Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A development team is designing an application that stores user session data in Azure Cosmos DB. Each session document contains a sessionId (unique), userId, timestamp, and a JSON field 'metadata' that can include various optional properties. The application frequently queries by userId to retrieve all sessions for a particular user. Which property should be chosen as the partition key to optimize query performance and ensure even data distribution?
Answer choices
Why each option matters
Good practice is not just finding the correct option. The wrong answers often show the exact trap the exam wants you to fall into.
A
Distractor review
sessionId
Using sessionId as partition key would make each document its own partition, so queries by userId would become cross-partition queries, scanning many physical partitions and increasing latency and RU consumption.
B
Best answer
userId
userId is the most common filter, and using it as partition key allows queries for a specific user to be routed to a single partition, offering fast and efficient reads.
C
Distractor review
timestamp
Timestamp can cause hot partitions if many sessions occur simultaneously, and it is not the primary query filter, leading to unnecessary cross-partition scans.
D
Distractor review
metadata
metadata is a JSON field with varying properties; it is not guaranteed to exist in all documents and cannot serve as a stable partition key for query routing and distribution.
Common exam trap
Common exam trap: answer the scenario, not the keyword
Many certification questions include familiar terms but test a specific constraint. Read the exact wording before choosing an answer that is generally true but wrong for this case.
Technical deep dive
How to think about this question
This question should be treated as a scenario, not a definition check. Identify the problem, the constraint and the best action. Then compare each option against those facts.
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.
- Use explanations to understand the rule behind the answer.
TExam Day Tips
- Underline the problem statement mentally.
- 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.
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.
More questions from this exam
Keep practising from the same exam bank, or move into a focused topic page if this question exposed a weak area.
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FAQ
Questions learners often ask
What does this DP-900 question test?
Read the scenario before looking for a memorised answer.
What is the correct answer to this question?
The correct answer is: userId — The partition key determines how data is distributed across physical partitions. For optimal query performance, the partition key should be the property most commonly used in queries (in this case, userId). This ensures that queries filtering by userId target a single partition (or a small number of partitions), maximizing efficiency. It also provides good data distribution if there are many different userIds. sessionId is unique per document, so each query would hit multiple partitions, causing cross-partition queries. timestamp might cause hot spots if many sessions are created at the same time, and it's not the primary query filter. metadata contains varied optional fields, making it unsuitable as a partition key.
What should I do if I get this DP-900 question wrong?
Then try more questions from the same exam bank and focus on understanding why the wrong options are tempting.
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