Consider the following log sequence of two transactions on a bank account, with initial balance 12000, that transfer 2000 to a mortagage payment and then apply a 5% interest. 1. T1 start 2. T1 B old = 1200 new = 10000 3. T1 M old = 0 new = 2000 4. T1 commit 5. T1 start6. T2 B old = 10000 new = 10500 7. T2 commit Suppose the database system crashes just before log record is written. When the system is started, which one statement is true of the recovery procedure?

We need not redo log records 2 and 3 because transaction T1 has committed

We must redo log record 6 to set B to 10500

We must redo log record 6 to set B to 10000 and the redo log records 2 and 3.

We need not redo log records 2 and 3 because transaction T1 has committed

We can apply redo and undo operations in arbitrary order because they are idempotent

Consider the following log sequence of two transactions on a bank acco

1.	Consider the following log sequence of two transactions on a bank account, with initial balance 12000, that transfer 2000 to a mortagage payment and then apply a 5% interest. 1. T₁ start 2. T₁ B old = 1200 new = 10000 3. T₁ M old = 0 new = 2000 4. T₁ commit 5. T₁ start 6. T₂ B old = 10000 new = 10500 7. T₂ commit Suppose the database system crashes just before log record is written. When the system is started, which one statement is true of the recovery procedure?
A.	We must redo log record 6 to set B to 10500
B.	We must redo log record 6 to set B to 10000 and the redo log records 2 and 3.
C.	We need not redo log records 2 and 3 because transaction T1 has committed
D.	We can apply redo and undo operations in arbitrary order because they are idempotent
Answer» C. We need not redo log records 2 and 3 because transaction T1 has committed

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