- A
The query does not use the partition key, causing a cross-partition scan.
When a query does not include the partition key, Cosmos DB must execute the query across all partitions, which increases latency and RU consumption. This is the most likely cause.
- B
The query is not using an index on the temperature field.
Why wrong: While indexes are important, Cosmos DB automatically indexes all fields by default. The absence of a partition key in the filter is the primary issue because it forces a full scan across partitions.
- C
The time range filter is too large, causing a full table scan.
Why wrong: A large time range can increase the number of documents scanned, but the main issue is that the query is cross-partition. Even with a small time range, the query would still need to search each partition for matching documents.
- D
The document size is too large, increasing RU per read.
Why wrong: Document size does affect RU consumption, but the dramatic increase in RUs from a query that omits the partition key is primarily due to cross-partition execution, not document size.
Quick Answer
The answer is that the query does not use the partition key, which forces a cross-partition scan. Without specifying deviceId in the filter, Azure Cosmos DB cannot route the request to a single physical partition; instead, it must fan out the query to every partition, scanning all documents across the container. This cross-partition query consumes significantly more request units (RUs) and takes longer because each partition is queried sequentially or in parallel, and results are merged server-side. On the DP-900 exam, this scenario tests your understanding of how partition key selection directly impacts query performance and cost—a common trap is assuming all queries run efficiently regardless of the filter. Remember the memory tip: “No key, full sweep”—if your WHERE clause omits the partition key, expect a slow, expensive cross-partition scan.
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. The scenario asks you to isolate a root cause — eliminate options that address a different problem before choosing. 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 smart building company stores IoT sensor data in Azure Cosmos DB using the NoSQL API. Each document contains fields: deviceId (partition key), timestamp, temperature, and humidity. The most common query is to retrieve all readings for a specific device within a time range, which runs efficiently. However, the analytics team occasionally runs a query to find all devices that reported a temperature above 50 degrees Celsius in the last hour, without specifying deviceId. This query is very slow and consumes a high number of request units (RUs). What is the most likely reason for the slow performance and high RU consumption?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"most likely"Why it matters: Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
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
The query does not use the partition key, causing a cross-partition scan.
The query does not include the partition key (deviceId) in the filter, so Azure Cosmos DB cannot route it to a single physical partition. Instead, it must fan out the query to every partition, scanning all documents across the container. This cross-partition query consumes significantly more RUs and takes longer because each partition must be queried sequentially or in parallel, and the results are merged server-side.
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.
- ✓
The query does not use the partition key, causing a cross-partition scan.
Why this is correct
When a query does not include the partition key, Cosmos DB must execute the query across all partitions, which increases latency and RU consumption. This is the most likely cause.
Clue confirmation
The clue word "most likely" in the question point toward this answer.
Related concept
Read the scenario before looking for a memorised answer.
- ✗
The query is not using an index on the temperature field.
Why it's wrong here
While indexes are important, Cosmos DB automatically indexes all fields by default. The absence of a partition key in the filter is the primary issue because it forces a full scan across partitions.
- ✗
The time range filter is too large, causing a full table scan.
Why it's wrong here
A large time range can increase the number of documents scanned, but the main issue is that the query is cross-partition. Even with a small time range, the query would still need to search each partition for matching documents.
- ✗
The document size is too large, increasing RU per read.
Why it's wrong here
Document size does affect RU consumption, but the dramatic increase in RUs from a query that omits the partition key is primarily due to cross-partition execution, not document size.
Common exam traps
Common exam trap: answer the scenario, not the keyword
The trap here is that candidates may assume indexing is the culprit (Option B) because they think a missing index causes slow queries, but Azure Cosmos DB indexes all fields automatically, so the real issue is the missing partition key forcing a cross-partition scan.
Detailed technical explanation
How to think about this question
Under the hood, Azure Cosmos DB uses a hash-based partition strategy: the partition key value is hashed to determine which physical partition stores the data. Without the partition key in the query filter, the query engine must issue a parallel query to every physical partition, and the RU charge is the sum of all partition-level query costs. In a real-world scenario, if the container has hundreds of partitions, this query could consume thousands of RUs even for a small result set, making it unsuitable for frequent or latency-sensitive operations.
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.
- →
Describe considerations for working with non-relational data on Azure — study guide chapter
Learn the concepts, then practise the questions
- →
Describe considerations for working with non-relational data on Azure practice questions
Targeted practice on this topic area only
- →
All DP-900 questions
982 questions across all exam domains
- →
Microsoft Azure Data Fundamentals DP-900 study guide
Full concept coverage aligned to exam objectives
- →
DP-900 practice test guide
How to use practice tests most effectively before exam day
Related practice questions
Related DP-900 practice-question pages
Use these pages to review the topic behind this question. This is how one missed question becomes focused revision.
Describe core data concepts practice questions
Practise DP-900 questions linked to Describe core data concepts.
Describe an analytics workload on Azure practice questions
Practise DP-900 questions linked to Describe an analytics workload on Azure.
Identify considerations for relational data on Azure practice questions
Practise DP-900 questions linked to Identify considerations for relational data on Azure.
Describe considerations for working with non-relational data on Azure practice questions
Practise DP-900 questions linked to Describe considerations for working with non-relational data on Azure.
DP-900 fundamentals practice questions
Practise DP-900 questions linked to DP-900 fundamentals.
DP-900 scenario practice questions
Practise DP-900 questions linked to DP-900 scenario.
DP-900 troubleshooting practice questions
Practise DP-900 questions linked to DP-900 troubleshooting.
Practice this exam
Start a free DP-900 practice session
Short sessions build daily habit. Longer sessions build exam-day stamina. Try a timed session to simulate real conditions.
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: The query does not use the partition key, causing a cross-partition scan. — The query does not include the partition key (deviceId) in the filter, so Azure Cosmos DB cannot route it to a single physical partition. Instead, it must fan out the query to every partition, scanning all documents across the container. This cross-partition query consumes significantly more RUs and takes longer because each partition must be queried sequentially or in parallel, and the results are merged server-side.
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: "most likely". Probability qualifier — the question wants the most probable cause or outcome, not a guaranteed one. Eliminate low-probability options.
What is the key concept behind this question?
Read the scenario before looking for a memorised answer.
About these practice questions
Courseiva creates original exam-style practice questions with explanations and wrong-answer analysis. It does not publish real exam questions, exam dumps, or protected exam content. Learn why practice questions differ from exam dumps →
Last reviewed: Jun 11, 2026
This DP-900 practice question is part of Courseiva's free Microsoft 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 DP-900 exam.
Question Discussion
Share a tip, memory trick, or ask about the reasoning behind this question. Do not post real exam questions, leaked content, braindumps, or copyrighted exam material. Comments are moderated and may be removed without notice.
Sign in to join the discussion.