Under the two-phase locking (2PL) protocol, what is a transaction forbidden to do once it has released its first lock?
Correct answer D. Acquire any new lock
Explanation
2PL splits each transaction into a growing phase, where it may obtain locks but not release any, and a shrinking phase, which starts at the first release, where it may only release locks. Acquiring a lock after releasing one breaks the protocol. Following 2PL guarantees conflict-serializable schedules, though it does not by itself prevent deadlocks or cascading aborts.
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