6.10. Memory management for events

Explicit expiration: The decision engine removes events that are explicitly set to expire in rules that declare the @expires tag:

declare StockPoint
  @expires( 30m )
end

This example rule sets any StockPoint events to expire after 30 minutes and to be removed from the KIE session if no other rules use the events.

Inferred expiration: The decision engine can calculate the expiration offset for a given event implicitly by analyzing the temporal constraints in the rules:

rule "Correlate orders"
when
  $bo : BuyOrder($id : id)
  $ae : AckOrder(id == $id, this after[0,10s] $bo)
then
  // Perform an action.
end

For this example rule, the decision engine automatically calculates that whenever a BuyOrder event occurs, the decision engine needs to store the event for up to 10 seconds and wait for the matching AckOrder event. After 10 seconds, the decision engine infers the expiration and removes the event from the KIE session. An AckOrder event can only match an existing BuyOrder event, so the decision engine infers the expiration if no match occurs and removes the event immediately.

The decision engine analyzes the entire KIE base to find the offset for every event type and to ensure that no other rules use the events that are pending removal. Whenever an implicit expiration clashes with an explicit expiration value, the decision engine uses the greater time frame of the two to store the event longer.