The GemFire cluster within a PCC service instance can handle events. An app registers interest in a particular event, and when the server detects the event, an app-defined callback (also called a handler or a listener) is invoked to handle the event.
There are three aspects to configuring and implementing an event:
- the app defines or specifies the event
- the app registers the event with or identifies the event to the system component that will detect the event
- the app defines the callback, which handles the event
Continuous queries use a GemFire OQL query on region data to define an event. A change in query results is the event. The app registers both the query and the callback to set up a continuous query. Each region operation invokes the query, leading to the naming of this type of event handling as continuous.
See Querying with OQL for details on the Object Query Language (OQL) and generating queries.