Sharding in Azure Cosmos DB: Scaling Your Data Horizontally

Sharding in Azure Cosmos DB: Scaling Your Data Horizontally


3 min read


In the world of distributed databases, managing large-scale datasets efficiently is a critical challenge. One powerful technique to address this challenge is sharding. In this blog post, we’ll explore what sharding is, its purpose, and how it works specifically in Azure Cosmos DB.

What is Sharding?

Sharding involves dividing a large database or dataset into smaller, more manageable parts called shards. Each shard contains a subset of the data, and together, they form the complete dataset. The primary goal of sharding is to improve scalability and performance in distributed systems.

Purpose of Sharding

  1. Scalability: Sharding allows us to scale horizontally by distributing data across multiple servers or nodes. As the dataset grows, we can add more shards to accommodate the increased load.

  2. Parallel Processing: Each shard can be processed independently, enabling better utilization of resources. Queries can run in parallel across shards, improving overall query performance.

  3. Load Balancing: Sharding helps distribute the load evenly. Without sharding, certain parts of the dataset (hotspots) might receive excessive traffic, leading to performance bottlenecks.

  4. Handling Large Datasets: When a dataset exceeds the capacity of a single database, sharding allows us to manage it effectively.

Sharding in Azure Cosmos DB

Azure Cosmos DB provides a powerful sharding mechanism using hash-distributed tables (also known as row-based sharding). Here’s how it works:

  1. Cluster Setup: We create a cluster with multiple worker nodes. These nodes collectively manage the shards.

  2. Distribution Column: A distribution column (e.g., email) is chosen based on which rows will be assigned to shards. For example, if we have a table of users, the email column could serve as the distribution key.

  3. Shard Creation: We create a table and distribute it into shards on the worker nodes using the create_distributed_table command.

  4. Hashing: Rows are assigned to shards based on a hash of the value in the distribution column. For instance, an email like “” would be hashed to determine the shard where it belongs.

  5. Query Execution: Queries can be executed in parallel across the shards, utilizing CPU and storage resources efficiently.


Suppose we have a table called “users” with an email column as the distribution column. Azure Cosmos DB assigns each row to a shard based on the email value. When querying for specific data, the system performs a mathematical operation to determine the shard responsible for that data.


Sharding in Azure Cosmos DB empowers us to handle massive datasets, achieve better performance, and scale horizontally. Whether you’re building a global-scale application or managing large volumes of data, understanding sharding is essential for efficient data management.

Remember, while sharding provides significant benefits, it also introduces complexities related to data consistency, failover, and rebalancing. As always, choose the right sharding strategy based on your application’s requirements.

Happy sharding! 🌐🔍🔗