The answer is Azure Cosmos DB materialized views (preview). This feature is correct because it pre-joins, aggregates, and transforms data from a source container into a separate, optimized container, allowing queries like filtering by `category` to run against pre-computed results rather than scanning the entire source. By avoiding full scans or expensive cross-partition queries, materialized views drastically reduce request unit (RU) consumption, making them ideal for your real-time inventory application’s frequent category lookups. On the Microsoft Azure Data Fundamentals DP-900 exam, this tests your understanding of how to optimize query performance and minimize RU costs using native Cosmos DB features—a common trap is confusing materialized views with change feed or indexing policies, which serve different purposes. Remember the mnemonic “Pre-compute to reduce compute”: materialized views store pre-computed results, so your queries consume fewer RUs.
DP-900 Describe core data concepts Practice Question
This DP-900 practice question tests your understanding of describe core data concepts. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. 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.
Your organization uses Azure Cosmos DB for a real-time inventory application. The data includes a container with items that have a `category` property. The operations team frequently queries for all items in a specific category. To optimize query performance and minimize request unit (RU) consumption, you decide to implement a materialized view. Which Azure Cosmos DB feature should you use to achieve this?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue: "minimum / minimize"
Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
Answer the question above first, then reveal the full breakdown to understand why each option is right or wrong.
Correct answer & explanation
✓
Materialized views (preview)
Option D is correct because Azure Cosmos DB's materialized views (preview) feature allows you to pre-join, aggregate, and transform data from a source container into a separate container optimized for specific query patterns, such as filtering by `category`. This reduces RU consumption by avoiding full scans or expensive cross-partition queries, as the view is pre-computed and indexed according to the target query.
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.
✗
Partition key design
Why it's wrong here
Partition key design distributes data but does not create materialized views.
✗
Change feed
Why it's wrong here
Change feed is used to capture data changes, not to create materialized views.
✗
Composite indexes
Why it's wrong here
Composite indexes improve query performance but do not create materialized views with pre-computed results.
✓
Materialized views (preview)
Why this is correct
Azure Cosmos DB materialized views allow you to define a view that is automatically updated and optimized for common queries.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates confuse the change feed (a reactive stream of changes) with materialized views (a persisted, queryable snapshot), or assume that composite indexes alone can achieve the same pre-computation benefits as a materialized view.
Detailed technical explanation
How to think about this question
Under the hood, materialized views in Azure Cosmos DB are implemented as a separate container that is automatically populated and kept in sync with the source container via the change feed. The view definition can include projections, filters, and aggregations, and the view container can have its own indexing policy and partition key, allowing queries against the view to be served with minimal RU cost. A real-world scenario is a real-time inventory dashboard that needs to show total stock per category; without a materialized view, each query would scan all items, but with a materialized view, the aggregated counts are pre-computed and updated incrementally.
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
An e-commerce site experiences heavy traffic on Black Friday and near-zero traffic during off-peak weeks. Rather than provisioning permanent large VMs, the team uses auto-scaling groups that add capacity automatically under load and reduce it overnight. Questions like this test whether you understand elasticity, availability zones, and cloud compute scaling patterns.
Related glossary terms
Concepts from this question explained
These glossary pages explain the core terms tested in this DP-900 question in full detail.
Describe core data concepts — This question tests Describe core data concepts — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: Materialized views (preview) — Option D is correct because Azure Cosmos DB's materialized views (preview) feature allows you to pre-join, aggregate, and transform data from a source container into a separate container optimized for specific query patterns, such as filtering by `category`. This reduces RU consumption by avoiding full scans or expensive cross-partition queries, as the view is pre-computed and indexed according to the target query.
What should I do if I get this DP-900 question wrong?
Identify which exam domain this question belongs to, review the core concept, then practise similar questions from the same domain.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
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