Azure Cosmos DB: Hierarchical Partition Keys

Cosmos DB now supports multi-level partition keys. This solves the “hot partition” problem for multi-tenant applications.

var containerProperties = new ContainerProperties("Orders", 
    new List<string> { "/tenantId", "/year", "/orderId" });

Data is now partitioned by Tenant → Year → Order. This distributes write load across many physical partitions while allowing efficient queries within a tenant.