1. Fall 2006R McFadyen ACS 49021 Deadlock Prevention Strategies wait-die wound-wait schemes use transaction timestamps for the sake of deadlock prevention Both in wait-die and in wound-wait schemes, a rolled back transaction is restarted with its original timestamp. Older transactions have precedence over newer ones, and starvation is hence avoided.

2. Fall 2006R McFadyen ACS 49022 Deadlock Prevention Strategies wait-die scheme –older transaction waits for a younger transaction to release a data item. Younger transactions never wait for older ones; they are rolled back instead. –a transaction may die several times before acquiring needed data item

3. Fall 2006R McFadyen ACS 49023 Deadlock Prevention Strategies wound-wait scheme –older transaction wounds (forces rollback) of younger transaction instead of waiting for it. Younger transactions may wait for older ones. –may be fewer rollbacks than wait-die scheme.

4. Fall 2006R McFadyen ACS 49024 Deadlock Prevention Strategies T1 Begin transaction Read_item(customer ‘A’) Write_item(customer ‘A’) Read_item(order ‘123’) Write_item(order ‘123’) T2 Begin transaction Read_item(customer ‘A’) What occurs in the following schedule for a)wait-die? b)wound-wait?

5. Fall 2006R McFadyen ACS 49025 Deadlock Prevention Strategies T1 Begin transaction Read_item(customer ‘ A ’) Write_item(customer ‘ A ’) Read_item(order ‘123’) Write_item(order ‘123’) T2 Begin transaction Read_item(customer ‘A’) What occurs in the following schedule for a)wait-die? b)wound-wait?