Crate pallet_collator_selection

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Collator Selection pallet.

A pallet to manage collators in a parachain with council-approved candidacy.

§Overview

The Collator Selection pallet manages the collators of a parachain. Collation is not a secure activity and this pallet does not implement any game-theoretic mechanisms to meet BFT safety assumptions of the chosen set.

§Permissioned Candidacy System

As of this version, collator candidacy requires governance approval:

  1. Accounts must first apply via apply_for_candidacy (reserves bond)
  2. Governance reviews and either approves via approve_application (directly adds to candidates) or rejects via close_application (unreserves bond)
  3. Governance can force-remove candidates with slashing via kick_candidate
  4. Users can withdraw pending applications via close_application (only before processing)

The old register_as_candidate extrinsic is deprecated and will fail with a Permission error.

§Terminology

  • Collator: A parachain block producer.
  • Bond: An amount of Balance reserved for candidate registration.
  • Invulnerable: An account guaranteed to be in the collator set.
  • Pending Application: An application that has been submitted but not yet processed.

§Governance Origins

The pallet uses two configurable origins for governance actions:

  • GovernanceOrigin: Can approve/close candidacy applications
  • ForceRemovalOrigin: Can forcibly remove active candidates

§Implementation

The final Collators are aggregated from two individual lists:

  1. Invulnerables: a set of collators appointed by governance. These accounts will always be collators.
  2. Candidates: these are governance-approved candidates to the collation task and may or may not be elected as a final collator.

The current implementation resolves congestion of Candidates in a first-come-first-serve manner.

Candidates will not be allowed to get kicked or leave_intent if the total number of candidates fall below MinCandidates. This is for potential disaster recovery scenarios.

§Rewards

The Collator Selection pallet maintains an on-chain account (the “Pot”). In each block, the collator who authored it receives:

  • Half the value of the Pot.
  • Half the value of the transaction fees within the block. The other half of the transaction fees are deposited into the Pot.

To initiate rewards an ED needs to be transferred to the pot address.

Note: Eventually the Pot distribution may be modified as discussed in this issue.

Re-exports§

Modules§

  • pallet
    The pallet module in each FRAME pallet hosts the most important items needed to construct this pallet.
  • weights
    Autogenerated weights for pallet_collator_selection