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



Hi all,

[...]
> 
> External issues
> ===============
>       * picosat is built without tracing support (Bug#607943)

I'm aware of that, but please don't expect a solution before end of January (but
NMUs or patches are welcome!).

>       * picosat prefers B in A | B if B > A (higher version ID wins)

picosat doesn't care. If either of them poses a valid solution, it will give you
one of them. Which of them is chose purely depends on heuristics implemented in
picosat (might even be tied to the literal ids). If you want it to prefer a
different solution, that has to be encoded.

>       * picosat does not allow for optional clauses, Recommends are thus
>         treated as Depends. I should ask them if they are interested in
>         adding this.
> 

What would be the semantics of "optional clauses" in terms of Boolean
satisfiability? What I could envision, however, is adding additional clauses
after the first round of solving the problem for Depends, using incremental SAT
solving. Add one of the Recommends at a time and see whether the problem can
still be solved. My question here would in particular be which semantics users
can expect from "Recommends" - will these packages always be installed or just
as many as possible or ...? As a user of apt I'd expect that either all of them
or none of them gets installed (depending on my apt config). Therefore I don't
see any need for "optional clauses", but I have to admit that I'm not that much
into apt development.

[...]

Best regards,
Michael

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