ModifyNewCoins saves database lookups

When processing a new transaction, in addition to spending the Coins of its txin's it creates a new Coins for its outputs.  The existing ModifyCoins function will first make sure this Coins does not already exist.  It can not exist due to BIP 30, but because of that the lookup can't be cached and always has to go to the database.  Since we are creating the coins to match the new tx anyway, there is no point in checking if they exist first anyway.  However this should not be used for coinbase tx's in order to preserve the historical behavior of overwriting the two existing duplicate tx pairs.

1 files changed, 10 insertions, 3 deletions

diff --git a/src/main.cpp b/src/main.cpp
index 26a22ae6fd..270b4c063a 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -1285,10 +1285,17 @@ void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCach
                 undo.nVersion = coins->nVersion;
             }
         }
+        // add outputs
+        inputs.ModifyNewCoins(tx.GetHash())->FromTx(tx, nHeight);
+    }
+    else {
+        // add outputs for coinbase tx
+        // In this case call the full ModifyCoins which will do a database
+        // lookup to be sure the coins do not already exist otherwise we do not
+        // know whether to mark them fresh or not.  We want the duplicate coinbases
+        // before BIP30 to still be properly overwritten.
+        inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
     }
-
-    // add outputs
-    inputs.ModifyCoins(tx.GetHash())->FromTx(tx, nHeight);
 }
 
 void UpdateCoins(const CTransaction& tx, CValidationState &state, CCoinsViewCache &inputs, int nHeight)