when yo use change data capture and platform events in salesfroce ?

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Change Data Capture vs Platform Events

Both are part of Salesforce's event-driven architecture. They use a publish/subscribe model on the Event Bus, so publishers and subscribers are decoupled.

Change Data Capture (CDC)

Use it when you need to react to changes in Salesforce records.

  • Salesforce publishes the event automatically when a record is created, updated, deleted, or undeleted. You don't write any publishing code.
  • The event carries the changed fields, plus header details like the change type and the user who made the change.
  • You enable it per object (Setup > Change Data Capture), and the channel name looks like /data/AccountChangeEvent.

Typical use cases:

  • Syncing Salesforce data to an external system such as an ERP, data warehouse, or SAP, in near real time.
  • Keeping a replica or cache up to date without polling.
  • Audit or history tracking outside Salesforce.
  • Triggering Apex when specific fields on a record change.

Platform Events

Use them when you need to send custom business messages, not tied to a record change.

  • You define the event schema (a custom object ending in __e) with your own fields.
  • You publish explicitly, through Apex, Flow, the API, or an external system.
  • Subscribers can be Apex triggers, Flows, LWC/Aura (via empApi), or external systems (via CometD or the Pub/Sub API).

Typical use cases:

  • Integration with external systems, for example telling a billing system that "Order approved, start invoicing".
  • Decoupling processes, for example CPQ quote approved → trigger order creation and fulfillment.
  • Inbound events from external systems (IoT, payment gateway) that need to trigger logic in Salesforce.
  • Fire-and-forget processing, or breaking out of transaction and governor limit constraints.
  • Notifying the UI in real time.

Key differences

CDCPlatform Events
TriggerAutomatic on record DMLExplicit publish
SchemaFixed, mirrors the object's fieldsCustom, you define it
PayloadChanged fields onlyWhatever you define
PurposeData replication and syncBusiness or process messaging
SetupEnable per objectCreate the event definition

How to say it in an interview

"I use CDC when the source of truth is a Salesforce record and an external system needs to stay in sync with its changes. Salesforce publishes the event automatically, so there's no custom code on the publisher side. I use Platform Events when I need to communicate a business event or custom payload that isn't just a record change, or when I need loose coupling between processes or systems. For example, in an Order-to-Cash flow, CDC on Account keeps the ERP customer master in sync, while a Platform Event like Order_Approved__e tells the billing system to generate an invoice."

Follow-up points they may ask

  • Replay: Both retain events for 72 hours. Subscribers can replay from a stored replay ID to recover missed events.
  • Limits: Event delivery is asynchronous, and there are daily event delivery and publishing allocations that depend on your edition.
  • Publish behavior: Platform Events can be "Publish Immediately" or "Publish After Commit". Use After Commit when the subscriber depends on the data being saved.
  • Transaction boundary: Event publishing isn't rolled back with DML if you use Publish Immediately.
  • CDC gotcha: Enabling CDC on an object doesn't include everything by default. Check which standard objects support it, and note that Enterprise Edition allows only a limited number of selected entities unless you have an add-on license.

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