Partition Key
← Back to DP-420 Terminology Reference
Category: Data Modeling & Partitioning
Summary: Property used to distribute items across physical partitions for scalability.
Overview
A partition key is a JSON property (or path) chosen for each item in a container that Azure Cosmos DB uses to distribute data across physical partitions for scalability, and to route requests efficiently. Choosing an appropriate partition key — one with high cardinality and even access/storage distribution — is one of the most critical design decisions in Azure Cosmos DB for NoSQL, directly affecting cost, throughput distribution, and query efficiency.
[Image: dualPartKey.jpeg]
More Info & Links
DP-420 Style Practice Questions
Q1. What is the primary purpose of a partition key in Azure Cosmos DB?
- A. Distributing data and requests across physical partitions for scalability
- B. Encrypting data at rest
- C. Defining the container's indexing policy
- D. Setting the default consistency level
Q2. What characteristic should a good partition key generally have?
- A. High cardinality with evenly distributed access patterns
- B. Low cardinality with only a few possible values
- C. The same value for every item in the container
- D. A value that changes on every write
Answer Key
Answers are listed at the very end so you can attempt the questions first.
- Q1 (Partition Key): A. Distributing data and requests across physical partitions for scalability — The partition key determines how data is distributed across physical partitions, which is central to scalability.
- Q2 (Partition Key): A. High cardinality with evenly distributed access patterns — A good partition key has many distinct values and spreads read/write load evenly, avoiding 'hot partitions'.
DP-420: Designing and Implementing Cloud-Native Applications Using Microsoft Azure Cosmos DB — term detail page
