Pacman 6 introduced ParallelDownloads config option. When it used, pacman downloads several packages at once, but usually from single mirror, which limited total download speed a lot. Any way to randomize mirrors or something like that?
Download speed with ParallelDownloads, without ParallelDownloads
Negative answer : Not possible (unless you can modify the source-code of pacman).
The reason the option you're asking for was never added, is perhaps that if the mirrors are not in sync, the user will end up with a mess.
The rational behind the current implementation option was probably that it was only intended so that large packages will not block the downloading of small ones.
I note that if the chosen (one) mirror limits the download speed of its connections, usually opening multiple connections to the same target can overcome this limitation.
However, if the download speed from the mirror is satisfactory with
one connection, choosing ParallelDownloads might even slow-down
the download, because each of the several connections will share
bandwidth with the others, and their competition over the local and
network resources will only waste time and prevent the connections
from reaching maximal bandwidth.
As of June 2023 pacman still does not support this.
If you are OK with a Python + Aria2 based downloading wrapper you can use Powerpill from the AUR. It's highly configurable and can download from multiple mirrors while grabbing the correct version specified in the primary mirror's databases.
With some tweaked routing rules I use it download from 2 internet uplinks simultaneously.
