- A
BigQuery
Why wrong: BigQuery is for analytics, but the scenario does not specify analytics as a separate database; it could be used, but the question asks for two databases for the given purposes.
- B
Memorystore
For low-latency key-value session data.
- C
Firestore
Why wrong: Firestore is a document database, but Memorystore is better for session caching with lower latency.
- D
Cloud Spanner
Why wrong: Spanner is globally distributed relational, but not needed for a simple catalog; Cloud SQL is sufficient.
- E
Cloud SQL
For the relational product catalog.
Question 826 of 999
PCD Practice Question: Manage a Solution that Can Span Multiple Database Systems
This PCD practice question tests your understanding of manage a solution that can span multiple database systems. 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 company is designing a polyglot persistence architecture for an e-commerce platform. They need to store product catalog (relational), session data (low-latency key-value), and analytics data (large-scale SQL queries). Which TWO Google Cloud databases should they use? (Choose two.)
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
Memorystore is correct because it provides a managed in-memory data store (Redis or Memcached) that delivers sub-millisecond latency for session data, which is a key-value workload requiring fast reads and writes. This directly satisfies the low-latency key-value requirement for session management in the polyglot persistence architecture.
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.
- ✗
BigQuery
Why it's wrong here
BigQuery is for analytics, but the scenario does not specify analytics as a separate database; it could be used, but the question asks for two databases for the given purposes.
- ✓
Memorystore
Why this is correct
For low-latency key-value session data.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Firestore
Why it's wrong here
Firestore is a document database, but Memorystore is better for session caching with lower latency.
- ✗
Cloud Spanner
Why it's wrong here
Spanner is globally distributed relational, but not needed for a simple catalog; Cloud SQL is sufficient.
- ✓
Cloud SQL
Why this is correct
For the relational product catalog.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
In Google Cloud exams, candidates often confuse the use cases of Cloud Spanner, Firestore, and Memorystore. Cloud Spanner is a globally distributed relational database, not ideal for low-latency key-value session data. Firestore is a document database, but not specifically optimized for sub-millisecond key-value access. Memorystore is purpose-built for in-memory, sub-millisecond key-value workloads, making it the correct choice for session data in a polyglot persistence architecture.
Trap categories for this question
Scenario analysis trap
BigQuery is for analytics, but the scenario does not specify analytics as a separate database; it could be used, but the question asks for two databases for the given purposes.
Detailed technical explanation
How to think about this question
Memorystore uses the Redis protocol (RESP) or Memcached ASCII protocol, allowing direct use of existing client libraries and commands like GET/SET for session tokens. Under the hood, it stores all data in RAM with optional persistence to disk via AOF or RDB snapshots, but for session data, the ephemeral nature is acceptable, and the sub-millisecond latency is achieved by avoiding disk I/O. In a real-world e-commerce platform, session data is typically stored with a TTL (time-to-live) to auto-expire, which Memorystore supports natively via the EXPIRE command.
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
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FAQ
Questions learners often ask
What does this PCD question test?
Manage a Solution that Can Span Multiple Database Systems — This question tests Manage a Solution that Can Span Multiple Database Systems — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Memorystore — Memorystore is correct because it provides a managed in-memory data store (Redis or Memcached) that delivers sub-millisecond latency for session data, which is a key-value workload requiring fast reads and writes. This directly satisfies the low-latency key-value requirement for session management in the polyglot persistence architecture.
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 →
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Last reviewed: Jul 4, 2026
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