Change Data Capture event is a notification that Salesforce sends when a change to a Salesforce record occurs as part of a create, update, delete, or undelete operation.

When we are saving a record in salesforce it causes the platform to start apex transaction . Change event triggers run asynchronously after the apex transaction is completed. Perform resource-intensive business logic asynchronously in the change event trigger and keep transaction-based logic in the Apex object trigger. By decoupling the processing of changes, change event triggers can help reduce transaction processing time.

How it works ?

First enable change data capture in your org.
1. steps : Setup -> Integrations -> Change Data Capture

2. Move object you want to enable Change Data Capture to Selected Entities.
(in developer org maximum 5 object can be selected)

Create Asynchronous Apex Triggers :
Steps : Developer Console -> File -> New -> Apex Trigger.
Naming convention to find change event object.
Standard Object : AccountChangeEvent [ObjectNameChangeEvent]
Custom Object : Data_Storage_Test__ChangeEvent [ObjectName__ChangeEvent]
Select the object and provide name for your Trigger.

trigger datastorageTriggerChangeEvent on Data_Storage_Test__ChangeEvent (after insert) {
    
    for(Data_Storage_Test__ChangeEvent rec : trigger.new){
        EventBus.ChangeEventHeader header = rec.ChangeEventHeader;
        if (header.changetype == 'CREATE') { 
            List<String> recordId = header.getRecordIds(); 
            //perform resource-intensive business logic here 
        }
        else if(header.changetype == 'UPDATE'){
            List<String> changedFields = header.changedfields; // list of fields updated
        }
        else if(header.changetype == 'DELETE'){
            
        }
        else if(header.changetype == 'UNDELETE'){
            
        }
    }
}

Debugging Asynchronous Apex Triggers :

Steps : Setup-> logs -> Debug Logs -> New.
Traced Entity Type : Automated Process
Debug Level : Default
Click Save.

you will be able to see debug logs generated from Asynchronous apex trigger.

Advantages:
Performance Comparison :

Performance in Duration(Approx) : O(N) where n = 1000000

we can clearly see reduced transaction processing time by using Asynchronous Apex triggers.