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Re: dep-trace v. tsort (dpkg, source, bsd, reason)

"John D. Hendrickson and Sara Darnell" <johnandsara2@cox.net> writes:

> Thanks !  I'm sure someone "is aware" :)  Was not sure it posted.
> Correct and yes your right, but not "optimal".  Let's say apt selected this depends list:
> A
> B C
> D
> All satisfied as a list to install, yes.  Should work, the book says.
> But if installed in order "C B D A" it may cause headaches (see below).

If it causes headaches then the packages are bugy because they did not
set the right dependencies. And if they did not set the right
dependencies no sorting tool will be able to sort them magically right.
Apt and dpkg already use all the dependency informations to sort
packages correctly. The order they find is not unique but is no better
or worse than any other order that doesn't break the dependency

> If optionally applied in order "A B C D", sorted by deps, success is more likely.

The dependencies of packages define a partial order and any order that
does not violate that partial order has to succeed. Otherwise the
packages dependencies are buggy.

And since people don't always install "A B C D" as set but frequently
just update a subset it is pretty much garantied that over time and many
many users any order of that set that is allowed will be tried. So this
really is a must work. There is no "is more likely", it has to work in
any order.

> ##### in a 90's release, "buzz", install guide called lack of order "a bit loopy"

Dpkg and its frontends have come a long way sinze buzz.


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