Consider schedules S3, S4, and S5 below. Determine whether each schedule is strict, cascadeless, recoverable, or nonrecoverable.
(Determine the strictest recoverability condition that each schedule satisfies).
S3: r1 (X); r2 (Z); r1 (Z); r3 (X); r3 (Y); w1 (X); c1; w3 (Y); c3; r2 (Y); w2 (Z); w2 (Y); c2;
S4: r1 (X); r2 (Z); r1 (Z); r3 (X); r3 (Y); w1 (X); w3 (Y); r2 (Y); w2 (Z); w2 (Y); c1; c2; c3;
S5: r1 (X); r2 (Z); r3 (X); r1 (Z); r2 (Y); r3 (Y); w1 (X); c1; w2 (Z); w3 (Y); w2 (Y); c3; c2;
Answers
Answer:
Recoverable Schedule: The transaction which does uncommitted read operation should not commit before the commit/rollback of the transaction which updated that data item.
Non-recoverable Schedule: Opposite of recoverable schedule
Cascadeless Schedule: No uncommitted read is allowed.
Strict Recoverable Schedule: Read/Write(WR,WW) operations are not allowed by any other transactions until the transaction commit/rollback which updated a data item.
S3: recoverable, cascadeless, strict recoverable
S4: there is a dirty read between W3(Y) and R2(Y) hence not cascadeless, Not recoverable because T2 is committing before T3
S5: No dirty read hence recoverable and cascadeless shecdule but not strict recoverable because WW exists between W3(Y) and W2(Y)
Answer:
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