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Eventual Consistency in CosmosDB

Explanation

Eventual consistency is one of the several consistency models supported by CosmosDB. In an eventually consistent system, updates made to a data item may not be immediately visible to all clients. Instead, eventually, all replicas will converge to the same state. This model prioritizes availability and partition tolerance over consistency and is often used in distributed systems.

Syntax

There is no specific syntax for enabling eventual consistency in CosmosDB. Instead, you can choose the consistency level when you create or update a database account or a container. The consistency levels that support eventual consistency are:

  • Eventual: All replicas will eventually converge to the same state.
  • ConsistentPrefix: All replica reads will return a prefix of all writes with no gaps.

Example

To create a container with eventual consistency using the CosmosDB SDK for .NET, you can use the following code snippet:

CosmosClient client = new CosmosClient("Connection string");
Database database = await client.CreateDatabaseIfNotExistsAsync("mydb");
Container container = await database.CreateContainerIfNotExistsAsync("mycontainer", "/partitionKey");
await container.ReadItemAsync<dynamic>(id: "myitemid", new PartitionKey("mypartitionkey"), new RequestOptions
{
    ConsistencyLevel = ConsistencyLevel.Eventual
});

Output

The output of the example code above will be the item with Id: "myitemid" and PartitionKey: "mypartitionkey", read with eventual consistency.

Use

Eventual consistency is often used in distributed systems that prioritize partition tolerance and availability over consistency. It can be a good choice for scenarios where it is acceptable for clients to see stale data, as long as the system converges to the correct state eventually.

Important Points

Here are some important points to keep in mind when using eventual consistency in CosmosDB:

  • Eventual consistency may lead to stale data being read by clients.
  • Eventual consistency is useful in distributed systems that prioritize availability and partition tolerance over consistency.
  • By default, CosmosDB uses session consistency, which guarantees strong consistency within the same session.
  • CosmosDB offers several other consistency levels to choose from, depending on your specific needs.

Summary

Eventual consistency is one of the consistency models supported by CosmosDB. It prioritizes availability and partition tolerance over consistency, allowing updates to propagate to replicas asynchronously. This can be a good choice for distributed systems where clients can tolerate seeing stale data. CosmosDB offers several consistency levels to choose from, depending on your specific needs.

SessionConfiguration
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