presto-hive/src/main/java/io/prestosql/plugin/hive/HiveTransactionManager.java/HiveTransactionManager/put
class HiveTransactionManager:    public void put(ConnectorTransactionHandle transactionHandle, TransactionalMetadata metadata)
    {
        ConnectorMetadata previousValue = transactions.putIfAbsent(transactionHandle, metadata);
        checkState(previousValue == null);
    }