Transaction attributes and isolation not working as expected why ? !

Question

I have three beans participating in a TX
SeatBean ---- entity (BMP)
Res --------entity (BMP)
AgentBean --- session (SFSB)
AgentBean has bookSeat (seatNumber, amount) method that is being called by the client.
The Agent bean bookSeat (seatNumber, amount) method locates the seat bean with the given seat number if the booked field is null (means the seat is open for booking)
It sets the values for booking the seat (inserts a new record in Res table using ResBean and updates the Seat table using SeatBean )
In the AgentBean I make a check if the booked filed is Y or null.
If the field is Y it throws a RemoteException.
I gave Tx attributes in the ejb-jar.xml for ALL the beans as follows
In ejb-jar.xml <trans-attribute>Required</trans-attribute>
In weblogic-ejb-jar.xml
<transaction-isolation>
     <isolation-level>TRANSACTION_REPEATABLE_READ</isolation-level>
I opened two windows as use1 and user2
User1 makes search for a seat finds seat1 is not booked
User2 makes search for a seat finds seat1 is not booked
User1 books the seat
User2 books the seat (user2 action is initiated immediately after user1 initiates the action)
Use1 and user2 actions are successful. There are two records in Res table.
The seat table reflects the last changes. i.e user2 action.
My questions are
1.user2 should not get any search result till user1 intiated TX is complete
( i.e user2 should got get any search result till user1 commits or roll back because TRANSACTION_REPEATABLE_READ )
Why is that not happening?
2.Since user1 books the seat for customer1 and sets booked = Y in seat table
user should not be able to book the seat. but user2 actions are reflecting in DB.
What is going wrong?
Can any one explain?

Answer 1

The following szenario will executed as follows:
User1 makes search for a seat finds seat1 is not booked
User2 makes search for a seat finds seat1 is not booked
User1 books the seat
User2 books the seat
Use1 and user2 actions are successful. There are two records in Res table.1.) Agent Bean is a session bean with CMT:
User1: | AgentBean.searchNotBookedSeats()
Tx1 | call other EJBs with the same transaction
| context (required)
v <-- return
**) at this point the transaction is finished, the
isolation level is not used
User2: | AgentBean.searchNotBookedSeats()
Tx2 | call other EJBs with the same transaction
| context (required)
v <-- return
User1: | AgentBean.bookSeat(...)
Tx3 | Res.create(..) same transaction context
v <-- return
User2: | AgentBean.bookSeat(...)
Tx4 | Res.create(..) same transaction context
v <-- return
In this case there are four transaction used. The easiest way to
prevent that there exists more than one reservation for one seat is
to use a database constraint. That's the way I would solve the
problem.
Here is another solution:
2.) Agent Bean is a stateful session bean with BMT and the isolation
attribute is higher or equal REPEATABLE_READ:
User1: | AgentBean.searchNotBookedSeats()
Tx1 | call other EJBs with the same transaction
| context (required)
v <-- return
**) the method starts a transaction but does not
finish it.
User2: | AgentBean.searchNotBookedSeats()
Tx2 | call other EJBs with the same transaction
| context (required)
v <-- return
**) this method blocks until Tx1 will be finished
User1: | AgentBean.bookSeat(...)
Tx1 | Res.create(..) same transaction context
v <-- return
**) the method finish the transaction
User2: | AgentBean.bookSeat(...)
Tx2 | Res.create(..) same transaction context
v <-- return
In this case the isolation level will be used. The whole system is
blocked for the time between searching and booking a seat.
Thats not very good :-(
Best Regards and mery christmas
Markus