Tsvetomir Dimitrov
ff09b18d31
* Scraper processes CandidateBacked events * Change definition of best-effort * Fix `dispute-coordinator` tests * Unit test for dispute filtering * Clarification comment * Add tests * Fix logic If a dispute is not backed, not included and not confirmed we don't participate but we do import votes. * Add metrics for refrained participations * Revert "Add tests" This reverts commit 7b8391a087922ced942cde9cd2b50ff3f633efc0. * Revert "Unit test for dispute filtering" This reverts commit 92ba5fe678214ab360306313a33c781338e600a0. * fix dispute-coordinator tests * Fix scraping * new tests * Small fixes in guide * Apply suggestions from code review Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com> * Fix some comments and remove a pointless test * Code review feedback * Clarification comment in tests * Some tests * Reference counted `CandidateHash` in scraper * Proper handling for Backed and Included candidates in scraper Backed candidates which are not included should be kept for a predetermined window of finalized blocks. E.g. if a candidate is backed but not included in block 2, and the window size is 2, the same candidate should be cleaned after block 4 is finalized. Add reference counting for candidates in scraper. A candidate can be added on multiple block heights so we have to make sure we don't clean it prematurely from the scraper. Add tests. * Update comments in tests * Guide update * Fix cleanup logic for `backed_candidates_by_block_number` * Simplify cleanup * Make spellcheck happy * Update tests * Extract candidate backing logic in separate struct * Code review feedback * Treat backed and included candidates in the same fashion * Update some comments * Small improvements in test * spell check * Fix some more comments * clean -> prune * Code review feedback * Reword comment * spelling Co-authored-by: Andrei Sandu <54316454+sandreim@users.noreply.github.com>
Disputes Subsystems
This section is for the node-side subsystems that lead to participation in disputes. There are five major roles that validator nodes must participate in when it comes to disputes
* Detection. Detect bad parablocks, either during candidate backing or approval checking, and initiate a dispute.
* Participation. Participate in active disputes. When a node becomes aware of a dispute, it should recover the data for the disputed block, check the validity of the parablock, and issue a statement regarding the validity of the parablock.
* Distribution. Validators should notify each other of active disputes and relevant statements over the network.
* Submission. When authoring a block, a validator should inspect the state of the parent block and provide any information about disputes that the chain needs as part of the ParaInherent. This should initialize new disputes on-chain as necessary.
* Fork-choice and Finality. When observing a block issuing a DisputeRollback digest in the header, that branch of the relay chain should be abandoned all the way back to the indicated block. When voting on chains in GRANDPA, no chains that contain blocks with active disputes or disputes that concluded invalid should be voted on.
Components
Dispute Coordinator
This component is responsible for coordinating other subsystems around disputes.
This component should track all statements received from all validators over some window of sessions. This includes backing statements, approval votes, and statements made specifically for disputes. This will be used to identify disagreements or instances where validators conflict with themselves.
This is responsible for tracking and initiating disputes. Disputes will be initiated either externally by another subsystem which has identified an issue with a parablock or internally upon observing two statements which conflict with each other on the validity of a parablock.
No more than one statement by each validator on each side of the dispute needs to be stored. That is, validators are allowed to participate on both sides of the dispute, although we won't write code to do so. Such behavior has negative extractable value in the runtime.
This will notify the dispute participation subsystem of a new dispute if the local validator has not issued any statements on the disputed candidate already.
Locally authored statements related to disputes will be forwarded to the dispute distribution subsystem.
This subsystem also provides two further behaviors for the interactions between disputes and fork-choice
- Enhancing the finality voting rule. Given description of a chain and candidates included at different heights in that chain, it returns the BlockHash corresponding to the highest BlockNumber that there are no disputes before. I expect that we will slightly change ApprovalVoting::ApprovedAncestor to return this set and then the target block to vote on will be further constrained by this function.
- Chain roll-backs. Whenever importing new blocks, the header should be scanned for a roll-back digest. If there is one, the chain should be rolled back according to the digest. I expect this would be implemented with a ChainApi function and possibly an ApprovalVoting function to clean up the approval voting DB.
Dispute Participation
This subsystem ties together the dispute tracker, availability recovery, candidate validation, and dispute distribution subsystems. When notified of a new dispute by the Dispute Tracker, the data should be recovered, the validation code loaded from the relay chain, and the candidate is executed.
A statement depending on the outcome of the execution is produced, signed, and imported to the dispute tracker.
Dispute Distribution
This is a networking component by which validators notify each other of live disputes and statements on those disputes.
Validators will in the future distribute votes to each other via the network, but at the moment learn of disputes just from watching the chain.