Exams / DVA-C02 / Caching and specialised data stores / Question 1
DVA-C02 practice question: Caching and specialised data stores
Development with AWS Services A free question from our original DVA-C02 practice exam. Try it, then open the answer to see why each option is right or wrong.
A product catalogue service reads from an Amazon RDS database and is adding Amazon ElastiCache. Only a small share of products are viewed often, and the team wants to cache only the data that is actually requested. Prices change a few times a day, and a cached price must not be more than 15 minutes out of date. Which strategy fits best?
Choose one answer.
- AA. Write-through caching only, updating the cache on every database write.
- BB. Lazy loading, with a time to live of 15 minutes on each cached item.
- CC. Lazy loading with no expiry, so items stay in the cache as long as possible.
- DD. Load the whole catalogue into the cache at start-up and never expire it.
Show the answer and explanation
Answer: B
- A. Wrong: Write-through caches every written item, including products nobody views, which wastes memory (cache churn).
- B. Right: Correct. Lazy loading caches only items that are read, and the TTL makes stale entries expire within 15 minutes.
- C. Wrong: Without a TTL, a cached price is never refreshed after a change, so data can stay stale indefinitely.
- D. Wrong: This caches unread data and leaves every entry stale once prices change.
Explanation
Lazy loading fills the cache on a miss, so only requested data is stored, but cached data can become stale. Adding a TTL limits how stale it can get. Write-through keeps data fresh but caches everything that is written. Choosing a strategy means weighing freshness, memory use and miss penalty.
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