Why is the default priority higher (in numbers lower) than cache.nixos.org?

[SuperSandro2000]

Hydra explicitly sets 100 https://github.com/NixOS/hydra/blob/58707438ba092e767fd8a0a079a264caa742eeee/src/lib/Hydra/Controller/Root.pm#L349-L351

Why does harmonia set 30 when cache.nixos.org sets 40? Shouldn't we be by default higher to use the likely faster cache.nixos.org?

My suggestion would be to set by default 50 and advise people to change it if necessary.

[Mic92]

I never changed the default when I took the project, so I don't know why harmonia was set up this way.

[Mic92]

If this is a cache in your local network it might make sense to have it higher than cache.nixos.org. Also harmonia with zstd and threads will be much faster than hydra's naive xz based substitution.

[SuperSandro2000]

It is a bit hard to find a sensible default here. If you have roaming machine like a laptop than being in the same network as harmonia it should be preferred but if you are roaming or somewhere else than cache.nixos.org is usually a lot faster.

[Mic92]

I guess in that case we should just stick to one default and document what to use when and make the priority configurable. One argument to have the priority higher is that it saves cost for the NixOS foundation and if you server has gigabit connection than it's probably fine to use it whenever possible. Of course people having their binary cache at home can set it up differently.