- A
Bigtable
Why wrong: Bigtable is wide-column NoSQL for analytical workloads, not for session state or pub/sub.
- B
Cloud SQL
Why wrong: Cloud SQL is relational and higher latency for session state; not designed for pub/sub.
- C
Firestore
Why wrong: Firestore can store session data but does not natively support pub/sub messaging.
- D
Memorystore for Redis
Redis excels at session store, pub/sub, and caching with sub-millisecond latency.
Question 58 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.
A mobile app team wants to store user session state with low latency and support for pub/sub messaging. They need a managed service that automatically scales. Which database is BEST suited for this?
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 best choice because it provides an in-memory data store with sub-millisecond latency, ideal for session state caching, and natively supports pub/sub messaging via Redis Pub/Sub. As a managed service, it automatically handles scaling and failover, meeting the team's requirements without operational overhead.
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.
- ✗
Bigtable
Why it's wrong here
Bigtable is wide-column NoSQL for analytical workloads, not for session state or pub/sub.
- ✗
Cloud SQL
Why it's wrong here
Cloud SQL is relational and higher latency for session state; not designed for pub/sub.
- ✗
Firestore
Why it's wrong here
Firestore can store session data but does not natively support pub/sub messaging.
- ✓
Memorystore for Redis
Why this is correct
Redis excels at session store, pub/sub, and caching with sub-millisecond latency.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the distinction between real-time database listeners (like Firestore) and true pub/sub messaging, leading candidates to mistakenly choose Firestore for pub/sub needs when it only supports document-level real-time updates, not a general publish-subscribe channel.
Detailed technical explanation
How to think about this question
Redis Pub/Sub uses a fire-and-forget messaging model where publishers send messages to channels without persistence, and subscribers receive them in real-time. For session state, Redis stores data as key-value pairs in memory, enabling O(1) read/write operations. In a real-world scenario, a gaming app could use Redis to store player session tokens and broadcast game state changes via pub/sub, achieving latency under 1 millisecond.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
What to study next
Got this wrong? Here's your next step.
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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 best choice because it provides an in-memory data store with sub-millisecond latency, ideal for session state caching, and natively supports pub/sub messaging via Redis Pub/Sub. As a managed service, it automatically handles scaling and failover, meeting the team's requirements without operational overhead.
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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