The answer is a) It improves upon the two-phased commit by requiring that locks be acquired at the start of a transaction.
Reason: The 3PC is an extension or you can say developed from 2PC that avoids blocking of an operation. It just ensures that first n sites have intended to commit a transaction that means it acquires commits or locks before the start of any transaction to avoid any blocking.
Option b) is wrong as it does not allow coordination, it just let all the other sites do their transaction if any other site is blocked, so no coordination is there between sites that they will wait till their coordinator is corrected.
Option c) is wrong as lock operations are shared between other connections as when their coordinator fails, the new coordinator agrees to the old coordinator that they had shared locks before and they can start their transaction.
Option d) is wrong as option a) is correct.
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Answer:
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