less allocation

versiondb/tmdb/store.go

@@ -34,58 +34,59 @@ func NewStore(plainDB, historyDB, changesetDB dbm.DB) *Store {
 
 // PutAtVersion implements VersionStore interface
 // TODO reduce allocation within iterations.
-func (s *Store) PutAtVersion(version int64, changeSet []types.StoreKVPair) error {
+func (s *Store) PutAtVersion(version int64, changeSet []types.StoreKVPair) (err error) {
 	plainBatch := s.plainDB.NewBatch()
 	defer plainBatch.Close()
 	historyBatch := s.historyDB.NewBatch()
 	defer historyBatch.Close()
 	changesetBatch := s.changesetDB.NewBatch()
 	defer changesetBatch.Close()
 
+	var key, original []byte
 	for _, pair := range changeSet {
-		key := prependStoreKey(pair.StoreKey, pair.Key)
+		key = prependStoreKey(pair.StoreKey, pair.Key)
 
 		if version == 0 {
 			// genesis state is written into plain state directly
 			if pair.Delete {
 				return errors.New("can't delete at genesis")
 			}
-			if err := plainBatch.Set(key, pair.Value); err != nil {
-				return err
+			if err = plainBatch.Set(key, pair.Value); err != nil {
+				return
 			}
 			continue
 		}
 
-		original, err := s.plainDB.Get(key)
+		original, err = s.plainDB.Get(key)
 		if err != nil {
-			return err
+			return
 		}
 		if bytes.Equal(original, pair.Value) {
 			// do nothing if the value is not changed
 			continue
 		}
 
 		// write history index
-		if err := WriteHistoryIndex(s.historyDB, historyBatch, key, uint64(version)); err != nil {
-			return err
+		if err = WriteHistoryIndex(s.historyDB, historyBatch, key, uint64(version)); err != nil {
+			return
 		}
 
 		// write the old value to changeset
 		if len(original) > 0 {
 			changesetKey := append(sdk.Uint64ToBigEndian(uint64(version)), key...)
-			if err := changesetBatch.Set(changesetKey, original); err != nil {
-				return err
+			if err = changesetBatch.Set(changesetKey, original); err != nil {
+				return
 			}
 		}
 
 		// write the new value to plain state
 		if pair.Delete {
-			if err := plainBatch.Delete(key); err != nil {
-				return err
+			if err = plainBatch.Delete(key); err != nil {
+				return
 			}
 		} else {
-			if err := plainBatch.Set(key, pair.Value); err != nil {
-				return err
+			if err = plainBatch.Set(key, pair.Value); err != nil {
+				return
 			}
 		}
 	}