A delta event reports that an entity changed by carrying its identifier and only the attributes modified by that change. For a profile update, it can publish a phone-number change rather than resend the complete profile. This reduces message size and bandwidth, but consumers must interpret and apply partial updates correctly. section 6.2.2 section 6.7
Choose delta events when the change itself is more useful than repeatedly transmitting complete state:
- Send the entity identifier together with the changed attribute or attributes, such as userId and newPhoneNumber. section 6.2.2
- Reduce payload size and bandwidth usage compared with fact events, which carry all entity attributes. section 6.7
- Accept greater consumer responsibility: consumers must understand partial changes and may need prior state or event history. section 6.7
- Govern the event with a version-controlled schema and compatibility rules so producers and consumers can evolve without misinterpretation. section 6.7
Phone number update
A UserPhoneNumberUpdated event identifies user 12345 and carries only the new phone number, rather than repeating the profile's name, email, addresses, and social accounts.
