jakarta ee - EJB 3.0 - Nested Transaction != Requires New?

Question

I just read the Transactions Chapter (10) of "Mastering EJB 3.0" and now I'm confused about nested transactions.

The book says

"The EJB-defined transaction manager does not support nested transactions; it requires support for only flat transactions." (Site 278, Note)

This fact is described not only by this book, I found this statement in other books / websites.

But if I call a "Requires New" annotated Method from a, let's say "Required" annotated Methode, what I have is a nested transaction, isn't it? I can roll back the inner transaction or commit it, without affecting the outer transaction. And if I want the outer Transaction to be aborted, I throw an EJBException back and the whole transaction will be rolled back.

So is it just that this behavior is not required by the EJB 3.0 specification or have i misunderstood something? I just can't get the difference between nested transactions and the described behavior.

Regards Norman

Answer 1

RequiresNew does not create a nested transaction because the first transaction is suspended while the second transaction is running. A nested transaction looks like this:

Nested transaction example
> method1 - begin tran1
  > method2 - begin tran2
    workA
  < method2 - commit tran2
< method1 - rollback tran1 (tran2 also rolled back because it's nested)

Instead, RequiresNew looks like this:

EJB RequiresNew example
> method1 - begin tran1
  > method2 - suspend tran1, begin tran2
    workA
  < method2 - commit tran2, resume tran1
< method1 - rollback tran1 (tran2 remains committed)