diff --git a/LedgerHistory.cpp b/LedgerHistory.cpp
index 80ec1b1e5..918bcb206 100644
--- a/LedgerHistory.cpp
+++ b/LedgerHistory.cpp
@@ -7,55 +7,63 @@
 #include "Config.h"
 #include "Application.h"
 
+#ifndef CACHED_LEDGER_NUM
+#define CACHED_LEDGER_NUM 512
+#endif
+
+#ifndef CACHED_LEDGER_AGE
+#define CACHED_LEDGER_AGE 60
+#endif
+
+LedgerHistory::LedgerHistory() : mLedgersByHash(CACHED_LEDGER_NUM, CACHED_LEDGER_AGE)
+{
+;
+}
+
 void LedgerHistory::addLedger(Ledger::pointer ledger)
 {
-	uint256 h(ledger->getHash());
-	boost::recursive_mutex::scoped_lock sl(mLock);
-	mLedgersByHash.insert(std::make_pair(h, ledger));
+	mLedgersByHash.canonicalize(ledger->getHash(), ledger);
 }
 
 void LedgerHistory::addAcceptedLedger(Ledger::pointer ledger)
 {
 	assert(ledger && ledger->isAccepted());
 	uint256 h(ledger->getHash());
-	boost::recursive_mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLedgersByHash.peekMutex());
+	mLedgersByHash.canonicalize(h, ledger);
 	mLedgersByIndex.insert(std::make_pair(ledger->getLedgerSeq(), ledger));
-	mLedgersByHash.insert(std::make_pair(h, ledger));
 	theApp->getIOService().post(boost::bind(&Ledger::saveAcceptedLedger, ledger));
 }
 
 Ledger::pointer LedgerHistory::getLedgerBySeq(uint32 index)
 {
-	boost::recursive_mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLedgersByHash.peekMutex());
 	std::map<uint32, Ledger::pointer>::iterator it(mLedgersByIndex.find(index));
 	if(it!=mLedgersByIndex.end()) return it->second;
 	sl.unlock();
 
 	Ledger::pointer ret(Ledger::loadByIndex(index));
 	if(!ret) return ret;
-
 	assert(ret->getLedgerSeq()==index);
-	uint256 h=ret->getHash();
+
 	sl.lock();
+	mLedgersByHash.canonicalize(ret->getHash(), ret);
 	mLedgersByIndex.insert(std::make_pair(index, ret));
-	mLedgersByHash.insert(std::make_pair(h, ret));
 	return ret;
 }
 
 Ledger::pointer LedgerHistory::getLedgerByHash(const uint256& hash)
 {
-	boost::recursive_mutex::scoped_lock sl(mLock);
-	std::map<uint256, Ledger::pointer>::iterator it(mLedgersByHash.find(hash));
-	if(it!=mLedgersByHash.end()) return it->second;
-	sl.unlock();
+	Ledger::pointer ret=mLedgersByHash.fetch(hash);
+	if(ret) return ret;
 
-	Ledger::pointer ret=Ledger::loadByHash(hash);
+	ret=Ledger::loadByHash(hash);
 	if(!ret) return ret;
-
 	assert(ret->getHash()==hash);
-	sl.lock();
-	mLedgersByHash.insert(std::make_pair(hash, ret));
-	if(ret->isAccepted()) mLedgersByIndex.insert(std::make_pair(ret->getLedgerSeq(), ret));
+
+	boost::recursive_mutex::scoped_lock sl(mLedgersByHash.peekMutex());
+	mLedgersByHash.canonicalize(hash, ret);
+	if(ret->isAccepted()) mLedgersByIndex[ret->getLedgerSeq()]=ret;
 	return ret;
 }
 
@@ -63,20 +71,16 @@ Ledger::pointer LedgerHistory::canonicalizeLedger(Ledger::pointer ledger, bool s
 {
 	uint256 h(ledger->getHash());
 
-	boost::recursive_mutex::scoped_lock sl(mLock);
 	if(!save)
 	{ // return input ledger if not in map, otherwise, return corresponding map ledger
-		std::map<uint256, Ledger::pointer>::iterator it(mLedgersByHash.find(h));
-		if(it!=mLedgersByHash.end()) return it->second;
-	}
-	else
-	{ // save input ledger in map if not in map, otherwise return corresponding map ledger
-		std::pair<std::map<uint256,
-			Ledger::pointer>::iterator, bool> sp(mLedgersByHash.insert(std::make_pair(h, ledger)));
-		if(!sp.second) // ledger was not inserted
-			return sp.first->second;
-		if(ledger->isAccepted())
-			mLedgersByIndex.insert(std::make_pair(ledger->getLedgerSeq(), ledger));
+		Ledger::pointer ret=mLedgersByHash.fetch(h);
+		if(ret) return ret;
+		return ledger;
 	}
+	
+	// save input ledger in map if not in map, otherwise return corresponding map ledger
+	boost::recursive_mutex::scoped_lock sl(mLedgersByHash.peekMutex());
+	mLedgersByHash.canonicalize(h, ledger);
+	if(ledger->isAccepted()) mLedgersByIndex[ledger->getLedgerSeq()]=ledger;
 	return ledger;
 }
diff --git a/LedgerHistory.h b/LedgerHistory.h
index 205a2a7bb..9073adf26 100644
--- a/LedgerHistory.h
+++ b/LedgerHistory.h
@@ -1,17 +1,16 @@
 #ifndef __LEDGERHISTORY__
 #define __LEDGERHISTORY__
 
+#include "TaggedCache.h"
 #include "Ledger.h"
 
 class LedgerHistory
 {
-	boost::recursive_mutex mLock;
-
-	std::map<uint32, Ledger::pointer> mLedgersByIndex;
-	std::map<uint256, Ledger::pointer> mLedgersByHash;
+	TaggedCache<uint256, Ledger> mLedgersByHash;
+	std::map<uint32, Ledger::pointer> mLedgersByIndex; // accepted ledgers
 
 public:
-	LedgerHistory() { ; }
+	LedgerHistory();
 	
 	void addLedger(Ledger::pointer ledger);
 	void addAcceptedLedger(Ledger::pointer ledger);
@@ -21,4 +20,4 @@ public:
 	Ledger::pointer canonicalizeLedger(Ledger::pointer, bool cache);
 };
 
-#endif
\ No newline at end of file
+#endif
diff --git a/TaggedCache.h b/TaggedCache.h
index 6ae3185ee..a77709b81 100644
--- a/TaggedCache.h
+++ b/TaggedCache.h
@@ -3,6 +3,7 @@
 
 #include <map>
 
+#include <boost/thread/recursive_mutex.hpp>
 #include <boost/shared_ptr.hpp>
 
 // This class implemented a cache and a map. The cache keeps objects alive
@@ -21,7 +22,7 @@ public:
 	typedef std::pair<time_t, data_ptr> cache_entry;
 
 protected:
-	mutable boost::mutex mLock;
+	mutable boost::recursive_mutex mLock;
 
 	int mTargetSize, mTargetAge;
 	std::map<key_type, cache_entry> mCache;		// Hold strong reference to recent objects
@@ -43,8 +44,10 @@ public:
 
 	bool touch(const key_type& key);
 	bool del(const key_type& key);
-	boost::shared_ptr<c_Data> canonicalize(const key_type& key, boost::shared_ptr<c_Data> data);
+	bool canonicalize(const key_type& key, boost::shared_ptr<c_Data>& data);
 	boost::shared_ptr<c_Data> fetch(const key_type& key);
+
+	boost::recursive_mutex& peekMutex() { return mLock; }
 };
 
 template<typename c_Key, typename c_Data> int TaggedCache<c_Key, c_Data>::getTargetSize() const
@@ -65,13 +68,13 @@ template<typename c_Key, typename c_Data> int TaggedCache<c_Key, c_Data>::getTar
 
 template<typename c_Key, typename c_Data> int TaggedCache<c_Key, c_Data>::getCacheSize()
 {
-	boost::mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLock);
 	return mCache.size();
 }
 
 template<typename c_Key, typename c_Data> void TaggedCache<c_Key, c_Data>::sweep()
 {
-	boost::mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLock);
 
 	if(mCache.size()<mTargetSize) return;
 
@@ -110,7 +113,7 @@ template<typename c_Key, typename c_Data> void TaggedCache<c_Key, c_Data>::sweep
 
 template<typename c_Key, typename c_Data> bool TaggedCache<c_Key, c_Data>::touch(const key_type& key)
 {	// If present, make current in cache
-	boost::mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLock);
 
 	// Is the object in the map?
 	typename std::map<key_type, weak_data_ptr>::iterator mit=mMap.find(key);
@@ -136,7 +139,7 @@ template<typename c_Key, typename c_Data> bool TaggedCache<c_Key, c_Data>::touch
 
 template<typename c_Key, typename c_Data> bool TaggedCache<c_Key, c_Data>::del(const key_type& key)
 {	// Remove from cache, map unaffected
-	boost::mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLock);
 
 	typename std::map<key_type, cache_entry>::iterator cit=mCache.find(key);
 	if(cit==mCache.end()) return false;
@@ -145,57 +148,62 @@ template<typename c_Key, typename c_Data> bool TaggedCache<c_Key, c_Data>::del(c
 }
 
 template<typename c_Key, typename c_Data>
-boost::shared_ptr<c_Data> TaggedCache<c_Key, c_Data>::canonicalize(const key_type& key,
-		boost::shared_ptr<c_Data> data)
+bool TaggedCache<c_Key, c_Data>::canonicalize(const key_type& key, boost::shared_ptr<c_Data>& data)
 {	// Return canonical value, store if needed, refresh in cache
-	boost::mutex::scoped_lock sl(mLock);
+	// Return values: true=we had the data already
+	boost::recursive_mutex::scoped_lock sl(mLock);
 
 	typename std::map<key_type, weak_data_ptr>::iterator mit=mMap.find(key);
 	if(mit==mMap.end())
 	{ // not in map
 		mCache.insert(std::make_pair(key, std::make_pair(time(NULL), data)));
 		mMap.insert(std::make_pair(key, data));
-		return data;
+		return false;
 	}
-	if(mit->second->expired())
+	if(mit->second.expired())
 	{ // in map, but expired
 		mit->second=data;
 		mCache.insert(std::make_pair(key, std::make_pair(time(NULL), data)));
-		return data;
+		return false;
 	}
+	
+	data=mit->second.lock();
+	assert(!!data);
 
 	// Valid in map, is it in cache?
 	typename std::map<key_type, cache_entry>::iterator cit=mCache.find(key);
 	if(cit!=mCache.end())
-		cit->second->first=time(NULL); // Yes, refesh
+		cit->second.first=time(NULL); // Yes, refesh
 	else // no, add to cache
-		cit.insert(std::make_pair(key, std::make_pair(time(NULL), weak_data_ptr(mit->second))));
+		mCache.insert(std::make_pair(key, std::make_pair(time(NULL), data)));
 
-	return mit->second;
+	return true;
 }
 
 template<typename c_Key, typename c_Data>
 boost::shared_ptr<c_Data> TaggedCache<c_Key, c_Data>::fetch(const key_type& key)
 {
-	boost::mutex::scoped_lock sl(mLock);
+	boost::recursive_mutex::scoped_lock sl(mLock);
 
 	// Is it in the map?
 	typename std::map<key_type, weak_data_ptr>::iterator mit=mMap.find(key);
 	if(mit==mMap.end()) return data_ptr(); // No, we're done
-	if(mit->second->expired())
+	if(mit->second.expired())
 	{ // in map, but expired
 		mMap.erase(mit);
 		return data_ptr();
 	}
 
+	boost::shared_ptr<c_Data> data=mit->second.lock();
+	
 	// Valid in map, is it in the cache?
 	typename std::map<key_type, cache_entry>::iterator cit=mCache.find(key);
 	if(cit!=mCache.end())
-		cit->second->first=time(NULL); // Yes, refresh
+		cit->second.first=time(NULL); // Yes, refresh
 	else // No, add to cache
-		cit.insert(std::make_pair(key, std::make_pair(time(NULL), weak_data_ptr(mit->second))));
+		mCache.insert(std::make_pair(key, std::make_pair(time(NULL), data)));
 
-	return mit->second;
+	return data;
 }
 
 #endif