- A
Cloud SQL
Why wrong: Cloud SQL is a relational database; not designed for sub-millisecond cache access.
- B
Cloud Bigtable
Why wrong: Bigtable is a NoSQL database but not designed for low-latency caching or pub/sub.
- C
Memorystore for Redis
Redis provides in-memory caching with sub-millisecond latency and built-in pub/sub messaging.
- D
Firestore
Why wrong: Firestore is a document database with higher latency than in-memory cache.
Question 319 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.
An organization wants to cache frequently accessed session data for a web application to reduce database load. They require sub-millisecond latency and support for pub/sub messaging. Which Google Cloud service should they 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 it provides an in-memory data store with sub-millisecond latency, ideal for caching frequently accessed session data. It also natively supports pub/sub messaging via Redis's built-in PUBLISH/SUBSCRIBE commands, meeting both requirements precisely.
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 SQL
Why it's wrong here
Cloud SQL is a relational database; not designed for sub-millisecond cache access.
- ✗
Cloud Bigtable
Why it's wrong here
Bigtable is a NoSQL database but not designed for low-latency caching or pub/sub.
- ✓
Memorystore for Redis
Why this is correct
Redis provides in-memory caching with sub-millisecond latency and built-in pub/sub messaging.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Firestore
Why it's wrong here
Firestore is a document database with higher latency than in-memory cache.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse Firestore's real-time listeners with pub/sub messaging, overlooking that Firestore lacks the dedicated pub/sub channel model and sub-millisecond cache performance required for session caching.
Detailed technical explanation
How to think about this question
Redis achieves sub-millisecond latency by storing all data in RAM and using an event-driven, single-threaded reactor model (based on the ae event loop) to process commands without context-switching overhead. Its pub/sub implementation uses channels where publishers send messages to all subscribers without message persistence, making it suitable for real-time notifications but not for reliable queuing. In a real-world scenario, session data cached in Redis can be invalidated via pub/sub messages when a user logs out across multiple instances, ensuring cache consistency 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 company's IT admin needs to give a contractor read-only access to production logs without sharing account credentials. Using role-based access control (RBAC) and temporary scoped permissions — not a permanent shared password — is the correct pattern. Questions like this test whether you can apply least-privilege access across cloud identity services.
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 it provides an in-memory data store with sub-millisecond latency, ideal for caching frequently accessed session data. It also natively supports pub/sub messaging via Redis's built-in PUBLISH/SUBSCRIBE commands, meeting both requirements precisely.
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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