Understand conflict resolution policies

Completed

Out of the box, Azure Cosmos DB’s multi-region write feature has automatic conflict management built in. Conflicts can occur when clients concurrently update the same item in multiple regions. There are three types of conflicts:

Type	Description
Insert	This conflict occurs when more than one item is inserted simultaneously with the same unique identifier in multiple regions
Replace	Replace conflicts occur when multiple client applications update the same item concurrently in separate regions
Delete	Delete conflicts occurs when a client is attempting to update an item that has been deleted in another region at the same time

The default conflict resolution policy in Azure Cosmos DB is Last Write Wins. This policy uses the timestamp (_ts) to determine which item wrote last. In simple terms, if multiple items are in conflict, the item with the largest value for the _ts property will win. In the case of a delete conflict, the operation to delete an item will always win out over other operations.

While the _ts property is the default for the Last Write Wins policy, you can configure any numeric property for this policy by configuring a conflict resolution path. You can use the .NET SDK for Azure Cosmos DB for NoSQL to configure the custom conflict resolution path.

In this example, a new container named products is created with a custom conflict resolution path of /sortableTimestamp.

Database database = client.GetDatabase("cosmicworks");

ContainerProperties properties = new("products", "/categoryId")
{
    ConflictResolutionPolicy = new ConflictResolutionPolicy()
    {
        Mode = ConflictResolutionMode.LastWriterWins,
        ResolutionPath = "/sortableTimestamp",
    }
};

Container container = database.CreateContainerIfNotExistsAsync(properties);

Note

You can only set a conflict resolution policy on newly created containers.