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PCDE Practice Question: Design innovative, scalable, and highly available cloud database solutions
A company is migrating an on-premises OLTP application to Google Cloud. The application requires high concurrency (up to 5,000 simultaneous connections) and uses a relational schema with strong transactional integrity. Which database service is the MOST suitable?
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 SQL
Cloud SQL supports up to 4,096 connections by default (configurable) and provides full transactional integrity. For 5,000 connections, Cloud SQL can be configured with appropriate instance sizing. Spanner also supports transactions but is overkill for a single-region OLTP migration. BigQuery is for analytics, Firestore is NoSQL.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Firestore
Why it's wrong here
Firestore is a NoSQL document database; it does not support the relational schema required.
- ✓
Cloud SQL
Why this is correct
Cloud SQL provides full SQL compatibility, high connection limits, and strong consistency for OLTP workloads.
- ✗
BigQuery
Why it's wrong here
BigQuery is an analytics data warehouse, not designed for high-concurrency transactional writes.
- ✗
Cloud Spanner
Why it's wrong here
Cloud Spanner is designed for globally distributed, petabyte-scale relational workloads requiring extreme horizontal scalability and strong consistency across regions. While it offers strong transactional integrity and can handle high concurrency, its distributed architecture introduces complexity and higher operational costs that are typically unwarranted for a straightforward on-premises OLTP migration without explicit global distribution or petabyte-scale data requirements. It would be the correct choice if the application specifically demanded seamless, global horizontal scaling beyond a single regional database's capabilities.
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