In polkadot staking what's the difference between Validators and Para Validators?

Question

In Polkadot staking, validators are identified as either Relaychain validators or Para Validators.

This appears to mean that a validator has is started with arguments that allow it to validate (randomly selected?) parachain blocks. Still, I cannot find that argument in the options to run a Polkadot node.

So what is the difference between the two types of validators?

I may be looking at this the wrong way around. Perhaps it is a collator from a Parachain that has its Polkadot startup arguments set to validate on the Polkadot chain as well - in which case, I could see how this could be both a Relaychain Validator and a Parachain Collator at the same time. Is this the answer?

Answer 1

Validators are selected and assigned to parachains by the randomized Validator Assignment routine on-chain. Let's look at this snapshot of parachain validation on https://polkadot.js.org/apps/#/parachains

At the time of writing this response, there are 28 parachains that are assigned 5 validators each. That would be 140 para validators in this era. The remaining (297 - 140 = 157) validators in the active set will only participate in the relay chain block production and finality.

Proof of Validity (PoV) check on parachain blocks is computationally more intensive. Hence, for that work, para validators earn more era points, resulting in an uptick in the earned rewards.

As more parachains run on Polkadot, more validators will take part in para validation. If you are interested in learning about the validation protocol, please refer to this protocol overview document.