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Failure Detection

This document discusses several key concepts in distributed systems, including failure detection mechanisms like ping-ack in synchronous and asynchronous systems, vector timestamps, reliable multicast, and consensus formation in the face of failures. It covers essential algorithms for mutual exclusion, leader election, and Byzantine fault tolerance. The document also explores the implications of the CAP theorem, the two-phase commit protocol, and the challenges of gossip protocols in message distribution. Each topic is accompanied by relevant questions to reinforce understanding of these critical concepts.

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Failure Detection

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  1. Failure Detection • The ping-ack failure detector in a synchronoussystemsatisfies • A: completeness • B: accuracy • C: neither • D: both

  2. Failure Detection • The ping-ack failure detector in anasynchronoussystemsatisfies • A: completeness • B: accuracy • C: neither • D: both

  3. Vector timestamps • Which of these timestamps is concurrent with (1,2,3) • A: (1,3,3) • B: (1,2,1) • C: (4,5,6) • D: (2,3,2)

  4. Consistent Cut • Whichofthesecutsisconsistent? • A: cut1 • B: cut2 cut1 cut2 e1 e3 P1 P2 e2 e4

  5. Reliable Multicast • In reliable multicast, what is the definition of “Integrity”? • A: A correctprocesspdeliversamessagematmostonce. • B: If acorrectprocessdeliversmessagem, thenalltheothercorrectprocessesingroup(m) willeventuallydeliverm. • C: If acorrectprocessmulticasts(sends) messagem, thenitwilleventuallydelivermitself.

  6. Multicast • State true or false: Any multicast that is both FIFO-ordered and totally ordered is thereby causally ordered. • A: True • B: False

  7. Consensus • For which of the following situations, consensus is possible: • A: synchronous system, failurespossible • B: asynchronous system, failuresimpossible • C: both • D: neither

  8. Mutual Exclusion • What properties does Token Ring mutual exclusion algorithm satisfy • A: Safety only • B: Safety & liveness • C: Safety & ordering • D: Safety, liveness, and ordering • E: none of the above

  9. Mutual Exclusion • What properties does Ricart & Agrawala mutual exclusion algorithm satisfy • A: Safety only • B: Safety & liveness • C: Safety & ordering • D: Safety, liveness, and ordering • E: none of the above

  10. Leader Election • Leader election in asynchronous systems is • A: possible • B: impossible

  11. Leader Election • Bully algorithm guarantees: • A: Safety • B: Liveness • C: Both • D: Neither

  12. Byzantine Generals Algorithm • What is the minimum number of nodes required to achieve agreement in Byzantine generals algorithm with f Byzantine faulty nodes? • A: f+1 • B: 2f+1 • C: 3f+1

  13. Routing Algorithms • In which routing algorithm each node talks only to its directly connected neighbors, but it tells them everything it has learned? • A: Link State routingalgorithm • B: Distance Vector routing algorithm

  14. Chord • How much state does a Chord peer maintain? • A: O(1) • B: O(log N / log log N) • C: O(log N) • D: O(√N) • E: O(N)

  15. Idempotence • Idempotent algorithms are needed when using • A: at most once invocation semantics • B: at least once invocation semantics

  16. RMI • To facilitate RMI, a stub object is maintained • A: on the client • B: on the server

  17. 2PL • Two-phase locking ensures that: • A: Transactions maintain serial equivalence • B: Deadlocks do not occur • C: Distributed transactions can commit atomically

  18. Quorum • In a system of 6 nodes, which of these is an invalid quorum configuration? • A: w=4, r=3 • B: w=6, r=3 • C: w=5, r=1 • D: w=6, r=1 • E: w=4, r=5

  19. Available Copies Replication • Available copies replication captures which two properties from the CAP theorem? • A: Consistency and Availability • B: Consistency and Partition-tolerance • C: Availability and Partition-tolerance

  20. Gossip protocols • What is the worst-case latency for distributing a message among N nodes through a gossip protocol • A: O(log N) • B: O(N0.5) • C: O(N) • D: unbounded

  21. Gossip protocols • What is the expected latency for distributing a message among N nodes through a gossip protocol • A: O(log N) • B: O(N0.5) • C: O(N) • D: unbounded

  22. Two-phase commit • If a participant has responded yes to a canCommit call and has not heard from the coordinator for a long time, it should: • A: abort • B: commit • C: call getDecision on the coordinator • D: keep waiting

  23. Routing Algorithms • Count-to-infinity is a problem of • A: Link State routingalgorithm • B: Distance Vector routing algorithm

  24. Distributed Shared Memory • False sharing leads to: • A: Excessive page transfers • B: Violations of sequential consistency • C: Deadlock

  25. CODA • Which of the CAP “vertices” does CODA sacrifice? • A: Consistency • B: Availability • C: Partition-tolerance

  26. Paxos • In Paxos, a distinguished proposer is used to: • A: ensure safety • B: ensure liveness • C: optimize performance

  27. Paxos • In Paxos, a distinguished listener is used to: • A: ensure safety • B: ensure liveness • C: optimize performance

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