Transaction problem with oracle adapter

Hi,
Here I build an integration over Oracle database. I start a transaction (by
publishing Adapter::beginTransaction event) and then make an update in
database. After that I end transaction with mode as
BrokerClient.TRANSACTION_MODE_ROLLBACK (i.e. 2). But even then update in
database are committed. Did anyone face same kind of problem?
All kind of suggestions are welcome.

Thanks,
Mani