Fixed Validator Rewards in an NPoS Substrate chain

Question

Is it possible to have fixed validator rewards on each epoch in a NPoS consensus based substrate chain. This suggests that the rewards are based on inflation and stake rate, and I've not seen any implementations with fixed rewards either.

Is it possible to do that?

Answer 1

Totally possible. The reward paid our per era is provided to staking as type EraPayout, which can be anything that implements trait EraPayout. You can have an implementation for this trait that ignores all the inputs and provides a constant value at each era.

A substrate-idiomatic way of doing that would be:

// Assuming this balance type.
type Balance = u128;

pub struct FixedEraPayout<P: Get<Balance>>(sp_std::marker::PhantomData<P>);
impl<P: Get<Balance>> EraPayout<Balance> for FixedEraPayout<P> {
    fn era_payout(
            _total_staked: Balance,
            _total_issuance: Balance,
            _era_duration_millis: u64,
        ) -> (Balance, Balance) {
        (P::get(), 0)
    }
}

Then you can reuse e.g. FixedEraPayout<ConstU128<100_000>> in different runtimes.