Change Data Capture Developer Guide

Change Data Capture
Keep Your External Data Current with Change Data Capture
Change Event Message Structure
Merged Change Events
Other Types of Change Events: Gap and Overflow Events
Subscribe to Change Events
Change Event Storage and Delivery
Subscription Channels
Compose Streams of Change Data Capture Notifications with Custom Channels
Example Diagrams for Channels and Channel Members
High-Level Replication Steps
Subscribe with CometD Using the EMP Connector Sample
Enrich Change Events with Extra Fields When Subscribed with CometD
Subscribe with Apex Triggers
Monitor Change Event Publishing and Delivery Usage
Security Considerations
Change Event Considerations
Standard Object Notes
Change Events for Fields
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Change Event Storage and Delivery

Change events are stored temporarily and subscribers can retrieve them during the retention window. The order of events delivered is based on the order of the corresponding committed transactions. Users with the proper permissions can receive events on a channel.

Temporary Storage in the Event Bus

Change events are based on platform events and share some of their characteristics for storage. Change event messages are stored in the event bus for three days. You can retrieve stored event messages from the event bus. Each event message contains the ReplayId field, which identifies the event in the stream and enables replaying the stream after a specific event. For more information, see Message Durability in the Streaming API Developer Guide.

Order of Events

The order of change events stored in the event bus corresponds to the order in which the transactions corresponding to the record changes are committed in Salesforce. If a transaction includes multiple changes, like a lead conversion, a change event is generated for each change with the same transactionKey but different sequenceNumber in the header. The sequenceNumber is the order of the change within the transaction.

When Salesforce receives a change event, it assigns a replay ID value to it and persists it in the event bus. Subscribers receive change events from the event bus in the order of the replay ID.

User Permissions Required

The subscriber must have one or more of the following permissions depending on the subscription channel: View All Data, View All Users, and View All for an object. See Required Permissions for Change Events Received by CometD Subscribers.