@deeky666 If we're going to add other configuration options for a transaction, it would make sense I guess, but as far as usability is concerned, I'm a bit worried that it could become cumbersome in the code to always do:

    $definition = new TransactionDefinition();
    $definition->setIsolationLevel(Connection::TRANSACTION_SERIALIZABLE);
    $em->createTransaction($definition);

Instead of:

    $em->createTransaction(Connection::TRANSACTION_SERIALIZABLE);