- A
PlayerID
Why wrong: Using PlayerID would distribute data across many partitions. Queries by GameID would need to fan out to all partitions that contain Players for that game, increasing RU consumption.
- B
GameID
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.
- C
Score
Why wrong: 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.
- D
Timestamp
Why wrong: 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.
DP-900 Practice Question: Describe considerations for working with non-relational data on Azure
This DP-900 practice question tests your understanding of describe considerations for working with non-relational data on azure. Match the stated requirement to the specific cloud service, access model, or configuration option — many options are valid in isolation but not for this scenario. A key principle to apply: a partition key determines how data is distributed across logical partitions in Azure Cosmos DB.. Once you have made your selection, read the full explanation to reinforce the concept and understand why each distractor is designed to mislead on exam day.
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?
Clue words in this question
Noticing these words before you look at the options changes how you read each choice.
Clue:
"minimum / minimize"Why it matters: Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
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.
Key principle: A partition key determines how data is distributed across logical partitions in Azure Cosmos DB.
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
Using PlayerID would distribute data across many partitions. Queries by GameID would need to fan out to all partitions that contain Players for that game, increasing RU consumption.
- ✓
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.
Clue confirmation
The clue word "minimum / minimize" in the question point toward this answer.
Related concept
A partition key determines how data is distributed across logical partitions in Azure Cosmos DB.
- ✗
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.
Common exam traps
Common exam trap: answer the scenario, not the keyword
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.
Detailed technical explanation
How to think about this question
Cosmos DB uses hash-based partitioning: the partition key value is hashed to determine the physical partition. Choosing GameID ensures all documents for the same game reside on the same partition, allowing the query to be served from a single replica set with minimal RU. In contrast, a cross-partition query requires the gateway to fan out to all partitions, merge results, and apply the ORDER BY, which can multiply RU cost by the number of partitions.
KKey Concepts to Remember
- A partition key determines how data is distributed across logical partitions in Azure Cosmos DB.
- Choosing the partition key based on common query filters minimizes Request Unit (RU) consumption.
- Queries that include the partition key in their filter are single-partition queries, which are highly efficient.
- Queries without the partition key in their filter are cross-partition queries, incurring higher RU costs.
TExam Day Tips
- 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.
Key takeaway
A partition key determines how data is distributed across logical partitions in Azure Cosmos DB.
Real-world example
How this comes up in practice
A startup's cloud architect reviews their monthly bill and notices costs are higher than expected for a long-running batch job. Switching from on-demand instances to Reserved Instances — or using Spot/Preemptible VMs — can reduce compute costs by up to 72 %. Questions like this test whether you understand the tradeoffs between commitment, flexibility, and cost across cloud pricing models.
What to study next
Got this wrong? Here's your next step.
Review a partition key determines how data is distributed across logical partitions in Azure Cosmos DB., then practise related DP-900 questions on the same topic to reinforce the concept.
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FAQ
Questions learners often ask
What does this DP-900 question test?
Describe considerations for working with non-relational data on Azure — This question tests Describe considerations for working with non-relational data on Azure — A partition key determines how data is distributed across logical partitions in Azure Cosmos DB..
What is the correct answer to this question?
The correct answer is: 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.
What should I do if I get this DP-900 question wrong?
Review a partition key determines how data is distributed across logical partitions in Azure Cosmos DB., then practise related DP-900 questions on the same topic to reinforce the concept.
Are there clue words in this question I should notice?
Yes — watch for: "minimum / minimize". Asks for the least resource use — fewest addresses, smallest subnet, lowest overhead. Eliminate over-provisioned options even if they would technically work.
What is the key concept behind this question?
A partition key determines how data is distributed across logical partitions in Azure Cosmos DB.
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Last reviewed: Jun 11, 2026
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