A product page runs the same expensive aggregate query for every visitor. The underlying data changes a handful of times a day. The database is at 90% processor utilisation and pages take 800 ms to render. Which change removes most of that work?
AWS Certified Cloud Practitioner (CLF-C02), objective 3. Cloud technology and services medium
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The options
Correct Put Amazon ElastiCache in front of the database and serve the repeated result from memory
Correct. The query result is identical for nearly every visitor and changes rarely, so computing it once and reading it from memory for the next few thousand requests removes the work entirely rather than redistributing it.
Not correct Add a read replica and send the product page's queries to it
Wrong as the best answer, though it is a reasonable step. It moves the load off the primary, but the same expensive query still runs once per visitor — you have bought a second machine to repeat the work on.
Not correct Move the database to a larger instance class
Wrong. It raises the ceiling at a permanently higher price and leaves the design unchanged, so the same problem returns with more traffic.
Not correct Migrate to Amazon DynamoDB
Wrong. The problem is that identical work is repeated, not that the data model is wrong. A migration is a large, risky answer to something a cache fixes in an afternoon.
Why
ElastiCache is managed in-memory caching — Redis or Valkey, and Memcached — used for microsecond reads on hot data, session stores and leaderboards; DynamoDB has its own in-memory accelerator, DAX. The cost of a cache is not money, it is staleness: you have to decide how out of date a reader may be and how the cache is invalidated when the data changes. Hold the distinction as: replicas spread the work out, caches avoid doing it.
Where this comes from
- Cited
- AWS exam guide task statement 3.4
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