PDE Storing the Data Practice Question
A mobile app needs an offline-first NoSQL database that syncs data across devices when connectivity is available. Which Google Cloud database meets these requirements?
⚠ Common exam trap
Watch out — candidates often confuse Google Bigtable's NoSQL label with a mobile-friendly NoSQL database, overlooking that Bigtable is designed for high-throughput analytical workloads, not for offline-first mobile sync with real-time listeners.
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, serverless, offline-first database that automatically syncs data across devices when connectivity is restored. It provides built-in offline persistence and real-time synchronization, making it ideal for mobile apps that need to work offline and sync later.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Memorystore
Why it's wrong here
Memorystore is an in-memory cache with no durable device-local store or cross-device sync mechanism, so offline writes cannot persist or reconcile. It is tempting because Memorystore offers low-latency access, and would be correct for caching session or hot data behind an application, not as an offline-first mobile database.
- ✗
Cloud SQL
Why it's wrong here
Cloud SQL is a relational engine with no native offline-first client synchronisation, so device-local writes and conflict resolution across devices are not provided. It is tempting because Cloud SQL is a managed Google Cloud database, and would be correct for a server-side relational workload rather than mobile offline sync.
- ✗
Bigtable
Why it's wrong here
Bigtable is a wide-column store accessed through a server-side API, offering no embedded mobile client or offline write queue with sync. It is tempting because Bigtable is a NoSQL service, and would be correct for high-throughput analytical or time-series workloads, not device-resident offline-first storage.
- ✓
Firestore
Why this is correct
Firestore provides offline persistence through local caching, letting mobile apps read and write without connectivity, then synchronises changes automatically once the device reconnects. Its real-time listeners and multi-device sync satisfy the offline-first NoSQL requirement directly, unlike Cloud SQL or Bigtable, which demand continuous network access.
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 |
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Written by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
This PDE 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 PDE exam.