Virtual Labs

2-Phase Commit Protocol Simulation

Based on the simulation, what is the default outcome if a participant fails before voting?

a: The transaction commits. Explanation

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b: The transaction aborts. Explanation

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c: The other participants decide the outcome. Explanation

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d: The system waits indefinitely. Explanation

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In the simulation, what did you observe when the coordinator failed after sending the `GLOBAL_COMMIT` message but before receiving all `ACK`s?

a: The transaction was rolled back. Explanation

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b: The participants that sent an ACK remained committed, others aborted. Explanation

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c: Upon recovery, the coordinator re-sends the `GLOBAL_COMMIT` to ensure all participants receive it. Explanation

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d: The participants were blocked forever. Explanation

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What is the purpose of the `ACK` message sent from participants to the coordinator in Phase 2?

a: To vote for the transaction. Explanation

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b: To confirm they have received and executed the final decision. Explanation

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c: To request the final decision. Explanation

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d: To tell the coordinator they are ready. Explanation

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If a network partition separates a participant from the coordinator after the participant has voted `VOTE_COMMIT`, what is the participant's status?

a: It can safely abort because of the network failure. Explanation

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b: It must remain in the `READY` state, blocked until communication is restored. Explanation

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c: It can ask other participants for the final decision. Explanation

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d: It will automatically commit after a timeout. Explanation

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The simulation demonstrates that 2PC guarantees atomicity. What is the primary trade-off for this guarantee?

a: High network bandwidth usage. Explanation

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b: The potential for participants to become blocked. Explanation

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c: It is very slow even without failures. Explanation

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d: It requires all participants to have identical hardware. Explanation

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Why can't a participant that voted `VOTE_COMMIT` and is now blocked just decide to abort after a timeout?

a: Because it might be the only participant that wants to abort. Explanation

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b: Because the coordinator might have already decided to commit and informed other participants. Explanation

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c: Because its log is locked in a read-only state. Explanation

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d: Because it is against the rules of the simulation. Explanation

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Consider a scenario not in the simulation: a `GLOBAL_COMMIT` message from the coordinator to one participant is lost. What prevents this participant from being blocked forever?

a: The participant will eventually time out and abort. Explanation

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b: The coordinator, not receiving an `ACK`, will periodically re-send the `GLOBAL_COMMIT`. Explanation

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c: The participant can infer a commit from the silence. Explanation

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d: The other participants will detect the issue and re-send the message. Explanation

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If the simulation used a non-blocking protocol like 3PC, what would a participant do if the coordinator crashed after the 'pre-commit' phase?

a: It would still be blocked, just like in 2PC. Explanation

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b: It would contact the other participants to elect a new coordinator and safely decide to commit. Explanation

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c: It would automatically abort. Explanation

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d: It would wait for the original coordinator to recover. Explanation

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The simulation shows that the coordinator is a single point of failure. In a real-world, high-availability system, how is this typically addressed?

a: By using a much more powerful computer for the coordinator. Explanation

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b: By having a backup coordinator that is manually promoted in case of failure. Explanation

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c: By using a consensus algorithm like Paxos or Raft to create a replicated, fault-tolerant coordinator service. Explanation

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d: By eliminating the coordinator and using a fully decentralized protocol. Explanation

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