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Design Scalable and Highly Available Cloud Database Solutions →mediumMultiple SelectObjective-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. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 financial services company uses BigQuery for analytics but needs to store transactional data with strong consistency and sub-millisecond latency. They are considering Cloud SQL, Cloud Spanner, and Firestore. Which two services meet all requirements? (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

✓

Cloud Spanner

Cloud Spanner is the only service that meets both strong consistency and sub-millisecond latency for transactional workloads. It provides global strong consistency using TrueTime and supports ACID transactions with sub-millisecond latency. Cloud SQL provides strong consistency but is limited to single-region deployment and cannot achieve sub-millisecond latency at scale. Bigtable offers low latency but only eventual consistency, not strong consistency. Memorystore is a caching layer and not a transactional database. Firestore offers strong consistency but typically does not guarantee sub-millisecond latency for high-throughput transactional data and is not designed for financial transactional systems.

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 Spanner

    Why this is correct

    Cloud Spanner provides strong consistency and sub-millisecond latency for transactional workloads.

    Related concept

    Read the scenario before looking for a memorised answer.

  • ✗

    Cloud SQL

    Why it's wrong here

    Cloud SQL does not guarantee sub-millisecond latency; it is in single-digit ms range.

  • ✗

    Bigtable

    Why it's wrong here

    Bigtable does not provide strong cross-row consistency.

  • ✗

    Memorystore

    Why it's wrong here

    Memorystore is an in-memory cache, not a transactional database with strong consistency.

  • ✗

    Firestore

    Why it's wrong here

    Firestore does not provide sub-millisecond latency; it offers moderate latency.

Common exam traps

Common exam trap: answer the scenario, not the keyword

A common misconception is that Cloud SQL can meet sub-millisecond latency at scale, but candidates forget that Cloud SQL is limited by single-region deployment and cannot horizontally scale writes, making it unsuitable for high-throughput transactional systems.

Detailed technical explanation

How to think about this question

Cloud Spanner achieves strong consistency through the TrueTime API, which uses GPS and atomic clocks to assign globally consistent timestamps, ensuring linearizability across all nodes. Sub-millisecond latency is achieved via a distributed query execution engine and a Paxos-based replication protocol that minimizes commit latency. In a real-world financial scenario, this allows a bank to process a payment transaction across continents with the same consistency as a local database, without sacrificing performance.

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.

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: Cloud Spanner — Cloud Spanner is the only service that meets both strong consistency and sub-millisecond latency for transactional workloads. It provides global strong consistency using TrueTime and supports ACID transactions with sub-millisecond latency. Cloud SQL provides strong consistency but is limited to single-region deployment and cannot achieve sub-millisecond latency at scale. Bigtable offers low latency but only eventual consistency, not strong consistency. Memorystore is a caching layer and not a transactional database. Firestore offers strong consistency but typically does not guarantee sub-millisecond latency for high-throughput transactional data and is not designed for financial transactional systems.

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.

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Last reviewed: Jul 4, 2026

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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.