More performance optimizations (#1814)

* Buffered DB

* Use identity hash for MemoryDB

* Various tweaks

* Delayed DB compression

* Reduce last_hashes cloning

* Keep state cache

* Updating tests

* Optimized to_big_int

* Fixing build with stable

* Safer code

ethcore/src/client/client.rs

@@ -246,13 +246,13 @@ impl Client {
 		}
 	}
 
-	fn build_last_hashes(&self, parent_hash: H256) -> LastHashes {
+	fn build_last_hashes(&self, parent_hash: H256) -> Arc<LastHashes> {
 		{
 			let hashes = self.last_hashes.read();
 			if hashes.front().map_or(false, |h| h == &parent_hash) {
 				let mut res = Vec::from(hashes.clone());
 				res.resize(256, H256::default());
-				return res;
+				return Arc::new(res);
 			}
 		}
 		let mut last_hashes = LastHashes::new();
@@ -268,7 +268,7 @@ impl Client {
 		}
 		let mut cached_hashes = self.last_hashes.write();
 		*cached_hashes = VecDeque::from(last_hashes.clone());
-		last_hashes
+		Arc::new(last_hashes)
 	}
 
 	fn check_and_close_block(&self, block: &PreverifiedBlock) -> Result<LockedBlock, ()> {
@@ -413,6 +413,7 @@ impl Client {
 			}
 		}
 
+		self.db.flush().expect("DB flush failed.");
 		imported
 	}
 
@@ -440,7 +441,7 @@ impl Client {
 		// CHECK! I *think* this is fine, even if the state_root is equal to another
 		// already-imported block of the same number.
 		// TODO: Prove it with a test.
-		block.drain().commit(&batch, number, hash, ancient).expect("State DB commit failed.");
+		block.drain().commit(&batch, number, hash, ancient).expect("DB commit failed.");
 
 		let route = self.chain.insert_block(&batch, block_data, receipts);
 		self.tracedb.import(&batch, TraceImportRequest {
@@ -451,7 +452,7 @@ impl Client {
 			retracted: route.retracted.len()
 		});
 		// Final commit to the DB
-		self.db.write(batch).expect("State DB write failed.");
+		self.db.write_buffered(batch).expect("DB write failed.");
 		self.chain.commit();
 
 		self.update_last_hashes(&parent, hash);
@@ -975,7 +976,7 @@ impl BlockChainClient for Client {
 	}
 
 	fn last_hashes(&self) -> LastHashes {
-		self.build_last_hashes(self.chain.best_block_hash())
+		(*self.build_last_hashes(self.chain.best_block_hash())).clone()
 	}
 
 	fn queue_transactions(&self, transactions: Vec<Bytes>) {
@@ -1059,6 +1060,7 @@ impl MiningBlockChainClient for Client {
 				precise_time_ns() - start,
 			);
 		});
+		self.db.flush().expect("DB flush failed.");
 		Ok(h)
 	}
 }

ethcore/src/client/test_client.rs

@@ -272,7 +272,7 @@ impl MiningBlockChainClient for TestBlockChainClient {
 			false,
 			db,
 			&genesis_header,
-			last_hashes,
+			Arc::new(last_hashes),
 			author,
 			gas_range_target,
 			extra_data