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Alexandru Gheorghe
a84dd0dba5
Initial implementation for the plan discussed here: https://github.com/paritytech/polkadot-sdk/issues/701 Built on top of https://github.com/paritytech/polkadot-sdk/pull/1178 v0: https://github.com/paritytech/polkadot/pull/7554, ## Overall idea When approval-voting checks a candidate and is ready to advertise the approval, defer it in a per-relay chain block until we either have MAX_APPROVAL_COALESCE_COUNT candidates to sign or a candidate has stayed MAX_APPROVALS_COALESCE_TICKS in the queue, in both cases we sign what candidates we have available. This should allow us to reduce the number of approvals messages we have to create/send/verify. The parameters are configurable, so we should find some values that balance: - Security of the network: Delaying broadcasting of an approval shouldn't but the finality at risk and to make sure that never happens we won't delay sending a vote if we are past 2/3 from the no-show time. - Scalability of the network: MAX_APPROVAL_COALESCE_COUNT = 1 & MAX_APPROVALS_COALESCE_TICKS =0, is what we have now and we know from the measurements we did on versi, it bottlenecks approval-distribution/approval-voting when increase significantly the number of validators and parachains - Block storage: In case of disputes we have to import this votes on chain and that increase the necessary storage with MAX_APPROVAL_COALESCE_COUNT * CandidateHash per vote. Given that disputes are not the normal way of the network functioning and we will limit MAX_APPROVAL_COALESCE_COUNT in the single digits numbers, this should be good enough. Alternatively, we could try to create a better way to store this on-chain through indirection, if that's needed. ## Other fixes: - Fixed the fact that we were sending random assignments to non-validators, that was wrong because those won't do anything with it and they won't gossip it either because they do not have a grid topology set, so we would waste the random assignments. - Added metrics to be able to debug potential no-shows and mis-processing of approvals/assignments. ## TODO: - [x] Get feedback, that this is moving in the right direction. @ordian @sandreim @eskimor @burdges, let me know what you think. - [x] More and more testing. - [x] Test in versi. - [x] Make MAX_APPROVAL_COALESCE_COUNT & MAX_APPROVAL_COALESCE_WAIT_MILLIS a parachain host configuration. - [x] Make sure the backwards compatibility works correctly - [x] Make sure this direction is compatible with other streams of work: https://github.com/paritytech/polkadot-sdk/issues/635 & https://github.com/paritytech/polkadot-sdk/issues/742 - [x] Final versi burn-in before merging --------- Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>
Approval Subsystems
The approval subsystems implement the node-side of the Approval Protocol.
We make a divide between the assignment/voting logic and the distribution logic that distributes assignment certifications and approval votes. The logic in the assignment and voting also informs the GRANDPA voting rule on how to vote.
These subsystems are intended to flag issues and begin participating in live disputes. Dispute subsystems also track all observed votes (backing, approval, and dispute-specific) by all validators on all candidates.