GCP Professional Data Engineer Practice Question

Your company is rewriting its popular mobile game backend on Google Cloud. Requirements:

store JSON-like player profiles and nested game state
deliver sub-second real-time updates to millions of connected clients worldwide
SDKs must cache data locally and automatically synchronize when devices regain connectivity
simple, granular security rules per document path. Analytics engineers will later stream change logs into BigQuery. Which managed storage service best satisfies the serving workload?

Cloud SQL for PostgreSQL
Cloud Bigtable
Firestore (Native mode)
BigQuery

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Answer Description

Firestore (in Native mode) is designed for mobile, web, and server applications that need flexible JSON-like documents arranged in hierarchical collections. It offers real-time listeners that push sub-second updates to connected clients and scales automatically to millions of concurrent connections. The client SDKs include built-in offline persistence that caches data locally and reconciles changes when connectivity returns. Security rules can be defined down to the individual document path, supporting fine-grained access control required by the game. Finally, Firestore provides a managed export connector that streams document changes into BigQuery, meeting the analytics team's needs.

Bigtable delivers low-latency access but lacks native client SDKs with offline sync and fine-grained document-level security. Cloud SQL offers ACID transactions but cannot scale to millions of simultaneous real-time connections. BigQuery is optimized for analytical queries, not as a low-latency operational data store for mobile clients. Therefore, Firestore is the most appropriate choice.

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