Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A social media application stores user posts in Azure Cosmos DB using the NoSQL API. Each document includes: PostID (unique), UserID, Timestamp, Content. The most common query is: 'Get all posts for a specific UserID, sorted by Timestamp descending.' Which partition key should be chosen to distribute load evenly across physical partitions while also supporting this query efficiently?
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
PostID
Using PostID as the partition key would distribute posts evenly, but the query for all posts of a user would need to fan out across all partitions because posts for the same user would be scattered. This increases RU consumption and latency.
B
Best answer
UserID
UserID groups all posts for a user into one logical partition, making the query efficient. With many users, the load is balanced across physical partitions, avoiding hot spots.
C
Distractor review
Timestamp
Using Timestamp as partition key often leads to hot partitions because many writes may happen at the same time (e.g., burst of posts), causing throttling. It also does not support the query efficiently because posts for a user would be scattered.
D
Distractor review
Content
Content is not suitable as a partition key because it is typically long, variable, and leads to high cardinality without logical grouping that matches the query pattern. It would cause inefficient queries.
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 — Choosing UserID as the partition key ensures that all posts for a given user are stored in the same logical partition, making the query efficient (a single partition query). Assuming many users, the workload distributes evenly across partitions, avoiding hot partitions. PostID would scatter posts randomly, making the query a fan-out. Timestamp would cause hot partitions if many writes happen at the same time. Content is not a good partition key due to high cardinality and unpredictability.
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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