The answer is Cloud Spanner. This is the correct choice because it is the only Google Cloud database service that delivers globally consistent, strongly relational data across continents while handling high write throughput, achieved through synchronous replication, TrueTime for external consistency, and Paxos-based consensus. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of when to choose Spanner over Bigtable or Firestore—a common trap is selecting Bigtable for high throughput, but Bigtable lacks strong cross-region consistency. Remember that Spanner is the only option that combines SQL, global strong consistency, and horizontal write scalability. A useful memory tip: think of Spanner as the "global glue" that holds consistent transactions together across continents, unlike eventually consistent alternatives that sacrifice accuracy for speed.
PCDE Plan and manage database infrastructure Practice Question
This PCDE practice question tests your understanding of plan and manage database infrastructure. 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 global e-commerce platform needs a database that supports strong consistency across multiple continents and can handle high write throughput. Which database service should they choose?
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 correct choice because it provides globally distributed, strongly consistent relational database service with synchronous replication across regions and continents, supporting external consistency and high write throughput via TrueTime and Paxos-based consensus. This meets the requirement for strong consistency across multiple continents and high write throughput, which is not achievable with traditional single-region or eventually consistent databases.
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 for PostgreSQL
Why it's wrong here
Cloud SQL is regional, not global, and cannot provide strong consistency across continents without complex replication.
✗
Cloud Firestore
Why it's wrong here
Firestore provides regional strong consistency but not global strong consistency; multi-region mode offers eventual consistency.
✓
Cloud Spanner
Why this is correct
Cloud Spanner offers global strong consistency and high write throughput, making it ideal for global e-commerce.
Related concept
Read the scenario before looking for a memorised answer.
✗
Cloud Bigtable
Why it's wrong here
Bigtable is not strongly consistent across regions and is optimized for analytical workloads rather than transactional ones.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates often confuse 'strong consistency' with 'eventual consistency' and choose Cloud Bigtable or Cloud Firestore for their high throughput, failing to recognize that only Cloud Spanner provides both strong consistency and horizontal scalability across continents.
Detailed technical explanation
How to think about this question
Cloud Spanner uses TrueTime, a globally synchronized clock based on GPS and atomic clocks, to enforce external consistency across distributed transactions, ensuring that reads and writes are globally ordered. Under the hood, Spanner employs a Paxos-based consensus protocol for synchronous replication across zones and regions, with each tablet having a Paxos group that commits writes before acknowledging to the client, guaranteeing strong consistency even during regional failures. In a real-world scenario, a global e-commerce platform processing orders and inventory updates across continents requires Spanner's ability to handle millions of writes per second while maintaining ACID transactions, which is impossible with eventually consistent systems like Bigtable or Firestore.
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.
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — 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 correct choice because it provides globally distributed, strongly consistent relational database service with synchronous replication across regions and continents, supporting external consistency and high write throughput via TrueTime and Paxos-based consensus. This meets the requirement for strong consistency across multiple continents and high write throughput, which is not achievable with traditional single-region or eventually consistent databases.
What should I do if I get this PCDE 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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Question Discussion
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