Distributed capstone: free-recall review
Free-recall prompts spanning the whole distributed track — quorum, fencing, clocks, sagas, retries, idempotency — answered in your own words before revealing the model answer.
Retrieval beats re-reading. For each prompt, reconstruct a full answer from memory — spanning multiple lessons in the track — before you open the model answer. The effort of recall is what makes the synthesis stick.
Reconstruct the track’s spine without looking back: quorum overlap, fencing against a stale leader, logical clocks, saga compensations, retry budgets, and the idempotency key that ties them all together at the seams.
- 01State the quorum rule R + W > N and explain what each side of it buys you in the order pipeline.
- 02Why can't a stale leader protect the system by checking 'am I still leader?' before writing, and what does protect it?
- 03Why can't you order events across services with wall-clock timestamps, and what do you use instead?
- 04Why is there no distributed ACID transaction across the four services, and what replaces rollback?
- 05Explain retry amplification and the retry budget that bounds it.
- 06Why is idempotency the load-bearing primitive, and what distinguishes a correct key from one that silently fails?
If you reconstructed each answer from memory, you hold the track’s spine: R + W > N gives read-your-write overlap, fencing tokens defend against a paused stale leader because a self-check cannot, logical or bounded-uncertainty clocks order events that wall clocks cannot, sagas replace distributed ACID with compensations, retry budgets bound amplification, and idempotency keyed on business intent makes at-least-once safe across every seam. The capstone insight: each is correct alone — the failures live where they compose. Now when you read an incident report where every dashboard stayed green, you know the first place to look is the seam between two correct layers — and the first question to ask is whether a shared business key crossed it.
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