blockchain_db: allocate known size vector only once

src/blockchain_db/blockchain_db.cpp

@@ -170,7 +170,7 @@ void BlockchainDB::add_transaction(const crypto::hash& blk_hash, const transacti
 
   uint64_t tx_id = add_transaction_data(blk_hash, tx, tx_hash, tx_prunable_hash);
 
-  std::vector<uint64_t> amount_output_indices;
+  std::vector<uint64_t> amount_output_indices(tx.vout.size());
 
   // iterate tx.vout using indices instead of C++11 foreach syntax because
   // we need the index
@@ -183,13 +183,13 @@ void BlockchainDB::add_transaction(const crypto::hash& blk_hash, const transacti
       cryptonote::tx_out vout = tx.vout[i];
       rct::key commitment = rct::zeroCommit(vout.amount);
       vout.amount = 0;
-      amount_output_indices.push_back(add_output(tx_hash, vout, i, tx.unlock_time,
-        &commitment));
+      amount_output_indices[i] = add_output(tx_hash, vout, i, tx.unlock_time,
+        &commitment);
     }
     else
     {
-      amount_output_indices.push_back(add_output(tx_hash, tx.vout[i], i, tx.unlock_time,
-        tx.version > 1 ? &tx.rct_signatures.outPk[i].mask : NULL));
+      amount_output_indices[i] = add_output(tx_hash, tx.vout[i], i, tx.unlock_time,
+        tx.version > 1 ? &tx.rct_signatures.outPk[i].mask : NULL);
     }
   }
   add_tx_amount_output_indices(tx_id, amount_output_indices);