- A
A. Store comments in a separate container to isolate the data.
Why wrong: Storing comments in a different container is a possible solution but adds overhead in terms of cross-container queries and separate RU billing. The recommended pattern in Cosmos DB is to use separate documents within the same container with a reference field, which is simpler and more efficient.
- B
B. Store comments as separate documents and reference them from the post document via a comments array of IDs.
This approach decouples comments from the post document. When retrieving a post for the feed, the application reads only the post document, avoiding the large comments array. This reduces RU consumption and improves latency. Comments can be loaded on demand when needed.
- C
C. Use a vertical partition within the same document to separate the comments array.
Why wrong: Vertical partitioning within a document is not a concept in NoSQL databases like Cosmos DB. Documents are stored as a single JSON object; there is no way to selectively retrieve parts of a document without reading the entire thing.
- D
D. Migrate the data to Azure SQL Database to use normalized tables and indexes.
Why wrong: Migrating to a different database platform is not a data modeling optimization for Cosmos DB. The scenario explicitly involves Cosmos DB, and the best practice is to model the data appropriately within the same service.
DP-900 Practice Question: Describe considerations for working with non-relational data on Azure
This DP-900 practice question tests your understanding of describe considerations for working with non-relational data on azure. 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.
A social media company stores user posts in Azure Cosmos DB. Each post document contains fields like postId, userId, content, timestamp, and an array of comments. The comments array can grow large (hundreds per post), and the application frequently retrieves a post without its comments to display in a feed. To optimize read performance and minimize request units (RU) consumption, which data modeling approach should the company adopt?
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 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
B. Store comments as separate documents and reference them from the post document via a comments array of IDs.
Option B is correct because storing comments as separate documents and referencing them via an array of IDs in the post document allows the application to retrieve the post without comments in a single point read, consuming minimal request units (RUs). This avoids loading the large comments array when only the post metadata is needed for the feed, significantly reducing RU consumption and improving read performance in Azure Cosmos DB.
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.
- ✗
A. Store comments in a separate container to isolate the data.
Why it's wrong here
Storing comments in a different container is a possible solution but adds overhead in terms of cross-container queries and separate RU billing. The recommended pattern in Cosmos DB is to use separate documents within the same container with a reference field, which is simpler and more efficient.
- ✓
B. Store comments as separate documents and reference them from the post document via a comments array of IDs.
Why this is correct
This approach decouples comments from the post document. When retrieving a post for the feed, the application reads only the post document, avoiding the large comments array. This reduces RU consumption and improves latency. Comments can be loaded on demand when needed.
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.
- ✗
C. Use a vertical partition within the same document to separate the comments array.
Why it's wrong here
Vertical partitioning within a document is not a concept in NoSQL databases like Cosmos DB. Documents are stored as a single JSON object; there is no way to selectively retrieve parts of a document without reading the entire thing.
- ✗
D. Migrate the data to Azure SQL Database to use normalized tables and indexes.
Why it's wrong here
Migrating to a different database platform is not a data modeling optimization for Cosmos DB. The scenario explicitly involves Cosmos DB, and the best practice is to model the data appropriately within the same service.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may think embedding the comments array is always optimal for performance, but they overlook that reading the entire document with a large array wastes RUs when only the post metadata is needed, making reference-based modeling more efficient for this access pattern.
Trap categories for this question
Scenario analysis trap
Migrating to a different database platform is not a data modeling optimization for Cosmos DB. The scenario explicitly involves Cosmos DB, and the best practice is to model the data appropriately within the same service.
Detailed technical explanation
How to think about this question
In Azure Cosmos DB, point reads (reading a single document by its ID and partition key) cost 1 RU for documents up to 1 KB, while queries that scan the comments array incur additional RU based on the array size. By storing comments as separate documents with a common partition key (e.g., postId), the application can fetch the post document alone (1 RU) and lazily load comments only when needed, avoiding the RU cost of retrieving the entire embedded array. This pattern is known as 'reference-based modeling' and is recommended for frequently accessed parent documents with large, rarely needed child arrays.
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.
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FAQ
Questions learners often ask
What does this DP-900 question test?
Describe considerations for working with non-relational data on Azure — This question tests Describe considerations for working with non-relational data on Azure — Read the scenario before looking for a memorised answer..
What is the correct answer to this question?
The correct answer is: B. Store comments as separate documents and reference them from the post document via a comments array of IDs. — Option B is correct because storing comments as separate documents and referencing them via an array of IDs in the post document allows the application to retrieve the post without comments in a single point read, consuming minimal request units (RUs). This avoids loading the large comments array when only the post metadata is needed for the feed, significantly reducing RU consumption and improving read performance in Azure Cosmos DB.
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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Last reviewed: Jun 11, 2026
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