Question 1mediummultiple choice
Full question →mediummultiple choiceObjective-mapped
A smart building company stores sensor data from thousands of IoT devices as JSON documents in Azure Cosmos DB using the NoSQL API. Each document contains fields: deviceId (string), timestamp (datetime), temperature (float), humidity (float), and additional device-specific fields (e.g., motionDetected, CO2level). The most common query is: SELECT * FROM c WHERE c.deviceId = 'sensor-123' AND c.timestamp >= '2025-01-01' AND c.timestamp < '2025-02-01' ORDER BY c.timestamp DESC. Which indexing strategy will provide the best performance for this query?
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
Use the default indexing policy that automatically indexes all properties
The default policy indexes each property individually, which can support equality filters but is not optimal for range queries combined with sorting by timestamp; it may result in a slower execution.
B
Best answer
Create a composite index on (deviceId ASC, timestamp DESC)
This composite index matches the query predicates: first seeks on deviceId equality, then efficiently performs a range scan on timestamp in descending order, avoiding an in-memory sort.
C
Distractor review
Disable indexing for all properties to speed up writes
Without any indexes, every query will scan the entire container, causing extremely poor read performance for the given workload.
D
Distractor review
Create a spatial index on the deviceId field
Spatial indexes are for geospatial queries (e.g., ST_DISTANCE, ST_WITHIN) and are not helpful for equality and range queries on deviceId and timestamp.
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.
Question 1
A data engineer needs to process streaming data from IoT devices and store the results in Azure Data Lake Storage for long-term analytics. The data must be processed in near real-time to detect anomalies and trigger alerts. Which Azure service should the engineer use for stream processing?
Question 2
A data engineer needs to query data stored in CSV files in Azure Data Lake Storage Gen2 using T-SQL in Azure Synapse Analytics, without loading the data into the database. Which feature should they use?
Question 3
A data engineer needs to process raw clickstream data from multiple websites that is stored in Azure Blob Storage as JSON files. The processing must run automatically every hour, transform the data into a structured format for reporting, and handle schema changes in the source data without manual intervention. Which Azure service should be used?
Question 4
A data engineer is designing a data lake architecture in Azure. They plan to first ingest raw data from various sources into a landing zone in Azure Data Lake Storage Gen2. Then they will clean, validate, and deduplicate that data in a second zone. Finally, they will create aggregated, business-ready datasets in a third zone for analysts. This layered approach is known as which architecture?
Question 5
A data engineer needs to transform large datasets stored in Azure Data Lake Storage Gen2 using Python and Apache Spark. They want a serverless compute option that automatically scales and requires no cluster management. Which Azure service should they use?
Question 6
A company collects customer feedback forms. Each form contains always-present fields like CustomerID and SubmissionDate, but also a free-text Comments field and optional fields like Rating or ProductCategory that vary between forms. How should this data be classified?
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: Create a composite index on (deviceId ASC, timestamp DESC) — A composite index on (deviceId ASC, timestamp DESC) is ideal because it allows the query engine to efficiently locate documents for a specific deviceId and then scan the timestamp range in reverse order (since the index is ordered descending on timestamp). The default indexing policy would index all properties automatically but may not be optimized for sorting and range queries. Turning off indexing would make every query a full scan. A spatial index is for geospatial queries, not relevant here.
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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