Wanted to get some relevant linkage in this thread:
http://www.archlinux.org/pipermail/pacman-dev/2006-October/006113.html http://www.archlinux.org/pipermail/pacman-dev/2007-November/009936.html http://www.archlinux.org/pipermail/pacman-dev/2007-November/010278.html
I am going to try really hard to keep this civil in here, so please do the same. I post the above links for this reason- this idea has come up many times before. And every time it doesn't seem to catch the attention of our devs. To find out why, you are going to have to do some reading of the above threads.
This is not to say it can't be done. I just don't think those of us that are currently coding a lot of things for pacman find this to be a priority or a big problem in our minds, and/or think there are other ways to better solve the problem, such as reading straight from a tar.gz database which libarchive makes *really* easy, but the current pacman code needs some work to support. I would be very interested in working on a refactoring so that multiple backends could be possible- the code as it currently stands makes that awfully hard.
As I've already pointed out inside the previous linked thread ( http://bbs.archlinux.org/viewtopic.php?id=42374 ) I've already read all the previous "sqlite" discussions. What about the "libarchive" way? Well... it IS a step forward compared to the current backend. I think this is still worse than a sqlite based approach however it IS definitely a good improvement.