fe/src/main/java/org/apache/impala/catalog/events/ExternalEventsProcessor.java

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package org.apache.impala.catalog.events;

import org.apache.impala.catalog.CatalogException;
import org.apache.impala.thrift.TEventProcessorMetrics;
import org.apache.impala.thrift.TEventProcessorMetricsSummaryResponse;

/**
 * Interface to process external events
 */
public interface ExternalEventsProcessor {
  /**
   * Start the event processing. This could also be used to initialize the configuration
   * like polling interval of the event processor
   */
  void start();

  /**
   * Get the current event id on metastore. Useful for restarting the event processing
   * from a given event id
   */
  long getCurrentEventId() throws CatalogException;

  /**
   * Pauses the event processing. Use <code>start(fromEventId)</code> method below to
   * restart the event processing
   */
  void pause();

  /**
   * Starts the event processing from the given eventId. This method can be used to jump
   * ahead in the event processing under certain cases where it is okay skip certain
   * events
   */
  void start(long fromEventId);

  /**
   * Shutdown the events processor. Cannot be restarted again.
   */
  void shutdown();

  /**
   * Implements the core logic of processing external events
   */
  void processEvents();

  /**
   * Gets the event processor status and metrics. This method is used to show up the
   * metrics on the metrics UI page
   */
  TEventProcessorMetrics getEventProcessorMetrics();

  /**
   * Gets a detailed view of the event processor which can be used to populate the
   * content of a dedicated page for the event processor
   */
  TEventProcessorMetricsSummaryResponse getEventProcessorSummary();
}