From 193d615f9acd80fb674866491442a558af9f6196 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 12:41:31 +0100
Subject: [PATCH 01/15] First JournalDB implementation.

---
 util/src/error.rs     |   7 +++
 util/src/journaldb.rs | 123 ++++++++++++++++++++++++++++++++++++++++++
 util/src/lib.rs       |   1 +
 util/src/overlaydb.rs |  15 +++---
 4 files changed, 139 insertions(+), 7 deletions(-)
 create mode 100644 util/src/journaldb.rs

diff --git a/util/src/error.rs b/util/src/error.rs
index 04f7b96ce..d9687183d 100644
--- a/util/src/error.rs
+++ b/util/src/error.rs
@@ -22,6 +22,7 @@ pub enum UtilError {
 	BaseData(BaseDataError),
 	Network(NetworkError),
 	Decoder(DecoderError),
+	SimpleString(String),
 	BadSize,
 }
 
@@ -73,6 +74,12 @@ impl From<::rlp::DecoderError> for UtilError {
 	}
 }
 
+impl From<String> for UtilError {
+	fn from(err: String) -> UtilError {
+		UtilError::SimpleString(err)
+	}
+}
+
 // TODO: uncomment below once https://github.com/rust-lang/rust/issues/27336 sorted.
 /*#![feature(concat_idents)]
 macro_rules! assimilate {
diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
new file mode 100644
index 000000000..2dda47eba
--- /dev/null
+++ b/util/src/journaldb.rs
@@ -0,0 +1,123 @@
+//! Disk-backed HashDB implementation.
+
+use std::env;
+use common::*;
+use rlp::*;
+use hashdb::*;
+use overlaydb::*;
+use rocksdb::{DB, Writable};
+
+#[derive(Clone)]
+/// Implementation of the HashDB trait for a disk-backed database with a memory overlay
+/// and latent-removal semantics.
+///
+/// Like OverlayDB, there is a memory overlay; `commit()` must be called in order to 
+/// write operations out to disk. Unlike OverlayDB, `remove()` operations do not take effect
+/// immediately. Rather some age (based on a linear but arbitrary metric) must pass before
+/// the removals actually take effect.
+pub struct JournalDB {
+	forward: OverlayDB,
+	backing: Arc<DB>,
+	inserts: Vec<H256>,
+	removes: Vec<H256>,
+}
+
+impl JournalDB {
+	/// Create a new instance given a `backing` database.
+	pub fn new(backing: DB) -> JournalDB {
+		let db = Arc::new(backing);
+		// TODO: check it doesn't overwrite anything before.
+		// TODO: proper handling of errors (return )
+		JournalDB {
+			forward: OverlayDB::new_with_arc(db.clone()),
+			backing: db,
+			inserts: vec![],
+			removes: vec![],
+		}
+	}
+
+	/// Create a new instance with an anonymous temporary database.
+	pub fn new_temp() -> JournalDB {
+		let mut dir = env::temp_dir();
+		dir.push(H32::random().hex());
+		Self::new(DB::open_default(dir.to_str().unwrap()).unwrap())
+	}
+
+	/// Get a clone of the overlay db portion of this.
+	pub fn to_overlaydb(&self) -> OverlayDB { self.forward.clone() }
+
+	/// Commit all recent insert operations and historical removals from the old era
+	/// to the backing database.
+	pub fn commit(&mut self, now: u64, id: &H256, end_era: u64, canon_id: &H256) -> Result<u32, UtilError> {
+		// journal format: 
+		// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
+		// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
+		// [era, n] => [ ... ]
+
+		// TODO: store last_era, reclaim_period.
+
+		// when we make a new commit, we journal the inserts and removes.
+		// for each end_era that we journaled that we are no passing by, 
+		// we remove all of its removes assuming it is canonical and all
+		// of its inserts otherwise.
+
+		// record new commit's details.
+		{
+			let mut index = 0usize;
+			let mut last;
+
+			while try!(self.backing.get({
+				let mut r = RlpStream::new_list(2);
+				r.append(&now);
+				r.append(&index);
+				last = r.out();
+				&last
+			})).is_some() {
+				index += 1;
+			}
+
+			let mut r = RlpStream::new_list(3);
+			r.append(id);
+			r.append(&self.inserts);
+			r.append(&self.removes);
+			try!(self.backing.put(&last, &r.out()));
+		}
+
+		// apply old commits' details
+		let mut index = 0usize;
+		let mut last;
+		while let Some(rlp_data) = try!(self.backing.get({
+			let mut r = RlpStream::new_list(2);
+			r.append(&end_era);
+			r.append(&index);
+			last = r.out();
+			&last
+		})) {
+			let rlp = Rlp::new(&rlp_data);
+			let to_remove: Vec<H256> = rlp.val_at(if *canon_id == rlp.val_at(0) {2} else {1});
+			for i in to_remove.iter() {
+				self.forward.remove(i);
+			}
+			try!(self.backing.delete(&last));
+			index += 1;
+		}
+
+		self.inserts.clear();
+		self.removes.clear();
+
+		self.forward.commit()
+	}
+
+	/// Revert all operations on this object (i.e. `insert()`s and `removes()`s) since the
+	/// last `commit()`.
+	pub fn revert(&mut self) { self.forward.revert(); self.removes.clear(); }
+}
+
+impl HashDB for JournalDB {
+	fn keys(&self) -> HashMap<H256, i32> { self.forward.keys() }
+	fn lookup(&self, key: &H256) -> Option<&[u8]> { self.forward.lookup(key) }
+	fn exists(&self, key: &H256) -> bool { self.forward.exists(key) }
+	fn insert(&mut self, value: &[u8]) -> H256 { let r = self.forward.insert(value); self.inserts.push(r.clone()); r }
+	fn emplace(&mut self, key: H256, value: Bytes) { self.inserts.push(key.clone()); self.forward.emplace(key, value); }
+	fn kill(&mut self, key: &H256) { self.removes.push(key.clone()); }
+}
diff --git a/util/src/lib.rs b/util/src/lib.rs
index 4bc47e61c..34961f1de 100644
--- a/util/src/lib.rs
+++ b/util/src/lib.rs
@@ -69,6 +69,7 @@ pub mod sha3;
 pub mod hashdb;
 pub mod memorydb;
 pub mod overlaydb;
+pub mod journaldb;
 pub mod math;
 pub mod chainfilter;
 pub mod crypto;
diff --git a/util/src/overlaydb.rs b/util/src/overlaydb.rs
index 1006cd28c..6330f1e25 100644
--- a/util/src/overlaydb.rs
+++ b/util/src/overlaydb.rs
@@ -15,11 +15,11 @@ use rocksdb::{DB, Writable, IteratorMode};
 #[derive(Clone)]
 /// Implementation of the HashDB trait for a disk-backed database with a memory overlay.
 ///
-/// The operations `insert()` and `kill()` take place on the memory overlay; batches of
+/// The operations `insert()` and `remove()` take place on the memory overlay; batches of
 /// such operations may be flushed to the disk-backed DB with `commit()` or discarded with
 /// `revert()`.
 ///
-/// `lookup()` and `exists()` maintain normal behaviour - all `insert()` and `kill()` 
+/// `lookup()` and `contains()` maintain normal behaviour - all `insert()` and `remove()` 
 /// queries have an immediate effect in terms of these functions.
 pub struct OverlayDB {
 	overlay: MemoryDB,
@@ -28,8 +28,11 @@ pub struct OverlayDB {
 
 impl OverlayDB {
 	/// Create a new instance of OverlayDB given a `backing` database.
-	pub fn new(backing: DB) -> OverlayDB {
-		OverlayDB{ overlay: MemoryDB::new(), backing: Arc::new(backing) }
+	pub fn new(backing: DB) -> OverlayDB { Self::new_with_arc(Arc::new(backing)) }
+
+	/// Create a new instance of OverlayDB given a `backing` database.
+	pub fn new_with_arc(backing: Arc<DB>) -> OverlayDB {
+		OverlayDB{ overlay: MemoryDB::new(), backing: backing }
 	}
 
 	/// Create a new instance of OverlayDB with an anonymous temporary database.
@@ -70,9 +73,7 @@ impl OverlayDB {
 		let mut ret = 0u32;
 		for i in self.overlay.drain().into_iter() {
 			let (key, (value, rc)) = i;
-			// until we figure out state trie pruning, only commit stuff when it has a strictly positive delkta of RCs - 
-			// this prevents RCs being reduced to 0 where the DB would pretent that the node had been removed.
-			if rc > 0 {
+			if rc != 0 {
 				match self.payload(&key) {
 					Some(x) => {
 						let (back_value, back_rc) = x;

From 28c07cba52cac3cc95c20b9339831b41dc94482d Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 13:30:01 +0100
Subject: [PATCH 02/15] JournalDB passing all tests.

---
 util/src/journaldb.rs | 132 +++++++++++++++++++++++++++++++++++-------
 1 file changed, 111 insertions(+), 21 deletions(-)

diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index 2dda47eba..011d46663 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -26,8 +26,6 @@ impl JournalDB {
 	/// Create a new instance given a `backing` database.
 	pub fn new(backing: DB) -> JournalDB {
 		let db = Arc::new(backing);
-		// TODO: check it doesn't overwrite anything before.
-		// TODO: proper handling of errors (return )
 		JournalDB {
 			forward: OverlayDB::new_with_arc(db.clone()),
 			backing: db,
@@ -48,7 +46,7 @@ impl JournalDB {
 
 	/// Commit all recent insert operations and historical removals from the old era
 	/// to the backing database.
-	pub fn commit(&mut self, now: u64, id: &H256, end_era: u64, canon_id: &H256) -> Result<u32, UtilError> {
+	pub fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, &H256)>) -> Result<u32, UtilError> {
 		// journal format: 
 		// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
 		// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
@@ -81,30 +79,31 @@ impl JournalDB {
 			r.append(&self.inserts);
 			r.append(&self.removes);
 			try!(self.backing.put(&last, &r.out()));
+			self.inserts.clear();
+			self.removes.clear();
 		}
 
 		// apply old commits' details
-		let mut index = 0usize;
-		let mut last;
-		while let Some(rlp_data) = try!(self.backing.get({
-			let mut r = RlpStream::new_list(2);
-			r.append(&end_era);
-			r.append(&index);
-			last = r.out();
-			&last
-		})) {
-			let rlp = Rlp::new(&rlp_data);
-			let to_remove: Vec<H256> = rlp.val_at(if *canon_id == rlp.val_at(0) {2} else {1});
-			for i in to_remove.iter() {
-				self.forward.remove(i);
+		if let Some((end_era, canon_id)) = end {
+			let mut index = 0usize;
+			let mut last;
+			while let Some(rlp_data) = try!(self.backing.get({
+				let mut r = RlpStream::new_list(2);
+				r.append(&end_era);
+				r.append(&index);
+				last = r.out();
+				&last
+			})) {
+				let rlp = Rlp::new(&rlp_data);
+				let to_remove: Vec<H256> = rlp.val_at(if *canon_id == rlp.val_at(0) {2} else {1});
+				for i in to_remove.iter() {
+					self.forward.remove(i);
+				}
+				try!(self.backing.delete(&last));
+				index += 1;
 			}
-			try!(self.backing.delete(&last));
-			index += 1;
 		}
 
-		self.inserts.clear();
-		self.removes.clear();
-
 		self.forward.commit()
 	}
 
@@ -121,3 +120,94 @@ impl HashDB for JournalDB {
 	fn emplace(&mut self, key: H256, value: Bytes) { self.inserts.push(key.clone()); self.forward.emplace(key, value); }
 	fn kill(&mut self, key: &H256) { self.removes.push(key.clone()); }
 }
+
+#[cfg(test)]
+mod tests {
+	use common::*;
+	use super::*;
+	use hashdb::*;
+
+	#[test]
+	fn long_history() {
+		// history is 3
+		let mut jdb = JournalDB::new_temp();
+		let h = jdb.insert(b"foo");
+		jdb.commit(0, &b"0".sha3(), None).unwrap();
+		assert!(jdb.exists(&h));
+		jdb.remove(&h);
+		jdb.commit(1, &b"1".sha3(), None).unwrap();
+		assert!(jdb.exists(&h));
+		jdb.commit(2, &b"2".sha3(), None).unwrap();
+		assert!(jdb.exists(&h));
+		jdb.commit(3, &b"3".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		assert!(jdb.exists(&h));
+		jdb.commit(4, &b"4".sha3(), Some((1, &b"1".sha3()))).unwrap();
+		assert!(!jdb.exists(&h));
+	}
+
+	#[test]
+	fn complex() {
+		// history is 1
+		let mut jdb = JournalDB::new_temp();
+
+		let foo = jdb.insert(b"foo");
+		let bar = jdb.insert(b"bar");
+		jdb.commit(0, &b"0".sha3(), None).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(jdb.exists(&bar));
+
+		jdb.remove(&foo);
+		jdb.remove(&bar);
+		let baz = jdb.insert(b"baz");
+		jdb.commit(1, &b"1".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(jdb.exists(&bar));
+		assert!(jdb.exists(&baz));
+
+		let foo = jdb.insert(b"foo");
+		jdb.remove(&baz);
+		jdb.commit(2, &b"2".sha3(), Some((1, &b"1".sha3()))).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(!jdb.exists(&bar));
+		assert!(jdb.exists(&baz));
+
+		jdb.remove(&foo);
+		jdb.commit(3, &b"3".sha3(), Some((2, &b"2".sha3()))).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(!jdb.exists(&bar));
+		assert!(!jdb.exists(&baz));
+
+		jdb.commit(4, &b"4".sha3(), Some((3, &b"3".sha3()))).unwrap();
+		assert!(!jdb.exists(&foo));
+		assert!(!jdb.exists(&bar));
+		assert!(!jdb.exists(&baz));
+	}
+
+	#[test]
+	fn fork() {
+		// history is 1
+		let mut jdb = JournalDB::new_temp();
+
+		let foo = jdb.insert(b"foo");
+		let bar = jdb.insert(b"bar");
+		jdb.commit(0, &b"0".sha3(), None).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(jdb.exists(&bar));
+
+		jdb.remove(&foo);
+		let baz = jdb.insert(b"baz");
+		jdb.commit(1, &b"1a".sha3(), Some((0, &b"0".sha3()))).unwrap();
+
+		jdb.remove(&bar);
+		jdb.commit(1, &b"1b".sha3(), Some((0, &b"0".sha3()))).unwrap();
+
+		assert!(jdb.exists(&foo));
+		assert!(jdb.exists(&bar));
+		assert!(jdb.exists(&baz));
+
+		jdb.commit(2, &b"2b".sha3(), Some((1, &b"1b".sha3()))).unwrap();
+		assert!(jdb.exists(&foo));
+		assert!(!jdb.exists(&baz));
+		assert!(!jdb.exists(&bar));
+	}
+}

From b9b08af518e6e8a4a6a36b3a89695cf7c6208c28 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 13:54:46 +0100
Subject: [PATCH 03/15] Use JournalDB instead of OverlayDB.

---
 src/account.rs         | 10 +++++-----
 src/block.rs           | 16 ++++++++--------
 src/blockchain.rs      |  2 +-
 src/client.rs          | 14 +++++++++-----
 src/ethereum/ethash.rs |  4 ++--
 src/ethereum/mod.rs    |  2 +-
 src/spec.rs            |  5 +++--
 src/state.rs           | 12 ++++++------
 util/src/journaldb.rs  |  4 ++--
 util/src/lib.rs        |  1 +
 util/src/overlaydb.rs  | 13 +++++++++----
 11 files changed, 47 insertions(+), 36 deletions(-)

diff --git a/src/account.rs b/src/account.rs
index 8c36c7cbd..c64e80ed8 100644
--- a/src/account.rs
+++ b/src/account.rs
@@ -236,7 +236,7 @@ mod tests {
 
 	#[test]
 	fn storage_at() {
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 		let rlp = {
 			let mut a = Account::new_contract(U256::from(69u8));
 			a.set_storage(H256::from(&U256::from(0x00u64)), H256::from(&U256::from(0x1234u64)));
@@ -254,7 +254,7 @@ mod tests {
 
 	#[test]
 	fn note_code() {
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 
 		let rlp = {
 			let mut a = Account::new_contract(U256::from(69u8));
@@ -273,7 +273,7 @@ mod tests {
 	#[test]
 	fn commit_storage() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 		a.set_storage(x!(0), x!(0x1234));
 		assert_eq!(a.storage_root(), None);
 		a.commit_storage(&mut db);
@@ -283,7 +283,7 @@ mod tests {
 	#[test]
 	fn commit_remove_commit_storage() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 		a.set_storage(x!(0), x!(0x1234));
 		a.commit_storage(&mut db);
 		a.set_storage(x!(1), x!(0x1234));
@@ -296,7 +296,7 @@ mod tests {
 	#[test]
 	fn commit_code() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 		a.init_code(vec![0x55, 0x44, 0xffu8]);
 		assert_eq!(a.code_hash(), SHA3_EMPTY);
 		a.commit_code(&mut db);
diff --git a/src/block.rs b/src/block.rs
index d149d6132..d47fccc26 100644
--- a/src/block.rs
+++ b/src/block.rs
@@ -103,7 +103,7 @@ pub struct SealedBlock {
 
 impl<'x, 'y> OpenBlock<'x, 'y> {
 	/// Create a new OpenBlock ready for transaction pushing.
-	pub fn new<'a, 'b>(engine: &'a Engine, db: OverlayDB, parent: &Header, last_hashes: &'b LastHashes, author: Address, extra_data: Bytes) -> OpenBlock<'a, 'b> {
+	pub fn new<'a, 'b>(engine: &'a Engine, db: JournalDB, parent: &Header, last_hashes: &'b LastHashes, author: Address, extra_data: Bytes) -> OpenBlock<'a, 'b> {
 		let mut r = OpenBlock {
 			block: Block::new(State::from_existing(db, parent.state_root().clone(), engine.account_start_nonce())),
 			engine: engine,
@@ -241,7 +241,7 @@ impl<'x, 'y> ClosedBlock<'x, 'y> {
 	pub fn reopen(self) -> OpenBlock<'x, 'y> { self.open_block }
 
 	/// Drop this object and return the underlieing database.
-	pub fn drain(self) -> OverlayDB { self.open_block.block.state.drop().1 }
+	pub fn drain(self) -> JournalDB { self.open_block.block.state.drop().1 }
 }
 
 impl SealedBlock {
@@ -256,7 +256,7 @@ impl SealedBlock {
 	}
 
 	/// Drop this object and return the underlieing database.
-	pub fn drain(self) -> OverlayDB { self.block.state.drop().1 }
+	pub fn drain(self) -> JournalDB { self.block.state.drop().1 }
 }
 
 impl IsBlock for SealedBlock {
@@ -264,7 +264,7 @@ impl IsBlock for SealedBlock {
 }
 
 /// Enact the block given by `block_bytes` using `engine` on the database `db` with given `parent` block header
-pub fn enact<'x, 'y>(block_bytes: &[u8], engine: &'x Engine, db: OverlayDB, parent: &Header, last_hashes: &'y LastHashes) -> Result<ClosedBlock<'x, 'y>, Error> {
+pub fn enact<'x, 'y>(block_bytes: &[u8], engine: &'x Engine, db: JournalDB, parent: &Header, last_hashes: &'y LastHashes) -> Result<ClosedBlock<'x, 'y>, Error> {
 	{
 		let header = BlockView::new(block_bytes).header_view();
 		let s = State::from_existing(db.clone(), parent.state_root().clone(), engine.account_start_nonce());
@@ -284,7 +284,7 @@ pub fn enact<'x, 'y>(block_bytes: &[u8], engine: &'x Engine, db: OverlayDB, pare
 }
 
 /// Enact the block given by `block_bytes` using `engine` on the database `db` with given `parent` block header. Seal the block aferwards
-pub fn enact_and_seal(block_bytes: &[u8], engine: &Engine, db: OverlayDB, parent: &Header, last_hashes: &LastHashes) -> Result<SealedBlock, Error> {
+pub fn enact_and_seal(block_bytes: &[u8], engine: &Engine, db: JournalDB, parent: &Header, last_hashes: &LastHashes) -> Result<SealedBlock, Error> {
 	let header = BlockView::new(block_bytes).header_view();
 	Ok(try!(try!(enact(block_bytes, engine, db, parent, last_hashes)).seal(header.seal())))
 }
@@ -294,7 +294,7 @@ fn open_block() {
 	use spec::*;
 	let engine = Spec::new_test().to_engine().unwrap();
 	let genesis_header = engine.spec().genesis_header();
-	let mut db = OverlayDB::new_temp();
+	let mut db = JournalDB::new_temp();
 	engine.spec().ensure_db_good(&mut db);
 	let last_hashes = vec![genesis_header.hash()];
 	let b = OpenBlock::new(engine.deref(), db, &genesis_header, &last_hashes, Address::zero(), vec![]);
@@ -308,13 +308,13 @@ fn enact_block() {
 	let engine = Spec::new_test().to_engine().unwrap();
 	let genesis_header = engine.spec().genesis_header();
 
-	let mut db = OverlayDB::new_temp();
+	let mut db = JournalDB::new_temp();
 	engine.spec().ensure_db_good(&mut db);
 	let b = OpenBlock::new(engine.deref(), db, &genesis_header, &vec![genesis_header.hash()], Address::zero(), vec![]).close().seal(vec![]).unwrap();
 	let orig_bytes = b.rlp_bytes();
 	let orig_db = b.drain();
 
-	let mut db = OverlayDB::new_temp();
+	let mut db = JournalDB::new_temp();
 	engine.spec().ensure_db_good(&mut db);
 	let e = enact_and_seal(&orig_bytes, engine.deref(), db, &genesis_header, &vec![genesis_header.hash()]).unwrap();
 
diff --git a/src/blockchain.rs b/src/blockchain.rs
index f08d15057..f19b958c5 100644
--- a/src/blockchain.rs
+++ b/src/blockchain.rs
@@ -251,7 +251,7 @@ impl BlockChain {
 	/// Ensure that the best block does indeed have a state_root in the state DB.
 	/// If it doesn't, then rewind down until we find one that does and delete data to ensure that
 	/// later blocks will be reimported. 
-	pub fn ensure_good(&mut self, _state: &OverlayDB) {
+	pub fn ensure_good(&mut self, _state: &JournalDB) {
 		unimplemented!();
 	}
 
diff --git a/src/client.rs b/src/client.rs
index 3ee84ccd7..fe3eee242 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -104,10 +104,12 @@ pub trait BlockChainClient : Sync + Send {
 pub struct Client {
 	chain: Arc<RwLock<BlockChain>>,
 	engine: Arc<Box<Engine>>,
-	state_db: OverlayDB,
+	state_db: JournalDB,
 	queue: BlockQueue,
 }
 
+const HISTORY: u64 = 1000;
+
 impl Client {
 	/// Create a new client with given spec and DB path.
 	pub fn new(spec: Spec, path: &Path, message_channel: IoChannel<NetSyncMessage> ) -> Result<Client, Error> {
@@ -135,11 +137,12 @@ impl Client {
 		let mut state_path = path.to_path_buf();
 		state_path.push("state");
 		let db = DB::open(&opts, state_path.to_str().unwrap()).unwrap();
-		let mut state_db = OverlayDB::new(db);
+		let mut state_db = JournalDB::new(db);
 		
 		let engine = Arc::new(try!(spec.to_engine()));
-		engine.spec().ensure_db_good(&mut state_db);
-		state_db.commit().expect("Error commiting genesis state to state DB");
+		if engine.spec().ensure_db_good(&mut state_db) {
+			state_db.commit(0, &engine.spec().genesis_header().hash(), None).expect("Error commiting genesis state to state DB");
+		}
 
 //		chain.write().unwrap().ensure_good(&state_db);
 
@@ -196,7 +199,8 @@ impl Client {
 		}
 
 		self.chain.write().unwrap().insert_block(&bytes); //TODO: err here?
-		match result.drain().commit() {
+		let ancient = if header.number() >= HISTORY { Some(header.number() - HISTORY) } else { None };
+		match result.drain().commit(header.number(), &header.hash(), ancient.map(|n|(n, self.chain.read().unwrap().block_hash(n).unwrap()))) {
 			Ok(_) => (),
 			Err(e) => {
 				warn!(target: "client", "State DB commit failed: {:?}", e);
diff --git a/src/ethereum/ethash.rs b/src/ethereum/ethash.rs
index 99ffc3186..a5a1175fe 100644
--- a/src/ethereum/ethash.rs
+++ b/src/ethereum/ethash.rs
@@ -211,7 +211,7 @@ fn on_close_block() {
 	use super::*;
 	let engine = new_morden().to_engine().unwrap();
 	let genesis_header = engine.spec().genesis_header();
-	let mut db = OverlayDB::new_temp();
+	let mut db = JournalDB::new_temp();
 	engine.spec().ensure_db_good(&mut db);
 	let last_hashes = vec![genesis_header.hash()];
 	let b = OpenBlock::new(engine.deref(), db, &genesis_header, &last_hashes, Address::zero(), vec![]);
@@ -224,7 +224,7 @@ fn on_close_block_with_uncle() {
 	use super::*;
 	let engine = new_morden().to_engine().unwrap();
 	let genesis_header = engine.spec().genesis_header();
-	let mut db = OverlayDB::new_temp();
+	let mut db = JournalDB::new_temp();
 	engine.spec().ensure_db_good(&mut db);
 	let last_hashes = vec![genesis_header.hash()];
 	let mut b = OpenBlock::new(engine.deref(), db, &genesis_header, &last_hashes, Address::zero(), vec![]);
diff --git a/src/ethereum/mod.rs b/src/ethereum/mod.rs
index 603a64e7d..25a804db3 100644
--- a/src/ethereum/mod.rs
+++ b/src/ethereum/mod.rs
@@ -40,7 +40,7 @@ mod tests {
 	fn ensure_db_good() {
 		let engine = new_morden().to_engine().unwrap();
 		let genesis_header = engine.spec().genesis_header();
-		let mut db = OverlayDB::new_temp();
+		let mut db = MemoryDB::new_temp();
 		engine.spec().ensure_db_good(&mut db);
 		let s = State::from_existing(db.clone(), genesis_header.state_root.clone(), engine.account_start_nonce());
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000001")), U256::from(1u64));
diff --git a/src/spec.rs b/src/spec.rs
index b174b0e9f..e93b460c8 100644
--- a/src/spec.rs
+++ b/src/spec.rs
@@ -220,7 +220,7 @@ impl FromJson for Spec {
 
 impl Spec {
 	/// Ensure that the given state DB has the trie nodes in for the genesis state.
-	pub fn ensure_db_good(&self, db: &mut HashDB) {
+	pub fn ensure_db_good(&self, db: &mut HashDB) -> bool {
 		if !db.contains(&self.state_root()) {
 			info!("Populating genesis state...");
 			let mut root = H256::new(); 
@@ -232,7 +232,8 @@ impl Spec {
 			}
 			assert!(db.contains(&self.state_root()));
 			info!("Genesis state is ready");
-		}
+			true
+		} else { false }
 	}
 
 	/// Create a new Spec from a JSON UTF-8 data resource `data`.
diff --git a/src/state.rs b/src/state.rs
index a186d6cd6..e325b8d34 100644
--- a/src/state.rs
+++ b/src/state.rs
@@ -10,7 +10,7 @@ pub type ApplyResult = Result<Receipt, Error>;
 /// Representation of the entire state of all accounts in the system.
 #[derive(Clone)]
 pub struct State {
-	db: OverlayDB,
+	db: JournalDB,
 	root: H256,
 	cache: RefCell<HashMap<Address, Option<Account>>>,
 
@@ -19,7 +19,7 @@ pub struct State {
 
 impl State {
 	/// Creates new state with empty state root
-	pub fn new(mut db: OverlayDB, account_start_nonce: U256) -> State {
+	pub fn new(mut db: JournalDB, account_start_nonce: U256) -> State {
 		let mut root = H256::new();
 		{
 			// init trie and reset root too null
@@ -35,7 +35,7 @@ impl State {
 	}
 
 	/// Creates new state with existing state root
-	pub fn from_existing(db: OverlayDB, root: H256, account_start_nonce: U256) -> State {
+	pub fn from_existing(db: JournalDB, root: H256, account_start_nonce: U256) -> State {
 		{
 			// trie should panic! if root does not exist
 			let _ = SecTrieDB::new(&db, &root);
@@ -51,11 +51,11 @@ impl State {
 
 	/// Create temporary state object
 	pub fn new_temp() -> State {
-		Self::new(OverlayDB::new_temp(), U256::from(0u8))
+		Self::new(JournalDB::new_temp(), U256::from(0u8))
 	}
 
 	/// Destroy the current object and return root and database.
-	pub fn drop(self) -> (H256, OverlayDB) {
+	pub fn drop(self) -> (H256, JournalDB) {
 		(self.root, self.db)
 	}
 
@@ -65,7 +65,7 @@ impl State {
 	}
 
 	/// Expose the underlying database; good to use for calling `state.db().commit()`.
-	pub fn db(&mut self) -> &mut OverlayDB {
+	pub fn db(&mut self) -> &mut JournalDB {
 		&mut self.db
 	}
 
diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index 011d46663..8dd49cda1 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -46,7 +46,7 @@ impl JournalDB {
 
 	/// Commit all recent insert operations and historical removals from the old era
 	/// to the backing database.
-	pub fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, &H256)>) -> Result<u32, UtilError> {
+	pub fn commit(&mut self, now: u64, id: &H256, end: Option<(u64, H256)>) -> Result<u32, UtilError> {
 		// journal format: 
 		// [era, 0] => [ id, [insert_0, ...], [remove_0, ...] ]
 		// [era, 1] => [ id, [insert_0, ...], [remove_0, ...] ]
@@ -95,7 +95,7 @@ impl JournalDB {
 				&last
 			})) {
 				let rlp = Rlp::new(&rlp_data);
-				let to_remove: Vec<H256> = rlp.val_at(if *canon_id == rlp.val_at(0) {2} else {1});
+				let to_remove: Vec<H256> = rlp.val_at(if canon_id == rlp.val_at(0) {2} else {1});
 				for i in to_remove.iter() {
 					self.forward.remove(i);
 				}
diff --git a/util/src/lib.rs b/util/src/lib.rs
index 34961f1de..204266c54 100644
--- a/util/src/lib.rs
+++ b/util/src/lib.rs
@@ -89,6 +89,7 @@ pub use rlp::*;
 pub use hashdb::*;
 pub use memorydb::*;
 pub use overlaydb::*;
+pub use journaldb::*;
 pub use math::*;
 pub use chainfilter::*;
 pub use crypto::*;
diff --git a/util/src/overlaydb.rs b/util/src/overlaydb.rs
index 6330f1e25..3c2286657 100644
--- a/util/src/overlaydb.rs
+++ b/util/src/overlaydb.rs
@@ -131,10 +131,15 @@ impl OverlayDB {
 
 	/// Get the refs and value of the given key.
 	fn put_payload(&self, key: &H256, payload: (Bytes, u32)) {
-		let mut s = RlpStream::new_list(2);
-		s.append(&payload.1);
-		s.append(&payload.0);
-		self.backing.put(&key.bytes(), &s.out()).expect("Low-level database error. Some issue with your hard disk?");
+		if payload.1 > 0 {
+			let mut s = RlpStream::new_list(2);
+			s.append(&payload.1);
+			s.append(&payload.0);
+			self.backing.put(&key.bytes(), &s.out()).expect("Low-level database error. Some issue with your hard disk?");
+		} else {
+			self.backing.delete(&key.bytes()).expect("Low-level database error. Some issue with your hard disk?");
+		}
+
 	}
 }
 

From 7b0e4af078eac3b63147fefaf90674e780373d5f Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 14:44:06 +0100
Subject: [PATCH 04/15] Compact state DB finished. Closes #172

---
 src/client.rs         | 6 +++---
 src/sync/chain.rs     | 2 +-
 util/src/journaldb.rs | 1 +
 util/src/overlaydb.rs | 8 ++++++--
 4 files changed, 11 insertions(+), 6 deletions(-)

diff --git a/src/client.rs b/src/client.rs
index fe3eee242..cb1f4672d 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -117,7 +117,7 @@ impl Client {
 		let mut opts = Options::new();
 		opts.create_if_missing(true);
 		opts.set_max_open_files(256);
-		opts.set_use_fsync(false);
+		/*opts.set_use_fsync(false);
 		opts.set_bytes_per_sync(8388608);
 		opts.set_disable_data_sync(false);
 		opts.set_block_cache_size_mb(1024);
@@ -132,7 +132,7 @@ impl Client {
 		opts.set_max_background_compactions(4);
 		opts.set_max_background_flushes(4);
 		opts.set_filter_deletes(false);
-		opts.set_disable_auto_compactions(true);		
+		opts.set_disable_auto_compactions(false);*/
 
 		let mut state_path = path.to_path_buf();
 		state_path.push("state");
@@ -207,7 +207,7 @@ impl Client {
 				return;
 			}
 		}
-		info!(target: "client", "Imported #{} ({})", header.number(), header.hash());
+		debug!(target: "client", "Imported #{} ({})", header.number(), header.hash());
 	}
 }
 
diff --git a/src/sync/chain.rs b/src/sync/chain.rs
index 43f5968f4..40dbc6c9c 100644
--- a/src/sync/chain.rs
+++ b/src/sync/chain.rs
@@ -471,7 +471,7 @@ impl ChainSync {
 	pub fn on_peer_aborting(&mut self, io: &mut SyncIo, peer: PeerId) {
 		trace!(target: "sync", "== Disconnecting {}", peer);
 		if self.peers.contains_key(&peer) {
-			info!(target: "sync", "Disconneced {}:{}", peer, io.peer_info(peer));
+			info!(target: "sync", "Disconnected {}:{}", peer, io.peer_info(peer));
 			self.clear_peer_download(peer);
 			self.peers.remove(&peer);
 			self.continue_sync(io);
diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index 8dd49cda1..803c0a8c3 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -100,6 +100,7 @@ impl JournalDB {
 					self.forward.remove(i);
 				}
 				try!(self.backing.delete(&last));
+				info!("JournalDB: delete journal for time #{}.{}, (canon was {}): {} entries", end_era, index, canon_id, to_remove.len());
 				index += 1;
 			}
 		}
diff --git a/util/src/overlaydb.rs b/util/src/overlaydb.rs
index 3c2286657..1d369af96 100644
--- a/util/src/overlaydb.rs
+++ b/util/src/overlaydb.rs
@@ -71,6 +71,7 @@ impl OverlayDB {
 	/// ```
 	pub fn commit(&mut self) -> Result<u32, UtilError> {
 		let mut ret = 0u32;
+		let mut deletes = 0usize;
 		for i in self.overlay.drain().into_iter() {
 			let (key, (value, rc)) = i;
 			if rc != 0 {
@@ -81,7 +82,7 @@ impl OverlayDB {
 						if total_rc < 0 {
 							return Err(From::from(BaseDataError::NegativelyReferencedHash));
 						}
-						self.put_payload(&key, (back_value, total_rc as u32));
+						deletes += if self.put_payload(&key, (back_value, total_rc as u32)) {1} else {0};
 					}
 					None => {
 						if rc < 0 {
@@ -93,6 +94,7 @@ impl OverlayDB {
 				ret += 1;
 			}
 		}
+		info!("OverlayDB::commit() deleted {} nodes", deletes);
 		Ok(ret)
 	}
 
@@ -130,14 +132,16 @@ impl OverlayDB {
 	}
 
 	/// Get the refs and value of the given key.
-	fn put_payload(&self, key: &H256, payload: (Bytes, u32)) {
+	fn put_payload(&self, key: &H256, payload: (Bytes, u32)) -> bool {
 		if payload.1 > 0 {
 			let mut s = RlpStream::new_list(2);
 			s.append(&payload.1);
 			s.append(&payload.0);
 			self.backing.put(&key.bytes(), &s.out()).expect("Low-level database error. Some issue with your hard disk?");
+			false
 		} else {
 			self.backing.delete(&key.bytes()).expect("Low-level database error. Some issue with your hard disk?");
+			true
 		}
 
 	}

From 0222b3e08154dd385cf9ca01dd8e8017fd6ec150 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 14:51:49 +0100
Subject: [PATCH 05/15] Reduce log verbosity.

---
 util/src/journaldb.rs | 2 +-
 util/src/overlaydb.rs | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index 803c0a8c3..db45d51c7 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -100,7 +100,7 @@ impl JournalDB {
 					self.forward.remove(i);
 				}
 				try!(self.backing.delete(&last));
-				info!("JournalDB: delete journal for time #{}.{}, (canon was {}): {} entries", end_era, index, canon_id, to_remove.len());
+				trace!("JournalDB: delete journal for time #{}.{}, (canon was {}): {} entries", end_era, index, canon_id, to_remove.len());
 				index += 1;
 			}
 		}
diff --git a/util/src/overlaydb.rs b/util/src/overlaydb.rs
index 1d369af96..07c992693 100644
--- a/util/src/overlaydb.rs
+++ b/util/src/overlaydb.rs
@@ -94,7 +94,7 @@ impl OverlayDB {
 				ret += 1;
 			}
 		}
-		info!("OverlayDB::commit() deleted {} nodes", deletes);
+		trace!("OverlayDB::commit() deleted {} nodes", deletes);
 		Ok(ret)
 	}
 

From 1eafdc70087202f5fb9fe6a8ccc10b6641098dbd Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 15:47:50 +0100
Subject: [PATCH 06/15] PR fixes.

---
 src/client.rs             | 1 -
 util/src/journaldb.rs     | 6 +++---
 util/src/rlp/rlpstream.rs | 8 ++++++++
 3 files changed, 11 insertions(+), 4 deletions(-)

diff --git a/src/client.rs b/src/client.rs
index cb1f4672d..dc8bf3608 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -1,6 +1,5 @@
 use util::*;
 use rocksdb::{Options, DB};
-use rocksdb::DBCompactionStyle::DBUniversalCompaction;
 use blockchain::{BlockChain, BlockProvider};
 use views::BlockView;
 use error::*;
diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index db45d51c7..a4032c154 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -68,7 +68,7 @@ impl JournalDB {
 				let mut r = RlpStream::new_list(2);
 				r.append(&now);
 				r.append(&index);
-				last = r.out();
+				last = r.drain();
 				&last
 			})).is_some() {
 				index += 1;
@@ -78,7 +78,7 @@ impl JournalDB {
 			r.append(id);
 			r.append(&self.inserts);
 			r.append(&self.removes);
-			try!(self.backing.put(&last, &r.out()));
+			try!(self.backing.put(&last, r.as_raw()));
 			self.inserts.clear();
 			self.removes.clear();
 		}
@@ -91,7 +91,7 @@ impl JournalDB {
 				let mut r = RlpStream::new_list(2);
 				r.append(&end_era);
 				r.append(&index);
-				last = r.out();
+				last = r.drain();
 				&last
 			})) {
 				let rlp = Rlp::new(&rlp_data);
diff --git a/util/src/rlp/rlpstream.rs b/util/src/rlp/rlpstream.rs
index b8954ae6f..a30978f24 100644
--- a/util/src/rlp/rlpstream.rs
+++ b/util/src/rlp/rlpstream.rs
@@ -142,6 +142,14 @@ impl RlpStream {
 			self.note_appended(1);
 		}
 	}
+
+	/// Drain the object and return the underlying ElasticArray.
+	pub fn drain(self) -> ElasticArray1024<u8> {
+		match self.is_finished() {
+			true => self.encoder.bytes,
+			false => panic!()
+		}
+	}
 }
 
 struct BasicEncoder {

From bd21c6c327cd69c4df2f4bf104a23fdc020e32b1 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 15:48:38 +0100
Subject: [PATCH 07/15] note_used and cache management datatypes.

---
 src/blockchain.rs | 39 +++++++++++++++++++++++++++++++++++++--
 1 file changed, 37 insertions(+), 2 deletions(-)

diff --git a/src/blockchain.rs b/src/blockchain.rs
index f19b958c5..b55b71fdb 100644
--- a/src/blockchain.rs
+++ b/src/blockchain.rs
@@ -96,6 +96,17 @@ pub trait BlockProvider {
 	}
 }
 
+#[derive(Debug, Hash, Eq, PartialEq, Clone)]
+struct CacheID {
+	id: H256,
+	extra: usize
+}
+
+struct CacheManager {
+	cache_usage: VecDeque<HashSet<CacheID>>,
+	in_use: HashSet<CacheID>,
+}
+
 /// Structure providing fast access to blockchain data.
 ///
 /// **Does not do input data verification.**
@@ -113,7 +124,9 @@ pub struct BlockChain {
 	blocks_blooms: RwLock<HashMap<H256, BlocksBlooms>>,
 
 	extras_db: DB,
-	blocks_db: DB
+	blocks_db: DB,
+
+	cache_man: RwLock<CacheManager>,
 }
 
 impl BlockProvider for BlockChain {
@@ -158,6 +171,10 @@ impl BlockProvider for BlockChain {
 	}
 }
 
+const COLLECTION_QUEUE_SIZE: usize = 2;
+const MIN_CACHE_SIZE: usize = 1;
+const MAX_CACHE_SIZE: usize = 1024 * 1024 * 1;
+
 impl BlockChain {
 	/// Create new instance of blockchain from given Genesis
 	///
@@ -206,7 +223,8 @@ impl BlockChain {
 			block_logs: RwLock::new(HashMap::new()),
 			blocks_blooms: RwLock::new(HashMap::new()),
 			extras_db: extras_db,
-			blocks_db: blocks_db
+			blocks_db: blocks_db,
+			cache_man: RwLock::new(CacheManager{cache_usage: VecDeque::new(), in_use: HashSet::new()}),
 		};
 
 		// load best block
@@ -537,6 +555,23 @@ impl BlockChain {
 		self.block_logs.write().unwrap().squeeze(size.block_logs);
 		self.blocks_blooms.write().unwrap().squeeze(size.blocks_blooms);
 	}
+
+	fn note_used(&self, id: CacheID) {
+		let mut cache_man = self.cache_man.write().unwrap();
+		cache_man.cache_usage[0].insert(id.clone());
+		// TODO: check more than just the first?
+		if cache_man.cache_usage[1].contains(&id) {
+			cache_man.cache_usage[1].remove(&id);
+		}
+		else {
+			cache_man.in_use.insert(id);
+		}
+	}
+
+	/// Ticks our cache system and throws out any old data.
+	pub fn tick(&self) {
+
+	}
 }
 
 #[cfg(test)]

From 76cded453bfeb629dc6e935f699ed2293ff045d2 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 19:23:28 +0100
Subject: [PATCH 08/15] Cache manager. Closes #135

---
 src/bin/client.rs |  4 ++-
 src/blockchain.rs | 71 +++++++++++++++++++++++++++++++++++++++--------
 src/client.rs     | 18 +++++++++++-
 src/extras.rs     |  4 ++-
 4 files changed, 82 insertions(+), 15 deletions(-)

diff --git a/src/bin/client.rs b/src/bin/client.rs
index a862737be..19ae5bfd8 100644
--- a/src/bin/client.rs
+++ b/src/bin/client.rs
@@ -53,7 +53,9 @@ impl IoHandler<NetSyncMessage> for ClientIoHandler {
 
 	fn timeout<'s>(&'s mut self, _io: &mut IoContext<'s, NetSyncMessage>, timer: TimerToken) {
 		if self.timer == timer {
-			println!("Chain info: {:?}", self.client.read().unwrap().deref().chain_info());
+			self.client.tick();
+			println!("Chain info: {}", self.client.read().unwrap().deref().chain_info());
+			println!("Cache info: {:?}", self.client.read().unwrap().deref().cache_info());
 		}
 	}
 }
diff --git a/src/blockchain.rs b/src/blockchain.rs
index b55b71fdb..d0b97a0ff 100644
--- a/src/blockchain.rs
+++ b/src/blockchain.rs
@@ -30,6 +30,11 @@ pub struct CacheSize {
 	pub blocks_blooms: usize
 }
 
+impl CacheSize {
+	/// Total amount used by the cache.
+	fn total(&self) -> usize { self.blocks + self.block_details + self.transaction_addresses + self.block_logs + self.blocks_blooms }
+}
+
 /// Information about best block gathered together
 struct BestBlock {
 	pub hash: H256,
@@ -97,9 +102,9 @@ pub trait BlockProvider {
 }
 
 #[derive(Debug, Hash, Eq, PartialEq, Clone)]
-struct CacheID {
-	id: H256,
-	extra: usize
+enum CacheID {
+	Block(H256),
+	Extras(ExtrasIndex, H256),
 }
 
 struct CacheManager {
@@ -149,6 +154,8 @@ impl BlockProvider for BlockChain {
 		let opt = self.blocks_db.get(hash)
 			.expect("Low level database error. Some issue with disk?");
 
+		self.note_used(CacheID::Block(hash.clone()));
+
 		match opt {
 			Some(b) => {
 				let bytes: Bytes = b.to_vec();
@@ -214,6 +221,9 @@ impl BlockChain {
 		blocks_path.push("blocks");
 		let blocks_db = DB::open_default(blocks_path.to_str().unwrap()).unwrap();
 
+		let mut cache_man = CacheManager{cache_usage: VecDeque::new(), in_use: HashSet::new()};
+		(0..COLLECTION_QUEUE_SIZE).foreach(|_| cache_man.cache_usage.push_back(HashSet::new()));
+
 		let bc = BlockChain {
 			best_block: RwLock::new(BestBlock::new()),
 			blocks: RwLock::new(HashMap::new()),
@@ -224,7 +234,7 @@ impl BlockChain {
 			blocks_blooms: RwLock::new(HashMap::new()),
 			extras_db: extras_db,
 			blocks_db: blocks_db,
-			cache_man: RwLock::new(CacheManager{cache_usage: VecDeque::new(), in_use: HashSet::new()}),
+			cache_man: RwLock::new(cache_man),
 		};
 
 		// load best block
@@ -515,6 +525,10 @@ impl BlockChain {
 			}
 		}
 
+		if let Some(h) = hash.as_h256() {
+			self.note_used(CacheID::Extras(T::extras_index(), h.clone()));
+		}
+
 		self.extras_db.get_extras(hash).map(| t: T | {
 			let mut write = cache.write().unwrap();
 			write.insert(hash.clone(), t.clone());
@@ -556,21 +570,54 @@ impl BlockChain {
 		self.blocks_blooms.write().unwrap().squeeze(size.blocks_blooms);
 	}
 
+	/// Let the cache system know that a cacheable item has been used.
 	fn note_used(&self, id: CacheID) {
 		let mut cache_man = self.cache_man.write().unwrap();
-		cache_man.cache_usage[0].insert(id.clone());
-		// TODO: check more than just the first?
-		if cache_man.cache_usage[1].contains(&id) {
-			cache_man.cache_usage[1].remove(&id);
-		}
-		else {
-			cache_man.in_use.insert(id);
+		if !cache_man.cache_usage[0].contains(&id) {
+			cache_man.cache_usage[0].insert(id.clone());
+			if cache_man.in_use.contains(&id) {
+				if let Some(c) = cache_man.cache_usage.iter_mut().skip(1).find(|e|e.contains(&id)) {
+					c.remove(&id);
+				}
+			} else {
+				cache_man.in_use.insert(id);
+			}
 		}
 	}
 
 	/// Ticks our cache system and throws out any old data.
-	pub fn tick(&self) {
+	pub fn collect_garbage(&self, force: bool) {
+		// TODO: check time.
+		let timeout = true;
 
+		let t = self.cache_size().total();
+		if t < MIN_CACHE_SIZE || (!timeout && (!force || t < MAX_CACHE_SIZE)) { return; }
+
+		let mut cache_man = self.cache_man.write().unwrap();
+		let mut blocks = self.blocks.write().unwrap();
+		let mut block_details = self.block_details.write().unwrap();
+		let mut block_hashes = self.block_hashes.write().unwrap();
+		let mut transaction_addresses = self.transaction_addresses.write().unwrap();
+		let mut block_logs = self.block_logs.write().unwrap();
+		let mut blocks_blooms = self.blocks_blooms.write().unwrap();
+
+		for id in cache_man.cache_usage.pop_back().unwrap().into_iter() {
+			cache_man.in_use.remove(&id);
+			match id {
+				CacheID::Block(h) => { blocks.remove(&h); },
+				CacheID::Extras(ExtrasIndex::BlockDetails, h) => { block_details.remove(&h); },
+				CacheID::Extras(ExtrasIndex::TransactionAddress, h) => { transaction_addresses.remove(&h); },
+				CacheID::Extras(ExtrasIndex::BlockLogBlooms, h) => { block_logs.remove(&h); },
+				CacheID::Extras(ExtrasIndex::BlocksBlooms, h) => { blocks_blooms.remove(&h); },
+				_ => panic!(),
+			}
+		}
+		cache_man.cache_usage.push_front(HashSet::new());
+
+		// TODO: handle block_hashes properly.
+		block_hashes.clear();
+
+		// TODO: m_lastCollection = chrono::system_clock::now();
 	}
 }
 
diff --git a/src/client.rs b/src/client.rs
index dc8bf3608..0d9e94606 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -1,6 +1,6 @@
 use util::*;
 use rocksdb::{Options, DB};
-use blockchain::{BlockChain, BlockProvider};
+use blockchain::{BlockChain, BlockProvider, CacheSize};
 use views::BlockView;
 use error::*;
 use header::BlockNumber;
@@ -40,6 +40,12 @@ pub struct BlockChainInfo {
 	pub best_block_number: BlockNumber
 }
 
+impl fmt::Display for BlockChainInfo {
+	fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+		write!(f, "#{}.{}", self.best_block_number, self.best_block_hash)
+	}
+}
+
 /// Block queue status
 #[derive(Debug)]
 pub struct BlockQueueStatus {
@@ -208,6 +214,16 @@ impl Client {
 		}
 		debug!(target: "client", "Imported #{} ({})", header.number(), header.hash());
 	}
+
+	/// Get info on the cache.
+	pub fn cache_info(&self) -> CacheSize {
+		self.chain.read().unwrap().cache_size()
+	}
+
+	/// Tick the client.
+	pub fn tick(&self) {
+		self.chain.read().unwrap().collect_garbage(false);
+	}
 }
 
 impl BlockChainClient for Client {
diff --git a/src/extras.rs b/src/extras.rs
index ed0032698..8052af791 100644
--- a/src/extras.rs
+++ b/src/extras.rs
@@ -3,7 +3,7 @@ use header::BlockNumber;
 use rocksdb::{DB, Writable};
 
 /// Represents index of extra data in database
-#[derive(Copy, Clone)]
+#[derive(Copy, Debug, Hash, Eq, PartialEq, Clone)]
 pub enum ExtrasIndex {
 	BlockDetails = 0,
 	BlockHash = 1,
@@ -59,6 +59,7 @@ impl ExtrasReadable for DB {
 /// Implementations should convert arbitrary type to database key slice
 pub trait ExtrasSliceConvertable {
 	fn to_extras_slice(&self, i: ExtrasIndex) -> H264;
+	fn as_h256(&self) -> Option<&H256> { None }
 }
 
 impl ExtrasSliceConvertable for H256 {
@@ -67,6 +68,7 @@ impl ExtrasSliceConvertable for H256 {
 		slice[32] = i as u8;
 		slice
 	}
+	fn as_h256(&self) -> Option<&H256> { Some(self) }
 }
 
 impl ExtrasSliceConvertable for U256 {

From a2860eb1151b986f6f93f4c448edadab67dc729a Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 19:34:30 +0100
Subject: [PATCH 09/15] Fix client builds.

---
 src/bin/client.rs | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/bin/client.rs b/src/bin/client.rs
index 19ae5bfd8..6f0f4f475 100644
--- a/src/bin/client.rs
+++ b/src/bin/client.rs
@@ -53,9 +53,10 @@ impl IoHandler<NetSyncMessage> for ClientIoHandler {
 
 	fn timeout<'s>(&'s mut self, _io: &mut IoContext<'s, NetSyncMessage>, timer: TimerToken) {
 		if self.timer == timer {
-			self.client.tick();
-			println!("Chain info: {}", self.client.read().unwrap().deref().chain_info());
-			println!("Cache info: {:?}", self.client.read().unwrap().deref().cache_info());
+			let client = self.client.read().unwrap();
+			client.tick();
+			println!("Chain info: {}", client.chain_info());
+			println!("Cache info: {:?}", client.cache_info());
 		}
 	}
 }

From 40d9cbdeafb5dd4a8599ed6e30e5d9f402949a0b Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 23:23:32 +0100
Subject: [PATCH 10/15] Delta-based logging. Closes #181

---
 src/bin/client.rs | 43 ++++++++++++++++++++++++++++++++++++++++---
 src/client.rs     | 26 +++++++++++++++++++++++++-
 2 files changed, 65 insertions(+), 4 deletions(-)

diff --git a/src/bin/client.rs b/src/bin/client.rs
index 6f0f4f475..3335d8a72 100644
--- a/src/bin/client.rs
+++ b/src/bin/client.rs
@@ -12,6 +12,7 @@ use util::*;
 use ethcore::client::*;
 use ethcore::service::ClientService;
 use ethcore::ethereum;
+use ethcore::blockchain::CacheSize;
 use ethcore::sync::*;
 
 fn setup_log() {
@@ -29,7 +30,7 @@ fn main() {
 	setup_log();
 	let spec = ethereum::new_frontier();
 	let mut service = ClientService::start(spec).unwrap();
-	let io_handler  = Box::new(ClientIoHandler { client: service.client(), timer: 0 });
+	let io_handler  = Box::new(ClientIoHandler { client: service.client(), timer: 0, info: Default::default() });
 	service.io().register_handler(io_handler).expect("Error registering IO handler");
 	loop {
 		let mut cmd = String::new();
@@ -40,10 +41,47 @@ fn main() {
 	}
 }
 
+#[derive(Default, Debug)]
+struct Informant {
+	chain_info: Option<BlockChainInfo>,
+	cache_info: Option<CacheSize>,
+	report: Option<ClientReport>,
+}
+
+impl Informant {
+	pub fn tick(&mut self, client: &Client) {
+		// 5 seconds betwen calls. TODO: calculate this properly.
+		let dur = 5usize;
+
+		let chain_info = client.chain_info();
+		let cache_info = client.cache_info();
+		let report = client.report();
+
+		if let (_, &Some(ref last_cache_info), &Some(ref last_report)) = (&self.chain_info, &self.cache_info, &self.report) {
+			println!("[ {} {} ]---[ {} blk/s | {} tx/s | {} gas/s  //···{}···//  {} ({}) bl  {} ({}) ex ]",
+				chain_info.best_block_number,
+				chain_info.best_block_hash,
+				(report.blocks_imported - last_report.blocks_imported) / dur,
+				(report.transactions_applied - last_report.transactions_applied) / dur,
+				(report.gas_processed - last_report.gas_processed) / From::from(dur),
+				0, // TODO: peers
+				cache_info.blocks,
+				cache_info.blocks as isize - last_cache_info.blocks as isize,
+				cache_info.block_details,
+				cache_info.block_details as isize - last_cache_info.block_details as isize
+			);
+		}
+
+		self.chain_info = Some(chain_info);
+		self.cache_info = Some(cache_info);
+		self.report = Some(report);
+	}
+}
 
 struct ClientIoHandler {
 	client: Arc<RwLock<Client>>,
 	timer: TimerToken,
+	info: Informant,
 }
 
 impl IoHandler<NetSyncMessage> for ClientIoHandler {
@@ -55,8 +93,7 @@ impl IoHandler<NetSyncMessage> for ClientIoHandler {
 		if self.timer == timer {
 			let client = self.client.read().unwrap();
 			client.tick();
-			println!("Chain info: {}", client.chain_info());
-			println!("Cache info: {:?}", client.cache_info());
+			self.info.tick(client.deref());
 		}
 	}
 }
diff --git a/src/client.rs b/src/client.rs
index f8c8e8bb8..cf57e6a07 100644
--- a/src/client.rs
+++ b/src/client.rs
@@ -105,12 +105,28 @@ pub trait BlockChainClient : Sync + Send {
 	fn chain_info(&self) -> BlockChainInfo;
 }
 
+#[derive(Default, Clone, Debug, Eq, PartialEq)]
+pub struct ClientReport {
+	pub blocks_imported: usize,
+	pub transactions_applied: usize,
+	pub gas_processed: U256,
+}
+
+impl ClientReport {
+	pub fn accrue_block(&mut self, block: &PreVerifiedBlock) {
+		self.blocks_imported += 1;
+		self.transactions_applied += block.transactions.len();
+		self.gas_processed += block.header.gas_used;
+	}
+}
+
 /// Blockchain database client backed by a persistent database. Owns and manages a blockchain and a block queue.
 pub struct Client {
 	chain: Arc<RwLock<BlockChain>>,
 	engine: Arc<Box<Engine>>,
 	state_db: JournalDB,
 	queue: BlockQueue,
+	report: ClientReport,
 }
 
 const HISTORY: u64 = 1000;
@@ -156,6 +172,7 @@ impl Client {
 			engine: engine.clone(),
 			state_db: state_db,
 			queue: BlockQueue::new(engine, message_channel),
+			report: Default::default(),
 		})
 	}
 
@@ -228,7 +245,9 @@ impl Client {
 					return;
 				}
 			}
-			info!(target: "client", "Imported #{} ({})", header.number(), header.hash());
+			self.report.accrue_block(&block);
+
+			trace!(target: "client", "Imported #{} ({})", header.number(), header.hash());
 		}
 	}
 
@@ -237,6 +256,11 @@ impl Client {
 		self.chain.read().unwrap().cache_size()
 	}
 
+	/// Get the report.
+	pub fn report(&self) -> ClientReport {
+		self.report.clone()
+	}
+
 	/// Tick the client.
 	pub fn tick(&self) {
 		self.chain.read().unwrap().collect_garbage(false);

From a9a4da4b3e33beaef36425defe833d96bde2faf5 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 23:50:40 +0100
Subject: [PATCH 11/15] Fix test build.

---
 util/src/journaldb.rs | 18 +++++++++---------
 1 file changed, 9 insertions(+), 9 deletions(-)

diff --git a/util/src/journaldb.rs b/util/src/journaldb.rs
index a4032c154..ada9c0d2b 100644
--- a/util/src/journaldb.rs
+++ b/util/src/journaldb.rs
@@ -140,9 +140,9 @@ mod tests {
 		assert!(jdb.exists(&h));
 		jdb.commit(2, &b"2".sha3(), None).unwrap();
 		assert!(jdb.exists(&h));
-		jdb.commit(3, &b"3".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		jdb.commit(3, &b"3".sha3(), Some((0, b"0".sha3()))).unwrap();
 		assert!(jdb.exists(&h));
-		jdb.commit(4, &b"4".sha3(), Some((1, &b"1".sha3()))).unwrap();
+		jdb.commit(4, &b"4".sha3(), Some((1, b"1".sha3()))).unwrap();
 		assert!(!jdb.exists(&h));
 	}
 
@@ -160,25 +160,25 @@ mod tests {
 		jdb.remove(&foo);
 		jdb.remove(&bar);
 		let baz = jdb.insert(b"baz");
-		jdb.commit(1, &b"1".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		jdb.commit(1, &b"1".sha3(), Some((0, b"0".sha3()))).unwrap();
 		assert!(jdb.exists(&foo));
 		assert!(jdb.exists(&bar));
 		assert!(jdb.exists(&baz));
 
 		let foo = jdb.insert(b"foo");
 		jdb.remove(&baz);
-		jdb.commit(2, &b"2".sha3(), Some((1, &b"1".sha3()))).unwrap();
+		jdb.commit(2, &b"2".sha3(), Some((1, b"1".sha3()))).unwrap();
 		assert!(jdb.exists(&foo));
 		assert!(!jdb.exists(&bar));
 		assert!(jdb.exists(&baz));
 
 		jdb.remove(&foo);
-		jdb.commit(3, &b"3".sha3(), Some((2, &b"2".sha3()))).unwrap();
+		jdb.commit(3, &b"3".sha3(), Some((2, b"2".sha3()))).unwrap();
 		assert!(jdb.exists(&foo));
 		assert!(!jdb.exists(&bar));
 		assert!(!jdb.exists(&baz));
 
-		jdb.commit(4, &b"4".sha3(), Some((3, &b"3".sha3()))).unwrap();
+		jdb.commit(4, &b"4".sha3(), Some((3, b"3".sha3()))).unwrap();
 		assert!(!jdb.exists(&foo));
 		assert!(!jdb.exists(&bar));
 		assert!(!jdb.exists(&baz));
@@ -197,16 +197,16 @@ mod tests {
 
 		jdb.remove(&foo);
 		let baz = jdb.insert(b"baz");
-		jdb.commit(1, &b"1a".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		jdb.commit(1, &b"1a".sha3(), Some((0, b"0".sha3()))).unwrap();
 
 		jdb.remove(&bar);
-		jdb.commit(1, &b"1b".sha3(), Some((0, &b"0".sha3()))).unwrap();
+		jdb.commit(1, &b"1b".sha3(), Some((0, b"0".sha3()))).unwrap();
 
 		assert!(jdb.exists(&foo));
 		assert!(jdb.exists(&bar));
 		assert!(jdb.exists(&baz));
 
-		jdb.commit(2, &b"2b".sha3(), Some((1, &b"1b".sha3()))).unwrap();
+		jdb.commit(2, &b"2b".sha3(), Some((1, b"1b".sha3()))).unwrap();
 		assert!(jdb.exists(&foo));
 		assert!(!jdb.exists(&baz));
 		assert!(!jdb.exists(&bar));

From ab0aabf02c1cf66c0bc74b448534ab37c802273c Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Mon, 18 Jan 2016 23:54:16 +0100
Subject: [PATCH 12/15] PR suggestion.

---
 util/src/overlaydb.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/util/src/overlaydb.rs b/util/src/overlaydb.rs
index 07c992693..e8492091f 100644
--- a/util/src/overlaydb.rs
+++ b/util/src/overlaydb.rs
@@ -137,7 +137,7 @@ impl OverlayDB {
 			let mut s = RlpStream::new_list(2);
 			s.append(&payload.1);
 			s.append(&payload.0);
-			self.backing.put(&key.bytes(), &s.out()).expect("Low-level database error. Some issue with your hard disk?");
+			self.backing.put(&key.bytes(), s.as_raw()).expect("Low-level database error. Some issue with your hard disk?");
 			false
 		} else {
 			self.backing.delete(&key.bytes()).expect("Low-level database error. Some issue with your hard disk?");

From ec3bc85f222028bad6484b459ca77365a52461da Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Tue, 19 Jan 2016 11:53:38 +0100
Subject: [PATCH 13/15] Fix tests.

---
 src/account.rs | 10 +++++-----
 1 file changed, 5 insertions(+), 5 deletions(-)

diff --git a/src/account.rs b/src/account.rs
index c64e80ed8..c6c4136df 100644
--- a/src/account.rs
+++ b/src/account.rs
@@ -236,7 +236,7 @@ mod tests {
 
 	#[test]
 	fn storage_at() {
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 		let rlp = {
 			let mut a = Account::new_contract(U256::from(69u8));
 			a.set_storage(H256::from(&U256::from(0x00u64)), H256::from(&U256::from(0x1234u64)));
@@ -254,7 +254,7 @@ mod tests {
 
 	#[test]
 	fn note_code() {
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 
 		let rlp = {
 			let mut a = Account::new_contract(U256::from(69u8));
@@ -273,7 +273,7 @@ mod tests {
 	#[test]
 	fn commit_storage() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 		a.set_storage(x!(0), x!(0x1234));
 		assert_eq!(a.storage_root(), None);
 		a.commit_storage(&mut db);
@@ -283,7 +283,7 @@ mod tests {
 	#[test]
 	fn commit_remove_commit_storage() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 		a.set_storage(x!(0), x!(0x1234));
 		a.commit_storage(&mut db);
 		a.set_storage(x!(1), x!(0x1234));
@@ -296,7 +296,7 @@ mod tests {
 	#[test]
 	fn commit_code() {
 		let mut a = Account::new_contract(U256::from(69u8));
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 		a.init_code(vec![0x55, 0x44, 0xffu8]);
 		assert_eq!(a.code_hash(), SHA3_EMPTY);
 		a.commit_code(&mut db);

From af3d76fbf14df4c5ad6f2b5eeb1ac0aa914e3ba9 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Tue, 19 Jan 2016 11:56:41 +0100
Subject: [PATCH 14/15] Another fix.

---
 src/ethereum/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ethereum/mod.rs b/src/ethereum/mod.rs
index 25a804db3..d9be7be85 100644
--- a/src/ethereum/mod.rs
+++ b/src/ethereum/mod.rs
@@ -40,7 +40,7 @@ mod tests {
 	fn ensure_db_good() {
 		let engine = new_morden().to_engine().unwrap();
 		let genesis_header = engine.spec().genesis_header();
-		let mut db = MemoryDB::new_temp();
+		let mut db = MemoryDB::new();
 		engine.spec().ensure_db_good(&mut db);
 		let s = State::from_existing(db.clone(), genesis_header.state_root.clone(), engine.account_start_nonce());
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000001")), U256::from(1u64));

From e82bcedf2e69c74af381b03ededa1db709a04b14 Mon Sep 17 00:00:00 2001
From: Gav Wood <gav@ethcore.io>
Date: Tue, 19 Jan 2016 11:57:10 +0100
Subject: [PATCH 15/15] Fix again.

---
 src/ethereum/mod.rs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/ethereum/mod.rs b/src/ethereum/mod.rs
index d9be7be85..e97ac79a3 100644
--- a/src/ethereum/mod.rs
+++ b/src/ethereum/mod.rs
@@ -40,7 +40,7 @@ mod tests {
 	fn ensure_db_good() {
 		let engine = new_morden().to_engine().unwrap();
 		let genesis_header = engine.spec().genesis_header();
-		let mut db = MemoryDB::new();
+		let mut db = JournalDB::new_temp();
 		engine.spec().ensure_db_good(&mut db);
 		let s = State::from_existing(db.clone(), genesis_header.state_root.clone(), engine.account_start_nonce());
 		assert_eq!(s.balance(&address_from_hex("0000000000000000000000000000000000000001")), U256::from(1u64));