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Re: [UPLOADED] RFC: The Future of Solving Dependency Problems in APT (SAT, CUDF)



On Tue, Dec 28, 2010 at 03:47:22PM +0100, Julian Andres Klode wrote:
> Not really, you can declare literals more or less important than
> others which deals with almost every case I throw at it.
> 
>         /* Keep manually installed packages or installed packages that are
>          * candidates on the system and non-candidates away if possible. */
>         if (is_installed && (!is_automatic || cand == ver))
>             picosat_set_more_important_lit(var(ver));
>         else if (!is_installed && cand != ver)   
>             picosat_set_more_important_lit(var(ver));

Problem is: by doing this, you're now adding quite some implicit
requirements not only on a SAT solver (which is just one among several
possible solving techniques), but also on a solver that supports an
interface like the above. The possibility of changing the solver
according to a standardized interface of the user is, if not
jeopardized, significantly diminished.

> The solver will first try to solve the problems by setting
> non-candidate versions to -1 and installed versions (manually
> installed or candidates) to 1 and then trying other solutions.

It sounds like it will explode pretty soon. Have you tried running it
with several suites (e.g. stable+testing+unstable) trying to install
packages from the non-default-candidate suite?

Don't get me wrong, I'm far from being in a position of arguing in favor
or against any specific solver. Nonetheless I'm more than convinced that
blessing a specific solver is risky as it's very difficult, later on, to
get rid of the implicit requirements that the blessing poses. In looking
for a better solver than current APT's, it is worth to make an effort to
standardize over an interface that makes no assumptions on specific
solving techniques. It does not necessarily need to be CUDF, but it
should have some of its good properties, like solver technique
independence. (i.e. AOL on Pietro's mail)

Cheers.

-- 
Stefano Zacchiroli -o- PhD in Computer Science \ PostDoc @ Univ. Paris 7
zack@{upsilon.cc,pps.jussieu.fr,debian.org} -<>- http://upsilon.cc/zack/
Quando anche i santi ti voltano le spalle, |  .  |. I've fans everywhere
ti resta John Fante -- V. Capossela .......| ..: |.......... -- C. Adams

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