1. Recovery and Concurrency Recovery Transaction Sync Point Commit Rollback Failure System Media Tran 1 Tran 2Tran 3 Tran 4 Journal(log file)

2. Time tctf Checkpoint System failure T1 T2 T3 T4 T5 T2T3T4 T2 T5 T4 Undo List Redo List

3. Concurrency The Lost Update problem The Uncommitted Dependency problem The Inconsistent analysis problem

4. Transaction ATransaction B t1 Retrieve p t2 Retrieve p --- Update p --- Update p --- t3 t4 Lost update problem

5. Transaction ATransaction B t1 Retrieve p t2 Update p --- Rollback --- t3 t4 Uncommitted dependency problem ---

6. Transaction ATransaction B t1 Update p t2 Update p --- Rollback --- t3 t4 Uncommitted dependency problem ---

7. Transaction ATransaction B t1 t2 Update ACC 3 30 -> 20 --- Retrieve ACC 1 Sum = 40 --- t3 t4 Inconsistent analysis problem --- Retrieve ACC 2 Sum = 90 Retrieve ACC 3 Sum = 40 Retrieve ACC 1 t5 --- Update ACC 1 40 -> 50 t6 t7 t8 Commit Retrieve ACC 3 sum = 110 ACC 1ACC 2ACC 3 40 50 30

8. Locking XS- XNNY SNYY -YYY Shared Locks (S locks) Exclusive Locks (X locks)

9. Transaction ATransaction B t1 Retrieve p (acquire S lock on p) t2 Retrieve p (acquire S lock on p) --- Update p (request X lock on p) --- waitUpdate p (request X lock on p) t3 t4 Lost update problem wait ---

10. Transaction ATransaction B t1 Update p (request X lock on p) t2 Update p (acquire X lock on p) --- Commit / Rollback (release X lock on p) --- t3 t4 Uncommitted dependency problem wait --- wait Resume:Update p (acquire X lock on p)

11. Transaction ATransaction B t1 t2 Update ACC 3 (acquire X lock on ACC 3) 30 -> 20 --- Retrieve ACC 1 (acquire S lock on ACC 1) Sum = 40 --- t3 t4 --- Retrieve ACC 2: (acquire S lock on ACC 2) Sum = 90 Retrieve ACC 3 (acquire S lock on ACC 3) Retrieve ACC 1 (acquire S lock on ACC 1) t5 --- Update ACC 1 Request X lock on ACC 3) t6 t7 t8 wait Retrieve ACC 3 (request S lock on ACC 3) ACC 1ACC 2ACC 3 40 50 30 --- wait