Switch CCoinsView and chainstate db from per-txid to per-txout

This patch makes several related changes:
* Changes the CCoinsView virtual methods (GetCoins, HaveCoins, ...)
  to be COutPoint/Coin-based rather than txid/CCoins-based.
* Changes the chainstate db to a new incompatible format that is also
  COutPoint/Coin based.
* Implements reconstruction code for hash_serialized_2.
* Adapts the coins_tests unit tests (thanks to Russell Yanofsky).

A side effect of the new CCoinsView model is that we can no longer
use the (unreliable) test for transaction outputs in the UTXO set
to determine whether we already have a particular transaction.

15 files changed, 359 insertions, 369 deletions

diff --git a/src/coins.cpp b/src/coins.cpp
index 8b2f148379..38b8df1713 100644
--- a/src/coins.cpp
+++ b/src/coins.cpp
@@ -42,41 +42,40 @@ bool CCoins::Spend(uint32_t nPos)
     return true;
 }
 
-bool CCoinsView::GetCoins(const uint256 &txid, CCoins &coins) const { return false; }
-bool CCoinsView::HaveCoins(const uint256 &txid) const { return false; }
+bool CCoinsView::GetCoins(const COutPoint &outpoint, Coin &coin) const { return false; }
+bool CCoinsView::HaveCoins(const COutPoint &outpoint) const { return false; }
 uint256 CCoinsView::GetBestBlock() const { return uint256(); }
 bool CCoinsView::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return false; }
 CCoinsViewCursor *CCoinsView::Cursor() const { return 0; }
 
 
 CCoinsViewBacked::CCoinsViewBacked(CCoinsView *viewIn) : base(viewIn) { }
-bool CCoinsViewBacked::GetCoins(const uint256 &txid, CCoins &coins) const { return base->GetCoins(txid, coins); }
-bool CCoinsViewBacked::HaveCoins(const uint256 &txid) const { return base->HaveCoins(txid); }
+bool CCoinsViewBacked::GetCoins(const COutPoint &outpoint, Coin &coin) const { return base->GetCoins(outpoint, coin); }
+bool CCoinsViewBacked::HaveCoins(const COutPoint &outpoint) const { return base->HaveCoins(outpoint); }
 uint256 CCoinsViewBacked::GetBestBlock() const { return base->GetBestBlock(); }
 void CCoinsViewBacked::SetBackend(CCoinsView &viewIn) { base = &viewIn; }
 bool CCoinsViewBacked::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) { return base->BatchWrite(mapCoins, hashBlock); }
 CCoinsViewCursor *CCoinsViewBacked::Cursor() const { return base->Cursor(); }
 size_t CCoinsViewBacked::EstimateSize() const { return base->EstimateSize(); }
 
-SaltedTxidHasher::SaltedTxidHasher() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
+SaltedOutpointHasher::SaltedOutpointHasher() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
 
-CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), cachedCoinsUsage(0) { }
+CCoinsViewCache::CCoinsViewCache(CCoinsView *baseIn) : CCoinsViewBacked(baseIn), cachedCoinsUsage(0) {}
 
 size_t CCoinsViewCache::DynamicMemoryUsage() const {
     return memusage::DynamicUsage(cacheCoins) + cachedCoinsUsage;
 }
 
-CCoinsMap::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
-    CCoinsMap::iterator it = cacheCoins.find(txid);
+CCoinsMap::iterator CCoinsViewCache::FetchCoins(const COutPoint &outpoint) const {
+    CCoinsMap::iterator it = cacheCoins.find(outpoint);
     if (it != cacheCoins.end())
         return it;
-    CCoins tmp;
-    if (!base->GetCoins(txid, tmp))
+    Coin tmp;
+    if (!base->GetCoins(outpoint, tmp))
         return cacheCoins.end();
-    CCoinsMap::iterator ret = cacheCoins.insert(std::make_pair(txid, CCoinsCacheEntry())).first;
-    tmp.swap(ret->second.coins);
+    CCoinsMap::iterator ret = cacheCoins.emplace(std::piecewise_construct, std::forward_as_tuple(outpoint), std::forward_as_tuple(std::move(tmp))).first;
     if (ret->second.coins.IsPruned()) {
-        // The parent only has an empty entry for this txid; we can consider our
+        // The parent only has an empty entry for this outpoint; we can consider our
         // version as fresh.
         ret->second.flags = CCoinsCacheEntry::FRESH;
     }
@@ -84,10 +83,10 @@ CCoinsMap::iterator CCoinsViewCache::FetchCoins(const uint256 &txid) const {
     return ret;
 }
 
-bool CCoinsViewCache::GetCoins(const uint256 &txid, CCoins &coins) const {
-    CCoinsMap::const_iterator it = FetchCoins(txid);
+bool CCoinsViewCache::GetCoins(const COutPoint &outpoint, Coin &coin) const {
+    CCoinsMap::const_iterator it = FetchCoins(outpoint);
     if (it != cacheCoins.end()) {
-        coins = it->second.coins;
+        coin = it->second.coins;
         return true;
     }
     return false;
@@ -98,23 +97,18 @@ void CCoinsViewCache::AddCoin(const COutPoint &outpoint, Coin&& coin, bool possi
     if (coin.out.scriptPubKey.IsUnspendable()) return;
     CCoinsMap::iterator it;
     bool inserted;
-    std::tie(it, inserted) = cacheCoins.emplace(std::piecewise_construct, std::forward_as_tuple(outpoint.hash), std::tuple<>());
+    std::tie(it, inserted) = cacheCoins.emplace(std::piecewise_construct, std::forward_as_tuple(outpoint), std::tuple<>());
     bool fresh = false;
     if (!inserted) {
         cachedCoinsUsage -= it->second.coins.DynamicMemoryUsage();
     }
     if (!possible_overwrite) {
-        if (it->second.coins.IsAvailable(outpoint.n)) {
+        if (!it->second.coins.IsPruned()) {
             throw std::logic_error("Adding new coin that replaces non-pruned entry");
         }
-        fresh = it->second.coins.IsPruned() && !(it->second.flags & CCoinsCacheEntry::DIRTY);
+        fresh = !(it->second.flags & CCoinsCacheEntry::DIRTY);
     }
-    if (it->second.coins.vout.size() <= outpoint.n) {
-        it->second.coins.vout.resize(outpoint.n + 1);
-    }
-    it->second.coins.vout[outpoint.n] = std::move(coin.out);
-    it->second.coins.nHeight = coin.nHeight;
-    it->second.coins.fCoinBase = coin.fCoinBase;
+    it->second.coins = std::move(coin);
     it->second.flags |= CCoinsCacheEntry::DIRTY | (fresh ? CCoinsCacheEntry::FRESH : 0);
     cachedCoinsUsage += it->second.coins.DynamicMemoryUsage();
 }
@@ -130,58 +124,38 @@ void AddCoins(CCoinsViewCache& cache, const CTransaction &tx, int nHeight) {
 }
 
 void CCoinsViewCache::SpendCoin(const COutPoint &outpoint, Coin* moveout) {
-    CCoinsMap::iterator it = FetchCoins(outpoint.hash);
+    CCoinsMap::iterator it = FetchCoins(outpoint);
     if (it == cacheCoins.end()) return;
     cachedCoinsUsage -= it->second.coins.DynamicMemoryUsage();
-    if (moveout && it->second.coins.IsAvailable(outpoint.n)) {
-        *moveout = Coin(it->second.coins.vout[outpoint.n], it->second.coins.nHeight, it->second.coins.fCoinBase);
+    if (moveout) {
+        *moveout = std::move(it->second.coins);
     }
-    it->second.coins.Spend(outpoint.n); // Ignore return value: SpendCoin has no effect if no UTXO found.
-    if (it->second.coins.IsPruned() && it->second.flags & CCoinsCacheEntry::FRESH) {
+    if (it->second.flags & CCoinsCacheEntry::FRESH) {
         cacheCoins.erase(it);
     } else {
-        cachedCoinsUsage += it->second.coins.DynamicMemoryUsage();
         it->second.flags |= CCoinsCacheEntry::DIRTY;
-    }
-}
-
-const CCoins* CCoinsViewCache::AccessCoins(const uint256 &txid) const {
-    CCoinsMap::const_iterator it = FetchCoins(txid);
-    if (it == cacheCoins.end()) {
-        return NULL;
-    } else {
-        return &it->second.coins;
+        it->second.coins.Clear();
     }
 }
 
 static const Coin coinEmpty;
 
-const Coin CCoinsViewCache::AccessCoin(const COutPoint &outpoint) const {
-    CCoinsMap::const_iterator it = FetchCoins(outpoint.hash);
-    if (it == cacheCoins.end() || !it->second.coins.IsAvailable(outpoint.n)) {
+const Coin& CCoinsViewCache::AccessCoin(const COutPoint &outpoint) const {
+    CCoinsMap::const_iterator it = FetchCoins(outpoint);
+    if (it == cacheCoins.end()) {
         return coinEmpty;
     } else {
-        return Coin(it->second.coins.vout[outpoint.n], it->second.coins.nHeight, it->second.coins.fCoinBase);
+        return it->second.coins;
     }
 }
 
-
-bool CCoinsViewCache::HaveCoins(const uint256 &txid) const {
-    CCoinsMap::const_iterator it = FetchCoins(txid);
-    // We're using vtx.empty() instead of IsPruned here for performance reasons,
-    // as we only care about the case where a transaction was replaced entirely
-    // in a reorganization (which wipes vout entirely, as opposed to spending
-    // which just cleans individual outputs).
-    return (it != cacheCoins.end() && !it->second.coins.vout.empty());
-}
-
 bool CCoinsViewCache::HaveCoins(const COutPoint &outpoint) const {
-    CCoinsMap::const_iterator it = FetchCoins(outpoint.hash);
-    return (it != cacheCoins.end() && it->second.coins.IsAvailable(outpoint.n));
+    CCoinsMap::const_iterator it = FetchCoins(outpoint);
+    return (it != cacheCoins.end() && !it->second.coins.IsPruned());
 }
 
-bool CCoinsViewCache::HaveCoinsInCache(const uint256 &txid) const {
-    CCoinsMap::const_iterator it = cacheCoins.find(txid);
+bool CCoinsViewCache::HaveCoinsInCache(const COutPoint &outpoint) const {
+    CCoinsMap::const_iterator it = cacheCoins.find(outpoint);
     return it != cacheCoins.end();
 }
 
@@ -206,7 +180,7 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
                     // Otherwise we will need to create it in the parent
                     // and move the data up and mark it as dirty
                     CCoinsCacheEntry& entry = cacheCoins[it->first];
-                    entry.coins.swap(it->second.coins);
+                    entry.coins = std::move(it->second.coins);
                     cachedCoinsUsage += entry.coins.DynamicMemoryUsage();
                     entry.flags = CCoinsCacheEntry::DIRTY;
                     // We can mark it FRESH in the parent if it was FRESH in the child
@@ -233,7 +207,7 @@ bool CCoinsViewCache::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlockIn
                 } else {
                     // A normal modification.
                     cachedCoinsUsage -= itUs->second.coins.DynamicMemoryUsage();
-                    itUs->second.coins.swap(it->second.coins);
+                    itUs->second.coins = std::move(it->second.coins);
                     cachedCoinsUsage += itUs->second.coins.DynamicMemoryUsage();
                     itUs->second.flags |= CCoinsCacheEntry::DIRTY;
                     // NOTE: It is possible the child has a FRESH flag here in
@@ -258,7 +232,7 @@ bool CCoinsViewCache::Flush() {
     return fOk;
 }
 
-void CCoinsViewCache::Uncache(const uint256& hash)
+void CCoinsViewCache::Uncache(const COutPoint& hash)
 {
     CCoinsMap::iterator it = cacheCoins.find(hash);
     if (it != cacheCoins.end() && it->second.flags == 0) {
@@ -273,9 +247,9 @@ unsigned int CCoinsViewCache::GetCacheSize() const {
 
 const CTxOut &CCoinsViewCache::GetOutputFor(const CTxIn& input) const
 {
-    const CCoins* coins = AccessCoins(input.prevout.hash);
-    assert(coins && coins->IsAvailable(input.prevout.n));
-    return coins->vout[input.prevout.n];
+    const Coin& coin = AccessCoin(input.prevout);
+    assert(!coin.IsPruned());
+    return coin.out;
 }
 
 CAmount CCoinsViewCache::GetValueIn(const CTransaction& tx) const
@@ -294,9 +268,7 @@ bool CCoinsViewCache::HaveInputs(const CTransaction& tx) const
 {
     if (!tx.IsCoinBase()) {
         for (unsigned int i = 0; i < tx.vin.size(); i++) {
-            const COutPoint &prevout = tx.vin[i].prevout;
-            const CCoins* coins = AccessCoins(prevout.hash);
-            if (!coins || !coins->IsAvailable(prevout.n)) {
+            if (!HaveCoins(tx.vin[i].prevout)) {
                 return false;
             }
         }
@@ -304,13 +276,9 @@ bool CCoinsViewCache::HaveInputs(const CTransaction& tx) const
     return true;
 }
 
-CCoinsViewCursor::~CCoinsViewCursor()
-{
-}
-
 static const size_t MAX_OUTPUTS_PER_BLOCK = MAX_BLOCK_BASE_SIZE /  ::GetSerializeSize(CTxOut(), SER_NETWORK, PROTOCOL_VERSION); // TODO: merge with similar definition in undo.h.
 
-const Coin AccessByTxid(const CCoinsViewCache& view, const uint256& txid)
+const Coin& AccessByTxid(const CCoinsViewCache& view, const uint256& txid)
 {
     COutPoint iter(txid, 0);
     while (iter.n < MAX_OUTPUTS_PER_BLOCK) {
diff --git a/src/coins.h b/src/coins.h
index fcf7c47a56..ae85a199ca 100644
--- a/src/coins.h
+++ b/src/coins.h
@@ -299,28 +299,28 @@ public:
     }
 };
 
-class SaltedTxidHasher
+class SaltedOutpointHasher
 {
 private:
     /** Salt */
     const uint64_t k0, k1;
 
 public:
-    SaltedTxidHasher();
+    SaltedOutpointHasher();
 
     /**
      * This *must* return size_t. With Boost 1.46 on 32-bit systems the
      * unordered_map will behave unpredictably if the custom hasher returns a
      * uint64_t, resulting in failures when syncing the chain (#4634).
      */
-    size_t operator()(const uint256& txid) const {
-        return SipHashUint256(k0, k1, txid);
+    size_t operator()(const COutPoint& id) const {
+        return SipHashUint256Extra(k0, k1, id.hash, id.n);
     }
 };
 
 struct CCoinsCacheEntry
 {
-    CCoins coins; // The actual cached data.
+    Coin coins; // The actual cached data.
     unsigned char flags;
 
     enum Flags {
@@ -333,20 +333,21 @@ struct CCoinsCacheEntry
          */
     };
 
-    CCoinsCacheEntry() : coins(), flags(0) {}
+    CCoinsCacheEntry() : flags(0) {}
+    explicit CCoinsCacheEntry(Coin&& coin_) : coins(std::move(coin_)), flags(0) {}
 };
 
-typedef std::unordered_map<uint256, CCoinsCacheEntry, SaltedTxidHasher> CCoinsMap;
+typedef std::unordered_map<COutPoint, CCoinsCacheEntry, SaltedOutpointHasher> CCoinsMap;
 
 /** Cursor for iterating over CoinsView state */
 class CCoinsViewCursor
 {
 public:
     CCoinsViewCursor(const uint256 &hashBlockIn): hashBlock(hashBlockIn) {}
-    virtual ~CCoinsViewCursor();
+    virtual ~CCoinsViewCursor() {}
 
-    virtual bool GetKey(uint256 &key) const = 0;
-    virtual bool GetValue(CCoins &coins) const = 0;
+    virtual bool GetKey(COutPoint &key) const = 0;
+    virtual bool GetValue(Coin &coin) const = 0;
     virtual unsigned int GetValueSize() const = 0;
 
     virtual bool Valid() const = 0;
@@ -362,17 +363,17 @@ private:
 class CCoinsView
 {
 public:
-    //! Retrieve the CCoins (unspent transaction outputs) for a given txid
-    virtual bool GetCoins(const uint256 &txid, CCoins &coins) const;
+    //! Retrieve the Coin (unspent transaction output) for a given outpoint.
+    virtual bool GetCoins(const COutPoint &outpoint, Coin &coin) const;
 
-    //! Just check whether we have data for a given txid.
-    //! This may (but cannot always) return true for fully spent transactions
-    virtual bool HaveCoins(const uint256 &txid) const;
+    //! Just check whether we have data for a given outpoint.
+    //! This may (but cannot always) return true for spent outputs.
+    virtual bool HaveCoins(const COutPoint &outpoint) const;
 
     //! Retrieve the block hash whose state this CCoinsView currently represents
     virtual uint256 GetBestBlock() const;
 
-    //! Do a bulk modification (multiple CCoins changes + BestBlock change).
+    //! Do a bulk modification (multiple Coin changes + BestBlock change).
     //! The passed mapCoins can be modified.
     virtual bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 
@@ -395,12 +396,12 @@ protected:
 
 public:
     CCoinsViewBacked(CCoinsView *viewIn);
-    bool GetCoins(const uint256 &txid, CCoins &coins) const;
-    bool HaveCoins(const uint256 &txid) const;
-    uint256 GetBestBlock() const;
+    bool GetCoins(const COutPoint &outpoint, Coin &coin) const override;
+    bool HaveCoins(const COutPoint &outpoint) const override;
+    uint256 GetBestBlock() const override;
     void SetBackend(CCoinsView &viewIn);
-    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
-    CCoinsViewCursor *Cursor() const;
+    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override;
+    CCoinsViewCursor *Cursor() const override;
     size_t EstimateSize() const override;
 };
 
@@ -416,41 +417,32 @@ protected:
     mutable uint256 hashBlock;
     mutable CCoinsMap cacheCoins;
 
-    /* Cached dynamic memory usage for the inner CCoins objects. */
+    /* Cached dynamic memory usage for the inner Coin objects. */
     mutable size_t cachedCoinsUsage;
 
 public:
     CCoinsViewCache(CCoinsView *baseIn);
 
     // Standard CCoinsView methods
-    bool GetCoins(const uint256 &txid, CCoins &coins) const;
-    bool HaveCoins(const uint256 &txid) const;
+    bool GetCoins(const COutPoint &outpoint, Coin &coin) const;
     bool HaveCoins(const COutPoint &outpoint) const;
     uint256 GetBestBlock() const;
     void SetBestBlock(const uint256 &hashBlock);
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
 
     /**
-     * Check if we have the given tx already loaded in this cache.
+     * Check if we have the given utxo already loaded in this cache.
      * The semantics are the same as HaveCoins(), but no calls to
      * the backing CCoinsView are made.
      */
-    bool HaveCoinsInCache(const uint256 &txid) const;
-
-    /**
-     * Return a pointer to CCoins in the cache, or NULL if not found. This is
-     * more efficient than GetCoins. Modifications to other cache entries are
-     * allowed while accessing the returned pointer.
-     */
-    const CCoins* AccessCoins(const uint256 &txid) const;
+    bool HaveCoinsInCache(const COutPoint &outpoint) const;
 
     /**
-     * Return a copy of a Coin in the cache, or a pruned one if not found. This is
+     * Return a reference to Coin in the cache, or a pruned one if not found. This is
      * more efficient than GetCoins. Modifications to other cache entries are
      * allowed while accessing the returned pointer.
-     * TODO: return a reference to a Coin after changing CCoinsViewCache storage.
      */
-    const Coin AccessCoin(const COutPoint &output) const;
+    const Coin& AccessCoin(const COutPoint &output) const;
 
     /**
      * Add a coin. Set potential_overwrite to true if a non-pruned version may
@@ -473,12 +465,12 @@ public:
     bool Flush();
 
     /**
-     * Removes the transaction with the given hash from the cache, if it is
+     * Removes the UTXO with the given outpoint from the cache, if it is
      * not modified.
      */
-    void Uncache(const uint256 &txid);
+    void Uncache(const COutPoint &outpoint);
 
-    //! Calculate the size of the cache (in number of transactions)
+    //! Calculate the size of the cache (in number of transaction outputs)
     unsigned int GetCacheSize() const;
 
     //! Calculate the size of the cache (in bytes)
@@ -500,7 +492,7 @@ public:
     const CTxOut &GetOutputFor(const CTxIn& input) const;
 
 private:
-    CCoinsMap::iterator FetchCoins(const uint256 &txid) const;
+    CCoinsMap::iterator FetchCoins(const COutPoint &outpoint) const;
 
     /**
      * By making the copy constructor private, we prevent accidentally using it when one intends to create a cache on top of a base cache.
@@ -515,6 +507,6 @@ private:
 void AddCoins(CCoinsViewCache& cache, const CTransaction& tx, int nHeight);
 
 //! Utility function to find any unspent output with a given txid.
-const Coin AccessByTxid(const CCoinsViewCache& cache, const uint256& txid);
+const Coin& AccessByTxid(const CCoinsViewCache& cache, const uint256& txid);
 
 #endif // BITCOIN_COINS_H
diff --git a/src/init.cpp b/src/init.cpp
index 3bbdb16c3b..4420b6f658 100644
--- a/src/init.cpp
+++ b/src/init.cpp
@@ -146,9 +146,9 @@ class CCoinsViewErrorCatcher : public CCoinsViewBacked
 {
 public:
     CCoinsViewErrorCatcher(CCoinsView* view) : CCoinsViewBacked(view) {}
-    bool GetCoins(const uint256 &txid, CCoins &coins) const {
+    bool GetCoins(const COutPoint &outpoint, Coin &coin) const override {
         try {
-            return CCoinsViewBacked::GetCoins(txid, coins);
+            return CCoinsViewBacked::GetCoins(outpoint, coin);
         } catch(const std::runtime_error& e) {
             uiInterface.ThreadSafeMessageBox(_("Error reading from database, shutting down."), "", CClientUIInterface::MSG_ERROR);
             LogPrintf("Error reading from database: %s\n", e.what());
diff --git a/src/net_processing.cpp b/src/net_processing.cpp
index 3102c2ef9a..1c99d047ed 100644
--- a/src/net_processing.cpp
+++ b/src/net_processing.cpp
@@ -911,12 +911,11 @@ bool static AlreadyHave(const CInv& inv) EXCLUSIVE_LOCKS_REQUIRED(cs_main)
                 recentRejects->reset();
             }
 
-            // Use pcoinsTip->HaveCoinsInCache as a quick approximation to exclude
-            // requesting or processing some txs which have already been included in a block
             return recentRejects->contains(inv.hash) ||
                    mempool.exists(inv.hash) ||
                    mapOrphanTransactions.count(inv.hash) ||
-                   pcoinsTip->HaveCoinsInCache(inv.hash);
+                   pcoinsTip->HaveCoinsInCache(COutPoint(inv.hash, 0)) || // Best effort: only try output 0 and 1
+                   pcoinsTip->HaveCoinsInCache(COutPoint(inv.hash, 1));
         }
     case MSG_BLOCK:
     case MSG_WITNESS_BLOCK:
diff --git a/src/qt/transactiondesc.cpp b/src/qt/transactiondesc.cpp
index d81188895b..78317c1121 100644
--- a/src/qt/transactiondesc.cpp
+++ b/src/qt/transactiondesc.cpp
@@ -293,13 +293,12 @@ QString TransactionDesc::toHTML(CWallet *wallet, CWalletTx &wtx, TransactionReco
         {
             COutPoint prevout = txin.prevout;
 
-            CCoins prev;
-            if(pcoinsTip->GetCoins(prevout.hash, prev))
+            Coin prev;
+            if(pcoinsTip->GetCoins(prevout, prev))
             {
-                if (prevout.n < prev.vout.size())
                 {
                     strHTML += "<li>";
-                    const CTxOut &vout = prev.vout[prevout.n];
+                    const CTxOut &vout = prev.out;
                     CTxDestination address;
                     if (ExtractDestination(vout.scriptPubKey, address))
                     {
diff --git a/src/rest.cpp b/src/rest.cpp
index 4a71010094..16c8c4f529 100644
--- a/src/rest.cpp
+++ b/src/rest.cpp
@@ -47,6 +47,9 @@ struct CCoin {
 
     ADD_SERIALIZE_METHODS;
 
+    CCoin() : nHeight(0) {}
+    CCoin(Coin&& in) : nHeight(in.nHeight), out(std::move(in.out)) {}
+
     template <typename Stream, typename Operation>
     inline void SerializationOp(Stream& s, Operation ser_action)
     {
@@ -509,20 +512,11 @@ static bool rest_getutxos(HTTPRequest* req, const std::string& strURIPart)
             view.SetBackend(viewMempool); // switch cache backend to db+mempool in case user likes to query mempool
 
         for (size_t i = 0; i < vOutPoints.size(); i++) {
-            CCoins coins;
-            uint256 hash = vOutPoints[i].hash;
             bool hit = false;
-            if (view.GetCoins(hash, coins)) {
-                if (coins.IsAvailable(vOutPoints[i].n) && !mempool.isSpent(vOutPoints[i])) {
-                    hit = true;
-                    // Safe to index into vout here because IsAvailable checked if it's off the end of the array, or if
-                    // n is valid but points to an already spent output (IsNull).
-                    CCoin coin;
-                    coin.nHeight = coins.nHeight;
-                    coin.out = coins.vout.at(vOutPoints[i].n);
-                    assert(!coin.out.IsNull());
-                    outs.push_back(coin);
-                }
+            Coin coin;
+            if (view.GetCoins(vOutPoints[i], coin) && !mempool.isSpent(vOutPoints[i])) {
+                hit = true;
+                outs.emplace_back(std::move(coin));
             }
 
             hits.push_back(hit);
diff --git a/src/rpc/blockchain.cpp b/src/rpc/blockchain.cpp
index 3e9b1a1b12..77f1dcb21f 100644
--- a/src/rpc/blockchain.cpp
+++ b/src/rpc/blockchain.cpp
@@ -816,24 +816,27 @@ static bool GetUTXOStats(CCoinsView *view, CCoinsStats &stats)
         stats.nHeight = mapBlockIndex.find(stats.hashBlock)->second->nHeight;
     }
     ss << stats.hashBlock;
+    uint256 prevkey;
+    std::map<uint32_t, Coin> outputs;
     while (pcursor->Valid()) {
         boost::this_thread::interruption_point();
-        uint256 key;
-        CCoins coins;
-        if (pcursor->GetKey(key) && pcursor->GetValue(coins)) {
-            std::map<uint32_t, Coin> outputs;
-            for (unsigned int i=0; i<coins.vout.size(); i++) {
-                CTxOut &out = coins.vout[i];
-                if (!out.IsNull()) {
-                    outputs[i] = Coin(std::move(out), coins.nHeight, coins.fCoinBase);
-                }
+        COutPoint key;
+        Coin coin;
+        if (pcursor->GetKey(key) && pcursor->GetValue(coin)) {
+            if (!outputs.empty() && key.hash != prevkey) {
+                ApplyStats(stats, ss, prevkey, outputs);
+                outputs.clear();
             }
-            ApplyStats(stats, ss, key, outputs);
+            prevkey = key.hash;
+            outputs[key.n] = std::move(coin);
         } else {
             return error("%s: unable to read value", __func__);
         }
         pcursor->Next();
     }
+    if (!outputs.empty()) {
+        ApplyStats(stats, ss, prevkey, outputs);
+    }
     stats.hashSerialized = ss.GetHash();
     stats.nDiskSize = view->EstimateSize();
     return true;
@@ -973,35 +976,37 @@ UniValue gettxout(const JSONRPCRequest& request)
     std::string strHash = request.params[0].get_str();
     uint256 hash(uint256S(strHash));
     int n = request.params[1].get_int();
+    COutPoint out(hash, n);
     bool fMempool = true;
     if (request.params.size() > 2)
         fMempool = request.params[2].get_bool();
 
-    CCoins coins;
+    Coin coin;
     if (fMempool) {
         LOCK(mempool.cs);
         CCoinsViewMemPool view(pcoinsTip, mempool);
-        if (!view.GetCoins(hash, coins) || mempool.isSpent(COutPoint(hash, n))) // TODO: this should be done by the CCoinsViewMemPool
+        if (!view.GetCoins(out, coin) || mempool.isSpent(out)) { // TODO: filtering spent coins should be done by the CCoinsViewMemPool
             return NullUniValue;
+        }
     } else {
-        if (!pcoinsTip->GetCoins(hash, coins))
+        if (!pcoinsTip->GetCoins(out, coin)) {
             return NullUniValue;
+        }
     }
-    if (n<0 || (unsigned int)n>=coins.vout.size() || coins.vout[n].IsNull())
-        return NullUniValue;
 
     BlockMap::iterator it = mapBlockIndex.find(pcoinsTip->GetBestBlock());
     CBlockIndex *pindex = it->second;
     ret.push_back(Pair("bestblock", pindex->GetBlockHash().GetHex()));
-    if ((unsigned int)coins.nHeight == MEMPOOL_HEIGHT)
+    if (coin.nHeight == MEMPOOL_HEIGHT) {
         ret.push_back(Pair("confirmations", 0));
-    else
-        ret.push_back(Pair("confirmations", pindex->nHeight - coins.nHeight + 1));
-    ret.push_back(Pair("value", ValueFromAmount(coins.vout[n].nValue)));
+    } else {
+        ret.push_back(Pair("confirmations", (int64_t)(pindex->nHeight - coin.nHeight + 1)));
+    }
+    ret.push_back(Pair("value", ValueFromAmount(coin.out.nValue)));
     UniValue o(UniValue::VOBJ);
-    ScriptPubKeyToUniv(coins.vout[n].scriptPubKey, o, true);
+    ScriptPubKeyToUniv(coin.out.scriptPubKey, o, true);
     ret.push_back(Pair("scriptPubKey", o));
-    ret.push_back(Pair("coinbase", coins.fCoinBase));
+    ret.push_back(Pair("coinbase", (bool)coin.fCoinBase));
 
     return ret;
 }
diff --git a/src/rpc/rawtransaction.cpp b/src/rpc/rawtransaction.cpp
index 3f7b6adead..8ecbf9ede5 100644
--- a/src/rpc/rawtransaction.cpp
+++ b/src/rpc/rawtransaction.cpp
@@ -219,9 +219,10 @@ UniValue gettxoutproof(const JSONRPCRequest& request)
             throw JSONRPCError(RPC_INVALID_ADDRESS_OR_KEY, "Block not found");
         pblockindex = mapBlockIndex[hashBlock];
     } else {
-        CCoins coins;
-        if (pcoinsTip->GetCoins(oneTxid, coins) && coins.nHeight > 0 && coins.nHeight <= chainActive.Height())
-            pblockindex = chainActive[coins.nHeight];
+        const Coin& coin = AccessByTxid(*pcoinsTip, oneTxid);
+        if (!coin.IsPruned() && coin.nHeight > 0 && coin.nHeight <= chainActive.Height()) {
+            pblockindex = chainActive[coin.nHeight];
+        }
     }
 
     if (pblockindex == NULL)
diff --git a/src/test/coins_tests.cpp b/src/test/coins_tests.cpp
index 3ad2625bab..8d519c644b 100644
--- a/src/test/coins_tests.cpp
+++ b/src/test/coins_tests.cpp
@@ -34,27 +34,27 @@ bool operator==(const Coin &a, const Coin &b) {
 class CCoinsViewTest : public CCoinsView
 {
     uint256 hashBestBlock_;
-    std::map<uint256, CCoins> map_;
+    std::map<COutPoint, Coin> map_;
 
 public:
-    bool GetCoins(const uint256& txid, CCoins& coins) const
+    bool GetCoins(const COutPoint& outpoint, Coin& coin) const
     {
-        std::map<uint256, CCoins>::const_iterator it = map_.find(txid);
+        std::map<COutPoint, Coin>::const_iterator it = map_.find(outpoint);
         if (it == map_.end()) {
             return false;
         }
-        coins = it->second;
-        if (coins.IsPruned() && insecure_rand() % 2 == 0) {
+        coin = it->second;
+        if (coin.IsPruned() && insecure_rand() % 2 == 0) {
             // Randomly return false in case of an empty entry.
             return false;
         }
         return true;
     }
 
-    bool HaveCoins(const uint256& txid) const
+    bool HaveCoins(const COutPoint& outpoint) const
     {
-        CCoins coins;
-        return GetCoins(txid, coins);
+        Coin coin;
+        return GetCoins(outpoint, coin);
     }
 
     uint256 GetBestBlock() const { return hashBestBlock_; }
@@ -106,7 +106,7 @@ static const unsigned int NUM_SIMULATION_ITERATIONS = 40000;
 // This is a large randomized insert/remove simulation test on a variable-size
 // stack of caches on top of CCoinsViewTest.
 //
-// It will randomly create/update/delete CCoins entries to a tip of caches, with
+// It will randomly create/update/delete Coin entries to a tip of caches, with
 // txids picked from a limited list of random 256-bit hashes. Occasionally, a
 // new tip is added to the stack of caches, or the tip is flushed and removed.
 //
@@ -124,7 +124,7 @@ BOOST_AUTO_TEST_CASE(coins_cache_simulation_test)
     bool missed_an_entry = false;
 
     // A simple map to track what we expect the cache stack to represent.
-    std::map<uint256, CCoins> result;
+    std::map<COutPoint, Coin> result;
 
     // The cache stack.
     CCoinsViewTest base; // A CCoinsViewTest at the bottom.
@@ -142,39 +142,38 @@ BOOST_AUTO_TEST_CASE(coins_cache_simulation_test)
         // Do a random modification.
         {
             uint256 txid = txids[insecure_rand() % txids.size()]; // txid we're going to modify in this iteration.
-            CCoins& coins = result[txid];
+            Coin& coin = result[COutPoint(txid, 0)];
             const Coin& entry = stack.back()->AccessCoin(COutPoint(txid, 0));
-            BOOST_CHECK((entry.IsPruned() && coins.IsPruned()) || entry == Coin(coins.vout[0], coins.nHeight, coins.fCoinBase));
+            BOOST_CHECK(coin == entry);
 
-            if (insecure_rand() % 5 == 0 || coins.IsPruned()) {
-                if (coins.IsPruned()) {
+            if (insecure_rand() % 5 == 0 || coin.IsPruned()) {
+                if (coin.IsPruned()) {
                     added_an_entry = true;
                 } else {
                     updated_an_entry = true;
                 }
-                coins.vout.resize(1);
-                coins.vout[0].nValue = insecure_rand();
+                coin.out.nValue = insecure_rand();
+                coin.nHeight = 1;
             } else {
-                coins.Clear();
+                coin.Clear();
                 removed_an_entry = true;
             }
-            if (coins.IsPruned()) {
+            if (coin.IsPruned()) {
                 stack.back()->SpendCoin(COutPoint(txid, 0));
             } else {
-                stack.back()->AddCoin(COutPoint(txid, 0), Coin(coins.vout[0], coins.nHeight, coins.fCoinBase), true);
+                stack.back()->AddCoin(COutPoint(txid, 0), Coin(coin), true);
             }
         }
 
         // Once every 1000 iterations and at the end, verify the full cache.
         if (insecure_rand() % 1000 == 1 || i == NUM_SIMULATION_ITERATIONS - 1) {
-            for (std::map<uint256, CCoins>::iterator it = result.begin(); it != result.end(); it++) {
-                const CCoins* coins = stack.back()->AccessCoins(it->first);
-                if (coins) {
-                    BOOST_CHECK(*coins == it->second);
-                    found_an_entry = true;
-                } else {
-                    BOOST_CHECK(it->second.IsPruned());
+            for (auto it = result.begin(); it != result.end(); it++) {
+                const Coin& coin = stack.back()->AccessCoin(it->first);
+                BOOST_CHECK(coin == it->second);
+                if (coin.IsPruned()) {
                     missed_an_entry = true;
+                } else {
+                    found_an_entry = true;
                 }
             }
             BOOST_FOREACH(const CCoinsViewCacheTest *test, stack) {
@@ -229,19 +228,19 @@ BOOST_AUTO_TEST_CASE(coins_cache_simulation_test)
     BOOST_CHECK(missed_an_entry);
 }
 
-typedef std::tuple<CTransaction,CTxUndo,CCoins> TxData;
 // Store of all necessary tx and undo data for next test
-std::map<uint256, TxData> alltxs;
-
-TxData &FindRandomFrom(const std::set<uint256> &txidset) {
-    assert(txidset.size());
-    std::set<uint256>::iterator txIt = txidset.lower_bound(GetRandHash());
-    if (txIt == txidset.end()) {
-        txIt = txidset.begin();
+typedef std::map<COutPoint, std::tuple<CTransaction,CTxUndo,Coin>> UtxoData;
+UtxoData utxoData;
+
+UtxoData::iterator FindRandomFrom(const std::set<COutPoint> &utxoSet) {
+    assert(utxoSet.size());
+    auto utxoSetIt = utxoSet.lower_bound(COutPoint(GetRandHash(), 0));
+    if (utxoSetIt == utxoSet.end()) {
+        utxoSetIt = utxoSet.begin();
     }
-    std::map<uint256, TxData>::iterator txdit = alltxs.find(*txIt);
-    assert(txdit != alltxs.end());
-    return txdit->second;
+    auto utxoDataIt = utxoData.find(*utxoSetIt);
+    assert(utxoDataIt != utxoData.end());
+    return utxoDataIt;
 }
 
 
@@ -254,7 +253,7 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
 {
     bool spent_a_duplicate_coinbase = false;
     // A simple map to track what we expect the cache stack to represent.
-    std::map<uint256, CCoins> result;
+    std::map<COutPoint, Coin> result;
 
     // The cache stack.
     CCoinsViewTest base; // A CCoinsViewTest at the bottom.
@@ -262,10 +261,10 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
     stack.push_back(new CCoinsViewCacheTest(&base)); // Start with one cache.
 
     // Track the txids we've used in various sets
-    std::set<uint256> coinbaseids;
-    std::set<uint256> disconnectedids;
-    std::set<uint256> duplicateids;
-    std::set<uint256> utxoset;
+    std::set<COutPoint> coinbaseids;
+    std::set<COutPoint> disconnectedids;
+    std::set<COutPoint> duplicateids;
+    std::set<COutPoint> utxoset;
 
     for (unsigned int i = 0; i < NUM_SIMULATION_ITERATIONS; i++) {
         uint32_t randiter = insecure_rand();
@@ -277,22 +276,22 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
             tx.vout.resize(1);
             tx.vout[0].nValue = i; //Keep txs unique unless intended to duplicate
             unsigned int height = insecure_rand();
-            CCoins oldcoins;
+            Coin oldcoins;
 
             // 2/20 times create a new coinbase
             if (randiter % 20 < 2 || coinbaseids.size() < 10) {
                 // 1/10 of those times create a duplicate coinbase
                 if (insecure_rand() % 10 == 0 && coinbaseids.size()) {
-                    TxData &txd = FindRandomFrom(coinbaseids);
+                    auto utxod = FindRandomFrom(coinbaseids);
                     // Reuse the exact same coinbase
-                    tx = std::get<0>(txd);
+                    tx = std::get<0>(utxod->second);
                     // shouldn't be available for reconnection if its been duplicated
-                    disconnectedids.erase(tx.GetHash());
+                    disconnectedids.erase(utxod->first);
 
-                    duplicateids.insert(tx.GetHash());
+                    duplicateids.insert(utxod->first);
                 }
                 else {
-                    coinbaseids.insert(tx.GetHash());
+                    coinbaseids.insert(COutPoint(tx.GetHash(), 0));
                 }
                 assert(CTransaction(tx).IsCoinBase());
             }
@@ -300,85 +299,82 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
             // 17/20 times reconnect previous or add a regular tx
             else {
 
-                uint256 prevouthash;
+                COutPoint prevout;
                 // 1/20 times reconnect a previously disconnected tx
                 if (randiter % 20 == 2 && disconnectedids.size()) {
-                    TxData &txd = FindRandomFrom(disconnectedids);
-                    tx = std::get<0>(txd);
-                    prevouthash = tx.vin[0].prevout.hash;
-                    if (!CTransaction(tx).IsCoinBase() && !utxoset.count(prevouthash)) {
-                        disconnectedids.erase(tx.GetHash());
+                    auto utxod = FindRandomFrom(disconnectedids);
+                    tx = std::get<0>(utxod->second);
+                    prevout = tx.vin[0].prevout;
+                    if (!CTransaction(tx).IsCoinBase() && !utxoset.count(prevout)) {
+                        disconnectedids.erase(utxod->first);
                         continue;
                     }
 
                     // If this tx is already IN the UTXO, then it must be a coinbase, and it must be a duplicate
-                    if (utxoset.count(tx.GetHash())) {
+                    if (utxoset.count(utxod->first)) {
                         assert(CTransaction(tx).IsCoinBase());
-                        assert(duplicateids.count(tx.GetHash()));
+                        assert(duplicateids.count(utxod->first));
                     }
-                    disconnectedids.erase(tx.GetHash());
+                    disconnectedids.erase(utxod->first);
                 }
 
                 // 16/20 times create a regular tx
                 else {
-                    TxData &txd = FindRandomFrom(utxoset);
-                    prevouthash = std::get<0>(txd).GetHash();
+                    auto utxod = FindRandomFrom(utxoset);
+                    prevout = utxod->first;
 
                     // Construct the tx to spend the coins of prevouthash
-                    tx.vin[0].prevout.hash = prevouthash;
-                    tx.vin[0].prevout.n = 0;
+                    tx.vin[0].prevout = prevout;
                     assert(!CTransaction(tx).IsCoinBase());
                 }
                 // In this simple test coins only have two states, spent or unspent, save the unspent state to restore
-                oldcoins = result[prevouthash];
+                oldcoins = result[prevout];
                 // Update the expected result of prevouthash to know these coins are spent
-                result[prevouthash].Clear();
+                result[prevout].Clear();
 
-                utxoset.erase(prevouthash);
+                utxoset.erase(prevout);
 
                 // The test is designed to ensure spending a duplicate coinbase will work properly
                 // if that ever happens and not resurrect the previously overwritten coinbase
-                if (duplicateids.count(prevouthash)) {
+                if (duplicateids.count(prevout)) {
                     spent_a_duplicate_coinbase = true;
                 }
 
             }
             // Update the expected result to know about the new output coins
-            result[tx.GetHash()].FromTx(tx, height);
+            assert(tx.vout.size() == 1);
+            const COutPoint outpoint(tx.GetHash(), 0);
+            result[outpoint] = Coin(tx.vout[0], height, CTransaction(tx).IsCoinBase());
 
             // Call UpdateCoins on the top cache
             CTxUndo undo;
             UpdateCoins(tx, *(stack.back()), undo, height);
 
             // Update the utxo set for future spends
-            utxoset.insert(tx.GetHash());
+            utxoset.insert(outpoint);
 
             // Track this tx and undo info to use later
-            alltxs.insert(std::make_pair(tx.GetHash(),std::make_tuple(tx,undo,oldcoins)));
+            utxoData.emplace(outpoint, std::make_tuple(tx,undo,oldcoins));
         } else if (utxoset.size()) {
             //1/20 times undo a previous transaction
-            TxData &txd = FindRandomFrom(utxoset);
-
-            CTransaction &tx = std::get<0>(txd);
-            CTxUndo &undo = std::get<1>(txd);
-            CCoins &origcoins = std::get<2>(txd);
+            auto utxod = FindRandomFrom(utxoset);
 
-            uint256 undohash = tx.GetHash();
+            CTransaction &tx = std::get<0>(utxod->second);
+            CTxUndo &undo = std::get<1>(utxod->second);
+            Coin &origcoins = std::get<2>(utxod->second);
 
             // Update the expected result
             // Remove new outputs
-            result[undohash].Clear();
+            result[utxod->first].Clear();
             // If not coinbase restore prevout
             if (!tx.IsCoinBase()) {
-                result[tx.vin[0].prevout.hash] = origcoins;
+                result[tx.vin[0].prevout] = origcoins;
             }
 
             // Disconnect the tx from the current UTXO
             // See code in DisconnectBlock
             // remove outputs
-            {
-                stack.back()->SpendCoin(COutPoint(undohash, 0));
-            }
+            stack.back()->SpendCoin(utxod->first);
             // restore inputs
             if (!tx.IsCoinBase()) {
                 const COutPoint &out = tx.vin[0].prevout;
@@ -386,23 +382,19 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
                 ApplyTxInUndo(std::move(coin), *(stack.back()), out);
             }
             // Store as a candidate for reconnection
-            disconnectedids.insert(undohash);
+            disconnectedids.insert(utxod->first);
 
             // Update the utxoset
-            utxoset.erase(undohash);
+            utxoset.erase(utxod->first);
             if (!tx.IsCoinBase())
-                utxoset.insert(tx.vin[0].prevout.hash);
+                utxoset.insert(tx.vin[0].prevout);
         }
 
         // Once every 1000 iterations and at the end, verify the full cache.
         if (insecure_rand() % 1000 == 1 || i == NUM_SIMULATION_ITERATIONS - 1) {
-            for (std::map<uint256, CCoins>::iterator it = result.begin(); it != result.end(); it++) {
-                const CCoins* coins = stack.back()->AccessCoins(it->first);
-                if (coins) {
-                    BOOST_CHECK(*coins == it->second);
-                } else {
-                    BOOST_CHECK(it->second.IsPruned());
-                }
+            for (auto it = result.begin(); it != result.end(); it++) {
+                const Coin& coin = stack.back()->AccessCoin(it->first);
+                BOOST_CHECK(coin == it->second);
             }
         }
 
@@ -443,50 +435,36 @@ BOOST_AUTO_TEST_CASE(updatecoins_simulation_test)
 BOOST_AUTO_TEST_CASE(ccoins_serialization)
 {
     // Good example
-    CDataStream ss1(ParseHex("0104835800816115944e077fe7c803cfa57f29b36bf87c1d358bb85e"), SER_DISK, CLIENT_VERSION);
-    CCoins cc1;
+    CDataStream ss1(ParseHex("97f23c835800816115944e077fe7c803cfa57f29b36bf87c1d35"), SER_DISK, CLIENT_VERSION);
+    Coin cc1;
     ss1 >> cc1;
     BOOST_CHECK_EQUAL(cc1.fCoinBase, false);
     BOOST_CHECK_EQUAL(cc1.nHeight, 203998);
-    BOOST_CHECK_EQUAL(cc1.vout.size(), 2);
-    BOOST_CHECK_EQUAL(cc1.IsAvailable(0), false);
-    BOOST_CHECK_EQUAL(cc1.IsAvailable(1), true);
-    BOOST_CHECK_EQUAL(cc1.vout[1].nValue, 60000000000ULL);
-    BOOST_CHECK_EQUAL(HexStr(cc1.vout[1].scriptPubKey), HexStr(GetScriptForDestination(CKeyID(uint160(ParseHex("816115944e077fe7c803cfa57f29b36bf87c1d35"))))));
+    BOOST_CHECK_EQUAL(cc1.out.nValue, 60000000000ULL);
+    BOOST_CHECK_EQUAL(HexStr(cc1.out.scriptPubKey), HexStr(GetScriptForDestination(CKeyID(uint160(ParseHex("816115944e077fe7c803cfa57f29b36bf87c1d35"))))));
 
     // Good example
-    CDataStream ss2(ParseHex("0109044086ef97d5790061b01caab50f1b8e9c50a5057eb43c2d9563a4eebbd123008c988f1a4a4de2161e0f50aac7f17e7f9555caa486af3b"), SER_DISK, CLIENT_VERSION);
-    CCoins cc2;
+    CDataStream ss2(ParseHex("8ddf77bbd123008c988f1a4a4de2161e0f50aac7f17e7f9555caa4"), SER_DISK, CLIENT_VERSION);
+    Coin cc2;
     ss2 >> cc2;
     BOOST_CHECK_EQUAL(cc2.fCoinBase, true);
     BOOST_CHECK_EQUAL(cc2.nHeight, 120891);
-    BOOST_CHECK_EQUAL(cc2.vout.size(), 17);
-    for (int i = 0; i < 17; i++) {
-        BOOST_CHECK_EQUAL(cc2.IsAvailable(i), i == 4 || i == 16);
-    }
-    BOOST_CHECK_EQUAL(cc2.vout[4].nValue, 234925952);
-    BOOST_CHECK_EQUAL(HexStr(cc2.vout[4].scriptPubKey), HexStr(GetScriptForDestination(CKeyID(uint160(ParseHex("61b01caab50f1b8e9c50a5057eb43c2d9563a4ee"))))));
-    BOOST_CHECK_EQUAL(cc2.vout[16].nValue, 110397);
-    BOOST_CHECK_EQUAL(HexStr(cc2.vout[16].scriptPubKey), HexStr(GetScriptForDestination(CKeyID(uint160(ParseHex("8c988f1a4a4de2161e0f50aac7f17e7f9555caa4"))))));
+    BOOST_CHECK_EQUAL(cc2.out.nValue, 110397);
+    BOOST_CHECK_EQUAL(HexStr(cc2.out.scriptPubKey), HexStr(GetScriptForDestination(CKeyID(uint160(ParseHex("8c988f1a4a4de2161e0f50aac7f17e7f9555caa4"))))));
 
     // Smallest possible example
-    CDataStream ssx(SER_DISK, CLIENT_VERSION);
-    BOOST_CHECK_EQUAL(HexStr(ssx.begin(), ssx.end()), "");
-
-    CDataStream ss3(ParseHex("0002000600"), SER_DISK, CLIENT_VERSION);
-    CCoins cc3;
+    CDataStream ss3(ParseHex("000006"), SER_DISK, CLIENT_VERSION);
+    Coin cc3;
     ss3 >> cc3;
     BOOST_CHECK_EQUAL(cc3.fCoinBase, false);
     BOOST_CHECK_EQUAL(cc3.nHeight, 0);
-    BOOST_CHECK_EQUAL(cc3.vout.size(), 1);
-    BOOST_CHECK_EQUAL(cc3.IsAvailable(0), true);
-    BOOST_CHECK_EQUAL(cc3.vout[0].nValue, 0);
-    BOOST_CHECK_EQUAL(cc3.vout[0].scriptPubKey.size(), 0);
+    BOOST_CHECK_EQUAL(cc3.out.nValue, 0);
+    BOOST_CHECK_EQUAL(cc3.out.scriptPubKey.size(), 0);
 
     // scriptPubKey that ends beyond the end of the stream
-    CDataStream ss4(ParseHex("0002000800"), SER_DISK, CLIENT_VERSION);
+    CDataStream ss4(ParseHex("000007"), SER_DISK, CLIENT_VERSION);
     try {
-        CCoins cc4;
+        Coin cc4;
         ss4 >> cc4;
         BOOST_CHECK_MESSAGE(false, "We should have thrown");
     } catch (const std::ios_base::failure& e) {
@@ -497,17 +475,16 @@ BOOST_AUTO_TEST_CASE(ccoins_serialization)
     uint64_t x = 3000000000ULL;
     tmp << VARINT(x);
     BOOST_CHECK_EQUAL(HexStr(tmp.begin(), tmp.end()), "8a95c0bb00");
-    CDataStream ss5(ParseHex("0002008a95c0bb0000"), SER_DISK, CLIENT_VERSION);
+    CDataStream ss5(ParseHex("00008a95c0bb00"), SER_DISK, CLIENT_VERSION);
     try {
-        CCoins cc5;
+        Coin cc5;
         ss5 >> cc5;
         BOOST_CHECK_MESSAGE(false, "We should have thrown");
     } catch (const std::ios_base::failure& e) {
     }
 }
 
-const static uint256 TXID;
-const static COutPoint OUTPOINT = {uint256(), 0};
+const static COutPoint OUTPOINT;
 const static CAmount PRUNED = -1;
 const static CAmount ABSENT = -2;
 const static CAmount FAIL = -3;
@@ -522,15 +499,15 @@ const static auto FLAGS = {char(0), FRESH, DIRTY, char(DIRTY | FRESH)};
 const static auto CLEAN_FLAGS = {char(0), FRESH};
 const static auto ABSENT_FLAGS = {NO_ENTRY};
 
-void SetCoinsValue(CAmount value, CCoins& coins)
+void SetCoinsValue(CAmount value, Coin& coin)
 {
     assert(value != ABSENT);
-    coins.Clear();
-    assert(coins.IsPruned());
+    coin.Clear();
+    assert(coin.IsPruned());
     if (value != PRUNED) {
-        coins.vout.emplace_back();
-        coins.vout.back().nValue = value;
-        assert(!coins.IsPruned());
+        coin.out.nValue = value;
+        coin.nHeight = 1;
+        assert(!coin.IsPruned());
     }
 }
 
@@ -544,24 +521,22 @@ size_t InsertCoinsMapEntry(CCoinsMap& map, CAmount value, char flags)
     CCoinsCacheEntry entry;
     entry.flags = flags;
     SetCoinsValue(value, entry.coins);
-    auto inserted = map.emplace(TXID, std::move(entry));
+    auto inserted = map.emplace(OUTPOINT, std::move(entry));
     assert(inserted.second);
     return inserted.first->second.coins.DynamicMemoryUsage();
 }
 
 void GetCoinsMapEntry(const CCoinsMap& map, CAmount& value, char& flags)
 {
-    auto it = map.find(TXID);
+    auto it = map.find(OUTPOINT);
     if (it == map.end()) {
         value = ABSENT;
         flags = NO_ENTRY;
     } else {
         if (it->second.coins.IsPruned()) {
-            assert(it->second.coins.vout.size() == 0);
             value = PRUNED;
         } else {
-            assert(it->second.coins.vout.size() == 1);
-            value = it->second.coins.vout[0].nValue;
+            value = it->second.coins.out.nValue;
         }
         flags = it->second.flags;
         assert(flags != NO_ENTRY);
diff --git a/src/test/test_bitcoin_fuzzy.cpp b/src/test/test_bitcoin_fuzzy.cpp
index e11e46bb02..de14251601 100644
--- a/src/test/test_bitcoin_fuzzy.cpp
+++ b/src/test/test_bitcoin_fuzzy.cpp
@@ -168,8 +168,8 @@ int do_fuzz()
         {
             try
             {
-                CCoins block;
-                ds >> block;
+                Coin coin;
+                ds >> coin;
             } catch (const std::ios_base::failure& e) {return 0;}
             break;
         }
diff --git a/src/txdb.cpp b/src/txdb.cpp
index f139384a22..19c9002506 100644
--- a/src/txdb.cpp
+++ b/src/txdb.cpp
@@ -14,6 +14,7 @@
 
 #include <boost/thread.hpp>
 
+static const char DB_COIN = 'C';
 static const char DB_COINS = 'c';
 static const char DB_BLOCK_FILES = 'f';
 static const char DB_TXINDEX = 't';
@@ -24,17 +25,40 @@ static const char DB_FLAG = 'F';
 static const char DB_REINDEX_FLAG = 'R';
 static const char DB_LAST_BLOCK = 'l';
 
+namespace {
+
+struct CoinsEntry {
+    COutPoint* outpoint;
+    char key;
+    CoinsEntry(const COutPoint* ptr) : outpoint(const_cast<COutPoint*>(ptr)), key(DB_COIN)  {}
+
+    template<typename Stream>
+    void Serialize(Stream &s) const {
+        s << key;
+        s << outpoint->hash;
+        s << VARINT(outpoint->n);
+    }
+
+    template<typename Stream>
+    void Unserialize(Stream& s) {
+        s >> key;
+        s >> outpoint->hash;
+        s >> VARINT(outpoint->n);
+    }
+};
+
+}
 
 CCoinsViewDB::CCoinsViewDB(size_t nCacheSize, bool fMemory, bool fWipe) : db(GetDataDir() / "chainstate", nCacheSize, fMemory, fWipe, true) 
 {
 }
 
-bool CCoinsViewDB::GetCoins(const uint256 &txid, CCoins &coins) const {
-    return db.Read(std::make_pair(DB_COINS, txid), coins);
+bool CCoinsViewDB::GetCoins(const COutPoint &outpoint, Coin &coin) const {
+    return db.Read(CoinsEntry(&outpoint), coin);
 }
 
-bool CCoinsViewDB::HaveCoins(const uint256 &txid) const {
-    return db.Exists(std::make_pair(DB_COINS, txid));
+bool CCoinsViewDB::HaveCoins(const COutPoint &outpoint) const {
+    return db.Exists(CoinsEntry(&outpoint));
 }
 
 uint256 CCoinsViewDB::GetBestBlock() const {
@@ -50,10 +74,11 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
     size_t changed = 0;
     for (CCoinsMap::iterator it = mapCoins.begin(); it != mapCoins.end();) {
         if (it->second.flags & CCoinsCacheEntry::DIRTY) {
+            CoinsEntry entry(&it->first);
             if (it->second.coins.IsPruned())
-                batch.Erase(std::make_pair(DB_COINS, it->first));
+                batch.Erase(entry);
             else
-                batch.Write(std::make_pair(DB_COINS, it->first), it->second.coins);
+                batch.Write(entry, it->second.coins);
             changed++;
         }
         count++;
@@ -63,13 +88,14 @@ bool CCoinsViewDB::BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) {
     if (!hashBlock.IsNull())
         batch.Write(DB_BEST_BLOCK, hashBlock);
 
-    LogPrint(BCLog::COINDB, "Committing %u changed transactions (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
-    return db.WriteBatch(batch);
+    bool ret = db.WriteBatch(batch);
+    LogPrint(BCLog::COINDB, "Committed %u changed transaction outputs (out of %u) to coin database...\n", (unsigned int)changed, (unsigned int)count);
+    return ret;
 }
 
 size_t CCoinsViewDB::EstimateSize() const
 {
-    return db.EstimateSize(DB_COINS, (char)(DB_COINS+1));
+    return db.EstimateSize(DB_COIN, (char)(DB_COIN+1));
 }
 
 CBlockTreeDB::CBlockTreeDB(size_t nCacheSize, bool fMemory, bool fWipe) : CDBWrapper(GetDataDir() / "blocks" / "index", nCacheSize, fMemory, fWipe) {
@@ -101,29 +127,31 @@ CCoinsViewCursor *CCoinsViewDB::Cursor() const
     /* It seems that there are no "const iterators" for LevelDB.  Since we
        only need read operations on it, use a const-cast to get around
        that restriction.  */
-    i->pcursor->Seek(DB_COINS);
+    i->pcursor->Seek(DB_COIN);
     // Cache key of first record
     if (i->pcursor->Valid()) {
-        i->pcursor->GetKey(i->keyTmp);
+        CoinsEntry entry(&i->keyTmp.second);
+        i->pcursor->GetKey(entry);
+        i->keyTmp.first = entry.key;
     } else {
         i->keyTmp.first = 0; // Make sure Valid() and GetKey() return false
     }
     return i;
 }
 
-bool CCoinsViewDBCursor::GetKey(uint256 &key) const
+bool CCoinsViewDBCursor::GetKey(COutPoint &key) const
 {
     // Return cached key
-    if (keyTmp.first == DB_COINS) {
+    if (keyTmp.first == DB_COIN) {
         key = keyTmp.second;
         return true;
     }
     return false;
 }
 
-bool CCoinsViewDBCursor::GetValue(CCoins &coins) const
+bool CCoinsViewDBCursor::GetValue(Coin &coin) const
 {
-    return pcursor->GetValue(coins);
+    return pcursor->GetValue(coin);
 }
 
 unsigned int CCoinsViewDBCursor::GetValueSize() const
@@ -133,14 +161,18 @@ unsigned int CCoinsViewDBCursor::GetValueSize() const
 
 bool CCoinsViewDBCursor::Valid() const
 {
-    return keyTmp.first == DB_COINS;
+    return keyTmp.first == DB_COIN;
 }
 
 void CCoinsViewDBCursor::Next()
 {
     pcursor->Next();
-    if (!pcursor->Valid() || !pcursor->GetKey(keyTmp))
+    CoinsEntry entry(&keyTmp.second);
+    if (!pcursor->Valid() || !pcursor->GetKey(entry)) {
         keyTmp.first = 0; // Invalidate cached key after last record so that Valid() and GetKey() return false
+    } else {
+        keyTmp.first = entry.key;
+    }
 }
 
 bool CBlockTreeDB::WriteBatchSync(const std::vector<std::pair<int, const CBlockFileInfo*> >& fileInfo, int nLastFile, const std::vector<const CBlockIndex*>& blockinfo) {
diff --git a/src/txdb.h b/src/txdb.h
index df164cb820..73011fe0f9 100644
--- a/src/txdb.h
+++ b/src/txdb.h
@@ -73,11 +73,11 @@ protected:
 public:
     CCoinsViewDB(size_t nCacheSize, bool fMemory = false, bool fWipe = false);
 
-    bool GetCoins(const uint256 &txid, CCoins &coins) const;
-    bool HaveCoins(const uint256 &txid) const;
-    uint256 GetBestBlock() const;
-    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock);
-    CCoinsViewCursor *Cursor() const;
+    bool GetCoins(const COutPoint &outpoint, Coin &coin) const override;
+    bool HaveCoins(const COutPoint &outpoint) const override;
+    uint256 GetBestBlock() const override;
+    bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override;
+    CCoinsViewCursor *Cursor() const override;
 
     size_t EstimateSize() const override;
 };
@@ -88,8 +88,8 @@ class CCoinsViewDBCursor: public CCoinsViewCursor
 public:
     ~CCoinsViewDBCursor() {}
 
-    bool GetKey(uint256 &key) const;
-    bool GetValue(CCoins &coins) const;
+    bool GetKey(COutPoint &key) const;
+    bool GetValue(Coin &coin) const;
     unsigned int GetValueSize() const;
 
     bool Valid() const;
@@ -99,7 +99,7 @@ private:
     CCoinsViewDBCursor(CDBIterator* pcursorIn, const uint256 &hashBlockIn):
         CCoinsViewCursor(hashBlockIn), pcursor(pcursorIn) {}
     std::unique_ptr<CDBIterator> pcursor;
-    std::pair<char, uint256> keyTmp;
+    std::pair<char, COutPoint> keyTmp;
 
     friend class CCoinsViewDB;
 };
diff --git a/src/txmempool.cpp b/src/txmempool.cpp
index 51b93e92ba..648b40a7a6 100644
--- a/src/txmempool.cpp
+++ b/src/txmempool.cpp
@@ -524,9 +524,9 @@ void CTxMemPool::removeForReorg(const CCoinsViewCache *pcoins, unsigned int nMem
                 indexed_transaction_set::const_iterator it2 = mapTx.find(txin.prevout.hash);
                 if (it2 != mapTx.end())
                     continue;
-                const CCoins *coins = pcoins->AccessCoins(txin.prevout.hash);
-                if (nCheckFrequency != 0) assert(coins);
-                if (!coins || (coins->IsCoinBase() && ((signed long)nMemPoolHeight) - coins->nHeight < COINBASE_MATURITY)) {
+                const Coin &coin = pcoins->AccessCoin(txin.prevout);
+                if (nCheckFrequency != 0) assert(!coin.IsPruned());
+                if (coin.IsPruned() || (coin.IsCoinBase() && ((signed long)nMemPoolHeight) - coin.nHeight < COINBASE_MATURITY)) {
                     txToRemove.insert(it);
                     break;
                 }
@@ -654,8 +654,7 @@ void CTxMemPool::check(const CCoinsViewCache *pcoins) const
                     parentSigOpCost += it2->GetSigOpCost();
                 }
             } else {
-                const CCoins* coins = pcoins->AccessCoins(txin.prevout.hash);
-                assert(coins && coins->IsAvailable(txin.prevout.n));
+                assert(pcoins->HaveCoins(txin.prevout));
             }
             // Check whether its inputs are marked in mapNextTx.
             auto it3 = mapNextTx.find(txin.prevout);
@@ -891,20 +890,24 @@ bool CTxMemPool::HasNoInputsOf(const CTransaction &tx) const
 
 CCoinsViewMemPool::CCoinsViewMemPool(CCoinsView* baseIn, const CTxMemPool& mempoolIn) : CCoinsViewBacked(baseIn), mempool(mempoolIn) { }
 
-bool CCoinsViewMemPool::GetCoins(const uint256 &txid, CCoins &coins) const {
+bool CCoinsViewMemPool::GetCoins(const COutPoint &outpoint, Coin &coin) const {
     // If an entry in the mempool exists, always return that one, as it's guaranteed to never
     // conflict with the underlying cache, and it cannot have pruned entries (as it contains full)
     // transactions. First checking the underlying cache risks returning a pruned entry instead.
-    CTransactionRef ptx = mempool.get(txid);
+    CTransactionRef ptx = mempool.get(outpoint.hash);
     if (ptx) {
-        coins = CCoins(*ptx, MEMPOOL_HEIGHT);
-        return true;
+        if (outpoint.n < ptx->vout.size()) {
+            coin = Coin(ptx->vout[outpoint.n], MEMPOOL_HEIGHT, false);
+            return true;
+        } else {
+            return false;
+        }
     }
-    return (base->GetCoins(txid, coins) && !coins.IsPruned());
+    return (base->GetCoins(outpoint, coin) && !coin.IsPruned());
 }
 
-bool CCoinsViewMemPool::HaveCoins(const uint256 &txid) const {
-    return mempool.exists(txid) || base->HaveCoins(txid);
+bool CCoinsViewMemPool::HaveCoins(const COutPoint &outpoint) const {
+    return mempool.exists(outpoint) || base->HaveCoins(outpoint);
 }
 
 size_t CTxMemPool::DynamicMemoryUsage() const {
@@ -1015,7 +1018,7 @@ void CTxMemPool::trackPackageRemoved(const CFeeRate& rate) {
     }
 }
 
-void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRemaining) {
+void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining) {
     LOCK(cs);
 
     unsigned nTxnRemoved = 0;
@@ -1046,11 +1049,10 @@ void CTxMemPool::TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRe
         if (pvNoSpendsRemaining) {
             BOOST_FOREACH(const CTransaction& tx, txn) {
                 BOOST_FOREACH(const CTxIn& txin, tx.vin) {
-                    if (exists(txin.prevout.hash))
-                        continue;
-                    auto iter = mapNextTx.lower_bound(COutPoint(txin.prevout.hash, 0));
-                    if (iter == mapNextTx.end() || iter->first->hash != txin.prevout.hash)
-                        pvNoSpendsRemaining->push_back(txin.prevout.hash);
+                    if (exists(txin.prevout.hash)) continue;
+                    if (!mapNextTx.count(txin.prevout)) {
+                        pvNoSpendsRemaining->push_back(txin.prevout);
+                    }
                 }
             }
         }
@@ -1067,3 +1069,5 @@ bool CTxMemPool::TransactionWithinChainLimit(const uint256& txid, size_t chainLi
     return it == mapTx.end() || (it->GetCountWithAncestors() < chainLimit &&
        it->GetCountWithDescendants() < chainLimit);
 }
+
+SaltedTxidHasher::SaltedTxidHasher() : k0(GetRand(std::numeric_limits<uint64_t>::max())), k1(GetRand(std::numeric_limits<uint64_t>::max())) {}
diff --git a/src/txmempool.h b/src/txmempool.h
index 6547f64f74..c86859118a 100644
--- a/src/txmempool.h
+++ b/src/txmempool.h
@@ -30,8 +30,8 @@
 class CAutoFile;
 class CBlockIndex;
 
-/** Fake height value used in CCoins to signify they are only in the memory pool (since 0.8) */
-static const unsigned int MEMPOOL_HEIGHT = 0x7FFFFFFF;
+/** Fake height value used in Coin to signify they are only in the memory pool (since 0.8) */
+static const uint32_t MEMPOOL_HEIGHT = 0x7FFFFFFF;
 
 struct LockPoints
 {
@@ -321,6 +321,20 @@ enum class MemPoolRemovalReason {
     REPLACED     //! Removed for replacement
 };
 
+class SaltedTxidHasher
+{
+private:
+    /** Salt */
+    const uint64_t k0, k1;
+
+public:
+    SaltedTxidHasher();
+
+    size_t operator()(const uint256& txid) const {
+        return SipHashUint256(k0, k1, txid);
+    }
+};
+
 /**
  * CTxMemPool stores valid-according-to-the-current-best-chain transactions
  * that may be included in the next block.
@@ -570,10 +584,10 @@ public:
     CFeeRate GetMinFee(size_t sizelimit) const;
 
     /** Remove transactions from the mempool until its dynamic size is <= sizelimit.
-      *  pvNoSpendsRemaining, if set, will be populated with the list of transactions
+      *  pvNoSpendsRemaining, if set, will be populated with the list of outpoints
       *  which are not in mempool which no longer have any spends in this mempool.
       */
-    void TrimToSize(size_t sizelimit, std::vector<uint256>* pvNoSpendsRemaining=NULL);
+    void TrimToSize(size_t sizelimit, std::vector<COutPoint>* pvNoSpendsRemaining=NULL);
 
     /** Expire all transaction (and their dependencies) in the mempool older than time. Return the number of removed transactions. */
     int Expire(int64_t time);
@@ -599,6 +613,13 @@ public:
         return (mapTx.count(hash) != 0);
     }
 
+    bool exists(const COutPoint& outpoint) const
+    {
+        LOCK(cs);
+        auto it = mapTx.find(outpoint.hash);
+        return (it != mapTx.end() && outpoint.n < it->GetTx().vout.size());
+    }
+
     CTransactionRef get(const uint256& hash) const;
     TxMempoolInfo info(const uint256& hash) const;
     std::vector<TxMempoolInfo> infoAll() const;
@@ -658,8 +679,8 @@ protected:
 
 public:
     CCoinsViewMemPool(CCoinsView* baseIn, const CTxMemPool& mempoolIn);
-    bool GetCoins(const uint256 &txid, CCoins &coins) const;
-    bool HaveCoins(const uint256 &txid) const;
+    bool GetCoins(const COutPoint &outpoint, Coin &coin) const;
+    bool HaveCoins(const COutPoint &outpoint) const;
 };
 
 #endif // BITCOIN_TXMEMPOOL_H
diff --git a/src/validation.cpp b/src/validation.cpp
index b295a7f86e..cf4dab420e 100644
--- a/src/validation.cpp
+++ b/src/validation.cpp
@@ -268,15 +268,15 @@ bool CheckSequenceLocks(const CTransaction &tx, int flags, LockPoints* lp, bool
         prevheights.resize(tx.vin.size());
         for (size_t txinIndex = 0; txinIndex < tx.vin.size(); txinIndex++) {
             const CTxIn& txin = tx.vin[txinIndex];
-            CCoins coins;
-            if (!viewMemPool.GetCoins(txin.prevout.hash, coins)) {
+            Coin coin;
+            if (!viewMemPool.GetCoins(txin.prevout, coin)) {
                 return error("%s: Missing input", __func__);
             }
-            if (coins.nHeight == MEMPOOL_HEIGHT) {
+            if (coin.nHeight == MEMPOOL_HEIGHT) {
                 // Assume all mempool transaction confirm in the next block
                 prevheights[txinIndex] = tip->nHeight + 1;
             } else {
-                prevheights[txinIndex] = coins.nHeight;
+                prevheights[txinIndex] = coin.nHeight;
             }
         }
         lockPair = CalculateSequenceLocks(tx, flags, &prevheights, index);
@@ -315,9 +315,9 @@ void LimitMempoolSize(CTxMemPool& pool, size_t limit, unsigned long age) {
         LogPrint(BCLog::MEMPOOL, "Expired %i transactions from the memory pool\n", expired);
     }
 
-    std::vector<uint256> vNoSpendsRemaining;
+    std::vector<COutPoint> vNoSpendsRemaining;
     pool.TrimToSize(limit, &vNoSpendsRemaining);
-    BOOST_FOREACH(const uint256& removed, vNoSpendsRemaining)
+    BOOST_FOREACH(const COutPoint& removed, vNoSpendsRemaining)
         pcoinsTip->Uncache(removed);
 }
 
@@ -344,7 +344,7 @@ static bool IsCurrentForFeeEstimation()
 
 bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const CTransactionRef& ptx, bool fLimitFree,
                               bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
-                              bool fOverrideMempoolLimit, const CAmount& nAbsurdFee, std::vector<uint256>& vHashTxnToUncache)
+                              bool fOverrideMempoolLimit, const CAmount& nAbsurdFee, std::vector<COutPoint>& vHashTxnToUncache)
 {
     const CTransaction& tx = *ptx;
     const uint256 hash = tx.GetHash();
@@ -437,30 +437,30 @@ bool AcceptToMemoryPoolWorker(CTxMemPool& pool, CValidationState& state, const C
         view.SetBackend(viewMemPool);
 
         // do we already have it?
-        bool fHadTxInCache = pcoinsTip->HaveCoinsInCache(hash);
-        if (view.HaveCoins(hash)) {
-            if (!fHadTxInCache)
-                vHashTxnToUncache.push_back(hash);
-            return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-known");
+        for (size_t out = 0; out < tx.vout.size(); out++) {
+            COutPoint outpoint(hash, out);
+            bool fHadTxInCache = pcoinsTip->HaveCoinsInCache(outpoint);
+            if (view.HaveCoins(outpoint)) {
+                if (!fHadTxInCache) {
+                    vHashTxnToUncache.push_back(outpoint);
+                }
+                return state.Invalid(false, REJECT_ALREADY_KNOWN, "txn-already-known");
+            }
         }
 
         // do all inputs exist?
-        // Note that this does not check for the presence of actual outputs (see the next check for that),
-        // and only helps with filling in pfMissingInputs (to determine missing vs spent).
         BOOST_FOREACH(const CTxIn txin, tx.vin) {
-            if (!pcoinsTip->HaveCoinsInCache(txin.prevout.hash))
-                vHashTxnToUncache.push_back(txin.prevout.hash);
-            if (!view.HaveCoins(txin.prevout.hash)) {
-                if (pfMissingInputs)
+            if (!pcoinsTip->HaveCoinsInCache(txin.prevout)) {
+                vHashTxnToUncache.push_back(txin.prevout);
+            }
+            if (!view.HaveCoins(txin.prevout)) {
+                if (pfMissingInputs) {
                     *pfMissingInputs = true;
+                }
                 return false; // fMissingInputs and !state.IsInvalid() is used to detect this condition, don't set state.Invalid()
             }
         }
 
-        // are the actual inputs available?
-        if (!view.HaveInputs(tx))
-            return state.Invalid(false, REJECT_DUPLICATE, "bad-txns-inputs-spent");
-
         // Bring the best block into scope
         view.GetBestBlock();
 
@@ -763,10 +763,10 @@ bool AcceptToMemoryPoolWithTime(CTxMemPool& pool, CValidationState &state, const
                         bool* pfMissingInputs, int64_t nAcceptTime, std::list<CTransactionRef>* plTxnReplaced,
                         bool fOverrideMempoolLimit, const CAmount nAbsurdFee)
 {
-    std::vector<uint256> vHashTxToUncache;
+    std::vector<COutPoint> vHashTxToUncache;
     bool res = AcceptToMemoryPoolWorker(pool, state, tx, fLimitFree, pfMissingInputs, nAcceptTime, plTxnReplaced, fOverrideMempoolLimit, nAbsurdFee, vHashTxToUncache);
     if (!res) {
-        BOOST_FOREACH(const uint256& hashTx, vHashTxToUncache)
+        BOOST_FOREACH(const COutPoint& hashTx, vHashTxToUncache)
             pcoinsTip->Uncache(hashTx);
     }
     // After we've (potentially) uncached entries, ensure our coins cache is still within its size limits
@@ -1762,12 +1762,12 @@ bool static FlushStateToDisk(CValidationState &state, FlushStateMode mode, int n
     }
     // Flush best chain related state. This can only be done if the blocks / block index write was also done.
     if (fDoFullFlush) {
-        // Typical CCoins structures on disk are around 128 bytes in size.
+        // Typical Coin structures on disk are around 48 bytes in size.
         // Pushing a new one to the database can cause it to be written
         // twice (once in the log, and once in the tables). This is already
         // an overestimation, as most will delete an existing entry or
         // overwrite one. Still, use a conservative safety factor of 2.
-        if (!CheckDiskSpace(128 * 2 * 2 * pcoinsTip->GetCacheSize()))
+        if (!CheckDiskSpace(48 * 2 * 2 * pcoinsTip->GetCacheSize()))
             return state.Error("out of disk space");
         // Flush the chainstate (which may refer to block index entries).
         if (!pcoinsTip->Flush())
@@ -1848,7 +1848,7 @@ void static UpdateTip(CBlockIndex *pindexNew, const CChainParams& chainParams) {
             }
         }
     }
-    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g tx=%lu date='%s' progress=%f cache=%.1fMiB(%utx)", __func__,
+    LogPrintf("%s: new best=%s height=%d version=0x%08x log2_work=%.8g tx=%lu date='%s' progress=%f cache=%.1fMiB(%utxo)", __func__,
       chainActive.Tip()->GetBlockHash().ToString(), chainActive.Height(), chainActive.Tip()->nVersion,
       log(chainActive.Tip()->nChainWork.getdouble())/log(2.0), (unsigned long)chainActive.Tip()->nChainTx,
       DateTimeStrFormat("%Y-%m-%d %H:%M:%S", chainActive.Tip()->GetBlockTime()),