As you read the paper, consider the following questions:
Question 1: Why is a two-phase commit protocol needed to ensure the atomicity and durability of distributed transactions?
Question 2: What happens if the coordinator crashes right after sending PREPARE messages to all subordinates? Assume that some subordinates already replied with a YES vote, while others did not yet take any action.
Question 3: What are the benefits of the presumed abort and presumed commit protocols?