Describe considerations for working with non-relational data on Azure →mediumMultiple ChoiceObjective-mapped
DP-900 Practice Question: Describe considerations for working with non-relational data on Azure
A gaming company stores player scores in Azure Cosmos DB using the NoSQL API. Each document contains fields: PlayerID (unique to the player), GameID, Score, Timestamp. The most common query is: 'Retrieve all scores for a specific GameID, ordered by Score descending.' Which property should be chosen as the partition key to minimize Request Unit (RU) consumption?
⚠ Common exam trap
The trap here is that candidates often pick a unique key like PlayerID thinking it ensures even distribution, but they overlook that the query pattern (filtering by GameID) must drive the partition key choice to avoid cross-partition queries.
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
✓
GameID
GameID is the correct partition key because the most common query filters on GameID, and Cosmos DB routes queries to the exact physical partition(s) containing that GameID's data. This minimizes RU consumption by avoiding cross-partition fan-out, as the query engine can target a single partition. Using any other field would force scanning multiple partitions, increasing RU cost.
Answer analysis
Option-by-option breakdown
For each option: why learners choose it and why it is or isn't the right answer here.
- ✗
PlayerID
Why it's wrong here
Choosing PlayerID as the partition key scatters scores for the same game across many physical partitions, because each player's data is stored separately. A query filtering only by GameID must then perform a cross-partition fan-out to every partition containing any score for that game, scanning all matching documents and dramatically increasing request unit (RU) consumption and latency. In Cosmos DB, such queries degrade from an efficient point read to a multi-partition query, and they also risk throttling under heavy load.
- ✓
GameID
Why this is correct
GameID is the attribute used in the query filter. Choosing it as the partition key ensures that all scores for a given game are co-located in one partition, allowing a point query to that single partition and minimizing RU cost.
- ✗
Score
Why it's wrong here
Score has high cardinality and is used for ordering, not filtering. Using Score as partition key would not narrow the query to a single partition; the query would need to read all partitions and then sort.
- ✗
Timestamp
Why it's wrong here
Timestamp is not used in the filter. A partition key on Timestamp would cause the query to scatter to many partitions (since scores for a given game could have many timestamps), leading to high RU consumption.
Go deeper
Related to this question
Learn chapter
Data Roles and Core Concepts
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
Azure Cosmos DB
Azure Cosmos DB is a fully managed, globally distributed NoSQL database service that offers fast reads and writes anywhere in the world with automatic scaling and multiple consistency models.
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