Azure Cosmos DB Change Feed Overview

Azure Cosmos DB Change Feed is a feature that allows you to receive notifications for changes made to documents within a container. It provides a sorted list of documents within a container that have been added or modified, enabling you to build real-time and event-driven applications. This guide will cover the syntax, examples, output, explanations, use cases, important points, and a summary of Azure Cosmos DB Change Feed.

Syntax

Azure Cosmos DB Change Feed is enabled at the container level. The key components include:

• Change Feed Processor: A component that reads and processes changes from the Change Feed.
• Start From the Beginning: Reading changes from the very beginning of the container.
• Start From Continuation Token: Reading changes from a specific point in the Change Feed.

Example

Enabling Change Feed for a container using the Azure Cosmos DB SDK for .NET:

var feedOptions = new ChangeFeedOptions
{
    StartFromBeginning = true
};

var feedIterator = container.GetChangeFeedIterator<dynamic>(feedOptions);

while (feedIterator.HasMoreResults)
{
    var feedResponse = await feedIterator.ReadNextAsync();
    
    foreach (var changedDocument in feedResponse)
    {
        // Process changed document
    }
}

Output

The output of the Change Feed is a stream of changed documents, including inserts and updates.

[
  { "_id": "document1", "field": "value1", "_ts": 1645342826 },
  { "_id": "document2", "field": "value2", "_ts": 1645342845 },
  // ... other changed documents
]

Explanation

• The Change Feed provides a chronological feed of changes made to documents in a container.
• The _ts (timestamp) property is used to indicate when the change occurred.

Use

Azure Cosmos DB Change Feed is used for:

• Building event-driven architectures where applications respond to changes in real-time.
• Implementing data synchronization across multiple distributed systems.
• Tracking and auditing changes to documents for compliance or analytics.

Important Points

• Change Feed is available for containers with the "Change Feed" feature enabled.
• It provides a consistent and ordered stream of changes.
• Change Feed can be read from the beginning or from a specific point using continuation tokens.

Summary

Azure Cosmos DB Change Feed is a powerful feature that allows developers to build reactive and real-time applications on top of Azure Cosmos DB. By providing a chronological stream of changes, it enables scenarios such as event sourcing, data synchronization, and real-time analytics. Understanding how to enable and consume the Change Feed is essential for developers working with Azure Cosmos DB.