diff --git a/Cargo.toml b/Cargo.toml
index 8450bf1b8..3a74bf589 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -13,6 +13,7 @@ ethcore-util = "0.1.0"
 rustc-serialize = "0.3"
 flate2 = "0.2"
 rocksdb = "0.2.1"
+heapsize = "0.2.0"
 
 evmjit = { path = "rust-evmjit", optional = true }
 
diff --git a/src/blockchain.rs b/src/blockchain.rs
index facb57cdb..6a48e12af 100644
--- a/src/blockchain.rs
+++ b/src/blockchain.rs
@@ -1,8 +1,9 @@
 use std::collections::HashMap;
-use std::sync::RwLock;
+use std::cell::{Cell, RefCell};
 use std::path::Path;
 use std::hash::Hash;
 use rocksdb::{DB, WriteBatch, Writable};
+use heapsize::HeapSizeOf;
 use util::hash::*;
 use util::uint::*;
 use util::rlp::*;
@@ -10,6 +11,7 @@ use util::hashdb::*;
 use util::overlaydb::*;
 use util::sha3::*;
 use util::bytes::*;
+use util::squeeze::*;
 use blockheader::*;
 use block::*;
 use verifiedblock::*;
@@ -19,6 +21,15 @@ use genesis::*;
 use extras::*;
 use transaction::*;
 
+#[derive(Debug)]
+pub struct CacheSize {
+	pub blocks: usize,
+	pub block_details: usize,
+	pub transaction_addresses: usize,
+	pub block_logs: usize,
+	pub blocks_blooms: usize
+}
+
 pub struct BlockChain {
 	// rlp list of 3
 	genesis_block: Bytes,
@@ -27,17 +38,17 @@ pub struct BlockChain {
 	genesis_hash: H256,
 	_genesis_state: HashMap<Address, Account>,
 
-	_last_block_number: U256,
+	last_block_number: Cell<U256>,
 
 	// block cache
-	blocks: RwLock<HashMap<H256, Bytes>>,
+	blocks: RefCell<HashMap<H256, Bytes>>,
 
 	// extra caches
 	block_details: Extras<H256, BlockDetails>,
 	block_hashes: Extras<U256, H256>,
 	transaction_addresses: Extras<H256, TransactionAddress>,
 	block_logs: Extras<H256, BlockLogBlooms>,
-	_blocks_blooms: Extras<H256, BlocksBlooms>,
+	blocks_blooms: Extras<H256, BlocksBlooms>,
 
 	extras_db: DB,
 	blocks_db: DB
@@ -65,7 +76,7 @@ impl BlockChain {
 	/// 	let genesis_hash = "d4e56740f876aef8c010b86a40d5f56745a118d0906a34e69aec8c0db1cb8fa3";
 	/// 	assert_eq!(bc.genesis_hash(), &H256::from_str(genesis_hash).unwrap());
 	/// 	assert!(bc.is_known(bc.genesis_hash()));
-	/// 	assert_eq!(bc.genesis_hash(), &bc.number_hash(&U256::from(0u8)).unwrap());
+	/// 	assert_eq!(bc.genesis_hash(), &bc.block_hash(&U256::from(0u8)).unwrap());
 	/// }
 	/// ```
 	pub fn new(genesis: Genesis, path: &Path) -> BlockChain {
@@ -103,38 +114,18 @@ impl BlockChain {
 			_genesis_header: genesis_header,
 			genesis_hash: genesis_hash,
 			_genesis_state: genesis_state,
-			_last_block_number: U256::from(0u8),
-			blocks: RwLock::new(HashMap::new()),
+			last_block_number: Cell::new(U256::from(0u8)),
+			blocks: RefCell::new(HashMap::new()),
 			block_details: Extras::new(ExtrasIndex::BlockDetails),
 			block_hashes: Extras::new(ExtrasIndex::BlockHash),
 			transaction_addresses: Extras::new(ExtrasIndex::TransactionAddress),
 			block_logs: Extras::new(ExtrasIndex::BlockLogBlooms),
-			_blocks_blooms: Extras::new(ExtrasIndex::BlocksBlooms),
+			blocks_blooms: Extras::new(ExtrasIndex::BlocksBlooms),
 			extras_db: extras_db,
 			blocks_db: blocks_db
 		}
 	}
 
-	pub fn genesis_block(&self, db: &OverlayDB) -> Block {
-		let root = HeaderView::new(&self.genesis_block).state_root();
-
-		if db.exists(&root) {
-			return Block::new_existing(db.clone(), root)
-		}
-
-		let _block = Block::new(db.clone());
-		// TODO: commit
-		//block.mutable_state().insert_accounts(&self.genesis_state);
-		// block.mutable_state().db().commit();
-		// TODO: set previous block
-		// TODO: reset current
-		unimplemented!()
-	}
-
-	pub fn verify_block<'a>(&self, _block: &'a [u8]) -> VerifiedBlock<'a> {
-		unimplemented!()
-	}
-
 	pub fn import_block(&self, _block: &[u8], _db: &OverlayDB) -> ImportRoute {
 		unimplemented!();
 	}
@@ -191,10 +182,20 @@ impl BlockChain {
 	}
 
 	/// Get the hash of given block's number
-	pub fn number_hash(&self, hash: &U256) -> Option<H256> {
+	pub fn block_hash(&self, hash: &U256) -> Option<H256> {
 		self.query_extras(hash, &self.block_hashes)
 	}
 
+	/// Get last block number
+	pub fn last_block_number(&self) -> U256 {
+		self.last_block_number.get()
+	}
+
+	/// Get the number of given block's hash
+	pub fn block_number(&self, hash: &H256) -> Option<U256> {
+		self.block(hash).map(|bytes| BlockView::new(&bytes).header_view().number())
+	}
+
 	/// Get the transactions' log blooms of a block
 	pub fn log_blooms(&self, hash: &H256) -> Option<BlockLogBlooms> {
 		self.query_extras(hash, &self.block_logs)
@@ -202,7 +203,7 @@ impl BlockChain {
 
 	fn block(&self, hash: &H256) -> Option<Bytes> {
 		{
-			let read = self.blocks.read().unwrap();
+			let read = self.blocks.borrow();
 			match read.get(hash) {
 				Some(v) => return Some(v.clone()),
 				None => ()
@@ -215,7 +216,7 @@ impl BlockChain {
 		match opt {
 			Some(b) => {
 				let bytes: Bytes = b.to_vec();
-				let mut write = self.blocks.write().unwrap();
+				let mut write = self.blocks.borrow_mut();
 				write.insert(hash.clone(), bytes.clone());
 				Some(bytes)
 			},
@@ -227,7 +228,7 @@ impl BlockChain {
 		T: Clone + Decodable, 
 		K: ExtrasSliceConvertable + Eq + Hash + Clone {
 		{
-			let read = cache.read().unwrap();
+			let read = cache.borrow();
 			match read.get(hash) {
 				Some(v) => return Some(v.clone()),
 				None => ()
@@ -240,7 +241,7 @@ impl BlockChain {
 		match opt {
 			Some(b) => {
 				let t: T = decode(&b);
-				let mut write = cache.write().unwrap();
+				let mut write = cache.borrow_mut();
 				write.insert(hash.clone(), t.clone());
 				Some(t)
 			},
@@ -251,7 +252,7 @@ impl BlockChain {
 	fn query_extras_exist<K, T>(&self, hash: &K, cache: &Extras<K, T>) -> bool where 
 		K: ExtrasSliceConvertable + Eq + Hash + Clone {
 		{
-			let read = cache.read().unwrap();
+			let read = cache.borrow();
 			match read.get(hash) {
 				Some(_) => return true,
 				None => ()
@@ -263,5 +264,25 @@ impl BlockChain {
 
 		opt.is_some()
 	}
+
+	/// Get current cache size
+	pub fn cache_size(&self) -> CacheSize {
+		CacheSize {
+			blocks: self.blocks.heap_size_of_children(),
+			block_details: self.block_details.heap_size_of_children(),
+			transaction_addresses: self.transaction_addresses.heap_size_of_children(),
+			block_logs: self.block_logs.heap_size_of_children(),
+			blocks_blooms: self.blocks_blooms.heap_size_of_children()
+		}
+	}
+
+	/// Squeeze the cache if its too big
+	pub fn squeeze_to_fit(&self, size: CacheSize) {
+		self.blocks.borrow_mut().squeeze(size.blocks);
+		self.block_details.borrow_mut().squeeze(size.block_details);
+		self.transaction_addresses.borrow_mut().squeeze(size.transaction_addresses);
+		self.block_logs.borrow_mut().squeeze(size.block_logs);
+		self.blocks_blooms.borrow_mut().squeeze(size.blocks_blooms);
+	}
 }
 
diff --git a/src/extras.rs b/src/extras.rs
index 5606f2e10..d0cfffd89 100644
--- a/src/extras.rs
+++ b/src/extras.rs
@@ -1,7 +1,8 @@
 use std::collections::HashMap;
-use std::sync::RwLock;
+use std::cell::RefCell;
 use std::ops::Deref;
 use std::hash::Hash;
+use heapsize::HeapSizeOf;
 use util::uint::*;
 use util::hash::*;
 use util::rlp::*;
@@ -18,18 +19,18 @@ pub enum ExtrasIndex {
 
 /// rw locked extra data with slice suffix
 // consifer if arc needed here, since blockchain itself will be wrapped
-pub struct Extras<K, T>(RwLock<HashMap<K, T>>, ExtrasIndex) where K: Eq + Hash;
+pub struct Extras<K, T>(RefCell<HashMap<K, T>>, ExtrasIndex) where K: Eq + Hash;
 
 impl<K, T> Extras<K, T> where K: Eq + Hash {
 	pub fn new(i: ExtrasIndex) -> Extras<K, T> {
-		Extras(RwLock::new(HashMap::new()), i)
+		Extras(RefCell::new(HashMap::new()), i)
 	}
 
 	pub fn index(&self) -> ExtrasIndex { self.1 }
 }
 
 impl<K, T> Deref for Extras<K, T> where K : Eq + Hash {
-	type Target = RwLock<HashMap<K, T>>;
+	type Target = RefCell<HashMap<K, T>>;
 
 	fn deref(&self) -> &Self::Target {
 		&self.0
@@ -63,6 +64,12 @@ pub struct BlockDetails {
 	pub children: Vec<H256>
 }
 
+impl HeapSizeOf for BlockDetails {
+	fn heap_size_of_children(&self) -> usize {
+		self.children.heap_size_of_children()
+	}
+}
+
 impl Decodable for BlockDetails {
 	fn decode<D>(decoder: &D) -> Result<Self, DecoderError> where D: Decoder {
 		let d = try!(decoder.as_list());
@@ -92,6 +99,12 @@ pub struct BlockLogBlooms {
 	pub blooms: Vec<H2048>
 }
 
+impl HeapSizeOf for BlockLogBlooms {
+	fn heap_size_of_children(&self) -> usize {
+		self.blooms.heap_size_of_children()
+	}
+}
+
 impl Decodable for BlockLogBlooms {
 	fn decode<D>(decoder: &D) -> Result<Self, DecoderError> where D: Decoder {
 		let block_blooms = BlockLogBlooms {
@@ -112,6 +125,10 @@ pub struct BlocksBlooms {
 	pub blooms: [H2048; 16]
 }
 
+impl HeapSizeOf for BlocksBlooms {
+	fn heap_size_of_children(&self) -> usize { 0 }
+}
+
 impl Clone for BlocksBlooms {
 	fn clone(&self) -> Self {
 		let mut blooms: [H2048; 16] = unsafe { ::std::mem::uninitialized() };
@@ -149,6 +166,10 @@ pub struct TransactionAddress {
 	pub index: u64
 }
 
+impl HeapSizeOf for TransactionAddress {
+	fn heap_size_of_children(&self) -> usize { 0 }
+}
+
 impl Decodable for TransactionAddress {
 	fn decode<D>(decoder: &D) -> Result<Self, DecoderError> where D: Decoder {
 		let d = try!(decoder.as_list());
diff --git a/src/lib.rs b/src/lib.rs
index cc1240233..feb0e6991 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -74,6 +74,7 @@ extern crate log;
 extern crate rustc_serialize;
 extern crate flate2;
 extern crate rocksdb;
+extern crate heapsize;
 
 extern crate env_logger;
 #[cfg(feature = "jit" )]
@@ -96,7 +97,6 @@ pub mod genesis;
 pub mod verifiedblock;
 pub mod importroute;
 
-
 pub mod networkparams;
 pub mod denominations;