PDE Storing the Data Practice Question
An application requires a globally distributed, strongly consistent database with 99.999% availability SLA. The workload is OLTP with high throughput across continents. Which service fits best?
⚠ Common exam trap
Candidates often confuse Cloud SQL cross-region replicas as providing strong consistency, but those replicas are eventually consistent due to asynchronous replication, and they do not meet the 99.999% SLA.
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 provides globally distributed, strongly consistent (external consistency via TrueTime) OLTP with 99.999% availability SLA. It supports high-throughput ACID transactions across continents using synchronous replication and atomic clocks, meeting all stated requirements.
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 with cross-region replicas
Why it's wrong here
Cross-region replicas provide asynchronous replication with a promotion-based failover, so they cannot deliver strong consistency across continents nor a 99.999% multi-region SLA. It tempts because Cloud SQL is the natural fit for regional OLTP workloads requiring relational semantics.
- ✗
Firestore
Why it's wrong here
Firestore offers multi-region strong consistency but caps throughput per document and lacks the relational transactions and scale the OLTP workload demands. It tempts for globally distributed mobile and web apps needing automatic multi-region replication with simple document reads.
- ✗
Cloud Bigtable
Why it's wrong here
Bigtable is a wide-column NoSQL store offering single-row atomicity, not multi-region strong consistency with relational transactions across continents. It tempts for high-throughput OLTP-style ingestion, and would be correct for time-series or analytical workloads needing low-latency key access at petabyte scale.
- ✓
Cloud Spanner
Why this is correct
Cloud Spanner provides external consistency globally through TrueTime, and its multi-region configurations carry a 99.999% availability SLA. That combination of strong consistency, cross-continent distribution and five-nines uptime matches the OLTP high-throughput requirement, unlike eventually consistent alternatives.
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