When using PdoSessionHandler with Oracle, Symfony 2.8 raises an exception:

Warning: PDOStatement::execute(): supplied argument is not a valid stream resource
500 Internal Server Error - ContextErrorException

Stack trace starts with:
in vendor\symfony\symfony\src\Symfony\Component\HttpFoundation\Session\Storage\Handler\PdoSessionHandler.php at line 538

When switching to mysql all works fine.