Membership and Failure Detection Checkpoint

Trace fresh cases, diagnose plausible bugs, and separate the exercise model from production guarantees.

Get every question correct to pass this checkpoint. You can review feedback, revise your answers, and submit again.

1. Local member x appears as (incarnation 3,heartbeat 40), then (3,2); remote has (3,8). What delta is required? Select one answer.

Select one answer.

Request x No delta because the later local entry wins Send x Both send and request x

2. Heartbeat input is [0,20,20,10,40]. How many positive adjacent intervals are retained? Enter one integer.

3. Two positive intervals average 10 ms. minSamples=3, and the latest heartbeat is very old. What must the evaluator report? Select one answer.

Select one answer.

MeanInterval=0, Phi=0, Suspect=false Phi grows without the minimum sample guard Suspect=true because elapsed time is sufficient MeanInterval=10, Phi=0, Suspect=false

4. The model returns phi=3. Which interpretation is justified? Select one answer.

Select one answer.

The chosen waiting-time model assigns tail probability about 0.001 to this delay There is a measured 99.9% chance the process crashed The process is certainly dead At least three independent reporters saw a crash

5. Quorums are 1 and 1. Alive node 5 receives suspect from a at incarnation 5, then confirm from a at 5. Final state? Select one answer.

Select one answer.

alive dead suspect with zero confirmation votes suspect because a cannot count in both phases

6. With suspect quorum 2: a suspects incarnation 7, alive 7 resets, then a and b suspect 7. Final state? Select one answer.

Select one answer.

alive with one vote because a was already counted dead suspect alive with zero votes because same-incarnation alive is ignored

7. A node is dead at incarnation 8. It receives alive 8 then alive 9. What happens? Select one answer.

Select one answer.

Both revive the node Neither can revive a dead node The first revives; the second is stale The first is ignored; the second revives and clears counters

8. A service invokes the round function repeatedly with only returned Member values. What extra state is needed for deduplication across calls? Select one answer.

Select one answer.

Reporter identities/history, which Member counters do not encode Nothing; vote counts identify the reporters Only the latest heartbeat timestamp A lower suspicion threshold

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