diff --git a/ethcore/src/account.rs b/ethcore/src/account.rs
index 19e5d648812..8291989102e 100644
--- a/ethcore/src/account.rs
+++ b/ethcore/src/account.rs
@@ -16,11 +16,12 @@
 
 //! Single account in the system.
 
+use std::collections::hash_map::Entry;
 use util::*;
 use pod_account::*;
 use account_db::*;
 
-use std::cell::{Ref, RefCell};
+use std::cell::{Ref, RefCell, Cell};
 
 /// Single account in the system.
 #[derive(Clone)]
@@ -39,6 +40,8 @@ pub struct Account {
 	code_cache: Bytes,
 	// Account is new or has been modified
 	filth: Filth,
+	// Cached address hash.
+	address_hash: Cell<Option<H256>>,
 }
 
 impl Account {
@@ -53,6 +56,7 @@ impl Account {
 			code_hash: Some(code.sha3()),
 			code_cache: code,
 			filth: Filth::Dirty,
+			address_hash: Cell::new(None),
 		}
 	}
 
@@ -66,6 +70,7 @@ impl Account {
 			code_hash: pod.code.as_ref().map(|c| c.sha3()),
 			code_cache: pod.code.as_ref().map_or_else(|| { warn!("POD account with unknown code is being created! Assuming no code."); vec![] }, |c| c.clone()),
 			filth: Filth::Dirty,
+			address_hash: Cell::new(None),
 		}
 	}
 
@@ -79,6 +84,7 @@ impl Account {
 			code_hash: Some(SHA3_EMPTY),
 			code_cache: vec![],
 			filth: Filth::Dirty,
+			address_hash: Cell::new(None),
 		}
 	}
 
@@ -93,6 +99,7 @@ impl Account {
 			code_hash: Some(r.val_at(3)),
 			code_cache: vec![],
 			filth: Filth::Clean,
+			address_hash: Cell::new(None),
 		}
 	}
 
@@ -107,6 +114,7 @@ impl Account {
 			code_hash: None,
 			code_cache: vec![],
 			filth: Filth::Dirty,
+			address_hash: Cell::new(None),
 		}
 	}
 
@@ -126,8 +134,17 @@ impl Account {
 
 	/// Set (and cache) the contents of the trie's storage at `key` to `value`.
 	pub fn set_storage(&mut self, key: H256, value: H256) {
-		self.storage_overlay.borrow_mut().insert(key, (Filth::Dirty, value));
-		self.filth = Filth::Dirty;
+		match self.storage_overlay.borrow_mut().entry(key) {
+			Entry::Occupied(ref mut entry) if entry.get().1 != value => {
+				entry.insert((Filth::Dirty, value));
+				self.filth = Filth::Dirty;
+			},
+			Entry::Vacant(entry) => {
+				entry.insert((Filth::Dirty, value));
+				self.filth = Filth::Dirty;
+			},
+			_ => (),
+		}
 	}
 
 	/// Get (and cache) the contents of the trie's storage at `key`.
@@ -158,6 +175,16 @@ impl Account {
 		self.code_hash.clone().unwrap_or(SHA3_EMPTY)
 	}
 
+	/// return the code hash associated with this account.
+	pub fn address_hash(&self, address: &Address) -> H256 {
+		let hash = self.address_hash.get();
+		hash.unwrap_or_else(|| {
+			let hash = address.sha3();
+			self.address_hash.set(Some(hash.clone()));
+			hash
+		})
+	}
+
 	/// returns the account's code. If `None` then the code cache isn't available -
 	/// get someone who knows to call `note_code`.
 	pub fn code(&self) -> Option<&[u8]> {
@@ -233,16 +260,20 @@ impl Account {
 
 	/// Increment the nonce of the account by one.
 	pub fn add_balance(&mut self, x: &U256) {
-		self.balance = self.balance + *x;
-		self.filth = Filth::Dirty;
+		if !x.is_zero() {
+			self.balance = self.balance + *x;
+			self.filth = Filth::Dirty;
+		}
 	}
 
 	/// Increment the nonce of the account by one.
 	/// Panics if balance is less than `x`
 	pub fn sub_balance(&mut self, x: &U256) {
-		assert!(self.balance >= *x);
-		self.balance = self.balance - *x;
-		self.filth = Filth::Dirty;
+		if !x.is_zero() {
+			assert!(self.balance >= *x);
+			self.balance = self.balance - *x;
+			self.filth = Filth::Dirty;
+		}
 	}
 
 	/// Commit the `storage_overlay` to the backing DB and update `storage_root`.
diff --git a/ethcore/src/state.rs b/ethcore/src/state.rs
index 612e5fe3d79..5da2010391d 100644
--- a/ethcore/src/state.rs
+++ b/ethcore/src/state.rs
@@ -181,7 +181,7 @@ impl State {
 	/// Mutate storage of account `address` so that it is `value` for `key`.
 	pub fn storage_at(&self, address: &Address, key: &H256) -> H256 {
 		self.ensure_cached(address, false,
-			|a| a.as_ref().map_or(H256::new(), |a|a.storage_at(&AccountDB::new(self.db.as_hashdb(), address), key)))
+			|a| a.as_ref().map_or(H256::new(), |a|a.storage_at(&AccountDB::from_hash(self.db.as_hashdb(), a.address_hash(address)), key)))
 	}
 
 	/// Mutate storage of account `a` so that it is `value` for `key`.
@@ -260,7 +260,7 @@ impl State {
 		for (address, ref mut a) in accounts.iter_mut() {
 			match a {
 				&mut&mut Some(ref mut account) if account.is_dirty() => {
-					let mut account_db = AccountDBMut::new(db, address);
+					let mut account_db = AccountDBMut::from_hash(db, account.address_hash(address));
 					account.commit_storage(trie_factory, &mut account_db);
 					account.commit_code(&mut account_db);
 				}
@@ -355,7 +355,8 @@ impl State {
 		}
 		if require_code {
 			if let Some(ref mut account) = self.cache.borrow_mut().get_mut(a).unwrap().as_mut() {
-				account.cache_code(&AccountDB::new(self.db.as_hashdb(), a));
+				let addr_hash = account.address_hash(a);
+				account.cache_code(&AccountDB::from_hash(self.db.as_hashdb(), addr_hash));
 			}
 		}
 
@@ -393,7 +394,8 @@ impl State {
 		RefMut::map(self.cache.borrow_mut(), |c| {
 			let account = c.get_mut(a).unwrap().as_mut().unwrap();
 			if require_code {
-				account.cache_code(&AccountDB::new(self.db.as_hashdb(), a));
+				let addr_hash = account.address_hash(a);
+				account.cache_code(&AccountDB::from_hash(self.db.as_hashdb(), addr_hash));
 			}
 			account
 		})