DP-900 Practice Question: Describe considerations for working with non-relational data on Azure
Your application uses Azure Table storage to store user preferences. You need to retrieve all preferences for a specific user quickly. Which key should you use as the partition key?
⚠ Common exam trap
DP-900 often tests the trade-off between even write distribution and query efficiency; candidates pick a random GUID for 'scalability' without realizing it destroys the ability to query by user efficiently.
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
✓
UserID
In Azure Table Storage, the partition key determines which partition stores the entity, and entities with the same partition key are stored together and can be retrieved with a single partition scan. Using UserID as the partition key groups all preferences for a user into one partition, enabling fast point queries by PartitionKey + RowKey.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
Region
Why it's wrong here
Region is a broad attribute shared by many users, so it does not uniquely identify an individual. If used as the partition key, all users in a single region would land in the same partition, potentially creating a hot partition when traffic concentrates there. Because a user's region can change or a user can have preferences recorded from different regions, their preferences would be scattered across multiple partitions, forcing slow cross-partition queries.
- ✗
Random GUID
Why it's wrong here
A random GUID gives every entity its own unique partition key, which maximises write distribution but completely destroys logical grouping. Since all preferences for one user would carry different GUIDs, retrieving a user's full set of preferences would require querying every partition in the table, a costly full scan. It also prevents the use of entity group transactions, because each entity would reside in a different partition, and it creates an unnecessarily high number of small partitions.
- ✓
UserID
Why this is correct
UserID is the natural partition key because it groups every preference row for a single user into the same partition, allowing their data to be retrieved with a fast, single-partition query. This design also enables entity group transactions, so multiple preference updates for a user can be applied atomically. Since each user forms a distinct, evenly distributed partition when user IDs are varied, it avoids hot partitions while matching the application's primary access pattern.
- ✗
Timestamp
Why it's wrong here
Timestamp is a continuous, ever-changing value with poor logical grouping; many users' preferences share identical timestamps, while one user's own preferences typically span many different times. Using it as a partition key would scatter a single user's data across numerous partitions, making a profile retrieval an expensive cross-partition query. Worse, the partition key is immutable in Azure Table storage, but a timestamp changes on every update, so an entity's partition key would need to change whenever it is modified, which is not allowed.
Go deeper
Related to this question
Learn chapter
Azure Data Lake Storage Gen2
Key term
Partition key
A partition key is a value used by database systems to distribute data across multiple storage partitions, enabling faster queries and efficient scaling.
Key term
Table
A table is a structured collection of data organized into rows and columns, used in databases and spreadsheets to store and manage information efficiently.
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Written and reviewed by Johnson Ajibi, MSc IT Security
Senior Network & Security Engineer · founder of Courseiva
Last reviewed September 2026 · checked against the official Microsoft exam blueprint
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