DVA-C02 Troubleshooting and Optimization Practice Question
This DVA-C02 practice question tests your understanding of troubleshooting and optimization. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. 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 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.
Option A is correct because setting a suitable Time-To-Live (TTL) on cached data ensures that stale entries are automatically evicted after a defined period. This forces the application to fetch fresh data from the primary database when the TTL expires, thereby maintaining cache coherence without requiring immediate invalidation on every write. In ElastiCache (Redis or Memcached), TTL is set per key using commands like EXPIRE or SETEX, and it is a simple, effective strategy for read-heavy workloads where eventual consistency is acceptable.
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 here is that candidates often confuse 'lazy loading' (which loads data into cache on a miss) with 'TTL-based expiration' (which evicts stale data), and they may incorrectly select Option E as a separate strategy when it is functionally identical to Option A; also, they may overlook that write-through caching (Option B) is a valid coherence strategy but is not listed as correct in this specific question because the exam expects the two most common and straightforward approaches: TTL and explicit invalidation.
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.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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. — Option A is correct because setting a suitable Time-To-Live (TTL) on cached data ensures that stale entries are automatically evicted after a defined period. This forces the application to fetch fresh data from the primary database when the TTL expires, thereby maintaining cache coherence without requiring immediate invalidation on every write. In ElastiCache (Redis or Memcached), TTL is set per key using commands like EXPIRE or SETEX, and it is a simple, effective strategy for read-heavy workloads where eventual consistency is acceptable.
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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Question Discussion
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