diff --git a/libdevcore/FixedHash.h b/libdevcore/FixedHash.h
index e68e2538e..2cf81cb77 100644
--- a/libdevcore/FixedHash.h
+++ b/libdevcore/FixedHash.h
@@ -64,6 +64,9 @@ public:
 	/// Convert from the corresponding arithmetic type.
 	FixedHash(Arith const& _arith) { toBigEndian(_arith, m_data); }
 
+	/// Convert from unsigned
+	explicit FixedHash(unsigned _u) { toBigEndian(_u, m_data); }
+
 	/// Explicitly construct, copying from a byte array.
 	explicit FixedHash(bytes const& _b, ConstructFromHashType _t = FailIfDifferent) { if (_b.size() == N) memcpy(m_data.data(), _b.data(), std::min<unsigned>(_b.size(), N)); else { m_data.fill(0); if (_t != FailIfDifferent) { auto c = std::min<unsigned>(_b.size(), N); for (unsigned i = 0; i < c; ++i) m_data[_t == AlignRight ? N - 1 - i : i] = _b[_t == AlignRight ? _b.size() - 1 - i : i]; } } }
 
diff --git a/libdevcore/Guards.h b/libdevcore/Guards.h
index 8d2e8961d..d060108ef 100644
--- a/libdevcore/Guards.h
+++ b/libdevcore/Guards.h
@@ -66,11 +66,11 @@ struct GenericUnguardSharedBool
 class SpinLock
 {
 public:
-	SpinLock() { lck.clear(); }
-	void lock() { while (lck.test_and_set(std::memory_order_acquire)) {} }
-	void unlock() { lck.clear(std::memory_order_release); }
+	SpinLock() { m_lock.clear(); }
+	void lock() { while (m_lock.test_and_set(std::memory_order_acquire)) {} }
+	void unlock() { m_lock.clear(std::memory_order_release); }
 private:
-	std::atomic_flag lck;
+	std::atomic_flag m_lock;
 };
 using SpinGuard = std::lock_guard<SpinLock>;
 
diff --git a/libethereum/BlockChain.cpp b/libethereum/BlockChain.cpp
index c51188506..204203c9d 100644
--- a/libethereum/BlockChain.cpp
+++ b/libethereum/BlockChain.cpp
@@ -293,13 +293,9 @@ LastHashes BlockChain::lastHashes(unsigned _n) const
 	Guard l(x_lastLastHashes);
 	if (m_lastLastHashesNumber != _n || m_lastLastHashes.empty())
 	{
-		LastHashes lastHashes(256);
+		m_lastLastHashes.resize(256);
 		for (unsigned i = 0; i < 256; ++i)
-		{
-			size_t prevIndex = m_lastLastHashesNumber - _n + i;
-			lastHashes[i] = (prevIndex < m_lastLastHashes.size()) ? m_lastLastHashes[prevIndex] : (_n >= i ? numberHash(_n - i) : h256());
-		}
-		m_lastLastHashes = std::move(lastHashes);
+			m_lastLastHashes[i] = _n >= i ? numberHash(_n - i) : h256();
 		m_lastLastHashesNumber = _n;
 	}
 	return m_lastLastHashes;
@@ -613,6 +609,7 @@ ImportRoute BlockChain::import(bytes const& _block, OverlayDB const& _db, Import
 		}
 
 		clog(BlockChainNote) << "   Imported and best" << td << " (#" << bi.number << "). Has" << (details(bi.parentHash).children.size() - 1) << "siblings. Route:" << route;
+		noteCanonChanged();
 
 		StructuredLogger::chainNewHead(
 			bi.headerHash(WithoutNonce).abridged(),
@@ -770,7 +767,7 @@ void BlockChain::noteUsed(h256 const& _h, unsigned _extra) const
 		m_inUse.insert(id);
 }
 
-template <class T> static unsigned getHashSize(map<h256, T> const& _map)
+template <class T> static unsigned getHashSize(unordered_map<h256, T> const& _map)
 {
 	unsigned ret = 0;
 	for (auto const& i: _map)
@@ -858,7 +855,7 @@ void BlockChain::garbageCollect(bool _force)
 		}
 	}
 	m_cacheUsage.pop_back();
-	m_cacheUsage.push_front(std::set<CacheID>{});
+	m_cacheUsage.push_front(std::unordered_set<CacheID>{});
 }
 
 void BlockChain::checkConsistency()
diff --git a/libethereum/BlockChain.h b/libethereum/BlockChain.h
index 5756d1811..f69f67a5d 100644
--- a/libethereum/BlockChain.h
+++ b/libethereum/BlockChain.h
@@ -28,6 +28,8 @@
 
 #include <deque>
 #include <chrono>
+#include <unordered_map>
+#include <unordered_set>
 #include <libdevcore/Log.h>
 #include <libdevcore/Exceptions.h>
 #include <libdevcore/Guards.h>
@@ -40,6 +42,11 @@
 #include "BlockQueue.h"
 namespace ldb = leveldb;
 
+template <> struct std::hash<std::pair<dev::h256, unsigned>>
+{
+	size_t operator()(const pair<dev::h256, unsigned> &x ) const { return std::hash<dev::h256>()(x.first) ^ std::hash<unsigned>()(x.second); }
+};
+
 namespace dev
 {
 
@@ -66,7 +73,7 @@ std::map<Address, Account> const& genesisState();
 
 ldb::Slice toSlice(h256 const& _h, unsigned _sub = 0);
 
-using BlocksHash = std::map<h256, bytes>;
+using BlocksHash = std::unordered_map<h256, bytes>;
 using TransactionHashes = h256s;
 using UncleHashes = h256s;
 using ImportRoute = std::pair<h256s, h256s>;
@@ -144,7 +151,7 @@ public:
 	UncleHashes uncleHashes() const { return uncleHashes(currentHash()); }
 	
 	/// Get the hash for a given block's number.
-	h256 numberHash(unsigned _i) const { if (!_i) return genesisHash(); return queryExtras<BlockHash, ExtraBlockHash>(h256(u256(_i)), m_blockHashes, x_blockHashes, NullBlockHash).value; }
+	h256 numberHash(unsigned _i) const { if (!_i) return genesisHash(); return queryExtras<BlockHash, ExtraBlockHash>(h256(_i), m_blockHashes, x_blockHashes, NullBlockHash).value; }
 
 	/// Get the last N hashes for a given block. (N is determined by the LastHashes type.)
 	LastHashes lastHashes() const { return lastHashes(number()); }
@@ -251,7 +258,7 @@ private:
 	void open(std::string const& _path, WithExisting _we = WithExisting::Trust);
 	void close();
 
-	template<class T, unsigned N> T queryExtras(h256 const& _h, std::map<h256, T>& _m, boost::shared_mutex& _x, T const& _n, ldb::DB* _extrasDB = nullptr) const
+	template<class T, unsigned N> T queryExtras(h256 const& _h, std::unordered_map<h256, T>& _m, boost::shared_mutex& _x, T const& _n, ldb::DB* _extrasDB = nullptr) const
 	{
 		{
 			ReadGuard l(_x);
@@ -295,11 +302,12 @@ private:
 
 	using CacheID = std::pair<h256, unsigned>;
 	mutable Mutex x_cacheUsage;
-	mutable std::deque<std::set<CacheID>> m_cacheUsage;
-	mutable std::set<CacheID> m_inUse;
+	mutable std::deque<std::unordered_set<CacheID>> m_cacheUsage;
+	mutable std::unordered_set<CacheID> m_inUse;
 	void noteUsed(h256 const& _h, unsigned _extra = (unsigned)-1) const;
 	std::chrono::system_clock::time_point m_lastCollection;
 
+	void noteCanonChanged() const { Guard l(x_lastLastHashes); m_lastLastHashes.clear(); }
 	mutable Mutex x_lastLastHashes;
 	mutable LastHashes m_lastLastHashes;
 	mutable unsigned m_lastLastHashesNumber = (unsigned)-1;
diff --git a/libethereum/BlockDetails.h b/libethereum/BlockDetails.h
index 0baacb4da..19e2c7c7a 100644
--- a/libethereum/BlockDetails.h
+++ b/libethereum/BlockDetails.h
@@ -21,6 +21,7 @@
 
 #pragma once
 
+#include <unordered_map>
 #pragma warning(push)
 #pragma warning(disable: 4100 4267)
 #include <leveldb/db.h>
@@ -114,12 +115,12 @@ struct TransactionAddress
 	static const unsigned size = 67;
 };
 
-using BlockDetailsHash = std::map<h256, BlockDetails>;
-using BlockLogBloomsHash = std::map<h256, BlockLogBlooms>;
-using BlockReceiptsHash = std::map<h256, BlockReceipts>;
-using TransactionAddressHash = std::map<h256, TransactionAddress>;
-using BlockHashHash = std::map<h256, BlockHash>;
-using BlocksBloomsHash = std::map<h256, BlocksBlooms>;
+using BlockDetailsHash = std::unordered_map<h256, BlockDetails>;
+using BlockLogBloomsHash = std::unordered_map<h256, BlockLogBlooms>;
+using BlockReceiptsHash = std::unordered_map<h256, BlockReceipts>;
+using TransactionAddressHash = std::unordered_map<h256, TransactionAddress>;
+using BlockHashHash = std::unordered_map<h256, BlockHash>;
+using BlocksBloomsHash = std::unordered_map<h256, BlocksBlooms>;
 
 static const BlockDetails NullBlockDetails;
 static const BlockLogBlooms NullBlockLogBlooms;