Approve multiple candidates with a single signature (#1191)

Initial implementation for the plan discussed here: #701
Built on top of #1178
v0: paritytech/polkadot#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:
#635 &
#742
- [x] Final versi burn-in before merging

---------

Signed-off-by: Alexandru Gheorghe <alexandru.gheorghe@parity.io>

.gitlab/pipeline/zombienet/polkadot.yml

@@ -131,6 +131,14 @@ zombienet-polkadot-functional-0008-dispute-old-finalized:
       --local-dir="${LOCAL_DIR}/functional"
       --test="0008-dispute-old-finalized.zndsl"
 
+zombienet-polkadot-functional-0009-approval-voting-coalescing:
+  extends:
+    - .zombienet-polkadot-common
+  script:
+    - /home/nonroot/zombie-net/scripts/ci/run-test-local-env-manager.sh
+      --local-dir="${LOCAL_DIR}/functional"
+      --test="0009-approval-voting-coalescing.zndsl"
+
 zombienet-polkadot-smoke-0001-parachains-smoke-test:
   extends:
     - .zombienet-polkadot-common

cumulus/client/relay-chain-minimal-node/src/blockchain_rpc_client.rs

@@ -24,7 +24,7 @@ use polkadot_overseer::{ChainApiBackend, RuntimeApiSubsystemClient};
 use polkadot_primitives::{
 	async_backing::{AsyncBackingParams, BackingState},
 	slashing,
-	vstaging::NodeFeatures,
+	vstaging::{ApprovalVotingParams, NodeFeatures},
 };
 use sc_authority_discovery::{AuthorityDiscovery, Error as AuthorityDiscoveryError};
 use sc_client_api::AuxStore;
@@ -427,6 +427,18 @@ impl RuntimeApiSubsystemClient for BlockChainRpcClient {
 		Ok(self.rpc_client.parachain_host_para_backing_state(at, para_id).await?)
 	}
 
+	/// Approval voting configuration parameters
+	async fn approval_voting_params(
+		&self,
+		at: Hash,
+		session_index: polkadot_primitives::SessionIndex,
+	) -> Result<ApprovalVotingParams, ApiError> {
+		Ok(self
+			.rpc_client
+			.parachain_host_staging_approval_voting_params(at, session_index)
+			.await?)
+	}
+
 	async fn node_features(&self, at: Hash) -> Result<NodeFeatures, ApiError> {
 		Ok(self.rpc_client.parachain_host_node_features(at).await?)
 	}

cumulus/client/relay-chain-rpc-interface/src/rpc_client.rs

@@ -32,7 +32,7 @@ use cumulus_primitives_core::{
 	relay_chain::{
 		async_backing::{AsyncBackingParams, BackingState},
 		slashing,
-		vstaging::NodeFeatures,
+		vstaging::{ApprovalVotingParams, NodeFeatures},
 		BlockNumber, CandidateCommitments, CandidateEvent, CandidateHash,
 		CommittedCandidateReceipt, CoreState, DisputeState, ExecutorParams, GroupRotationInfo,
 		Hash as RelayHash, Header as RelayHeader, InboundHrmpMessage, OccupiedCoreAssumption,
@@ -625,6 +625,19 @@ impl RelayChainRpcClient {
 	}
 
 	#[allow(missing_docs)]
+	pub async fn parachain_host_staging_approval_voting_params(
+		&self,
+		at: RelayHash,
+		_session_index: SessionIndex,
+	) -> Result<ApprovalVotingParams, RelayChainError> {
+		self.call_remote_runtime_function(
+			"ParachainHost_staging_approval_voting_params",
+			at,
+			None::<()>,
+		)
+		.await
+	}
+
 	pub async fn parachain_host_para_backing_state(
 		&self,
 		at: RelayHash,

cumulus/parachains/integration-tests/emulated/chains/relays/rococo/src/lib.rs

@@ -24,7 +24,7 @@ use emulated_integration_tests_common::{
 
 // Rococo declaration
 decl_test_relay_chains! {
-	#[api_version(9)]
+	#[api_version(10)]
 	pub struct Rococo {
 		genesis = genesis::genesis(),
 		on_init = (),

cumulus/parachains/integration-tests/emulated/chains/relays/westend/src/lib.rs

@@ -24,7 +24,7 @@ use emulated_integration_tests_common::{
 
 // Westend declaration
 decl_test_relay_chains! {
-	#[api_version(9)]
+	#[api_version(10)]
 	pub struct Westend {
 		genesis = genesis::genesis(),
 		on_init = (),

polkadot/Cargo.toml

@@ -64,7 +64,6 @@ jemalloc-allocator = [
 	"polkadot-node-core-pvf/jemalloc-allocator",
 	"polkadot-overseer/jemalloc-allocator",
 ]
-network-protocol-staging = ["polkadot-cli/network-protocol-staging"]
 
 
 # Enables timeout-based tests supposed to be run only in CI environment as they may be flaky

polkadot/cli/Cargo.toml

@@ -75,5 +75,3 @@ runtime-metrics = [
 	"polkadot-node-metrics/runtime-metrics",
 	"service/runtime-metrics",
 ]
-
-network-protocol-staging = ["service/network-protocol-staging"]