Page History

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• Changes to the Evictor interface :  addition of two new methods evictBefore and evictAfter, removal of the existing evict method
• Corresponding changes to CountEvicotCountEvictor, DeltaEvictor
• Renaming of the existing TimeEvictor as ProcessingTimeEvictor(since the current behavior of TimeEvictor does not consider the EventTime of the records) and addition of new class EventTimeEvictor.
• New overloaded method CountEvictor.of() that takes an additional parameter doEvictAfter, which decides whether to do eviction after the WindowFunction.
• Similar overloaded methods in DeltaEvictor, ProcessingTimeEvictor and EventTimeEvictor.

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public interface Evictor<T, W extends Window> extends Serializable {

   /**
    * Optionally evicts elements. Called before windowing function.
    * @param elements The elements currently in the pane.
    * @param size The current number of elements in the pane.
    * @param window The {@link Window}
    * @param evictorContext The context for the Evictor
     */
   void evictBefore(Iterable<StreamRecord<T>> elements, int size, W window, EvictorContext evictorContext);

   /**
    * Optionally evicts elements. Called after windowing function.
    * @param elements The elements currently in the pane.
    * @param size The current number of elements in the pane.
    * @param window The {@link Window}
    * @param evictorContext The context for the Evictor
    */
   void evictAfter(Iterable<StreamRecord<T>> elements, int size, W window, EvictorContext evictorContext);
 
  /**
   * A context object that is given to {@link Evictor} methods
   */
   interface EvictorContext {}
}

The Evictor has two methods, evictBefore  - called before the WindowFunction - and evictAfter - called after the WindowFunction. These methods receive an Iterable of all the elements in the pane and the number of elements in the pane. Evictor can choose to remove elements from the Iterable based on any condition that a user wishes to implement. The EvictorContext is an interface very similar to TriggerContext but for Evictors, I’m omitting it for brevity.

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