- A
Remove the ORDER BY clause to improve performance.
Why wrong: The application requires ordering; removing it changes functionality.
- B
Create a composite index on (city, name).
Why wrong: This does not cover the inequality on age; Firestore would still need to filter.
- C
Create a composite index on (city, age, name).
This index covers the equality, inequality, and ordering, allowing an efficient merge scan.
- D
Create a single-field index on 'name'.
Why wrong: Single-field index does not help with multi-field filter and order.
Question 60 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.
A Firestore database in Native mode has a collection with a composite index on fields (city, age). A new query filters on 'city == 'London' AND 'age > 30' ORDER BY 'name'. The query is slow and reads many documents. What should the engineer 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 a composite index on (city, age, name).
The query filters on `city == 'London'` and `age > 30`, then orders by `name`. For Firestore to efficiently satisfy both the equality and inequality filters combined with an `ORDER BY`, the composite index must include the fields in the correct order: equality fields first, then the inequality field, then the sort field. Option C provides the index `(city, age, name)`, which matches this pattern exactly, allowing Firestore to perform a targeted index scan without reading extra documents.
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.
- ✗
Remove the ORDER BY clause to improve performance.
Why it's wrong here
The application requires ordering; removing it changes functionality.
- ✗
Create a composite index on (city, name).
Why it's wrong here
This does not cover the inequality on age; Firestore would still need to filter.
- ✓
Create a composite index on (city, age, name).
Why this is correct
This index covers the equality, inequality, and ordering, allowing an efficient merge scan.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
Create a single-field index on 'name'.
Why it's wrong here
Single-field index does not help with multi-field filter and order.
Common exam traps
Common exam trap: answer the scenario, not the keyword
Cisco often tests the misconception that adding any index on the sort field alone (Option D) or on the equality and sort fields (Option B) is sufficient, but the trap is that Firestore requires the inequality filter field to be included in the composite index before the sort field to avoid a full scan.
Detailed technical explanation
How to think about this question
Firestore's query engine requires that composite indexes include all fields used in equality filters, inequality filters, and `ORDER BY` clauses, in that specific order, to avoid a zigzag merge or in-memory sorting. Under the hood, Firestore uses a B-tree-like structure where the index scan is efficient only when the leading fields match the query's filter order; otherwise, it performs a full index scan and then filters, which can be orders of magnitude slower. In a real-world scenario, a social media app querying users by city and age range sorted by name would see latency spikes and high document reads without this exact index.
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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Manage Database Solutions — study guide chapter
Learn the concepts, then practise the questions
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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 a composite index on (city, age, name). — The query filters on `city == 'London'` and `age > 30`, then orders by `name`. For Firestore to efficiently satisfy both the equality and inequality filters combined with an `ORDER BY`, the composite index must include the fields in the correct order: equality fields first, then the inequality field, then the sort field. Option C provides the index `(city, age, name)`, which matches this pattern exactly, allowing Firestore to perform a targeted index scan without reading extra documents.
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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