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Google ACE Practice Question: Migrating a legacy on-premises application to…
A company is migrating a legacy on-premises application to Google Cloud. The application stores structured transactional data in a relational database. The database currently handles 2,000 transactions per second (TPS) and is expected to grow to 10,000 TPS over the next year. The database size is 500 GB. The application requires strong consistency and the ability to run complex JOIN queries. Which Google Cloud database service should the company choose?
⚠ Common exam trap
The trap is choosing Cloud SQL based on familiarity or cost, but the high TPS requirement (10,000) signals the need for Cloud Spanner's horizontal scalability. Cloud Spanner is not only for global applications; it also serves high-throughput single-region workloads.
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 correct choice because it is a fully managed relational database that provides strong global consistency, supports complex SQL joins, and scales horizontally to easily handle 10,000 TPS. Cloud SQL, while supporting joins and ACID, is limited to vertical scaling and read replicas, which do not address the write throughput required at 10,000 TPS. Therefore, Cloud Spanner meets the application's requirements for high TPS, strong consistency, and complex queries.
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 is a globally distributed relational database that offers strong consistency and horizontal scalability, making it ideal for applications spanning multiple regions with extremely high throughput requirements. For a legacy on-premises application that likely operates at modest scale, Spanner's advanced features and associated costs are unnecessary. Migrating to Spanner would add significant operational complexity and expense without tangible benefits, making Cloud SQL for PostgreSQL a more proportionate and cost-effective choice.
- ✗
Cloud SQL for PostgreSQL
Why it's wrong here
Cloud SQL for PostgreSQL is a fully managed relational database service that provides traditional SQL support, including complex JOINs, subqueries, and ACID transactions, ensuring compatibility with legacy on-premises application code. It handles backups, replication, and maintenance automatically, reducing administrative burden while preserving the relational data model the application already depends on. With strong consistency and familiar PostgreSQL semantics, it is the natural migration target for a legacy relational workload.
- ✗
Cloud Bigtable
Why it's wrong here
Cloud Bigtable is a NoSQL, wide-column database designed for massive analytical and operational workloads such as time-series data, IoT, and financial analytics. It does not support SQL queries, JOIN operations, or multi-row transactions, which are fundamental to a legacy application relying on a relational schema. Migrating to Bigtable would require a complete redesign of the data layer, and its lack of relational features makes it unsuitable for this use case.
- ✗
Cloud Firestore
Why it's wrong here
Cloud Firestore is a flexible, serverless NoSQL document database geared toward mobile and web applications that need real-time synchronization and offline support. It stores data in documents and collections, with no native support for SQL JOINs or arbitrary query joining across collections, which legacy relational applications typically require. Firestore's document-oriented model would force a cumbersome re-architecture and would not preserve the application's existing query patterns.
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Key term
Google Cloud
Google Cloud is a suite of cloud computing services offered by Google that provides infrastructure, platform, and software solutions over the internet.
Key term
Service
A service is a software component or system that performs a specific function and is available to be used by other programs or users over a network.
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This ACE 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 ACE exam.