Upgrade from per-tx database to per-txout

src/coins.h

@@ -82,6 +82,7 @@ public:
     }
 };
 
+//! Legacy class to deserialize pre-pertxout database entries without reindex.
 class CCoins
 {
 public:

src/init.cpp

@@ -1455,6 +1455,12 @@ bool AppInitMain(boost::thread_group& threadGroup, CScheduler& scheduler)
                     //If we're reindexing in prune mode, wipe away unusable block files and all undo data files
                     if (fPruneMode)
                         CleanupBlockRevFiles();
+                } else {
+                    // If necessary, upgrade from older database format.
+                    if (!pcoinsdbview->Upgrade()) {
+                        strLoadError = _("Error upgrading chainstate database");
+                        break;
+                    }
                 }
 
                 if (!LoadBlockIndex(chainparams)) {

src/txdb.cpp

@@ -252,3 +252,48 @@ bool CBlockTreeDB::LoadBlockIndexGuts(std::function<CBlockIndex*(const uint256&)
 
     return true;
 }
+
+/** Upgrade the database from older formats.
+ *
+ * Currently implemented: from the per-tx utxo model (0.8..0.14.x) to per-txout.
+ */
+bool CCoinsViewDB::Upgrade() {
+    std::unique_ptr<CDBIterator> pcursor(db.NewIterator());
+    pcursor->Seek(std::make_pair(DB_COINS, uint256()));
+    if (!pcursor->Valid()) {
+        return true;
+    }
+
+    LogPrintf("Upgrading database...\n");
+    size_t batch_size = 1 << 24;
+    CDBBatch batch(db);
+    while (pcursor->Valid()) {
+        boost::this_thread::interruption_point();
+        std::pair<unsigned char, uint256> key;
+        if (pcursor->GetKey(key) && key.first == DB_COINS) {
+            CCoins old_coins;
+            if (!pcursor->GetValue(old_coins)) {
+                return error("%s: cannot parse CCoins record", __func__);
+            }
+            COutPoint outpoint(key.second, 0);
+            for (size_t i = 0; i < old_coins.vout.size(); ++i) {
+                if (!old_coins.vout[i].IsNull() && !old_coins.vout[i].scriptPubKey.IsUnspendable()) {
+                    Coin newcoin(std::move(old_coins.vout[i]), old_coins.nHeight, old_coins.fCoinBase);
+                    outpoint.n = i;
+                    CoinEntry entry(&outpoint);
+                    batch.Write(entry, newcoin);
+                }
+            }
+            batch.Erase(key);
+            if (batch.SizeEstimate() > batch_size) {
+                db.WriteBatch(batch);
+                batch.Clear();
+            }
+            pcursor->Next();
+        } else {
+            break;
+        }
+    }
+    db.WriteBatch(batch);
+    return true;
+}

src/txdb.h

@@ -77,6 +77,8 @@ public:
     bool BatchWrite(CCoinsMap &mapCoins, const uint256 &hashBlock) override;
     CCoinsViewCursor *Cursor() const override;
 
+    //! Attempt to update from an older database format. Returns whether an error occurred.
+    bool Upgrade();
     size_t EstimateSize() const override;
 };