On 20/01/11 00:07, Pierre Chapuis wrote:
On Wed, 19 Jan 2011 23:59:55 +1000, Allan McRae <allan@archlinux.org> wrote:
Huh? How is no dependency checks (-Sd) equivalent to complete dependency checking (-S with a transitive closure of dependencies)? They are polar opposites.
What I mean is that if a transitive closure of dependencies is performed at packaging time, then there is no need to check for dependencies when installing the original package.
Here is an example:
A depends on B and D B depends on C C depends on D and E
Currently the deps will be:
A -> B,D B -> C C -> D,E
When installing A, Pacman will:
1) check deps for A, start installing B and D 2) check deps for B and D, start installing C 3) check deps for C, start installing E
With a transitive closure scheme at packaging time, the deps would be:
A -> B,C,D,E B -> C,D,E C -> D,E
When installing A, Pacman could simply install B, C, D and E *without* checking their deps (-Sd) because these deps are necessarily already included in those for A.
The problem is that the transitive closure can not be assumed to be correct. e.g. At the time A is built: A -> B,C,D,E B -> C,D,E C -> D,E Then B is updated and B -> C,D,E,F. Now the assuming a transitive closure for the dependency list for A is incorrect. Installing the listed dependencies of A with the equivalent of -Sd would result in F not being installed which would break A through broken B. So either: 1) we require a largely unnecessary rebuild of A 2) we always check the dependencies of uninstalled dependencies. Note #2 is less burden on packagers and is more efficient in the examples given above if both B and D are installed (two checks vs four), and that will be the case for most system updates. When none of A - E are installed, they are probably equally efficient. Allan