Optimize level monitor reconstruction (#2461)

* Optimize level monitor reconstruction

* Fix counter increment and test

* Struct comments as doc comments

cumulus/client/consensus/common/src/level_monitor.rs

@@ -15,7 +15,7 @@
 // along with Cumulus.  If not, see <http://www.gnu.org/licenses/>.
 
 use sc_client_api::{blockchain::Backend as _, Backend, HeaderBackend as _};
-use sp_blockchain::{HashAndNumber, TreeRoute};
+use sp_blockchain::{HashAndNumber, HeaderMetadata, TreeRoute};
 use sp_runtime::traits::{Block as BlockT, NumberFor, One, Saturating, UniqueSaturatedInto, Zero};
 use std::{
 	collections::{HashMap, HashSet},
@@ -48,17 +48,17 @@ pub enum LevelLimit {
 
 /// Support structure to constrain the number of leaves at each level.
 pub struct LevelMonitor<Block: BlockT, BE> {
-	// Max number of leaves for each level.
+	/// Max number of leaves for each level.
 	level_limit: usize,
-	// Monotonic counter used to keep track of block freshness.
+	/// Monotonic counter used to keep track of block freshness.
 	pub(crate) import_counter: NumberFor<Block>,
-	// Map between blocks hashes and freshness.
+	/// Map between blocks hashes and freshness.
 	pub(crate) freshness: HashMap<Block::Hash, NumberFor<Block>>,
-	// Blockchain levels cache.
+	/// Blockchain levels cache.
 	pub(crate) levels: HashMap<NumberFor<Block>, HashSet<Block::Hash>>,
-	// Lower level number stored by the levels map.
+	/// Lower level number stored by the levels map.
 	lowest_level: NumberFor<Block>,
-	// Backend reference to remove blocks on level saturation.
+	/// Backend reference to remove blocks on level saturation.
 	backend: Arc<BE>,
 }
 
@@ -96,7 +96,9 @@ where
 	///
 	/// Level limits are not enforced during this phase.
 	fn restore(&mut self) {
+		const ERR_MSG: &str = "route from finalized to leaf should be available; qed";
 		let info = self.backend.blockchain().info();
+
 		log::debug!(
 			target: "parachain",
 			"Restoring chain level monitor from last finalized block: {} {}",
@@ -105,30 +107,24 @@ where
 
 		self.lowest_level = info.finalized_number;
 		self.import_counter = info.finalized_number;
-		self.block_imported(info.finalized_number, info.finalized_hash);
-
-		let mut counter_max = info.finalized_number;
 
 		for leaf in self.backend.blockchain().leaves().unwrap_or_default() {
-			let route =
-				sp_blockchain::tree_route(self.backend.blockchain(), info.finalized_hash, leaf)
-					.expect("Route from finalized to leaf should be available; qed");
-			if !route.retracted().is_empty() {
-				continue
-			}
-			route.enacted().iter().for_each(|elem| {
-				if !self.freshness.contains_key(&elem.hash) {
-					// Use the block height value as the freshness.
-					self.import_counter = elem.number;
-					self.block_imported(elem.number, elem.hash);
+			let mut meta = self.backend.blockchain().header_metadata(leaf).expect(ERR_MSG);
+
+			self.import_counter = self.import_counter.max(meta.number);
+
+			// Populate the monitor until we don't hit an already imported branch
+			while !self.freshness.contains_key(&meta.hash) {
+				self.freshness.insert(meta.hash, meta.number);
+				self.levels.entry(meta.number).or_default().insert(meta.hash);
+				if meta.number <= self.lowest_level {
+					break
 				}
-			});
-			counter_max = std::cmp::max(self.import_counter, counter_max);
+				meta = self.backend.blockchain().header_metadata(meta.parent).expect(ERR_MSG);
+			}
 		}
 
-		log::debug!(target: "parachain", "Restored chain level monitor up to height {}", counter_max);
-
-		self.import_counter = counter_max;
+		log::debug!(target: "parachain", "Restored chain level monitor up to height {}", self.import_counter);
 	}
 
 	/// Check and enforce the limit bound at the given height.
@@ -355,9 +351,9 @@ where
 
 	/// Add a new imported block information to the monitor.
 	pub fn block_imported(&mut self, number: NumberFor<Block>, hash: Block::Hash) {
+		self.import_counter += One::one();
 		self.freshness.insert(hash, self.import_counter);
 		self.levels.entry(number).or_default().insert(hash);
-		self.import_counter += One::one();
 
 		// Do cleanup once in a while, we are allowed to have some obsolete information.
 		let finalized_num = self.backend.blockchain().info().finalized_number;

cumulus/client/consensus/common/src/tests.rs

@@ -765,6 +765,12 @@ fn restore_limit_monitor() {
 		LevelLimit::Some(LEVEL_LIMIT),
 	);
 
+	let monitor_sd = para_import.monitor.clone().unwrap();
+
+	let monitor = monitor_sd.shared_data();
+	assert_eq!(monitor.import_counter, 3);
+	std::mem::drop(monitor);
+
 	let block13 = build_and_import_block_ext(
 		&*client,
 		BlockOrigin::Own,
@@ -783,14 +789,13 @@ fn restore_limit_monitor() {
 	let expected = vec![blocks1[1].header.hash(), block13.header.hash()];
 	assert_eq!(leaves, expected);
 
-	let monitor = para_import.monitor.unwrap();
-	let monitor = monitor.shared_data();
-	assert_eq!(monitor.import_counter, 5);
+	let monitor = monitor_sd.shared_data();
+	assert_eq!(monitor.import_counter, 4);
 	assert!(monitor.levels.iter().all(|(number, hashes)| {
 		hashes
 			.iter()
 			.filter(|hash| **hash != block13.header.hash())
 			.all(|hash| *number == *monitor.freshness.get(hash).unwrap())
 	}));
-	assert_eq!(*monitor.freshness.get(&block13.header.hash()).unwrap(), monitor.import_counter - 1);
+	assert_eq!(*monitor.freshness.get(&block13.header.hash()).unwrap(), monitor.import_counter);
 }