- A
Set a suitable TTL for cached data.
TTL ensures data is refreshed periodically.
- B
Use write-through caching.
Why wrong: Write-through updates cache on write, but does not invalidate stale data.
- C
Invalidate the cache entry when the underlying data is updated.
Cache invalidation ensures stale data is removed.
- D
Use read replicas of the database to serve read traffic.
Why wrong: Read replicas are not caching; they are database replicas.
- E
Implement lazy loading with a short TTL.
Why wrong: Lazy loading can serve stale data until TTL expires.
Question 1,546 of 1,616
How to Prevent Stale Data in Amazon ElastiCache
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
A developer is using Amazon ElastiCache to improve the performance of a read-heavy web application. After implementing caching, some users see stale data. Which TWO strategies can the developer use to ensure cache coherence?
Answer choices
Why each option matters
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Set a suitable TTL for cached data.
Options A and C are correct. Setting a suitable TTL (Option A) ensures that cached data is automatically evicted after a defined period, forcing a refresh from the database. Invalidating the cache entry when underlying data is updated (Option C) immediately removes stale data, ensuring subsequent reads fetch fresh data. Option B is incorrect because write-through caching is a cache writing policy, not a cache coherence strategy; it ensures cache freshness on writes but is not one of the two strategies asked for (TTL and invalidation). Option D is incorrect because read replicas offload read traffic but do not affect cache coherence. Option E is incorrect because lazy loading without TTL does not prevent stale data; it loads data on a miss but without expiration, stale data persists.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✓
Set a suitable TTL for cached data.
Why this is correct
TTL ensures data is refreshed periodically.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use write-through caching.
Why it's wrong here
Write-through updates cache on write, but does not invalidate stale data.
- ✓
Invalidate the cache entry when the underlying data is updated.
Why this is correct
Cache invalidation ensures stale data is removed.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Use read replicas of the database to serve read traffic.
Why it's wrong here
Read replicas are not caching; they are database replicas.
- ✗
Implement lazy loading with a short TTL.
Why it's wrong here
Lazy loading can serve stale data until TTL expires.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap is that candidates may incorrectly select Option B (write-through caching) as a coherence strategy, but the question expects the two most common and straightforward approaches: TTL and explicit cache invalidation. Additionally, candidates may confuse lazy loading (Option E) with TTL-based expiration, but lazy loading alone does not ensure cache coherence without an accompanying TTL.
Detailed technical explanation
How to think about this question
Cache coherence in distributed systems often relies on either expiration-based (TTL) or invalidation-based strategies. In ElastiCache for Redis, the EXPIRE command sets a key's TTL in seconds, and Redis uses an active expiry algorithm (sampling keys every 100ms) plus lazy expiry on access to remove expired keys. For invalidation, the application must explicitly delete or update the cache key (e.g., DEL command) when the underlying database record changes, which guarantees immediate consistency but requires careful coordination with write operations. In real-world scenarios, combining TTL with invalidation (e.g., write-through + TTL) is common to balance performance and freshness.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
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Troubleshooting and Optimization — study guide chapter
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FAQ
Questions learners often ask
What does this DVA-C02 question test?
Troubleshooting and Optimization — This question tests Troubleshooting and Optimization — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Set a suitable TTL for cached data. — Options A and C are correct. Setting a suitable TTL (Option A) ensures that cached data is automatically evicted after a defined period, forcing a refresh from the database. Invalidating the cache entry when underlying data is updated (Option C) immediately removes stale data, ensuring subsequent reads fetch fresh data. Option B is incorrect because write-through caching is a cache writing policy, not a cache coherence strategy; it ensures cache freshness on writes but is not one of the two strategies asked for (TTL and invalidation). Option D is incorrect because read replicas offload read traffic but do not affect cache coherence. Option E is incorrect because lazy loading without TTL does not prevent stale data; it loads data on a miss but without expiration, stale data persists.
What should I do if I get this DVA-C02 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 24, 2026
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