

It happens only with upgrades of releses since about the time that you
reported this, or from much more long ago?  (Say, 2005).


> Now I am running Debian stable, so my APT policy is (600, 'testing'), (700,
> 'stable'), (50, 'unstable')
>
> Unfortunately we just had a release, so the next opportunity to replicate
> the problem will be in a few years time. What kind of debugging output
> should I collect if/when it happens next time?

I never experienced this myself because I haven't dist-upgraded in the
last few years.  I usually run systems with unstable/testing, and
upgrade often and many times upgrading selected packages, as you said
above, always guiding the solution interactively.  Sometimes it takes
a while to calculate solutions, but not more than a few seconds.

Probably the information given is enough, I could attempt to reproduce
it using older releases.  The problem is to find time and gain
experience to tackle it; there may be exactly one person in the world
with enough experience in aptitude's resolver (his creator), and he
left long ago.


I think that the problem is that the possible universe of solutions is
vast, like a game of chess or guessing passwords, and the resolver
fails to find quick solutions.  Problems that make this worse are
things like enabling multi-arch or adding a full suite like unstable
or testing -- doubles the number of packages (equivalent to growing
the chess board, or guessing passwords with more characters), and the
number of possible solutions for upgrades grows exponentially.

If you upgrade from one vesion of stable to the next, and if you are
not doing this already, probably disabling the other releases and
keeping only stable it will help to cut down dramatically the number
of solutions that aptitude has to explore.  Maybe this still means
many hours, though.   And maybe previously installed packages (local,
or of testing and unstable) cause some problems that make fully
automatic solutions impossible or very costly to calculate.  But
still, it's the best advice that I can give for the time being.


Cheers.
-- 
Manuel A. Fernandez Montecelo <manuel.montezelo at gmail.com>