Multiple ChoiceHard 45s
Write skew under snapshot isolation
Two doctors each check that another doctor is on call, then both take leave, violating a rule that needs at least one. Under snapshot isolation this is possible because:
Options
- 1The two transactions write the exact same row version, so snapshot isolation should have flagged a conflict but let both commit
- 2Snapshot isolation lowers the effective isolation below read committed, which is why the anomaly is permitted and not blocked
- 3The database failed to acquire the row locks it needed, so it committed without validating against concurrent writers
- 4The transactions read overlapping data but write disjoint rows, so no write-write conflict is detected
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