helix-core/src/main/java/org/apache/helix/controller/rebalancer/StatefulRebalancer.java

package org.apache.helix.controller.rebalancer;

import java.util.Map;

import org.apache.helix.HelixRebalanceException;
import org.apache.helix.controller.dataproviders.BaseControllerDataProvider;
import org.apache.helix.controller.stages.CurrentStateOutput;
import org.apache.helix.model.IdealState;
import org.apache.helix.model.Resource;


/**
 * Allows one to come up with custom implementation of a stateful rebalancer.<br/>
 */
public interface StatefulRebalancer<T extends BaseControllerDataProvider> {

  /**
   * Reset the rebalancer to the initial state.
   */
  void reset();

  /**
   * Release all the resources and clean up all the rebalancer state.
   */
  void close();

  /**
   * Compute the new IdealStates for all the input resources. The IdealStates include both new
   * partition assignment (in the listFiles) and the new replica state mapping (in the mapFields).
   * @param clusterData The Cluster status data provider.
   * @param resourceMap A map containing all the rebalancing resources.
   * @param currentStateOutput The present Current States of the resources.
   * @return A map of the new IdealStates with the resource name as key.
   */
  Map<String, IdealState> computeNewIdealStates(T clusterData, Map<String, Resource> resourceMap,
      final CurrentStateOutput currentStateOutput) throws HelixRebalanceException;
}