Create a parathread auction module for collators to bid on parathread slots

[rphmeier]

This functionality was already implemented as a SignedExtension in the old Registrar prior to #1501. The same logic should be ported over here, except wrapping around the Paras and Scheduler modules. This should live in polkadot-runtime-common as it is "glue" code and not core code.

[coriolinus]

As I'm reading through this, I find myself getting more and more confused. What does this line even mean?

polkadot/runtime/common/src/registrar.rs

Line 616 in 3b62357

if let Call::select_parathread(id, collator, hash) = local_call {

That sure looks like it's using a function call as the receiver of an if let binding, which just doesn't make any sense to me.

[coriolinus]

Guessing that this has to do with macro magic by which Call::select_parathread is somehow simultaneously an enum variant and an actual function. (Apropos of external discussion: this does not feel like responsible use of great power.)

If I'm reading the code properly, the registrar code didn't actually implement any kind of priority queue selection mechanism which would make it an auction; it was more of a first-come, first-served parathread registration thing. This leads to two questions:

• If I'm reading the code incorrectly, where is the actual auction logic with bids etc?
• If I'm reading it correctly, should the new module allow competing parathreads to competitively bid on slots, or just do the same registration stuff that the existing code does?

[shawntabrizi]

@coriolinus you are correct that this is both an enum variant and a function name. Something that is mostly needed to get a complete list of the possible functions in a module. We then use this information to dispatch a call to the right function. So the extrinsic will say: "Module 1, Extrinsic 3", and we will look at the enum for module 1, and the 3rd item in the enum.

The way the auction works is through the "priority" of the tx. The TX queue order txs by priority, and one direct way a user can increase their priority is including a tip, which is some extra fee that is paid to the blockchain (and split between treasury and block producer).

So users who want to make their way into the auction must have the highest tip, thus forming a 1 block auction.

I talk about this at a high level including the signed extension here: https://youtu.be/95Ji5u0q3AU?t=1004

[coriolinus]

@shawntabrizi Thanks for the link! Watching that now.

[burdges]

oops wrong auction thread for my comment here.. ;)

[rphmeier]

@shawntabrizi still needed?

[shawntabrizi]

Yes, it is needed.

I can own this if needed at the appropriate time for implementation.

[rphmeier]

paritytech/polkadot-sdk#828 outdates this