rewards-statistics-collector subsystem

[EclesioMeloJunior]

Description

• Creates Rewards Statistics Collector subsytem
• Defines the subsystem messages

/// Messages sent to the Statistics Collector subsystem.
#[derive(Debug)]
pub enum StatisticsCollectorMessage {
	// Approval vote received
	ApprovalVoting(Hash, CandidateHash, (ValidatorIndex, DelayTranche)),

	// Candidate received enough approval and now is approved
	CandidateApproved(CandidateHash, Hash),

	// Set of candidates that has not shared votes in time
	ObservedNoShows(SessionIndex, Vec<ValidatorIndex>),

	// All relay block's candidates are approved, therefore relay block is approved
	RelayBlockApproved(Hash)
}

• Updated approval-voting to send data to the statistics collector subsystem

---

Next Steps

• Collect availability distribution/recovery metrics (upload & downloads)
  • Define subsystem messages
  • Update approval distribution to send messages
• Publish prometheus metrics
• Calculate approvals tallies

Deployment Plan

The goal is to release this subsystem under a feature flag to collect approvals tallies (amount of useful approval votes and no-shows happened in a given session per validator), and publish them as prometheus metrics so we can measure the tallies amongst a set of validators.

The next step is to build the flow that publishes the approvals tallies on-chain, so each active validator will have the opportunity to publish its own approvals tally, which them can be used to calculate the approvals rewards (based on the median of each validator's tally).

[cla-bot-2021]

User @EclesioMeloJunior, please sign the CLA here.

[alexggh]

I had a first pass, overall looks like it is moving into the right direction, thank you!

Left you some comments of things that I think needs addressing.

[burdges]

ref github.com/polkadot-fellows/RFCs/pull/119

[alexggh]

Left you two more small comments, other than that, it looks alright.