approval-voting: populate session cache in advance (#3954)

* try populating session cache in advance

* remove unused arg

* fmt

* fix compilation

* fix tests

* Revert "fix tests"

This reverts commit e8222b1108e09a39727a38e3b4e4c3061642a213.

* fix tests

* bump dispute window const by 1

* fix tests

polkadot/node/core/approval-voting/src/import.rs

@@ -324,7 +324,7 @@ pub(crate) async fn handle_new_head(
 		}
 	};
 
-	match state.session_window.cache_session_info_for_head(ctx, head, &header).await {
+	match state.session_window.cache_session_info_for_head(ctx, head).await {
 		Err(e) => {
 			tracing::debug!(
 				target: LOG_TARGET,
@@ -1236,7 +1236,7 @@ pub(crate) mod tests {
 					h,
 					RuntimeApiRequest::SessionIndexForChild(c_tx),
 				)) => {
-					assert_eq!(h, parent_hash.clone());
+					assert_eq!(h, hash);
 					let _ = c_tx.send(Ok(session));
 				}
 			);

polkadot/node/core/approval-voting/src/tests.rs

@@ -786,8 +786,8 @@ async fn import_block(
 				RuntimeApiRequest::SessionIndexForChild(s_tx)
 			)
 		) => {
-			let hash = &hashes[number.saturating_sub(1) as usize];
-			assert_eq!(req_block_hash, hash.0.clone());
+			let hash = &hashes[number as usize];
+			assert_eq!(req_block_hash, hash.0);
 			s_tx.send(Ok(number.into())).unwrap();
 		}
 	);

polkadot/node/core/dispute-coordinator/src/real/mod.rs

@@ -478,22 +478,7 @@ async fn handle_new_activations(
 	new_activations: impl IntoIterator<Item = Hash>,
 ) -> Result<(), Error> {
 	for new_leaf in new_activations {
-		let block_header = {
-			let (tx, rx) = oneshot::channel();
-
-			ctx.send_message(ChainApiMessage::BlockHeader(new_leaf, tx)).await;
-
-			match rx.await?? {
-				None => continue,
-				Some(header) => header,
-			}
-		};
-
-		match state
-			.rolling_session_window
-			.cache_session_info_for_head(ctx, new_leaf, &block_header)
-			.await
-		{
+		match state.rolling_session_window.cache_session_info_for_head(ctx, new_leaf).await {
 			Err(e) => {
 				tracing::warn!(
 					target: LOG_TARGET,

polkadot/node/primitives/src/lib.rs

@@ -69,7 +69,8 @@ pub const POV_BOMB_LIMIT: usize = (MAX_POV_SIZE * 4u32) as usize;
 /// On Polkadot this is 1 day, and on Kusama it's 6 hours.
 ///
 /// Number of sessions we want to consider in disputes.
-pub const DISPUTE_WINDOW: SessionIndex = 6;
+/// + 1 for the child's session.
+pub const DISPUTE_WINDOW: SessionIndex = 6 + 1;
 
 /// The cumulative weight of a block in a fork-choice rule.
 pub type BlockWeight = u32;

polkadot/node/subsystem-util/src/rolling_session_window.rs

@@ -19,7 +19,7 @@
 //! This is useful for consensus components which need to stay up-to-date about recent sessions but don't
 //! care about the state of particular blocks.
 
-use polkadot_primitives::v1::{Hash, Header, SessionIndex, SessionInfo};
+use polkadot_primitives::v1::{Hash, SessionIndex, SessionInfo};
 
 use futures::channel::oneshot;
 use polkadot_node_subsystem::{
@@ -131,7 +131,7 @@ impl RollingSessionWindow {
 	}
 
 	/// When inspecting a new import notification, updates the session info cache to match
-	/// the session of the imported block.
+	/// the session of the imported block's child.
 	///
 	/// this only needs to be called on heads where we are directly notified about import, as sessions do
 	/// not change often and import notifications are expected to be typically increasing in session number.
@@ -141,7 +141,6 @@ impl RollingSessionWindow {
 		&mut self,
 		ctx: &mut (impl SubsystemContext + overseer::SubsystemContext),
 		block_hash: Hash,
-		block_header: &Header,
 	) -> Result<SessionWindowUpdate, SessionsUnavailable> {
 		if self.window_size == 0 {
 			return Ok(SessionWindowUpdate::Unchanged)
@@ -150,11 +149,9 @@ impl RollingSessionWindow {
 		let session_index = {
 			let (s_tx, s_rx) = oneshot::channel();
 
-			// The genesis is guaranteed to be at the beginning of the session and its parent state
-			// is non-existent. Therefore if we're at the genesis, we request using its state and
-			// not the parent.
+			// We're requesting session index of a child to populate the cache in advance.
 			ctx.send_message(RuntimeApiMessage::Request(
-				if block_header.number == 0 { block_hash } else { block_header.parent_hash },
+				block_hash,
 				RuntimeApiRequest::SessionIndexForChild(s_tx),
 			))
 			.await;
@@ -289,9 +286,10 @@ mod tests {
 	use assert_matches::assert_matches;
 	use polkadot_node_subsystem::messages::{AllMessages, AvailabilityRecoveryMessage};
 	use polkadot_node_subsystem_test_helpers::make_subsystem_context;
+	use polkadot_primitives::v1::Header;
 	use sp_core::testing::TaskExecutor;
 
-	const TEST_WINDOW_SIZE: SessionIndex = 6;
+	const TEST_WINDOW_SIZE: SessionIndex = 6 + 1;
 
 	fn dummy_session_info(index: SessionIndex) -> SessionInfo {
 		SessionInfo {
@@ -329,9 +327,8 @@ mod tests {
 		let hash = header.hash();
 
 		let test_fut = {
-			let header = header.clone();
 			Box::pin(async move {
-				window.cache_session_info_for_head(&mut ctx, hash, &header).await.unwrap();
+				window.cache_session_info_for_head(&mut ctx, hash).await.unwrap();
 
 				assert_eq!(window.earliest_session, Some(expected_start_session));
 				assert_eq!(
@@ -348,7 +345,7 @@ mod tests {
 					h,
 					RuntimeApiRequest::SessionIndexForChild(s_tx),
 				)) => {
-					assert_eq!(h, header.parent_hash);
+					assert_eq!(h, hash);
 					let _ = s_tx.send(Ok(session));
 				}
 			);
@@ -497,9 +494,8 @@ mod tests {
 		let hash = header.hash();
 
 		let test_fut = {
-			let header = header.clone();
 			Box::pin(async move {
-				let res = window.cache_session_info_for_head(&mut ctx, hash, &header).await;
+				let res = window.cache_session_info_for_head(&mut ctx, hash).await;
 
 				assert!(res.is_err());
 			})
@@ -512,7 +508,7 @@ mod tests {
 					h,
 					RuntimeApiRequest::SessionIndexForChild(s_tx),
 				)) => {
-					assert_eq!(h, header.parent_hash);
+					assert_eq!(h, hash);
 					let _ = s_tx.send(Ok(session));
 				}
 			);
@@ -559,9 +555,8 @@ mod tests {
 		let hash = header.hash();
 
 		let test_fut = {
-			let header = header.clone();
 			Box::pin(async move {
-				window.cache_session_info_for_head(&mut ctx, hash, &header).await.unwrap();
+				window.cache_session_info_for_head(&mut ctx, hash).await.unwrap();
 
 				assert_eq!(window.earliest_session, Some(session));
 				assert_eq!(window.session_info, vec![dummy_session_info(session)]);