Thanks for the answers.
1) I am still not clear about it. I was asked in inteview about it. I do informed that, you can not delete record since it was locked by container. But they told me to assume that "record can be deleted from DB" and explain the consequences. I said, container throws SystemException. Is it not true? It looks like container can not able to find the row it is about to update just after transaction and not able to find it. So it's a irrecoverable system erorr?!!!
Well I got same question in another interview. I said, container throws ObjectNotFound exception, Thinking that it should be application exception and developer suppose to catch it in every entity bean. May be I was wrong in both answers.
So I am not sure which is the correct answere for it.
2) DD can be configured to make sure, MDB receives the expected message. Do we still need correction ID concept to be complete solution? if not when do we need correction IDs also?