> unless you run nix-collect-garbage periodically
nix.gc.automatic = true;
nix.gc.options = "--delete-older-than 10d";
I've found this useful to eliminate the rebuild loop: https://kokada.dev/blog/quick-bits-realise-nix-symlinks/ It lets you make the config of the program you choose a regular mutable file instead of a symlink so you can quickly iterate and test changes.
> In contrast, Arch Linux simply downloads prebuilt binaries via pacman or an AUR helper
If a binary exists. A lot of AUR packages I used to rely on didn't have a binary package (or the binary package was out of date) and would have to build from source. On nixos my machines are set up to use distributed builds (https://wiki.nixos.org/wiki/Distributed_build). Packages that do need built from source get built on my server downstairs. The server also runs a reverse proxy cache so I only need to download packages once per version.
Distributed AUR builds are possible on arch, but they require a lot of setup and are still fragile like regular AUR builds, your only choice of dependencies are what's currently available in the repos.
> On my machine, regular maintenance updates without proper caching easily take 4–5+ hours
It sounds like the author may be running the unstable release channel and/or using some heavy unstable packages. Which might explain a lot of other problems the author is having too.
Back when I used arch, I found that as time went on, my system would sort of accumulate packages. I would install $package, then in the next version of $package a dependency would be added on $dep. When I updated, $dep would be installed, then eventually $package would drop the dependency on $dep, but $dep would remain installed. I would periodically have to run pacman -R $(pacman -Qtqd | tr '\n' ' ') to clear out packages that were no longer required.
If the former, via substitutor (or if also using a remote builder), how do you manage when moving portable clients outside your LAN? E.g. traveling with your laptop? Do you tunnel back home, have a toggle to change substitutor priorities?
I find it the default timeout for unresponsive substituters excessively long, as well as the repeated retries for each requested derivation annoying, rather than it recalling and skipping unresponsive substituters for subsequent derivations in the same nix switch/build invocation.
Outside my LAN I do have the ability to tunnel home, but depending on the connection and the updates I just deal with the timeouts, or just wait until I get home.
I think technically you can override substituters using cli options but its not ideal. There are several proposals for configuring timeouts per substituter but none of them are merged yet.