Re: apt-get wrapper for maintaining Partial Mirrors

["Bernhard R. Link" <brlink@debian.org>]

* Joseph Rawson <umeboshi3@gmail.com> [090619 13:23]:
> On Friday 19 June 2009 05:09:31 Tzafrir Cohen wrote:
> > On Fri, Jun 19, 2009 at 01:52:43AM -0500, Joseph Rawson wrote:
> > > would be much more interested in making a tool that would make it easier
> > > to manage local/partial debian mirrors (i.e. one that helped resolve the
> > > dependencies), rather than have an apt-get wrapper.  I also think that
> > > once such a tool is made, it would make it easier to build an apt-get
> > > wrapper that works with it.  I don't think that viewing the problem with
> > > an "apt-get wrapper" solution is the best way to approach it, but I do
> > > think that it would be valuable once the underlying problems are solved.
> >
> > And reprepro does not fit the bill because?
> >
> It fits part of the bill, as it's an excellent tool for maintaining a
> repository, but it doesn't resolve dependencies (nor should it).

Actually, I'm quite open to having some depedency handling in reprepro
and already have written some simple prototype for a related project.
The problem is that calculating a simple cover of selected packages in
the dependency graph is not enough:

Usually the cover is not unique but the existance of alternatives in
dependencies causes multiple solutions. For an initial checkout that
is no problem, as one can choose one some set by some pseudo-random
selection (like "packages with alphabetically lower names get the
first depedency in an alternative tried first" and similar things
for virtual packages). The problem is that no such criterion can be
stable against changes in the partially mirrored distribution.

So in this cases knowing what packages upstream has and what packages
are wanted is not enough but one has to take into account what packages
are currently selected. And a simply covering no longer is enough but
one needs a full resolver knowing which installed states can be easily
brought to which other installed states. (and things get even more
complicated if the currently mirrored packages allow multiple subsets
which clients using this repository might have installed)...

Hochachtungsvoll,
	Bernhard R. Link