Override default consistency by using query request options

The query request options in Microsoft Azure Cosmos DB provide developers with the ability to override the default consistency settings for their queries. By specifying these options, you can control the trade-off between consistency and performance in your native applications. In this post, we will explore how to design and implement native applications using Azure Cosmos DB and leverage query request options to customize consistency.

Default Consistency Levels in Azure Cosmos DB

Azure Cosmos DB offers five consistency levels:

• Strong: Provides the most recent committed version of the data across all regions. However, it may impact performance due to cross-region communication.
• Bounded staleness: Ensures consistency within a specified lag time or a number of operations.
• Session: Guarantees strong consistency within a session and allows for eventual consistency across multiple sessions.
• Consistent prefix: Offers linearizability for read operations within a single partition key.
• Eventual consistency: Allows for the maximum level of scalability and performance, as it does not enforce any consistency guarantees.

The default consistency level is session, which provides a balance between strong consistency and performance.

Overriding the Default Consistency Level

To override the default consistency level, you can use the RequestOptions object in your query code. This object allows you to specify the desired consistency level for a particular query. Here’s an example:


$(document).ready(function () {
// Set up the RequestOptions object with desired consistency level
var options = new Microsoft.Azure.Documents.Client.RequestOptions();
options.consistencyLevel = Microsoft.Azure.Documents.ConsistencyLevel.Strong;

// Execute the query with the specified consistency level
client.queryDocuments(collectionLink, query, options).toArray(function (err, results) {
// Process query results here
});
});


In this example, we set the consistency level to “Strong” using the consistencyLevel property of the RequestOptions object. The query is then executed using the client.queryDocuments method, passing the collection link, query, and options as parameters.

Considerations for Overriding Consistency Levels

When overriding the default consistency level for individual queries, it’s important to consider the impact on scalability and availability. Strong consistency requires more resources and may affect the overall performance of your application. Therefore, it is recommended to carefully evaluate the requirements of your application before making extensive use of strong consistency.

Keep in mind that while strong consistency provides the most up-to-date data, it can introduce additional latency due to cross-region communication. It is crucial to find the right balance between consistency and performance based on the specific needs of your application.

Conclusion

Azure Cosmos DB allows developers to override the default consistency settings for queries using query request options. By specifying the desired consistency level, you can customize the trade-off between consistency and performance in your native applications. However, it is essential to carefully evaluate the impact of consistency levels on scalability and availability before making extensive use of strong consistency. With the flexibility offered by Azure Cosmos DB, you can design and implement native applications with the desired consistency guarantees.