Acredito que isso aqui resolve seu problema:
Fonte:
https://bbs.archlinux.org/viewtopic.php?id=199161 I realize I should have done the following before even posting this thread. Anyways, I did eventually solve the problem and - just in case - here is how:
1) boot from usb and chroot into system
arch-chroot /mnt/
2) clean pacman cache to force re-download of packages
pacman -Scc
3) re-install packages
pacman -S systemd ... ... ....
Then I tried to optimize the database and everything works as expected:
==> Finished. Your pacman database has