Question about Dynamic Redirects Example

[Kyoss79]

I have a pobably very simple question about the example with redirects coming from an external source,
in this case, upstash.

https://github.com/vercel/examples/tree/main/edge-middleware/redirects-upstash

Wenn next.config is instantiated, the rewrites is an async method that loads the redirects from upstash.

But how often is this done?
At every request?
Or every x minutes?

It would seem a big waste of resources (and time) if this gets loaded on every request.

Does anyone know how this works?
The Vercel example page is kind of slow (300ms for a page load), but maybe thats normal, or just on my end.

Thanks for your answers in advance.