Consistency Models and the CAP Trade-off · seed 1 · A4, ink-friendly. The answer key prints on its own page for grown-ups.

One copy or always open

Computing · Networks & Security · ages 20-22
Name ______________________   Date ____________

  1. Under eventual consistency, what happens to disagreeing copies?

    • They reconcile and converge later
    • They disagree forever
    • They delete themselves

  2. Under strong consistency, what does every reader see?

    • A random older copy
    • The latest write, as if one copy existed
    • Nothing until the next day

  3. During a network split a store can stay strongly consistent and fully available at once.

    Circle one:   True   False

  4. The same split happens under eventual consistency. What may each side do?

    • Shut down until an operator arrives
    • Keep serving and merge changes when the link heals
    • Refuse all reads and writes

  5. A split divides the store in two under strong consistency. What may each side do?

    • Both sides keep taking writes freely
    • Both sides delete their data
    • One side pauses writes so no split brain grows

  6. Should a shopping basket and a bank balance share one consistency choice?

    • No, the balance needs strong while the basket survives eventual
    • Yes, one database means one choice
    • No, the basket needs strong while the balance survives eventual

  7. A developer says eventual consistency means reads may return stale data forever. What is wrong?

    • Nothing, forever-stale is the definition
    • Convergence is promised: copies reconcile once the split heals
    • Stale reads never happen under eventual consistency

  8. A ticket shop sells the last seat twice during a split. Which choice caused it, and what fixes it?

    • Strong consistency caused it; go eventual
    • The split caused it; no model choice matters
    • Eventual consistency caused it; the seat count needs strong
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Answer key

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

One copy or always open W1-mt_j6qtpYPHsr-s1

  1. They reconcile and converge later · Temporary split followed by merging is the eventual promise.
  2. The latest write, as if one copy existed · One-copy behaviour is the whole definition of strong.
  3. False · A partition forces the choice: one copy behaviour or both sides serving.
  4. Keep serving and merge changes when the link heals · Availability wins now, agreement comes at healing time.
  5. One side pauses writes so no split brain grows · Refusing one side keeps the single-copy illusion intact.
  6. No, the balance needs strong while the basket survives eventual · Money must never blur, while merged baskets merely annoy.
  7. Convergence is promised: copies reconcile once the split heals · Eventual allows brief disagreement, never permanent split brain.
  8. Eventual consistency caused it; the seat count needs strong · Both sides serving means both can sell one last seat.
Worksheet · LightMySky