GATE CS 2021 Set 2 — Question 42
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Databases → Transactions & Concurrency → Conflict Serializability
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Question
Let be the following schedule of operations of three transactions , and in a relational database system:Consider the statements P and Q below:P: is conflict-serializable.
Q: If commits before finishes, then is recoverable.Which one of the following choices is correct?
Q: If commits before finishes, then is recoverable.Which one of the following choices is correct?
Correct answer
(B) P is true and Q is false.
Solution
1.Conflict Serializability (P): We check for conflicting operations between different transactions:
- On : precedes .
- On : precedes .
- On : precedes .
2.Recoverability (Q): A schedule is recoverable if for every pair of transactions and such that reads a data item previously written by , the commit of occurs before the commit of .
In , performs after has performed . Thus, reads from . For the schedule to be recoverable, must commit before . Statement Q says if commits before finishes, the schedule is recoverable, which is false. Statement Q is false.Continue learning with Success Tracker
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