Question

Choose the recovery log that is generated by the schedule below a) 1. start T1 2. start T2 3. update T1, AID, Aoriginal, Anew 4. commit T1 5. update T2, BID, Boriginal, Bnew 6. undo T2, BID, Boriginal 7. rollback

Choose the recovery log that is generated by the schedule below

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a)

1. start T1
2. start T2
3. update T1, AID, Aoriginal, Anew
4. commit T1
5. update T2, BID, Boriginal, Bnew
6. undo T2, BID, Boriginal
7. rollback T2
b)

1. start T1
2. update T1, AID, Aoriginal, Anew
3. start T2
4. update T2, BID, Boriginal, Bnew
5. undo T2, BID, Boriginal
6. commit T1
7. rollback T2
c)

1. start T1
2. update T1, AID, Aoriginal, Anew
3. start T2
4. commit T1
5. update T2, BID, Boriginal, Bnew
6. undo T2, BID, Boriginal
7. rollback T2

Answer 1

The correct recovery log matched with the given transaction schedule is option (a), which includes start operations, an update and commit for transaction T1, an update for T2, followed by an undo operation and a rollback for T2.

Step-by-step explanation:

The question relates to the generation of a recovery log for a database transaction schedule. The correct recovery log is a series of records that reflect the progression and management of transactions, including updates, commits, rollbacks, and undos. Based on the operations listed in the schedule, such as start operations, updates, commits, rollback instructions, and undo operations for transactions T1 and T2, the recovery log that corresponds to the actions taken would be:

• start T1
• start T2
• update T1, AID, Aoriginal, Anew
• commit T1
• update T2, BID, Boriginal, Bnew
• undo T2, BID, Boriginal
• rollback T2

This sequence reflects a recovery log where transaction T1 is successfully committed after its update, and transaction T2 is rolled back after its update, which necessitates an undo operation to restore the original value (Boriginal) for the item identified by BID. This corresponds to option (a) from the provided choices.