Cloud Digital Leader Google Cloud Products and Services Practice Question
A startup is building a mobile app and needs a real-time database that synchronises data across user devices automatically. The data model is document-based, and the app needs offline support. Which database should they use?
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
✓
Firestore
Firestore is a NoSQL document database designed for mobile and web apps with real-time synchronization, offline support, and automatic multi-device sync. Cloud SQL is relational and not designed for mobile offline sync. Bigtable is for time-series. Memorystore is a cache.
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 Bigtable
Why it's wrong here
Cloud Bigtable is a wide-column NoSQL database engineered for large-scale analytical and operational workloads, such as time-series and IoT data, with low single-digit millisecond latencies. However, it lacks mobile client SDKs with real-time listeners and offline persistence, and its data model is not designed for direct app-level synchronization. Building a real-time mobile app on Bigtable would require custom backend services to push updates and manage offline queues, making it a poor fit for this use case.
- ✗
Cloud SQL
Why it's wrong here
Cloud SQL is a fully managed relational database (MySQL, PostgreSQL, or SQL Server) that excels at transactional integrity and complex queries for traditional web applications. It does not natively support client-side offline data storage or real-time change subscriptions; mobile apps would need to implement a custom sync layer and handle connectivity intermittency, which adds significant engineering overhead. This makes Cloud SQL a poor fit for a mobile app requiring instant real-time updates and offline resilience.
- ✓
Firestore
Why this is correct
Firestore is a NoSQL document database with real-time synchronization built into its mobile SDKs, automatically pushing data changes to connected clients and persisting a local cache for offline operation. It resolves conflicts and syncs local writes when connectivity returns, enabling responsive, collaborative mobile experiences. Its flexible, schema-less document model maps naturally to app objects, making it the standard choice for real-time mobile apps.
- ✗
Memorystore
Why it's wrong here
Memorystore is a managed, in-memory caching service for Redis or Memcached, designed to accelerate data access with sub-millisecond latencies. It is not meant to be a durable system of record; data is volatile unless persistence is explicitly configured, and it provides no offline synchronization or real-time push for mobile clients. Using Memorystore as the primary database for a mobile app would risk data loss and require a separate backend to handle sync, so it is unsuitable here.
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Key term
Memorystore
A fully managed in-memory data store service that provides Redis and Memcached for caching, session storage, and real-time data processing.
Key term
Cloud SQL
Cloud SQL is a fully managed relational database service that lets you set up, maintain, and scale SQL databases (like MySQL, PostgreSQL, and SQL Server) in the cloud without managing the underlying infrastructure.
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