When to Arc state and when to not Arc state

[askasp]

Summary

I struggle a bit with understanding the implications of Arc in Axum state handler. I would really appreciate it if anyone has the time to clarify what is best practice here.
Specifically, i’m unsure if its enough to have the entire struct in an arc, or i also should have the db client in a separate one.
Alt1:

struct AppState{
  prisma_client: PrismaClient
  stripe_client: StripeClient
}

and then create one like this

let app_state = Arc::new(AppState{...})

let app = Router::new()
          .route("/user/:id", put(user::update))
          .route("/stripe", post(stripe::create))
          .with_state(app_state.clone()),
   

Or if i should wrap every part in each own Arc?
Alt2:

struct AppState{
  prisma_client: Arc<PrismaClient>
  stripe_client: Arc<StripeClient>
}

How would axum actually handle the later case? I’ve understood it so that it automatically clones the struct in each handler, is that correct?
Will i in the later case be able to do

pub async fn stripe(State(app_state): State<AppState>) {
  let query = app_state.prisma_client.query  

or do i need to explicitly clone the prisma_client here?

Generally i wonder what is the best practice, and the implications of each approach!

axum version

0.74

[wangziling]

Hi~ I thought that these two cases are all ok.

According to the existed practice about the crates.io.
https://github.com/rust-lang/crates.io/blob/e3a14fbc4beda762784daf59a946c18b26a8dc90/src/app.rs#L22

It only wrapped the config and storage with Arc, and I only found the .clone() of they two here: https://github.com/rust-lang/crates.io/blob/e3a14fbc4beda762784daf59a946c18b26a8dc90/src/tests/util/test_app.rs#L277.

Hmmm...
In my opinion, I thought that:

// let app_state = AppState {
//     config: Arc<Config>,
//     client: Arc<Client>,
//}

If we want to share the config or client in multiple places without clone themselves' metrics or data totally, then we need to wrap them with Arc as well. 😃