- A
Cloud Bigtable
Why wrong: Bigtable is a database, not a cache, and does not support pub/sub.
- B
Memorystore for Memcached
Why wrong: Memcached does not support pub/sub.
- C
Memorystore for Redis
Memorystore for Redis supports pub/sub for cache invalidation.
- D
Firestore
Why wrong: Firestore is a database, not a cache; it can be used as a real-time sync but not as a pub/sub cache layer.
Question 66 of 980
Design Scalable and Highly Available Cloud Database Solutions →mediumMultiple ChoiceObjective-mapped
PCD Practice Question: Design Scalable and Highly Available Cloud Database Solutions
This PCD practice question tests your understanding of design scalable and highly available cloud database solutions. 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.
You need a caching layer for a web application that handles high read traffic. The cache must support pub/sub messaging for cache invalidation across multiple servers. Which service should you use?
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
✓
Memorystore for Redis
Memorystore for Redis is the correct choice because Redis natively supports pub/sub messaging, which enables cache invalidation notifications across multiple application servers. This allows each server to subscribe to channels and receive real-time invalidation messages, ensuring cache consistency in a distributed environment. Memcached, in contrast, lacks pub/sub capabilities, making it unsuitable for this requirement.
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.
- ✗
Cloud Bigtable
Why it's wrong here
Bigtable is a database, not a cache, and does not support pub/sub.
- ✗
Memorystore for Memcached
Why it's wrong here
Memcached does not support pub/sub.
- ✓
Memorystore for Redis
Why this is correct
Memorystore for Redis supports pub/sub for cache invalidation.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Firestore
Why it's wrong here
Firestore is a database, not a cache; it can be used as a real-time sync but not as a pub/sub cache layer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Memcached with Redis, assuming both support pub/sub, but Memcached is purely a key-value cache with no messaging primitives, while Redis includes pub/sub as a built-in feature.
Detailed technical explanation
How to think about this question
Redis pub/sub uses channels and patterns (e.g., PSUBSCRIBE for pattern matching) to broadcast messages to all subscribers, making it ideal for cache invalidation events. Under the hood, Redis uses a fire-and-forget model for pub/sub, meaning messages are not persisted; if a subscriber is disconnected, it misses the invalidation message, so applications often combine it with key expiration or lazy validation for robustness. In a real-world scenario, a web application with multiple front-end servers can use Redis pub/sub to invalidate a cached product listing when an update occurs, ensuring all servers serve fresh data without polling the database.
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.
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FAQ
Questions learners often ask
What does this PCD question test?
Design Scalable and Highly Available Cloud Database Solutions — This question tests Design Scalable and Highly Available Cloud Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Memorystore for Redis — Memorystore for Redis is the correct choice because Redis natively supports pub/sub messaging, which enables cache invalidation notifications across multiple application servers. This allows each server to subscribe to channels and receive real-time invalidation messages, ensuring cache consistency in a distributed environment. Memcached, in contrast, lacks pub/sub capabilities, making it unsuitable for this requirement.
What should I do if I get this PCD 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.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jul 4, 2026
This PCD practice question is part of Courseiva's free Google Cloud certification practice question bank. Courseiva provides original exam-style practice questions with explanations, topic-based practice, mock exams, readiness tracking, and study analytics to help learners prepare for the PCD exam.
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