Quick Answer
Cloud Spanner is the correct choice because it is the only Google Cloud database that delivers global strong consistency across regions through synchronous replication and the TrueTime API, which globally synchronizes clocks to guarantee external consistency for ACID transactions. This technical capability directly solves the e-commerce platform’s requirement for consistent reads and writes worldwide, avoiding the eventual consistency trade-offs found in globally distributed databases like Bigtable or Firestore. On the Google Professional Cloud Database Engineer exam, this question tests your understanding of when to choose Spanner over regional or eventually consistent options—a common trap is assuming that any globally replicated database offers strong consistency, but only Spanner’s use of TrueTime and Paxos-based replication ensures it. Remember the mnemonic “STAR”: Strong consistency, TrueTime, ACID, Replicated globally.
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.
An e-commerce platform requires strong consistency across global regions. Which database service should they choose?
Cloud Bigtable
Why wrong: Bigtable offers eventual consistency, not strong consistency across regions.
Firestore
Why wrong: Firestore provides strong consistency for single-region databases, but multi-region offers weak consistency.
Cloud Spanner
Cloud Spanner provides globally distributed strong consistency.
Cloud SQL
Why wrong: Cloud SQL provides strong consistency but is not globally distributed; it is single-region.
Answer choices
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 strong consistency across global regions via synchronous replication and TrueTime, ensuring ACID transactions with external consistency. This meets the e-commerce platform's requirement for globally consistent reads and writes without eventual consistency trade-offs.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
For each option: why learners choose it and why it is or isn't the right answer here.
Cloud Bigtable
Why it's wrong here
Bigtable offers eventual consistency, not strong consistency across regions.
Firestore
Why it's wrong here
Firestore provides strong consistency for single-region databases, but multi-region offers weak consistency.
Cloud Spanner
Why this is correct
Cloud Spanner provides globally distributed strong consistency.
Related concept
Read the scenario before looking for a memorised answer.
Cloud SQL
Why it's wrong here
Cloud SQL provides strong consistency but is not globally distributed; it is single-region.
Common exam traps
The trap here is that candidates often confuse 'strong consistency' with 'eventual consistency' and pick Firestore for its real-time capabilities, overlooking that Firestore's multi-region mode sacrifices strong consistency for availability.
Detailed technical explanation
Cloud Spanner achieves global strong consistency by using TrueTime, a globally synchronized clock service that assigns commit timestamps with bounded uncertainty, enabling external consistency across distributed nodes. Under the hood, it uses Paxos-based synchronous replication across zones, meaning a write is not acknowledged until a majority of replicas in each participating region have committed, ensuring linearizability. In a real-world scenario, an e-commerce platform updating inventory in one region must immediately reflect that change globally to prevent overselling—Spanner's atomic clocks and synchronous replication guarantee this.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
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
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FAQ
Plan and manage database infrastructure — This question tests Plan and manage database infrastructure — Read the scenario before looking for a memorised answer..
The correct answer is: Cloud Spanner — Cloud Spanner is the correct choice because it provides strong consistency across global regions via synchronous replication and TrueTime, ensuring ACID transactions with external consistency. This meets the e-commerce platform's requirement for globally consistent reads and writes without eventual consistency trade-offs.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Read the scenario before looking for a memorised answer.
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Last reviewed: Jun 25, 2026
This PCDE 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 PCDE exam.
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