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ISRO | ISRO CS 2015 | Question 17

Consider the following log sequence of two transactions on a bank account, with initial balance 12000, that transfer 2000 to a mortgage 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. T2 start 6. T2 B old=10000 new=10500 7. T2 commit Suppose the database system crashes just before log record 7 is written. When the system is restarted, which one statement is true of the recovery procedure?


We must redo log record 6 to set B to 10500


We must undo log record 6 to set B to 10000 and then 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.


Please comment below if you find anything wrong in the above post
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