Set the appropriate consistency level for operations

Microsoft Azure offers five consistency levels for your operations:

1. Strong Consistency:

   • Provides linearizability, ensuring that all read operations return the most recent version of the data.
   • Offers the highest level of consistency but may have a performance impact due to the need for coordination and synchronization across multiple replicas.

2. Bounded Staleness Consistency:

   • Allows you to define a maximum lag in terms of time or versions for read operations.
   • Provides consistency within the specified time or version range, but may have a slight staleness for reads if the replicas have not caught up.

3. Session Consistency:

   • Guarantees consistency for read operations within a single session (client connection).
   • Offers a good balance between consistency and performance, suitable for most scenarios.

4. Consistent Prefix Consistency:

   • Ensures that read operations never see out-of-order writes.
   • Provides a consistent view of data but may not be the most recent version.

5. Eventual Consistency:

   • Offers the highest level of availability and lowest latency, but with no consistency guarantees.
   • Reads may reflect older versions of data, as updates are propagated asynchronously.

Setting the Appropriate Consistency Level

Choosing the right consistency level depends on your application requirements for consistency, availability, and performance. Here are some considerations to guide your decision:

1. Consistency Requirements:

   • If your application requires strong consistency for all operations, choose the Strong Consistency level.
   • If it can tolerate some level of staleness or eventual consistency, you can opt for other consistency levels depending on the trade-offs you are willing to make.

2. Availability:

   • If high availability is a key requirement, you may choose to sacrifice some level of consistency and opt for the Eventual Consistency level.
   • For scenarios where availability is important but stricter consistency is required, Session Consistency is a good option.

3. Performance:

   • Strong Consistency and Bounded Staleness Consistency may have a higher performance impact due to coordination across replicas.
   • If performance is critical, consider Session Consistency or Consistent Prefix Consistency to strike a balance between consistency and performance.

Setting the consistency level can be done at different levels in Azure, including the account level, container level, or even at the operation level in the application code. You can set the consistency level using SDKs or REST API calls.

Example: Setting Consistency Level using .NET SDK

To set the consistency level in your application code using the .NET SDK, you can use the following example code:

using Azure;
using Azure.Cosmos;

CosmosClient client = new CosmosClient(connectionString, options);
CosmosDatabase database = client.CreateDatabaseIfNotExistsAsync(databaseName).Result;
CosmosContainer container = database.CreateContainerIfNotExistsAsync(containerName, "/partitionKey").Result;

In this example, we create a CosmosClientOptions object and set the ConsistencyLevel property to the desired consistency level (in this case, Session Consistency). We then create a CosmosClient instance using the connection string and options and proceed to create the necessary database and container.

Conclusion

Setting the appropriate consistency level is crucial when developing solutions for Microsoft Azure. By understanding the different consistency levels available and considering your application’s requirements for consistency, availability, and performance, you can make an informed decision. Remember, the consistency level can be set at various levels, and it is important to choose the right level for each specific operation or scenario.