CS550 Advanced Operating Systems

Instructor: Xian-He Sun

Department of Computer Science

Homework 5 (Due Date: 4/14/09, Tuesday)

  1. Exercise 7.7 (Text: Tanenbaum and Steen, Prentice Hall)
    It is often argued that weak consistency models impose an extra burden for programmers. To what extent is this statement actually true?
  2. Exercise 6.10 (Text: Tanenbaum and Steen, Prentice Hall)
    Consider a personal mailbox for a mobile user, implemented as part of a wide-area distributed database. Wha t kind of client-centric consistency would be most appropriate?
  3. Exercise 6.13 (Text: Tanenbaum and Steen, Prentice Hall)
    When using a lease, is it necessary that the clocks of a client and the server, respectively, are tightly sychronized?
  4. Exercise 7.20 (Text: Tanenbaum and Steen, Prentice Hall)
    A file is replicated on 10 servers. List all the combinations of read quorum and write quorum that are per mitted by the voting algorithm.
  5. Exercise 8.3 (Text: Tanenbaum and Steen, Prentice Hall, v2)
    Q: Consider a Web browser that returns an outdated cached page instead of more recent one that had been updated at the server. Is this a failure, and if so, what kind of failure?
  6. Exercise 8.5 (Text: Tanenbaum and Steen, Prentice Hall)
    Q: How many failed elements (devices plus voters) can Fig. 7-2 handle? Give an example of the worst case that can be masked.
  7. Exercise 8.8 (Text: Tanenbaum and Steen, Prentice Hall)
    Q: With asynchronous RPCs, a client is blocked until its request has been accepted by the server (see Fig. 2-12). To what extent do failures affect the semantics of asynchronous RPCs?
  8. Exercise 8.10 (Text: Tanenbaum and Steen, Prentice Hall)
    Q: In reliable multicasting, is it always necessary that the communication layer keeps a copy of a message for retransmission purposes?
  9. Exercise 8.16 (Text: Tanenbaum and Steen, Prentice Hall)
    Q: In the two-phase commit protocol, why can blocking never be completely eliminated, even when the participants elect a new coordinator?
  10. Exercise 15.8 (Text: Coulouris, Dollimore, and Kindberg, Addison Wesley)
    An operation X upon an object o causes o to invoke an operation upon another object o'. It is now proposed to replicate o but not o'. Explain the difficulty that this raises concerning invocations upon o', and sugg est a solution.
  11. Exercise 15.9 (Text: Coulouris, Dollimore, and Kindberg, Addison Wesley)
    Explain the difference between linearizability and sequential consistency, and why the latter is more prati cal to implement, in general.
  12. Answer the question given on slides 23 of lecture 12.

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