Where: This change applies to Lightning Experience and Salesforce Classic in Enterprise, Performance, Unlimited, and Developer editions.
How: Standard-volume events created in API version 44.0 and earlier continue to be supported, but you can’t define new standard-volume events. You can define a high-volume platform event from the user interface or through Metadata API.
From the UI, in Setup, enter Platform Events in the Quick Find box, then select Platform Events. When completing the standard fields, select High Volume for Event Type.
In Metadata API, the event definition is represented in the CustomObject type with eventType set to HighVolume.
Publish and subscribe to high-volume platform events in the same way that you publish and subscribe to standard-volume platform events. You can use declarative tools, such as Process Builder and flow, or write code with Apex and CometD API apps.
High-volume platform events are published asynchronously so that the system can process high loads of events efficiently. The publishing call places the publish request in a queue. The event message might not be published immediately after the call returns, but it is published when system resources are available.
Usage-Based Event Entitlements
Each Salesforce edition provides a default allocation for the number of high-volume events delivered to CometD clients. You can purchase an add-on license to increase your daily CometD event delivery allocation. With the add-on license, the CometD event delivery allocation depends on your monthly entitlement and scales with it. With the add-on, you can exceed the daily equivalent allocation of the monthly entitlement by a certain amount for a 24-hour period. Event overages are calculated for a calendar month, starting with the first day of the month or your contract start date.
Monitor your high-volume event delivery usage and entitlement with the limits REST API resource. The entitlement and usage information is returned in the MonthlyPlatformEvents response value.
The usage-based entitlements and daily allocation only apply to CometD subscribers. They don’t apply to other subscribers, such as Apex triggers, processes, or flows.