PDE Storing the Data Practice Question
A data engineer must store JSON documents for a product catalog in Cloud Firestore. Some documents contain nested arrays of product variants that can exceed 1 MiB when serialized. The engineer wants to keep the catalog queryable with strong consistency and low latency. What should the engineer do?
⚠ Common exam trap
The trap here is assuming a paid or enterprise tier removes the Firestore 1 MiB document size limit, when in fact that limit is fixed across editions.
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
✓
Store each variant as a separate document in a subcollection and keep only summary fields in the parent document.
Firestore imposes a hard 1 MiB limit per document, so large nested arrays must be split across documents. Moving variants into a subcollection keeps each document within the limit while preserving strong consistency and low-latency queries, since subcollection documents are first-class documents in the same database.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Move the entire catalog to Cloud Bigtable and use row keys to model variant relationships.
Why it's wrong here
Bigtable is a wide-column NoSQL store optimized for high-throughput key access, not for strongly consistent document queries with flexible filters. Migrating the catalog would require rewriting the application and would not provide the same query model or strong consistency semantics for arbitrary document fields.
- ✓
Store each variant as a separate document in a subcollection and keep only summary fields in the parent document.
Why this is correct
Firestore enforces a 1 MiB document size limit, so moving large nested arrays into a subcollection keeps each document within the limit. Queries remain strongly consistent and low latency because subcollection documents are still part of the same Firestore database and can be queried directly.
- ✗
Store the variants as a base64-encoded string field inside the parent document.
Why it's wrong here
Encoding the variants as a base64 string increases the serialized size by roughly 33 percent and still counts against the 1 MiB document limit. It also makes the variants opaque to Firestore queries, defeating the requirement to keep the catalog queryable with strong consistency.
- ✗
Increase the Firestore document size limit by enabling the Enterprise edition of Firestore.
Why it's wrong here
Firestore does not offer an edition that raises the 1 MiB per-document limit; that limit is a hard platform constraint. Enabling an edition changes billing and feature tiers, not the maximum serialized document size, so this approach cannot accommodate the oversized variants.
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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 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.