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?
⚠ Common exam trap
GCDL often tests the difference between Firestore (document, real-time, offline) and Bigtable (wide-column, analytical) — candidates pick Bigtable for 'NoSQL' without checking the real-time sync and offline requirements.
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 Google Cloud's serverless, document-oriented NoSQL database that provides real-time synchronization across devices via listeners, plus built-in offline persistence for mobile and web SDKs. Its document/collection data model and automatic multi-device sync directly match the startup's 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 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.
Quick reference
Cloud Service Model Comparison
| Model | You Manage | Provider Manages | Examples |
|---|---|---|---|
| IaaS | OS, runtime, apps, data | Hardware, hypervisor, networking | EC2, Azure VMs, GCP Compute Engine |
| PaaS | Apps and data | OS, runtime, middleware, hardware | Elastic Beanstalk, Azure App Service |
| SaaS | Data and settings only | Everything else | Microsoft 365, Salesforce, Workday |
| FaaS / Serverless | Function code only | Infra, scaling, runtime | Lambda, Azure Functions, Cloud Run |
| CaaS | Containers and apps | Kubernetes, OS, hardware | EKS, AKS, GKE |
Go deeper
Related to this question
Learn chapter
Data Sovereignty and Compliance on Google Cloud
Key term
Model
In IT and AI, a model is a trained mathematical representation that learns patterns from data to make predictions or decisions.
Key term
Firestore
Firestore is a flexible, scalable, serverless NoSQL database from Google Cloud that automatically syncs data across applications in real time.
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JA
Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Google Cloud exam blueprint
This GCDL 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 GCDL exam.