Create containers with large partition key

Azure Cosmos DB uses hash-based partitioning scheme to achieve horizontal scaling of data. All the Azure Cosmos containers created before May 3 2019 use a hash function that computes hash based on the first 100 bytes of the partition key. If there are multiple partition keys that have the same first 100 bytes, then those logical partitions are considered as the same logical partition by the service. This can lead to issues like partition size quota being incorrect, and unique indexes being applied across the partition keys. Large partition keys are introduced to solve this issue. Azure Cosmos DB now supports large partition keys with values up to 2 KB.

Large partition keys are supported by using the functionality of an enhanced version of the hash function, which can generate a unique hash from large partition keys up to 2 KB. This hash version is also recommended for scenarios with high partition key cardinality irrespective of the size of the partition key. A partition key cardinality is defined as the number of unique logical partitions, for example in the order of ~30000 logical partitions in a container. This article describes how to create a container with a large partition key using the Azure portal and different SDKs.

Create a large partition key (.Net SDK V2)

When using the .Net SDK to create a container with large partition key, you should specify the PartitionKeyDefinitionVersion.V2 property. The following example shows how to specify the Version property within the PartitionKeyDefinition object and set it to PartitionKeyDefinitionVersion.V2:

DocumentCollection collection = await newClient.CreateDocumentCollectionAsync(
     new DocumentCollection
           Id = Guid.NewGuid().ToString(),
           PartitionKey = new PartitionKeyDefinition
             Paths = new Collection<string> {"/longpartitionkey" },
             Version = PartitionKeyDefinitionVersion.V2
      new RequestOptions { OfferThroughput = 400 });

Create a large partition key (Azure portal)

To create a large partition key, while you create a new container using the Azure portal, check the My partition key is larger than 100-bytes option. By default, all the new containers are opted into using the large partition keys. Unselect the checkbox if you don’t need large partition keys or if you have applications running on SDKs version older than 1.18.

Create large partition keys using Azure portal

Supported SDK versions

The Large partition keys are supported with the following minimum versions of SDKs:

SDK type Minimum version
.Net 1.18
Java sync 2.4.0
Java Async 2.5.0
REST API version higher than 2017-05-03 by using the x-ms-version request header.

Currently, you cannot use containers with large partition key within in Power BI and Azure Logic Apps. You can use containers without a large partition key from these applications.

Next steps