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Consider the following database schedule with two transactions, T1 and T2. S = r2(X); r1(X); r2(Y); w1(X); r1(Y); w2(X); a1; a2 where ri(Z) denotes a read operation by transaction Ti on a variable Z, wi(Z) denotes a write operation by Ti on a variable Z, and ai denotes abort by transaction Ti. Which one of the following statements about the above schedule is TRUE?

1. S is non-recoverable
2. S is recoverable, but has a cascading abort
3. S does not have a cascading abort
4. S is strict

Correct answer: S does not have a cascading abort

Solution

The schedule does not have a cascading abort because T1 reads the values of X and Y before T2 writes to X, meaning T1's operations are not dependent on T2's writes. Therefore, if T2 were to abort, T1 would not be affected by any uncommitted changes.

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