Add storage cache for child trie and notification internals (#2639)

* child cache, and test failing notifications

* fix tests and no listen child on top wildcard

* remove useless method

* bump impl version

* Update core/client/src/notifications.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update core/client/src/notifications.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update core/client/src/notifications.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* Update core/client/src/notifications.rs

Co-Authored-By: Tomasz Drwięga <tomusdrw@users.noreply.github.com>

* factoring notification methods to remove some redundant code.

* test child sub removal

* HStorage implementation and some type alias.

* Remove HStorage cache: does not fit

* fix removal

* Make cache use byte length (shared) instead of number of kv

* Make use of hashes cache in rpc

* applying ratio on different lru caches

* Fix format

* break a line

* Remove per element overhead of lru cache.

* typo

substrate/Cargo.lock

@@ -4023,8 +4023,8 @@ dependencies = [
  "kvdb 0.1.0 (git+https://github.com/paritytech/parity-common?rev=b0317f649ab2c665b7987b8475878fc4d2e1f81d)",
  "kvdb-memorydb 0.1.0 (git+https://github.com/paritytech/parity-common?rev=b0317f649ab2c665b7987b8475878fc4d2e1f81d)",
  "kvdb-rocksdb 0.1.4 (git+https://github.com/paritytech/parity-common?rev=b0317f649ab2c665b7987b8475878fc4d2e1f81d)",
+ "linked-hash-map 0.5.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "log 0.4.6 (registry+https://github.com/rust-lang/crates.io-index)",
- "lru-cache 0.1.2 (registry+https://github.com/rust-lang/crates.io-index)",
  "parity-codec 3.5.1 (registry+https://github.com/rust-lang/crates.io-index)",
  "parking_lot 0.8.0 (registry+https://github.com/rust-lang/crates.io-index)",
  "sr-primitives 2.0.0",

substrate/core/client/db/Cargo.toml

@@ -11,7 +11,7 @@ kvdb = { git = "https://github.com/paritytech/parity-common", rev="b0317f649ab2c
 # FIXME replace with release as soon as our rocksdb changes are released upstream https://github.com/paritytech/parity-common/issues/88
 kvdb-rocksdb = { git = "https://github.com/paritytech/parity-common", rev="b0317f649ab2c665b7987b8475878fc4d2e1f81d", optional = true }
 kvdb-memorydb = { git = "https://github.com/paritytech/parity-common", rev="b0317f649ab2c665b7987b8475878fc4d2e1f81d" }
-lru-cache = "0.1.1"
+linked-hash-map = "0.5"
 hash-db = { version = "0.12" }
 primitives = { package = "substrate-primitives", path = "../../primitives" }
 runtime_primitives = { package = "sr-primitives", path = "../../sr-primitives" }

substrate/core/client/db/src/lib.rs

@@ -38,6 +38,7 @@ use std::collections::HashMap;
 use client::backend::NewBlockState;
 use client::blockchain::HeaderBackend;
 use client::ExecutionStrategies;
+use client::backend::{StorageCollection, ChildStorageCollection};
 use parity_codec::{Decode, Encode};
 use hash_db::Hasher;
 use kvdb::{KeyValueDB, DBTransaction};
@@ -69,6 +70,9 @@ use client::in_mem::Backend as InMemoryBackend;
 const CANONICALIZATION_DELAY: u64 = 4096;
 const MIN_BLOCKS_TO_KEEP_CHANGES_TRIES_FOR: u32 = 32768;
 
+/// Default value for storage cache child ratio.
+const DEFAULT_CHILD_RATIO: (usize, usize) = (1, 10);
+
 /// DB-backed patricia trie state, transaction type is an overlay of changes to commit.
 pub type DbState = state_machine::TrieBackend<Arc<dyn state_machine::Storage<Blake2Hasher>>, Blake2Hasher>;
 
@@ -169,6 +173,8 @@ pub struct DatabaseSettings {
 	pub cache_size: Option<usize>,
 	/// State cache size.
 	pub state_cache_size: usize,
+	/// Ratio of cache size dedicated to child tries.
+	pub state_cache_child_ratio: Option<(usize, usize)>,
 	/// Path to the database.
 	pub path: PathBuf,
 	/// Pruning mode.
@@ -181,7 +187,10 @@ pub fn new_client<E, S, Block, RA>(
 	executor: E,
 	genesis_storage: S,
 	execution_strategies: ExecutionStrategies,
-) -> Result<client::Client<Backend<Block>, client::LocalCallExecutor<Backend<Block>, E>, Block, RA>, client::error::Error>
+) -> Result<
+	client::Client<Backend<Block>,
+	client::LocalCallExecutor<Backend<Block>, E>, Block, RA>, client::error::Error
+>
 	where
 		Block: BlockT<Hash=H256>,
 		E: CodeExecutor<Blake2Hasher> + RuntimeInfo,
@@ -363,7 +372,8 @@ impl<Block: BlockT> client::blockchain::ProvideCache<Block> for BlockchainDb<Blo
 pub struct BlockImportOperation<Block: BlockT, H: Hasher> {
 	old_state: CachingState<Blake2Hasher, RefTrackingState<Block>, Block>,
 	db_updates: PrefixedMemoryDB<H>,
-	storage_updates: Vec<(Vec<u8>, Option<Vec<u8>>)>,
+	storage_updates: StorageCollection,
+	child_storage_updates: ChildStorageCollection,
 	changes_trie_updates: MemoryDB<H>,
 	pending_block: Option<PendingBlock<Block>>,
 	aux_ops: Vec<(Vec<u8>, Option<Vec<u8>>)>,
@@ -455,8 +465,13 @@ where Block: BlockT<Hash=H256>,
 		Ok(())
 	}
 
-	fn update_storage(&mut self, update: Vec<(Vec<u8>, Option<Vec<u8>>)>) -> Result<(), client::error::Error> {
+	fn update_storage(
+		&mut self,
+		update: StorageCollection,
+		child_update: ChildStorageCollection,
+	) -> Result<(), client::error::Error> {
 		self.storage_updates = update;
+		self.child_storage_updates = child_update;
 		Ok(())
 	}
 
@@ -670,14 +685,14 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 	#[cfg(feature = "kvdb-rocksdb")]
 	fn new_inner(config: DatabaseSettings, canonicalization_delay: u64) -> Result<Self, client::error::Error> {
 		let db = crate::utils::open_database(&config, columns::META, "full")?;
-		Backend::from_kvdb(db as Arc<_>, config.pruning, canonicalization_delay, config.state_cache_size)
+		Backend::from_kvdb(db as Arc<_>, canonicalization_delay, &config)
 	}
 
 	#[cfg(not(feature = "kvdb-rocksdb"))]
 	fn new_inner(config: DatabaseSettings, canonicalization_delay: u64) -> Result<Self, client::error::Error> {
 		log::warn!("Running without the RocksDB feature. The database will NOT be saved.");
 		let db = Arc::new(kvdb_memorydb::create(crate::utils::NUM_COLUMNS));
-		Backend::from_kvdb(db as Arc<_>, config.pruning, canonicalization_delay, config.state_cache_size)
+		Backend::from_kvdb(db as Arc<_>, canonicalization_delay, &config)
 	}
 
 	#[cfg(any(test, feature = "test-helpers"))]
@@ -685,26 +700,36 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 		use utils::NUM_COLUMNS;
 
 		let db = Arc::new(::kvdb_memorydb::create(NUM_COLUMNS));
+		Self::new_test_db(keep_blocks, canonicalization_delay, db as Arc<_>)
+	}
 
+	#[cfg(any(test, feature = "test-helpers"))]
+	pub fn new_test_db(keep_blocks: u32, canonicalization_delay: u64, db: Arc<KeyValueDB>) -> Self {
+
+		let db_setting = DatabaseSettings {
+			cache_size: None,
+			state_cache_size: 16777216,
+			state_cache_child_ratio: Some((50, 100)),
+			path: Default::default(),
+			pruning: PruningMode::keep_blocks(keep_blocks),
+		};
 		Backend::from_kvdb(
-			db as Arc<_>,
-			PruningMode::keep_blocks(keep_blocks),
+			db,
 			canonicalization_delay,
-			16777216,
+			&db_setting,
 		).expect("failed to create test-db")
 	}
 
 	fn from_kvdb(
 		db: Arc<dyn KeyValueDB>,
-		pruning: PruningMode,
 		canonicalization_delay: u64,
-		state_cache_size: usize
+		config: &DatabaseSettings
 	) -> Result<Self, client::error::Error> {
-		let is_archive_pruning = pruning.is_archive();
+		let is_archive_pruning = config.pruning.is_archive();
 		let blockchain = BlockchainDb::new(db.clone())?;
 		let meta = blockchain.meta.clone();
 		let map_e = |e: state_db::Error<io::Error>| ::client::error::Error::from(format!("State database error: {:?}", e));
-		let state_db: StateDb<_, _> = StateDb::new(pruning, &StateMetaDb(&*db)).map_err(map_e)?;
+		let state_db: StateDb<_, _> = StateDb::new(config.pruning.clone(), &StateMetaDb(&*db)).map_err(map_e)?;
 		let storage_db = StorageDb {
 			db: db.clone(),
 			state_db,
@@ -722,7 +747,10 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 			changes_trie_config: Mutex::new(None),
 			blockchain,
 			canonicalization_delay,
-			shared_cache: new_shared_cache(state_cache_size),
+			shared_cache: new_shared_cache(
+				config.state_cache_size,
+				config.state_cache_child_ratio.unwrap_or(DEFAULT_CHILD_RATIO),
+			),
 			import_lock: Default::default(),
 		})
 	}
@@ -1094,6 +1122,7 @@ impl<Block: BlockT<Hash=H256>> Backend<Block> {
 				&enacted,
 				&retracted,
 				operation.storage_updates,
+				operation.child_storage_updates,
 				Some(hash),
 				Some(number),
 				|| is_best,
@@ -1200,6 +1229,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 			old_state,
 			db_updates: PrefixedMemoryDB::default(),
 			storage_updates: Default::default(),
+			child_storage_updates: Default::default(),
 			changes_trie_updates: MemoryDB::default(),
 			aux_ops: Vec::new(),
 			finalized_blocks: Vec::new(),
@@ -1348,7 +1378,7 @@ impl<Block> client::backend::Backend<Block, Blake2Hasher> for Backend<Block> whe
 	fn destroy_state(&self, state: Self::State) -> Result<(), client::error::Error> {
 		if let Some(hash) = state.cache.parent_hash.clone() {
 			let is_best = || self.blockchain.meta.read().best_hash == hash;
-			state.release().sync_cache(&[], &[], vec![], None, None, is_best);
+			state.release().sync_cache(&[], &[], vec![], vec![], None, None, is_best);
 		}
 		Ok(())
 	}
@@ -1473,7 +1503,7 @@ mod tests {
 			db.storage.db.clone()
 		};
 
-		let backend = Backend::<Block>::from_kvdb(backing, PruningMode::keep_blocks(1), 0, 16777216).unwrap();
+		let backend = Backend::<Block>::new_test_db(1, 0, backing);
 		assert_eq!(backend.blockchain().info().best_number, 9);
 		for i in 0..10 {
 			assert!(backend.blockchain().hash(i).unwrap().is_some())

substrate/core/client/db/src/storage_cache.rs

@@ -19,60 +19,158 @@
 use std::collections::{VecDeque, HashSet, HashMap};
 use std::sync::Arc;
 use parking_lot::{Mutex, RwLock, RwLockUpgradableReadGuard};
-use lru_cache::LruCache;
+use linked_hash_map::{LinkedHashMap, Entry};
 use hash_db::Hasher;
 use runtime_primitives::traits::{Block, Header};
 use state_machine::{backend::Backend as StateBackend, TrieBackend};
 use log::trace;
-
+use super::{StorageCollection, ChildStorageCollection};
+use std::hash::Hash as StdHash;
 const STATE_CACHE_BLOCKS: usize = 12;
 
 type StorageKey = Vec<u8>;
+type ChildStorageKey = (Vec<u8>, Vec<u8>);
 type StorageValue = Vec<u8>;
 
 /// Shared canonical state cache.
 pub struct Cache<B: Block, H: Hasher> {
 	/// Storage cache. `None` indicates that key is known to be missing.
-	storage: LruCache<StorageKey, Option<StorageValue>>,
+	lru_storage: LRUMap<StorageKey, Option<StorageValue>>,
 	/// Storage hashes cache. `None` indicates that key is known to be missing.
-	hashes: LruCache<StorageKey, Option<H::Out>>,
+	lru_hashes: LRUMap<StorageKey, OptionHOut<H::Out>>,
+	/// Storage cache for child trie. `None` indicates that key is known to be missing.
+	lru_child_storage: LRUMap<ChildStorageKey, Option<StorageValue>>,
 	/// Information on the modifications in recently committed blocks; specifically which keys
 	/// changed in which block. Ordered by block number.
 	modifications: VecDeque<BlockChanges<B::Header>>,
-	/// Maximum cache size available, in Bytes.
-	shared_cache_size: usize,
-	/// Used storage size, in Bytes.
-	storage_used_size: usize,
+}
+
+struct LRUMap<K, V>(LinkedHashMap<K, V>, usize, usize);
+
+/// Internal trait similar to `heapsize` but using
+/// a simply estimation.
+///
+/// This should not be made public, it is implementation
+/// detail trait. If it need to become public please
+/// consider using `malloc_size_of`.
+trait EstimateSize {
+	/// Return a size estimation of additional size needed
+	/// to cache this struct (in bytes).
+	fn estimate_size(&self) -> usize;
+}
+
+impl EstimateSize for Vec<u8> {
+	fn estimate_size(&self) -> usize {
+		self.capacity()
+	}
+}
+
+impl EstimateSize for Option<Vec<u8>> {
+	fn estimate_size(&self) -> usize {
+		self.as_ref().map(|v|v.capacity()).unwrap_or(0)
+	}
+}
+
+struct OptionHOut<T: AsRef<[u8]>>(Option<T>);
+
+impl<T: AsRef<[u8]>> EstimateSize for OptionHOut<T> {
+	fn estimate_size(&self) -> usize {
+		// capacity would be better
+		self.0.as_ref().map(|v|v.as_ref().len()).unwrap_or(0)
+	}
+}
+
+impl<T: EstimateSize> EstimateSize for (T, T) {
+	fn estimate_size(&self) -> usize {
+		self.0.estimate_size() + self.1.estimate_size()
+	}
+}
+
+impl<K: EstimateSize + Eq + StdHash, V: EstimateSize> LRUMap<K, V> {
+	fn remove(&mut self, k: &K) {
+		let map = &mut self.0;
+		let storage_used_size = &mut self.1;
+		if let Some(v) = map.remove(k) {
+			*storage_used_size -= k.estimate_size();
+			*storage_used_size -= v.estimate_size();
+		}
+	}
+
+	fn add(&mut self, k: K, v: V) {
+		let lmap = &mut self.0;
+		let storage_used_size = &mut self.1;
+		let limit = self.2;
+		let klen = k.estimate_size();
+		*storage_used_size += v.estimate_size();
+		// TODO assert k v size fit into limit?? to avoid insert remove?
+		match lmap.entry(k) {
+			Entry::Occupied(mut entry) => {
+				// note that in this case we are not running pure lru as 
+				// it would require to remove first
+				*storage_used_size -= entry.get().estimate_size();
+				entry.insert(v);
+			},
+			Entry::Vacant(entry) => {
+				*storage_used_size += klen;
+				entry.insert(v);
+			},
+		};
+
+		while *storage_used_size > limit {
+			if let Some((k,v)) = lmap.pop_front() {
+				*storage_used_size -= k.estimate_size();
+				*storage_used_size -= v.estimate_size();
+			} else {
+				// can happen fairly often as we get value from multiple lru
+				// and only remove from a single lru
+				break;
+			}
+		}
+	}
+
+	fn get<Q:?Sized>(&mut self, k: &Q) -> Option<&mut V>
+		where K: std::borrow::Borrow<Q>,
+			Q: StdHash + Eq {
+		self.0.get_refresh(k)
+	}
+
+	fn used_size(&self) -> usize {
+		self.1
+	}
+	fn clear(&mut self) {
+		self.0.clear();
+		self.1 = 0;
+	}
+
 }
  
 impl<B: Block, H: Hasher> Cache<B, H> {
 	/// Returns the used memory size of the storage cache in bytes.
 	pub fn used_storage_cache_size(&self) -> usize {
-		self.storage_used_size
+		self.lru_storage.used_size()
+			+ self.lru_child_storage.used_size()
+			//  ignore small hashes storage and self.lru_hashes.used_size()
 	}
 }
 
 pub type SharedCache<B, H> = Arc<Mutex<Cache<B, H>>>;
 
-/// Create new shared cache instance with given max memory usage.
-pub fn new_shared_cache<B: Block, H: Hasher>(shared_cache_size: usize) -> SharedCache<B, H> {
-	// we need to supply a max capacity to `LruCache`, but since
-	// we don't have any idea how large the size of each item
-	// that is stored will be we can't calculate the max amount
-	// of items properly from `shared_cache_size`.
-	//
-	// what we do instead is to supply `shared_cache_size` as the
-	// max upper bound capacity (this would only be reached if each
-	// item would be one byte).
-	// each time we store to the storage cache we verify the memory
-	// constraint and pop the lru item if space needs to be freed.
+/// Fix lru storage size for hash (small 64ko).
+const FIX_LRU_HASH_SIZE: usize = 65_536;
 
+/// Create a new shared cache instance with given max memory usage.
+pub fn new_shared_cache<B: Block, H: Hasher>(
+	shared_cache_size: usize,
+	child_ratio: (usize, usize),
+) -> SharedCache<B, H> {
+	let top = child_ratio.1.saturating_sub(child_ratio.0);
 	Arc::new(Mutex::new(Cache {
-		storage: LruCache::new(shared_cache_size),
-		hashes: LruCache::new(shared_cache_size),
+		lru_storage: LRUMap(LinkedHashMap::new(), 0,
+			shared_cache_size * top / child_ratio.1),
+		lru_hashes: LRUMap(LinkedHashMap::new(), 0, FIX_LRU_HASH_SIZE),
+		lru_child_storage: LRUMap(LinkedHashMap::new(), 0,
+			shared_cache_size * child_ratio.0 / child_ratio.1),
 		modifications: VecDeque::new(),
-		shared_cache_size: shared_cache_size,
-		storage_used_size: 0,
 	}))
 }
 
@@ -87,6 +185,8 @@ struct BlockChanges<B: Header> {
 	parent: B::Hash,
 	/// A set of modified storage keys.
 	storage: HashSet<StorageKey>,
+	/// A set of modified child storage keys.
+	child_storage: HashSet<ChildStorageKey>,
 	/// Block is part of the canonical chain.
 	is_canon: bool,
 }
@@ -97,6 +197,8 @@ struct LocalCache<H: Hasher> {
 	storage: HashMap<StorageKey, Option<StorageValue>>,
 	/// Storage hashes cache. `None` indicates that key is known to be missing.
 	hashes: HashMap<StorageKey, Option<H::Out>>,
+	/// Child storage cache. `None` indicates that key is known to be missing.
+	child_storage: HashMap<ChildStorageKey, Option<StorageValue>>,
 }
 
 /// Cache changes.
@@ -135,7 +237,8 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 		&mut self,
 		enacted: &[B::Hash],
 		retracted: &[B::Hash],
-		changes: Vec<(StorageKey, Option<StorageValue>)>,
+		changes: StorageCollection,
+		child_changes: ChildStorageCollection,
 		commit_hash: Option<B::Hash>,
 		commit_number: Option<<B::Header as Header>::Number>,
 		is_best: F,
@@ -155,7 +258,11 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 					m.is_canon = true;
 					for a in &m.storage {
 						trace!("Reverting enacted key {:?}", a);
-						CacheChanges::<H, B>::storage_remove(&mut cache.storage, a, &mut cache.storage_used_size);
+						cache.lru_storage.remove(a);
+					}
+					for a in &m.child_storage {
+						trace!("Reverting enacted child key {:?}", a);
+						cache.lru_child_storage.remove(a);
 					}
 					false
 				} else {
@@ -171,7 +278,11 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 					m.is_canon = false;
 					for a in &m.storage {
 						trace!("Retracted key {:?}", a);
-						CacheChanges::<H, B>::storage_remove(&mut cache.storage, a, &mut cache.storage_used_size);
+						cache.lru_storage.remove(a);
+					}
+					for a in &m.child_storage {
+						trace!("Retracted child key {:?}", a);
+						cache.lru_child_storage.remove(a);
 					}
 					false
 				} else {
@@ -182,7 +293,9 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 		if clear {
 			// We don't know anything about the block; clear everything
 			trace!("Wiping cache");
-			cache.storage.clear();
+			cache.lru_storage.clear();
+			cache.lru_child_storage.clear();
+			cache.lru_hashes.clear();
 			cache.modifications.clear();
 		}
 
@@ -192,12 +305,21 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 		if let Some(_) = self.parent_hash {
 			let mut local_cache = self.local_cache.write();
 			if is_best {
-				trace!("Committing {} local, {} hashes, {} modified entries", local_cache.storage.len(), local_cache.hashes.len(), changes.len());
+				trace!(
+					"Committing {} local, {} hashes, {} modified root entries, {} modified child entries",
+					local_cache.storage.len(),
+					local_cache.hashes.len(),
+					changes.len(),
+					child_changes.iter().map(|v|v.1.len()).sum::<usize>(),
+				);
 				for (k, v) in local_cache.storage.drain() {
-					CacheChanges::<H, B>::storage_insert(cache, k, v);
+					cache.lru_storage.add(k, v);
+				}
+				for (k, v) in local_cache.child_storage.drain() {
+					cache.lru_child_storage.add(k, v);
 				}
 				for (k, v) in local_cache.hashes.drain() {
-					cache.hashes.insert(k, v);
+					cache.lru_hashes.add(k, OptionHOut(v));
 				}
 			}
 		}
@@ -210,16 +332,28 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 				cache.modifications.pop_back();
 			}
 			let mut modifications = HashSet::new();
+			let mut child_modifications = HashSet::new();
+			child_changes.into_iter().for_each(|(sk, changes)|
 				for (k, v) in changes.into_iter() {
-				modifications.insert(k.clone());
+					let k = (sk.clone(), k);
 					if is_best {
-					cache.hashes.remove(&k);
-					CacheChanges::<H, B>::storage_insert(cache, k, v);
+						cache.lru_child_storage.add(k.clone(), v);
 					}
+					child_modifications.insert(k);
 				}
+			);
+			for (k, v) in changes.into_iter() {
+				if is_best {
+					cache.lru_hashes.remove(&k);
+					cache.lru_storage.add(k.clone(), v);
+				}
+				modifications.insert(k);
+			}
+
 			// Save modified storage. These are ordered by the block number.
 			let block_changes = BlockChanges {
 				storage: modifications,
+				child_storage: child_modifications,
 				number: *number,
 				hash: hash.clone(),
 				is_canon: is_best,
@@ -238,32 +372,6 @@ impl<H: Hasher, B: Block> CacheChanges<H, B> {
 		}
 	}
 
-	fn storage_insert(cache: &mut Cache<B, H>, k: StorageValue, v: Option<StorageValue>) {
-		if let Some(v_) = &v {
-			while cache.storage_used_size + v_.len() > cache.shared_cache_size {
-				// pop until space constraint satisfied
-				match cache.storage.remove_lru() {
-					Some((_, Some(popped_v))) =>
-						cache.storage_used_size = cache.storage_used_size - popped_v.len(),
-						Some((_, None)) => continue,
-						None => break,
-				};
-			}
-			cache.storage_used_size = cache.storage_used_size + v_.len();
-		}
-		cache.storage.insert(k, v);
-	}
-
-	fn storage_remove(
-		storage: &mut LruCache<StorageKey, Option<StorageValue>>,
-		k: &StorageKey,
-		storage_used_size: &mut usize,
-		) {
-		let v = storage.remove(k);
-		if let Some(Some(v_)) = v {
-			*storage_used_size = *storage_used_size - v_.len();
-		}
-	}
 }
 
 impl<H: Hasher, S: StateBackend<H>, B: Block> CachingState<H, S, B> {
@@ -276,6 +384,7 @@ impl<H: Hasher, S: StateBackend<H>, B: Block> CachingState<H, S, B> {
 				local_cache: RwLock::new(LocalCache {
 					storage: Default::default(),
 					hashes: Default::default(),
+					child_storage: Default::default(),
 				}),
 				parent_hash: parent_hash,
 			},
@@ -285,7 +394,8 @@ impl<H: Hasher, S: StateBackend<H>, B: Block> CachingState<H, S, B> {
 	/// Check if the key can be returned from cache by matching current block parent hash against canonical
 	/// state and filtering out entries modified in later blocks.
 	fn is_allowed(
-		key: &[u8],
+		key: Option<&[u8]>,
+		child_key: Option<&ChildStorageKey>,
 		parent_hash: &Option<B::Hash>,
 		modifications:
 		&VecDeque<BlockChanges<B::Header>>
@@ -314,11 +424,19 @@ impl<H: Hasher, S: StateBackend<H>, B: Block> CachingState<H, S, B> {
 				}
 				parent = &m.parent;
 			}
+			if let Some(key) = key {
 				if m.storage.contains(key) {
 					trace!("Cache lookup skipped for {:?}: modified in a later block", key);
 					return false;
 				}
 			}
+			if let Some(child_key) = child_key {
+				if m.child_storage.contains(child_key) {
+					trace!("Cache lookup skipped for {:?}: modified in a later block", child_key);
+					return false;
+				}
+			}
+		}
 		trace!("Cache lookup skipped for {:?}: parent hash is unknown", key);
 		false
 	}
@@ -336,13 +454,14 @@ impl<H: Hasher, S: StateBackend<H>, B:Block> StateBackend<H> for CachingState<H,
 
 	fn storage(&self, key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
 		let local_cache = self.cache.local_cache.upgradable_read();
+		// Note that local cache makes that lru is not refreshed
 		if let Some(entry) = local_cache.storage.get(key).cloned() {
 			trace!("Found in local cache: {:?}", key);
 			return Ok(entry)
 		}
 		let mut cache = self.cache.shared_cache.lock();
-		if Self::is_allowed(key, &self.cache.parent_hash, &cache.modifications) {
-			if let Some(entry) = cache.storage.get_mut(key).map(|a| a.clone()) {
+		if Self::is_allowed(Some(key), None, &self.cache.parent_hash, &cache.modifications) {
+			if let Some(entry) = cache.lru_storage.get(key).map(|a| a.clone()) {
 				trace!("Found in shared cache: {:?}", key);
 				return Ok(entry)
 			}
@@ -360,8 +479,8 @@ impl<H: Hasher, S: StateBackend<H>, B:Block> StateBackend<H> for CachingState<H,
 			return Ok(entry)
 		}
 		let mut cache = self.cache.shared_cache.lock();
-		if Self::is_allowed(key, &self.cache.parent_hash, &cache.modifications) {
-			if let Some(entry) = cache.hashes.get_mut(key).map(|a| a.clone()) {
+		if Self::is_allowed(Some(key), None, &self.cache.parent_hash, &cache.modifications) {
+			if let Some(entry) = cache.lru_hashes.get(key).map(|a| a.0.clone()) {
 				trace!("Found hash in shared cache: {:?}", key);
 				return Ok(entry)
 			}
@@ -373,7 +492,23 @@ impl<H: Hasher, S: StateBackend<H>, B:Block> StateBackend<H> for CachingState<H,
 	}
 
 	fn child_storage(&self, storage_key: &[u8], key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error> {
-		self.state.child_storage(storage_key, key)
+		let key = (storage_key.to_vec(), key.to_vec());
+		let local_cache = self.cache.local_cache.upgradable_read();
+		if let Some(entry) = local_cache.child_storage.get(&key).cloned() {
+			trace!("Found in local cache: {:?}", key);
+			return Ok(entry)
+		}
+		let mut cache = self.cache.shared_cache.lock();
+		if Self::is_allowed(None, Some(&key), &self.cache.parent_hash, &cache.modifications) {
+			if let Some(entry) = cache.lru_child_storage.get(&key).map(|a| a.clone()) {
+				trace!("Found in shared cache: {:?}", key);
+				return Ok(entry)
+			}
+		}
+		trace!("Cache miss: {:?}", key);
+		let value = self.state.child_storage(storage_key, &key.1[..])?;
+		RwLockUpgradableReadGuard::upgrade(local_cache).child_storage.insert(key, value.clone());
+		Ok(value)
 	}
 
 	fn exists_storage(&self, key: &[u8]) -> Result<bool, Self::Error> {
@@ -446,27 +581,27 @@ mod tests {
 		let h3a = H256::random();
 		let h3b = H256::random();
 
-		let shared = new_shared_cache::<Block, Blake2Hasher>(256*1024);
+		let shared = new_shared_cache::<Block, Blake2Hasher>(256*1024, (0,1));
 
 		// blocks  [ 3a(c) 2a(c) 2b 1b 1a(c) 0 ]
 		// state   [ 5     5     4  3  2     2 ]
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(root_parent.clone()));
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![2]))], Some(h0.clone()), Some(0), || true);
+		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![2]))], vec![], Some(h0.clone()), Some(0), || true);
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h0.clone()));
-		s.cache.sync_cache(&[], &[], vec![], Some(h1a.clone()), Some(1), || true);
+		s.cache.sync_cache(&[], &[], vec![], vec![], Some(h1a.clone()), Some(1), || true);
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h0.clone()));
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![3]))], Some(h1b.clone()), Some(1), || false);
+		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![3]))], vec![], Some(h1b.clone()), Some(1), || false);
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h1b.clone()));
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![4]))], Some(h2b.clone()), Some(2), || false);
+		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![4]))], vec![], Some(h2b.clone()), Some(2), || false);
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h1a.clone()));
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![5]))], Some(h2a.clone()), Some(2), || true);
+		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![5]))], vec![], Some(h2a.clone()), Some(2), || true);
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h2a.clone()));
-		s.cache.sync_cache(&[], &[], vec![], Some(h3a.clone()), Some(3), || true);
+		s.cache.sync_cache(&[], &[], vec![], vec![], Some(h3a.clone()), Some(3), || true);
 
 		let s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h3a.clone()));
 		assert_eq!(s.storage(&key).unwrap().unwrap(), vec![5]);
@@ -487,9 +622,10 @@ mod tests {
 			&[h1b.clone(), h2b.clone(), h3b.clone()],
 			&[h1a.clone(), h2a.clone(), h3a.clone()],
 			vec![],
+			vec![],
 			Some(h3b.clone()),
 			Some(3),
-			|| true
+			|| true,
 		);
 		let s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(h3a.clone()));
 		assert!(s.storage(&key).unwrap().is_none());
@@ -498,34 +634,71 @@ mod tests {
 	#[test]
 	fn should_track_used_size_correctly() {
 		let root_parent = H256::random();
-		let shared = new_shared_cache::<Block, Blake2Hasher>(5);
+		let shared = new_shared_cache::<Block, Blake2Hasher>(109, ((109-36), 109));
 		let h0 = H256::random();
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(root_parent.clone()));
 
 		let key = H256::random()[..].to_vec();
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![1, 2, 3]))], Some(h0.clone()), Some(0), || true);
-		assert_eq!(shared.lock().used_storage_cache_size(), 3 /* bytes */);
+		let s_key = H256::random()[..].to_vec();
+		s.cache.sync_cache(
+			&[],
+			&[],
+			vec![(key.clone(), Some(vec![1, 2, 3]))],
+			vec![],
+			Some(h0.clone()),
+			Some(0),
+			|| true,
+		);
+		// 32 key, 3 byte size
+		assert_eq!(shared.lock().used_storage_cache_size(), 35 /* bytes */);
 
 		let key = H256::random()[..].to_vec();
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![1, 2]))], Some(h0.clone()), Some(0), || true);
-		assert_eq!(shared.lock().used_storage_cache_size(), 5 /* bytes */);
+		s.cache.sync_cache(
+			&[],
+			&[],
+			vec![],
+			vec![(s_key.clone(), vec![(key.clone(), Some(vec![1, 2]))])],
+			Some(h0.clone()),
+			Some(0),
+			|| true,
+		);
+		// 35 + (2 * 32) key, 2 byte size
+		assert_eq!(shared.lock().used_storage_cache_size(), 101 /* bytes */);
 	}
 
 	#[test]
 	fn should_remove_lru_items_based_on_tracking_used_size() {
 		let root_parent = H256::random();
-		let shared = new_shared_cache::<Block, Blake2Hasher>(5);
+		let shared = new_shared_cache::<Block, Blake2Hasher>(36*3, (2,3));
 		let h0 = H256::random();
 
 		let mut s = CachingState::new(InMemory::<Blake2Hasher>::default(), shared.clone(), Some(root_parent.clone()));
 
 		let key = H256::random()[..].to_vec();
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![1, 2, 3, 4]))], Some(h0.clone()), Some(0), || true);
-		assert_eq!(shared.lock().used_storage_cache_size(), 4 /* bytes */);
+		s.cache.sync_cache(
+			&[],
+			&[],
+			vec![(key.clone(), Some(vec![1, 2, 3, 4]))],
+			vec![],
+			Some(h0.clone()),
+			Some(0),
+			|| true,
+		);
+		// 32 key, 4 byte size
+		assert_eq!(shared.lock().used_storage_cache_size(), 36 /* bytes */);
 
 		let key = H256::random()[..].to_vec();
-		s.cache.sync_cache(&[], &[], vec![(key.clone(), Some(vec![1, 2]))], Some(h0.clone()), Some(0), || true);
-		assert_eq!(shared.lock().used_storage_cache_size(), 2 /* bytes */);
+		s.cache.sync_cache(
+			&[],
+			&[],
+			vec![(key.clone(), Some(vec![1, 2]))],
+			vec![],
+			Some(h0.clone()),
+			Some(0),
+			|| true,
+		);
+		// 32 key, 2 byte size
+		assert_eq!(shared.lock().used_storage_cache_size(), 34 /* bytes */);
 	}
 }

substrate/core/client/src/backend.rs

@@ -28,6 +28,12 @@ use hash_db::Hasher;
 use trie::MemoryDB;
 use parking_lot::Mutex;
 
+/// In memory array of storage values.
+pub type StorageCollection = Vec<(Vec<u8>, Option<Vec<u8>>)>;
+
+/// In memory arrays of storage values for multiple child tries.
+pub type ChildStorageCollection = Vec<(Vec<u8>, StorageCollection)>;
+
 /// State of a new block.
 #[derive(Debug, Clone, Copy, PartialEq, Eq)]
 pub enum NewBlockState {
@@ -82,8 +88,12 @@ pub trait BlockImportOperation<Block, H> where
 	fn update_db_storage(&mut self, update: <Self::State as StateBackend<H>>::Transaction) -> error::Result<()>;
 	/// Inject storage data into the database replacing any existing data.
 	fn reset_storage(&mut self, top: StorageOverlay, children: ChildrenStorageOverlay) -> error::Result<H::Out>;
-	/// Set top level storage changes.
-	fn update_storage(&mut self, update: Vec<(Vec<u8>, Option<Vec<u8>>)>) -> error::Result<()>;
+	/// Set storage changes.
+	fn update_storage(
+		&mut self,
+		update: StorageCollection,
+		child_update: ChildStorageCollection,
+	) -> error::Result<()>;
 	/// Inject changes trie data into the database.
 	fn update_changes_trie(&mut self, update: MemoryDB<H>) -> error::Result<()>;
 	/// Insert auxiliary keys. Values are `None` if should be deleted.

substrate/core/client/src/client.rs

@@ -59,7 +59,10 @@ use state_machine::{
 };
 use hash_db::Hasher;
 
-use crate::backend::{self, BlockImportOperation, PrunableStateChangesTrieStorage};
+use crate::backend::{
+	self, BlockImportOperation, PrunableStateChangesTrieStorage,
+	StorageCollection, ChildStorageCollection
+};
 use crate::blockchain::{
 	self, Info as ChainInfo, Backend as ChainBackend,
 	HeaderBackend as ChainHeaderBackend, ProvideCache, Cache,
@@ -77,6 +80,7 @@ use substrate_telemetry::{telemetry, SUBSTRATE_INFO};
 
 use log::{info, trace, warn};
 
+
 /// Type that implements `futures::Stream` of block import events.
 pub type ImportNotifications<Block> = mpsc::UnboundedReceiver<BlockImportNotification<Block>>;
 
@@ -133,7 +137,15 @@ pub struct Client<B, E, Block, RA> where Block: BlockT {
 /// Client import operation, a wrapper for the backend.
 pub struct ClientImportOperation<Block: BlockT, H: Hasher<Out=Block::Hash>, B: backend::Backend<Block, H>> {
 	op: B::BlockImportOperation,
-	notify_imported: Option<(Block::Hash, BlockOrigin, Block::Header, bool, Option<Vec<(Vec<u8>, Option<Vec<u8>>)>>)>,
+	notify_imported: Option<(
+		Block::Hash,
+		BlockOrigin,
+		Block::Header,
+		bool,
+		Option<(
+			StorageCollection,
+			ChildStorageCollection,
+		)>)>,
 	notify_finalized: Vec<Block::Hash>,
 }
 
@@ -150,8 +162,10 @@ pub trait BlockchainEvents<Block: BlockT> {
 	/// Get storage changes event stream.
 	///
 	/// Passing `None` as `filter_keys` subscribes to all storage changes.
-	fn storage_changes_notification_stream(&self,
-		filter_keys: Option<&[StorageKey]>
+	fn storage_changes_notification_stream(
+		&self,
+		filter_keys: Option<&[StorageKey]>,
+		child_filter_keys: Option<&[(StorageKey, Option<Vec<StorageKey>>)]>,
 	) -> error::Result<StorageEventStream<Block::Hash>>;
 }
 
@@ -351,6 +365,14 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			.map(StorageData))
 	}
 
+	/// Given a `BlockId` and a key, return the value under the hash in that block.
+	pub fn storage_hash(&self, id: &BlockId<Block>, key: &StorageKey)
+		-> error::Result<Option<Block::Hash>> {
+		Ok(self.state_at(id)?
+			.storage_hash(&key.0).map_err(|e| error::Error::from_state(Box::new(e)))?
+		)
+	}
+
 	/// Given a `BlockId`, a key prefix, and a child storage key, return the matching child storage keys.
 	pub fn child_storage_keys(
 		&self,
@@ -378,6 +400,18 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			.map(StorageData))
 	}
 
+	/// Given a `BlockId`, a key and a child storage key, return the hash under the key in that block.
+	pub fn child_storage_hash(
+		&self,
+		id: &BlockId<Block>,
+		child_storage_key: &StorageKey,
+		key: &StorageKey
+	) -> error::Result<Option<Block::Hash>> {
+		Ok(self.state_at(id)?
+			.child_storage_hash(&child_storage_key.0, &key.0).map_err(|e| error::Error::from_state(Box::new(e)))?
+		)
+	}
+
 	/// Get the code at a given block.
 	pub fn code_at(&self, id: &BlockId<Block>) -> error::Result<Vec<u8>> {
 		Ok(self.storage(id, &StorageKey(well_known_keys::CODE.to_vec()))?
@@ -913,7 +947,7 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 			operation.op.update_db_storage(storage_update)?;
 		}
 		if let Some(storage_changes) = storage_changes.clone() {
-			operation.op.update_storage(storage_changes)?;
+			operation.op.update_storage(storage_changes.0, storage_changes.1)?;
 		}
 		if let Some(Some(changes_update)) = changes_update {
 			operation.op.update_changes_trie(changes_update)?;
@@ -942,7 +976,10 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 	) -> error::Result<(
 		Option<StorageUpdate<B, Block>>,
 		Option<Option<ChangesUpdate>>,
-		Option<Vec<(Vec<u8>, Option<Vec<u8>>)>>,
+		Option<(
+			Vec<(Vec<u8>, Option<Vec<u8>>)>,
+			Vec<(Vec<u8>, Vec<(Vec<u8>, Option<Vec<u8>>)>)>
+		)>
 	)>
 		where
 			E: CallExecutor<Block, Blake2Hasher> + Send + Sync + Clone,
@@ -985,7 +1022,9 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 
 				overlay.commit_prospective();
 
-				Ok((Some(storage_update), Some(changes_update), Some(overlay.into_committed().collect())))
+				let (top, children) = overlay.into_committed();
+				let children = children.map(|(sk, it)| (sk, it.collect())).collect();
+				Ok((Some(storage_update), Some(changes_update), Some((top.collect(), children))))
 			},
 			None => Ok((None, None, None))
 		}
@@ -1084,14 +1123,26 @@ impl<B, E, Block, RA> Client<B, E, Block, RA> where
 
 	fn notify_imported(
 		&self,
-		notify_import: (Block::Hash, BlockOrigin, Block::Header, bool, Option<Vec<(Vec<u8>, Option<Vec<u8>>)>>),
+		notify_import: (
+			Block::Hash, BlockOrigin,
+			Block::Header,
+			bool,
+			Option<(
+				Vec<(Vec<u8>, Option<Vec<u8>>)>,
+				Vec<(Vec<u8>, Vec<(Vec<u8>, Option<Vec<u8>>)>)>,
+				)
+			>),
 	) -> error::Result<()> {
 		let (hash, origin, header, is_new_best, storage_changes) = notify_import;
 
 		if let Some(storage_changes) = storage_changes {
 			// TODO [ToDr] How to handle re-orgs? Should we re-emit all storage changes?
 			self.storage_notifications.lock()
-				.trigger(&hash, storage_changes.into_iter());
+				.trigger(
+					&hash,
+					storage_changes.0.into_iter(),
+					storage_changes.1.into_iter().map(|(sk, v)| (sk, v.into_iter())),
+				);
 		}
 
 		let notification = BlockImportNotification::<Block> {
@@ -1467,8 +1518,12 @@ where
 	}
 
 	/// Get storage changes event stream.
-	fn storage_changes_notification_stream(&self, filter_keys: Option<&[StorageKey]>) -> error::Result<StorageEventStream<Block::Hash>> {
-		Ok(self.storage_notifications.lock().listen(filter_keys))
+	fn storage_changes_notification_stream(
+		&self,
+		filter_keys: Option<&[StorageKey]>,
+		child_filter_keys: Option<&[(StorageKey, Option<Vec<StorageKey>>)]>,
+	) -> error::Result<StorageEventStream<Block::Hash>> {
+		Ok(self.storage_notifications.lock().listen(filter_keys, child_filter_keys))
 	}
 }
 

substrate/core/client/src/in_mem.rs

@@ -33,7 +33,7 @@ use trie::MemoryDB;
 use consensus::well_known_cache_keys::Id as CacheKeyId;
 
 use crate::error;
-use crate::backend::{self, NewBlockState};
+use crate::backend::{self, NewBlockState, StorageCollection, ChildStorageCollection};
 use crate::light;
 use crate::leaves::LeafSet;
 use crate::blockchain::{self, BlockStatus, HeaderBackend};
@@ -515,7 +515,11 @@ where
 		Ok(())
 	}
 
-	fn update_storage(&mut self, _update: Vec<(Vec<u8>, Option<Vec<u8>>)>) -> error::Result<()> {
+	fn update_storage(
+		&mut self,
+		_update: StorageCollection,
+		_child_update: ChildStorageCollection,
+	) -> error::Result<()> {
 		Ok(())
 	}
 

substrate/core/client/src/lib.rs

@@ -59,7 +59,7 @@ pub use crate::client::{
 	new_in_mem,
 	BlockBody, BlockStatus, ImportNotifications, FinalityNotifications, BlockchainEvents,
 	BlockImportNotification, Client, ClientInfo, ExecutionStrategies,
-	LongestChain
+	LongestChain,
 };
 #[cfg(feature = "std")]
 pub use crate::notifications::{StorageEventStream, StorageChangeSet};

substrate/core/client/src/light/backend.rs

@@ -26,7 +26,10 @@ use runtime_primitives::{generic::BlockId, Justification, StorageOverlay, Childr
 use state_machine::{Backend as StateBackend, TrieBackend, backend::InMemory as InMemoryState};
 use runtime_primitives::traits::{Block as BlockT, NumberFor, Zero, Header};
 use crate::in_mem::{self, check_genesis_storage};
-use crate::backend::{AuxStore, Backend as ClientBackend, BlockImportOperation, RemoteBackend, NewBlockState};
+use crate::backend::{
+	AuxStore, Backend as ClientBackend, BlockImportOperation, RemoteBackend, NewBlockState,
+	StorageCollection, ChildStorageCollection,
+};
 use crate::blockchain::HeaderBackend as BlockchainHeaderBackend;
 use crate::error::{Error as ClientError, Result as ClientResult};
 use crate::light::blockchain::{Blockchain, Storage as BlockchainStorage};
@@ -310,7 +313,11 @@ where
 		Ok(())
 	}
 
-	fn update_storage(&mut self, _update: Vec<(Vec<u8>, Option<Vec<u8>>)>) -> ClientResult<()> {
+	fn update_storage(
+		&mut self,
+		_update: StorageCollection,
+		_child_update: ChildStorageCollection,
+	) -> ClientResult<()> {
 		// we're not storing anything locally => ignore changes
 		Ok(())
 	}

substrate/core/client/src/notifications.rs

@@ -30,18 +30,39 @@ use runtime_primitives::traits::Block as BlockT;
 #[derive(Debug)]
 pub struct StorageChangeSet {
 	changes: Arc<Vec<(StorageKey, Option<StorageData>)>>,
+	child_changes: Arc<Vec<(StorageKey, Vec<(StorageKey, Option<StorageData>)>)>>,
 	filter: Option<HashSet<StorageKey>>,
+	child_filters: Option<HashMap<StorageKey, Option<HashSet<StorageKey>>>>,
 }
 
 impl StorageChangeSet {
 	/// Convert the change set into iterator over storage items.
-	pub fn iter<'a>(&'a self) -> impl Iterator<Item=&'a (StorageKey, Option<StorageData>)> + 'a {
-		self.changes
+	pub fn iter<'a>(&'a self)
+		-> impl Iterator<Item=(Option<&'a StorageKey>, &'a StorageKey, Option<&'a StorageData>)> + 'a {
+		let top = self.changes
 			.iter()
 			.filter(move |&(key, _)| match self.filter {
 				Some(ref filter) => filter.contains(key),
 				None => true,
 			})
+			.map(move |(k,v)| (None, k, v.as_ref()));
+		let children = self.child_changes
+			.iter()
+			.filter_map(move |(sk, changes)| {
+				if let Some(cf) = self.child_filters.as_ref() {
+					if let Some(filter) = cf.get(sk) {
+						Some(changes
+							.iter()
+							.filter(move |&(key, _)| match filter {
+								Some(ref filter) => filter.contains(key),
+								None => true,
+							})
+							.map(move |(k,v)| (Some(sk), k, v.as_ref())))
+					} else { None }
+				} else { None	}
+			})
+			.flatten();
+		top.chain(children)
 	}
 }
 
@@ -56,9 +77,14 @@ pub struct StorageNotifications<Block: BlockT> {
 	next_id: SubscriberId,
 	wildcard_listeners: FnvHashSet<SubscriberId>,
 	listeners: HashMap<StorageKey, FnvHashSet<SubscriberId>>,
+	child_listeners: HashMap<StorageKey, (
+		HashMap<StorageKey, FnvHashSet<SubscriberId>>,
+		FnvHashSet<SubscriberId>
+	)>,
 	sinks: FnvHashMap<SubscriberId, (
 		mpsc::UnboundedSender<(Block::Hash, StorageChangeSet)>,
 		Option<HashSet<StorageKey>>,
+		Option<HashMap<StorageKey, Option<HashSet<StorageKey>>>>,
 	)>,
 }
 
@@ -68,6 +94,7 @@ impl<Block: BlockT> Default for StorageNotifications<Block> {
 			next_id: Default::default(),
 			wildcard_listeners: Default::default(),
 			listeners: Default::default(),
+			child_listeners: Default::default(),
 			sinks: Default::default(),
 		}
 	}
@@ -78,16 +105,24 @@ impl<Block: BlockT> StorageNotifications<Block> {
 	///
 	/// Note the changes are going to be filtered by listener's filter key.
 	/// In fact no event might be sent if clients are not interested in the changes.
-	pub fn trigger(&mut self, hash: &Block::Hash, changeset: impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)>) {
+	pub fn trigger(
+		&mut self,
+		hash: &Block::Hash,
+		changeset: impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
+		child_changeset: impl Iterator<
+			Item=(Vec<u8>, impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)>)
+		>,
+	) {
 		let has_wildcard = !self.wildcard_listeners.is_empty();
 
 		// early exit if no listeners
-		if !has_wildcard && self.listeners.is_empty() {
+		if !has_wildcard && self.listeners.is_empty() && self.child_listeners.is_empty() {
 			return;
 		}
 
 		let mut subscribers = self.wildcard_listeners.clone();
 		let mut changes = Vec::new();
+		let mut child_changes = Vec::new();
 
 		// Collect subscribers and changes
 		for (k, v) in changeset {
@@ -102,21 +137,47 @@ impl<Block: BlockT> StorageNotifications<Block> {
 				changes.push((k, v.map(StorageData)));
 			}
 		}
+		for (sk, changeset) in child_changeset {
+			let sk = StorageKey(sk);
+			if let Some((cl, cw)) = self.child_listeners.get(&sk) {
+				let mut changes = Vec::new();
+				for (k, v) in changeset {
+					let k = StorageKey(k);
+					let listeners = cl.get(&k);
+
+					if let Some(ref listeners) = listeners {
+						subscribers.extend(listeners.iter());
+					}
+
+					subscribers.extend(cw.iter());
+
+					if !cw.is_empty() || listeners.is_some() {
+						changes.push((k, v.map(StorageData)));
+					}
+				}
+				if !changes.is_empty() {
+					child_changes.push((sk, changes));
+				}
+			}
+		}
 
 		// Don't send empty notifications
-		if changes.is_empty() {
+		if changes.is_empty() && child_changes.is_empty() {
 			return;
 		}
 
 		let changes = Arc::new(changes);
+		let child_changes = Arc::new(child_changes);
 		// Trigger the events
 		for subscriber in subscribers {
 			let should_remove = {
-				let &(ref sink, ref filter) = self.sinks.get(&subscriber)
+				let &(ref sink, ref filter, ref child_filters) = self.sinks.get(&subscriber)
 					.expect("subscribers returned from self.listeners are always in self.sinks; qed");
 				sink.unbounded_send((hash.clone(), StorageChangeSet {
 					changes: changes.clone(),
+					child_changes: child_changes.clone(),
 					filter: filter.clone(),
+					child_filters: child_filters.clone(),
 				})).is_err()
 			};
 
@@ -126,53 +187,120 @@ impl<Block: BlockT> StorageNotifications<Block> {
 		}
 	}
 
-	fn remove_subscriber(&mut self, subscriber: SubscriberId) {
-		if let Some((_, filters)) = self.sinks.remove(&subscriber) {
+	fn remove_subscriber_from(
+		subscriber: &SubscriberId,
+		filters: &Option<HashSet<StorageKey>>,
+		listeners: &mut HashMap<StorageKey, FnvHashSet<SubscriberId>>,
+		wildcards: &mut FnvHashSet<SubscriberId>,
+	){
 		match filters {
 			None => {
-					self.wildcard_listeners.remove(&subscriber);
+				wildcards.remove(subscriber);
 			},
 			Some(filters) => {
-					for key in filters {
-						let remove_key = match self.listeners.get_mut(&key) {
+
+				for key in filters.iter() {
+					let remove_key = match listeners.get_mut(key) {
 						Some(ref mut set) => {
-								set.remove(&subscriber);
+							set.remove(subscriber);
 							set.is_empty()
 						},
 						None => false,
 					};
 
 					if remove_key {
-							self.listeners.remove(&key);
+						listeners.remove(key);
 					}
 				}
+			}
+		}
+	}
+
+	fn remove_subscriber(&mut self, subscriber: SubscriberId) {
+		if let Some((_, filters, child_filters)) = self.sinks.remove(&subscriber) {
+			Self::remove_subscriber_from(
+				&subscriber,
+				&filters,
+				&mut self.listeners,
+				&mut self.wildcard_listeners,
+			);
+			if let Some(child_filters) = child_filters.as_ref() {
+				for (c_key, filters) in child_filters {
+
+					if let Some((listeners, wildcards)) = self.child_listeners.get_mut(&c_key) {
+						Self::remove_subscriber_from(
+							&subscriber,
+							&filters,
+							&mut *listeners,
+							&mut *wildcards,
+						);
+
+						if listeners.is_empty() && wildcards.is_empty() {
+							self.child_listeners.remove(&c_key);
+						}
+					}
+				}
+			}
+		}
+	}
+
+	fn listen_from(
+		current_id: SubscriberId,
+		filter_keys: &Option<impl AsRef<[StorageKey]>>,
+		listeners: &mut HashMap<StorageKey, FnvHashSet<SubscriberId>>,
+		wildcards: &mut FnvHashSet<SubscriberId>,
+	) -> Option<HashSet<StorageKey>>
+	{
+		match filter_keys {
+			None => {
+				wildcards.insert(current_id);
+				None
 			},
-			}
+			Some(keys) => Some(keys.as_ref().iter().map(|key| {
+				listeners
+					.entry(key.clone())
+					.or_insert_with(Default::default)
+					.insert(current_id);
+				key.clone()
+			}).collect())
 		}
 	}
 
 	/// Start listening for particular storage keys.
-	pub fn listen(&mut self, filter_keys: Option<&[StorageKey]>) -> StorageEventStream<Block::Hash> {
+	pub fn listen(
+		&mut self,
+		filter_keys: Option<&[StorageKey]>,
+		filter_child_keys: Option<&[(StorageKey, Option<Vec<StorageKey>>)]>,
+	) -> StorageEventStream<Block::Hash> {
 		self.next_id += 1;
+		let current_id = self.next_id;
 
 		// add subscriber for every key
-		let keys = match filter_keys {
-			None => {
-				self.wildcard_listeners.insert(self.next_id);
-				None
-			},
-			Some(keys) => Some(keys.iter().map(|key| {
-				self.listeners
-					.entry(key.clone())
-					.or_insert_with(Default::default)
-					.insert(self.next_id);
-				key.clone()
-			}).collect())
-		};
+		let keys = Self::listen_from(
+			current_id,
+			&filter_keys,
+			&mut self.listeners,
+			&mut self.wildcard_listeners,
+		);
+		let child_keys = filter_child_keys.map(|filter_child_keys| {
+			filter_child_keys.iter().map(|(c_key, o_keys)| {
+				let (c_listeners, c_wildcards) = self.child_listeners
+					.entry(c_key.clone())
+					.or_insert_with(Default::default);
+
+				(c_key.clone(), Self::listen_from(
+					current_id,
+					o_keys,
+					&mut *c_listeners,
+					&mut *c_wildcards,
+				))
+			}).collect()
+		});
+
 
 		// insert sink
 		let (tx, rx) = mpsc::unbounded();
-		self.sinks.insert(self.next_id, (tx, keys));
+		self.sinks.insert(current_id, (tx, keys, child_keys));
 		rx
 	}
 }
@@ -182,13 +310,26 @@ mod tests {
 	use runtime_primitives::testing::{H256 as Hash, Block as RawBlock, ExtrinsicWrapper};
 	use super::*;
 	use futures::Stream;
+	use std::iter::{empty, Empty};
+
+	type TestChangeSet = (
+		Vec<(StorageKey, Option<StorageData>)>,
+		Vec<(StorageKey, Vec<(StorageKey, Option<StorageData>)>)>,
+	);
 
 	#[cfg(test)]
-	impl From<Vec<(StorageKey, Option<StorageData>)>> for StorageChangeSet {
-		fn from(changes: Vec<(StorageKey, Option<StorageData>)>) -> Self {
+	impl From<TestChangeSet> for StorageChangeSet {
+		fn from(changes: TestChangeSet) -> Self {
+			// warning hardcoded child trie wildcard to test upon
+			let child_filters = Some([
+				(StorageKey(vec![4]), None),
+				(StorageKey(vec![5]), None),
+			].into_iter().cloned().collect());
 			StorageChangeSet {
-				changes: Arc::new(changes),
+				changes: Arc::new(changes.0),
+				child_changes: Arc::new(changes.1),
 				filter: None,
+				child_filters,
 			}
 		}
 	}
@@ -206,43 +347,73 @@ mod tests {
 	fn triggering_change_should_notify_wildcard_listeners() {
 		// given
 		let mut notifications = StorageNotifications::<Block>::default();
-		let mut recv = notifications.listen(None).wait();
+		let child_filter = [(StorageKey(vec![4]), None)];
+		let mut recv = notifications.listen(None, Some(&child_filter[..])).wait();
 
 		// when
 		let changeset = vec![
 			(vec![2], Some(vec![3])),
 			(vec![3], None),
 		];
-		notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter());
+		let c_changeset_1 = vec![
+			(vec![5], Some(vec![4])),
+			(vec![6], None),
+		];
+		let c_changeset = vec![(vec![4], c_changeset_1)];
+		notifications.trigger(
+			&Hash::from_low_u64_be(1),
+			changeset.into_iter(),
+			c_changeset.into_iter().map(|(a,b)| (a, b.into_iter())),
+		);
 
 		// then
-		assert_eq!(recv.next().unwrap(), Ok((Hash::from_low_u64_be(1), vec![
+		assert_eq!(recv.next().unwrap(), Ok((Hash::from_low_u64_be(1), (vec![
 			(StorageKey(vec![2]), Some(StorageData(vec![3]))),
 			(StorageKey(vec![3]), None),
-		].into())));
+		], vec![(StorageKey(vec![4]), vec![
+			(StorageKey(vec![5]), Some(StorageData(vec![4]))),
+			(StorageKey(vec![6]), None),
+		])]).into())));
 	}
 
 	#[test]
 	fn should_only_notify_interested_listeners() {
 		// given
 		let mut notifications = StorageNotifications::<Block>::default();
-		let mut recv1 = notifications.listen(Some(&[StorageKey(vec![1])])).wait();
-		let mut recv2 = notifications.listen(Some(&[StorageKey(vec![2])])).wait();
+		let child_filter = [(StorageKey(vec![4]), Some(vec![StorageKey(vec![5])]))];
+		let mut recv1 = notifications.listen(Some(&[StorageKey(vec![1])]), None).wait();
+		let mut recv2 = notifications.listen(Some(&[StorageKey(vec![2])]), None).wait();
+		let mut recv3 = notifications.listen(Some(&[]), Some(&child_filter)).wait();
 
 		// when
 		let changeset = vec![
 			(vec![2], Some(vec![3])),
 			(vec![1], None),
 		];
-		notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter());
+		let c_changeset_1 = vec![
+			(vec![5], Some(vec![4])),
+			(vec![6], None),
+		];
+
+		let c_changeset = vec![(vec![4], c_changeset_1)];
+		notifications.trigger(
+			&Hash::from_low_u64_be(1),
+			changeset.into_iter(),
+			c_changeset.into_iter().map(|(a,b)| (a, b.into_iter())),
+		);
 
 		// then
-		assert_eq!(recv1.next().unwrap(), Ok((Hash::from_low_u64_be(1), vec![
+		assert_eq!(recv1.next().unwrap(), Ok((Hash::from_low_u64_be(1), (vec![
 			(StorageKey(vec![1]), None),
-		].into())));
-		assert_eq!(recv2.next().unwrap(), Ok((Hash::from_low_u64_be(1), vec![
+		], vec![]).into())));
+		assert_eq!(recv2.next().unwrap(), Ok((Hash::from_low_u64_be(1), (vec![
 			(StorageKey(vec![2]), Some(StorageData(vec![3]))),
-		].into())));
+		], vec![]).into())));
+		assert_eq!(recv3.next().unwrap(), Ok((Hash::from_low_u64_be(1), (vec![],
+		vec![
+			(StorageKey(vec![4]), vec![(StorageKey(vec![5]), Some(StorageData(vec![4])))]),
+		]).into())));
+
 	}
 
 	#[test]
@@ -250,11 +421,14 @@ mod tests {
 		// given
 		let mut notifications = StorageNotifications::<Block>::default();
 		{
-			let _recv1 = notifications.listen(Some(&[StorageKey(vec![1])])).wait();
-			let _recv2 = notifications.listen(Some(&[StorageKey(vec![2])])).wait();
-			let _recv3 = notifications.listen(None).wait();
+			let child_filter = [(StorageKey(vec![4]), Some(vec![StorageKey(vec![5])]))];
+			let _recv1 = notifications.listen(Some(&[StorageKey(vec![1])]), None).wait();
+			let _recv2 = notifications.listen(Some(&[StorageKey(vec![2])]), None).wait();
+			let _recv3 = notifications.listen(None, None).wait();
+			let _recv4 = notifications.listen(None, Some(&child_filter)).wait();
 			assert_eq!(notifications.listeners.len(), 2);
-			assert_eq!(notifications.wildcard_listeners.len(), 1);
+			assert_eq!(notifications.wildcard_listeners.len(), 2);
+			assert_eq!(notifications.child_listeners.len(), 1);
 		}
 
 		// when
@@ -262,11 +436,13 @@ mod tests {
 			(vec![2], Some(vec![3])),
 			(vec![1], None),
 		];
-		notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter());
+		let c_changeset = empty::<(_, Empty<_>)>();
+		notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter(), c_changeset);
 
 		// then
 		assert_eq!(notifications.listeners.len(), 0);
 		assert_eq!(notifications.wildcard_listeners.len(), 0);
+		assert_eq!(notifications.child_listeners.len(), 0);
 	}
 
 	#[test]
@@ -274,11 +450,12 @@ mod tests {
 		// given
 		let mut recv = {
 			let mut notifications = StorageNotifications::<Block>::default();
-			let recv = notifications.listen(None).wait();
+			let recv = notifications.listen(None, None).wait();
 
 			// when
 			let changeset = vec![];
-			notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter());
+			let c_changeset = empty::<(_, Empty<_>)>();
+			notifications.trigger(&Hash::from_low_u64_be(1), changeset.into_iter(), c_changeset);
 			recv
 		};
 

substrate/core/rpc/src/state/mod.rs

@@ -362,8 +362,9 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 	}
 
 	fn storage_hash(&self, key: StorageKey, block: Option<Block::Hash>) -> Result<Option<Block::Hash>> {
-		use runtime_primitives::traits::{Hash, Header as HeaderT};
-		Ok(self.storage(key, block)?.map(|x| <Block::Header as HeaderT>::Hashing::hash(&x.0)))
+		let block = self.unwrap_or_best(block)?;
+		trace!(target: "rpc", "Querying storage hash at {:?} for key {}", block, HexDisplay::from(&key.0));
+		Ok(self.client.storage_hash(&BlockId::Hash(block), &key)?)
 	}
 
 	fn storage_size(&self, key: StorageKey, block: Option<Block::Hash>) -> Result<Option<u64>> {
@@ -398,11 +399,13 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 		key: StorageKey,
 		block: Option<Block::Hash>
 	) -> Result<Option<Block::Hash>> {
-		use runtime_primitives::traits::{Hash, Header as HeaderT};
-		Ok(
-			self.child_storage(child_storage_key, key, block)?
-				.map(|x| <Block::Header as HeaderT>::Hashing::hash(&x.0))
-		)
+		let block = self.unwrap_or_best(block)?;
+		trace!(
+			target: "rpc", "Querying child storage hash at {:?} for key {}",
+			block,
+			HexDisplay::from(&key.0),
+		);
+		Ok(self.client.child_storage_hash(&BlockId::Hash(block), &child_storage_key, &key)?)
 	}
 
 	fn child_storage_size(
@@ -439,7 +442,10 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 		keys: Option<Vec<StorageKey>>
 	) {
 		let keys = Into::<Option<Vec<_>>>::into(keys);
-		let stream = match self.client.storage_changes_notification_stream(keys.as_ref().map(|x| &**x)) {
+		let stream = match self.client.storage_changes_notification_stream(
+			keys.as_ref().map(|x| &**x),
+			None
+		) {
 			Ok(stream) => stream,
 			Err(err) => {
 				let _ = subscriber.reject(error::Error::from(err).into());
@@ -466,7 +472,10 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 				.map_err(|e| warn!("Error creating storage notification stream: {:?}", e))
 				.map(|(block, changes)| Ok(StorageChangeSet {
 					block,
-					changes: changes.iter().cloned().collect(),
+					changes: changes.iter()
+						.filter_map(|(o_sk, k, v)| if o_sk.is_none() {
+							Some((k.clone(),v.cloned()))
+						} else { None }).collect(),
 				}));
 
 			sink
@@ -488,7 +497,8 @@ impl<B, E, Block, RA> StateApi<Block::Hash> for State<B, E, Block, RA> where
 
 	fn subscribe_runtime_version(&self, _meta: Self::Metadata, subscriber: Subscriber<RuntimeVersion>) {
 		let stream = match self.client.storage_changes_notification_stream(
-				Some(&[StorageKey(storage::well_known_keys::CODE.to_vec())])
+			Some(&[StorageKey(storage::well_known_keys::CODE.to_vec())]),
+			None,
 		) {
 			Ok(stream) => stream,
 			Err(err) => {

substrate/core/service/src/components.rs

@@ -499,6 +499,8 @@ impl<Factory: ServiceFactory> Components for FullComponents<Factory> {
 		let db_settings = client_db::DatabaseSettings {
 			cache_size: config.database_cache_size.map(|u| u as usize),
 			state_cache_size: config.state_cache_size,
+			state_cache_child_ratio:
+				config.state_cache_child_ratio.map(|v| (v, 100)),
 			path: config.database_path.as_str().into(),
 			pruning: config.pruning.clone(),
 		};
@@ -591,6 +593,8 @@ impl<Factory: ServiceFactory> Components for LightComponents<Factory> {
 		let db_settings = client_db::DatabaseSettings {
 			cache_size: None,
 			state_cache_size: config.state_cache_size,
+			state_cache_child_ratio:
+				config.state_cache_child_ratio.map(|v| (v, 100)),
 			path: config.database_path.as_str().into(),
 			pruning: config.pruning.clone(),
 		};

substrate/core/service/src/config.rs

@@ -50,6 +50,8 @@ pub struct Configuration<C, G: Serialize + DeserializeOwned + BuildStorage> {
 	pub database_cache_size: Option<u32>,
 	/// Size of internal state cache in Bytes
 	pub state_cache_size: usize,
+	/// Size in percent of cache size dedicated to child tries 
+	pub state_cache_child_ratio: Option<usize>, 
 	/// Pruning settings.
 	pub pruning: PruningMode,
 	/// Additional key seeds.
@@ -100,6 +102,7 @@ impl<C: Default, G: Serialize + DeserializeOwned + BuildStorage> Configuration<C
 			database_path: Default::default(),
 			database_cache_size: Default::default(),
 			state_cache_size: Default::default(),
+			state_cache_child_ratio: Default::default(),
 			keys: Default::default(),
 			custom: Default::default(),
 			pruning: PruningMode::default(),

substrate/core/service/test/src/lib.rs

@@ -139,6 +139,7 @@ fn node_config<F: ServiceFactory> (
 		database_path: root.join("db").to_str().unwrap().into(),
 		database_cache_size: None,
 		state_cache_size: 16777216,
+		state_cache_child_ratio: None,
 		pruning: Default::default(),
 		keys: keys,
 		chain_spec: (*spec).clone(),

substrate/core/state-machine/src/backend.rs

@@ -51,6 +51,11 @@ pub trait Backend<H: Hasher> {
 	/// Get keyed child storage or None if there is nothing associated.
 	fn child_storage(&self, storage_key: &[u8], key: &[u8]) -> Result<Option<Vec<u8>>, Self::Error>;
 
+	/// Get child keyed storage value hash or None if there is nothing associated.
+	fn child_storage_hash(&self, storage_key: &[u8], key: &[u8]) -> Result<Option<H::Out>, Self::Error> {
+		self.child_storage(storage_key, key).map(|v| v.map(|v| H::hash(&v)))
+	}
+
 	/// true if a key exists in storage.
 	fn exists_storage(&self, key: &[u8]) -> Result<bool, Self::Error> {
 		Ok(self.storage(key)?.is_some())

substrate/core/state-machine/src/overlayed_changes.rs

@@ -255,9 +255,13 @@ impl OverlayedChanges {
 	///
 	/// Panics:
 	/// Will panic if there are any uncommitted prospective changes.
-	pub fn into_committed(self) -> impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)> {
+	pub fn into_committed(self) -> (
+		impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)>,
+		impl Iterator<Item=(Vec<u8>, impl Iterator<Item=(Vec<u8>, Option<Vec<u8>>)>)>,
+	){
 		assert!(self.prospective.is_empty());
-		self.committed.top.into_iter().map(|(k, v)| (k, v.value))
+		(self.committed.top.into_iter().map(|(k, v)| (k, v.value)),
+			self.committed.children.into_iter().map(|(sk, v)| (sk, v.1.into_iter())))
 	}
 
 	/// Inserts storage entry responsible for current extrinsic index.