- A
Create a collection group index on the field.
Why wrong: Collection group indexes are for queries across subcollections.
- B
Create a composite index on the array field and another field.
Why wrong: Composite indexes don't apply to array fields; array queries need exemptions.
- C
Create an index exemption for the array field.
Index exemptions enable array indexing.
- D
Rely on the automatically created single-field index.
Why wrong: Automatic index does not support array queries.
Question 381 of 1,000
PCDOE Manage Database Solutions Practice Question
This PCDOE practice question tests your understanding of manage database solutions. Read the scenario carefully and evaluate each option against the stated constraints before committing to an answer. After answering, compare your reasoning against the explanation and wrong-answer breakdown below. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
An application uses Cloud Firestore. The team notices that queries on a collection with an array field are slow. They want to create an index on the array field. What should they do?
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
✓
Create an index exemption for the array field.
Option C is correct because Cloud Firestore does not support single-field indexes on array fields. To enable efficient queries on array fields, you must create an index exemption, which allows you to define a composite index that includes the array field. This gives you control over indexing behavior and improves query performance for array-containing collections.
Key principle: Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Create a collection group index on the field.
Why it's wrong here
Collection group indexes are for queries across subcollections.
- ✗
Create a composite index on the array field and another field.
Why it's wrong here
Composite indexes don't apply to array fields; array queries need exemptions.
- ✓
Create an index exemption for the array field.
Why this is correct
Index exemptions enable array indexing.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Rely on the automatically created single-field index.
Why it's wrong here
Automatic index does not support array queries.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Google Cloud often tests the misconception that array fields can be indexed automatically like other fields, leading candidates to rely on single-field indexes or composite indexes without special handling. However, Firestore requires an explicit index exemption for array fields to enable efficient queries, as they are not automatically indexed and cannot be used in composite indexes without this exemption.
Detailed technical explanation
How to think about this question
Firestore's automatic array index supports only equality queries (e.g., `array_contains`), not range or order-by queries on array elements. By creating an index exemption, you can disable the automatic array index and then define a composite index that includes the array field alongside other fields, enabling more efficient queries like `array_contains_any` or combined filters. This is particularly useful in scenarios where you need to query documents based on array membership along with other conditions, such as filtering products by tags and price range.
KKey Concepts to Remember
- Read the scenario before looking for a memorised answer.
- Find the constraint that changes the correct option.
- Eliminate answers that are true in general but not in this case.
TExam Day Tips
- Watch for words such as best, first, most likely and least administrative effort.
- Review why wrong options are wrong, not only why the correct option is correct.
Key takeaway
Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option.
Real-world example
How this comes up in practice
A cloud solutions architect for a retail company is evaluating services for a new workload. The correct answer here reflects best practice for the specific scenario described — not a general cloud recommendation. Answer the scenario, not the keyword: identify the specific constraint before choosing the most familiar-sounding option. Cloud exam questions reward reading the constraint carefully: the same technology can be right or wrong depending on the use case.
What to study next
Got this wrong? Here's your next step.
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
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FAQ
Questions learners often ask
What does this PCDOE question test?
Manage Database Solutions — This question tests Manage Database Solutions — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Create an index exemption for the array field. — Option C is correct because Cloud Firestore does not support single-field indexes on array fields. To enable efficient queries on array fields, you must create an index exemption, which allows you to define a composite index that includes the array field. This gives you control over indexing behavior and improves query performance for array-containing collections.
What should I do if I get this PCDOE question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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Last reviewed: Jul 4, 2026
This PCDOE 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 PCDOE exam.
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