Quorums, Leases and Changing the Membership · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

Quorums, leases and new members

Computing · Networks & Security · ages 22-23
Name ______________________   Date ____________

  1. What does a lease give a leader?

    • A bounded window of authority without asking
    • A larger hard drive
    • A new network address

  2. What must every read set and write set do?

    • Avoid each other completely
    • Intersect in at least one node
    • Contain all nodes

  3. Adding and removing cluster members in one step is safe.

    Circle one:   True   False

  4. Seven nodes run read quorum 3. What is the smallest write quorum that still overlaps every read?

    Answer: ______________

  5. A read-heavy shop on five nodes wants cheap reads. Which pairing fits?

    • Read 4 with write 2
    • Read 1 with write 1
    • Read 2 with write 4

  6. Clocks skew badly across the cluster. What threatens the leader's lease?

    • A rival leader believing itself in charge too
    • Faster disk writes
    • Shorter log entries

  7. Two membership changes are pending. What is the safe order?

    • Both at once to save time
    • Staged steps so one agreed set always exists
    • Remove everyone, then add fresh nodes

  8. Read 1 plus write 1 on five nodes is proposed for speed. What is the flaw?

    • Nothing, it is the fastest correct choice
    • Single-node sets are forbidden by law
    • The sets need not intersect, so stale reads follow
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Answer key

For grown-ups. Fold this page away before handing over the rest.

Quorums, leases and new members W1-mt_2uRmRqFutD-s1

  1. A bounded window of authority without asking · The lease rents authority for a fixed time.
  2. Intersect in at least one node · Overlap is what keeps reads fresh.
  3. False · One-step changes let old and new majorities disagree.
  4. 5 · Read plus write must exceed 7, so 3 plus 5 is the smallest fit.
  5. Read 2 with write 4 · Small reads stay cheap while big writes keep the overlap.
  6. A rival leader believing itself in charge too · Leases trust clocks, and skewed clocks double the crown.
  7. Staged steps so one agreed set always exists · Stages keep a single line of majorities from old set to new.
  8. The sets need not intersect, so stale reads follow · One plus one never exceeds five, so reads can miss writes.
Worksheet · LightMySky