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Google ACE Practice Question: A mobile app needs a managed database to store…
A mobile app needs a managed database to store user profiles with flexible nested structures that evolve frequently — new fields are added without schema migrations. Which GCP database service is most appropriate?
⚠ Common exam trap
Many candidates confuse Cloud Firestore with Cloud Bigtable, assuming both are NoSQL and therefore interchangeable, but Bigtable is designed for flat, wide-column data and lacks support for nested documents and real-time queries.
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 Firestore
Cloud Firestore is a NoSQL document database that supports flexible, nested data structures and automatically handles schema evolution. New fields can be added to documents at any time without requiring migrations, making it ideal for user profiles that change frequently. It also provides real-time synchronization and offline support, which are common requirements for mobile apps.
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 for PostgreSQL is a fully managed relational database that enforces a rigid, predefined schema. Adding a new field to an app profile requires an ALTER TABLE migration, which is operationally heavy and risky for frequently evolving JSON-like data. It also lacks native support for nested document queries, making it a poor fit for flexible, document-oriented app backends.
- ✗
Cloud Bigtable
Why it's wrong here
Cloud Bigtable is a wide-column NoSQL database optimized for high-throughput, low-latency analytics and IoT time-series workloads, not for storing nested JSON documents. Its data model is a sparse, sorted map of row keys and column families, and it does not support rich nested queries or ACID transactions across multiple rows. For a mobile/web application profile store that needs flexible schemas and real-time reads/writes, Bigtable is overkill and architecturally wrong.
- ✓
Cloud Firestore
Why this is correct
Cloud Firestore is a serverless, document-oriented NoSQL database that stores data as flexible JSON-like documents with nested fields. It supports schema evolution automatically—new fields can be added without migrations or downtime—and its real-time listeners and client SDKs are purpose-built for mobile/web app backends. Firestore also provides ACID transactions at the document level and auto-scaling, making it the ideal choice for storing app user profiles that change shape frequently.
- ✗
Cloud Spanner
Why it's wrong here
Cloud Spanner is a horizontally scalable, globally distributed relational database that combines strong consistency and SQL with a fixed relational schema. It demands schema definitions up front, and any change (adding a column for a new profile attribute) requires an ALTER TABLE operation, which conflicts with a flexible document use case. Spanner is designed for high-scale transactional workloads like financial ledgers, not for storing semi-structured nested data like application profiles.
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JA
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.