Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A media company stores user profiles in Azure Cosmos DB using the Core (SQL) API. Each profile document contains a userId (unique), name, email, and a subscriptions array containing objects with a serviceName and startDate. The application needs to efficiently retrieve a single user by userId and also run a query to find all users who have a subscription to the service 'PremiumVideo'. Which partition key design is most appropriate for this workload?
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
Partition key on email
Email is not the primary access pattern, and point reads by userId would become cross-partition queries, increasing latency and RU consumption.
B
Best answer
Partition key on userId
Correct. Partitioning by userId ensures even distribution and efficient point reads. The subscription query can still run as a cross-partition query, which is acceptable for this workload.
C
Distractor review
Partition key on serviceName (extracted from subscriptions array)
A partition key on serviceName would cause hot partitions if few services are popular, and point reads by userId would become cross-partition, slowing the primary access pattern.
D
Distractor review
Partition key on a composite key combining userId and serviceName
Azure Cosmos DB does not natively support composite partition keys in the same sense; you would have to concatenate values, which could be complex and still not ideal for the primary point-read pattern.
Common exam trap
Common exam trap: NAT rules depend on direction and matching traffic
NAT is not only about the public address. The inside/outside interface roles and the ACL or rule that matches traffic are just as important.
Technical deep dive
How to think about this question
NAT questions usually test address translation, overload/PAT behaviour, static mappings and whether the right traffic is being translated. Read the interface direction and address terms carefully.
KKey Concepts to Remember
- Static NAT maps one inside address to one outside address.
- PAT allows many inside hosts to share one public address using ports.
- Inside local and inside global describe the private and translated addresses.
- NAT ACLs identify traffic for translation, not always security filtering.
TExam Day Tips
- Identify inside and outside interfaces first.
- Check whether the scenario needs static NAT, dynamic NAT or PAT.
- Do not confuse NAT matching ACLs with normal packet-filtering intent.
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?
Static NAT maps one inside address to one outside address.
What is the correct answer to this question?
The correct answer is: Partition key on userId — Partition key selection in Azure Cosmos DB is critical for performance and scalability. The optimal partition key should distribute data evenly and support common query patterns. Here, the most frequent operation is a point read by userId, which requires a partition key that allows direct routing. Using userId as the partition key ensures even distribution and efficient point reads. The query for users with a specific subscription (the secondary pattern) becomes a cross-partition query, but this is acceptable and still performant. Other options lead either to hot partitions (serviceName) or to cross-partition reads for the primary pattern (email).
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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