From 50830796889ecaa458871f1db878c255dd2554cb Mon Sep 17 00:00:00 2001
From: Pieter Wuille <pieter.wuille@gmail.com>
Date: Tue, 25 Apr 2017 11:29:39 -0700
Subject: 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.
---
 src/txdb.cpp | 66 ++++++++++++++++++++++++++++++++++++++++++++----------------
 1 file changed, 49 insertions(+), 17 deletions(-)

(limited to 'src/txdb.cpp')

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) {
-- 
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