001/*
002 * Licensed to the Apache Software Foundation (ASF) under one
003 * or more contributor license agreements.  See the NOTICE file
004 * distributed with this work for additional information
005 * regarding copyright ownership.  The ASF licenses this file
006 * to you under the Apache License, Version 2.0 (the
007 * "License"); you may not use this file except in compliance
008 * with the License.  You may obtain a copy of the License at
009 *
010 *     http://www.apache.org/licenses/LICENSE-2.0
011 *
012 * Unless required by applicable law or agreed to in writing, software
013 * distributed under the License is distributed on an "AS IS" BASIS,
014 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
015 * See the License for the specific language governing permissions and
016 * limitations under the License.
017 */
018package org.apache.hadoop.hbase.master.balancer;
019
020import org.apache.yetus.audience.InterfaceAudience;
021
022/**
023 * Base class of StochasticLoadBalancer's Cost Functions.
024 */
025@InterfaceAudience.Private
026abstract class CostFunction {
027
028  public static final double COST_EPSILON = 0.0001;
029
030  private float multiplier = 0;
031
032  protected BalancerClusterState cluster;
033
034  boolean isNeeded() {
035    return true;
036  }
037
038  float getMultiplier() {
039    return multiplier;
040  }
041
042  void setMultiplier(float m) {
043    this.multiplier = m;
044  }
045
046  /**
047   * Called once per LB invocation to give the cost function to initialize it's state, and perform
048   * any costly calculation.
049   */
050  void prepare(BalancerClusterState cluster) {
051    this.cluster = cluster;
052  }
053
054  /**
055   * Called once per cluster Action to give the cost function an opportunity to update it's state.
056   * postAction() is always called at least once before cost() is called with the cluster that this
057   * action is performed on.
058   */
059  void postAction(BalanceAction action) {
060    switch (action.getType()) {
061      case NULL:
062        break;
063      case ASSIGN_REGION:
064        AssignRegionAction ar = (AssignRegionAction) action;
065        regionMoved(ar.getRegion(), -1, ar.getServer());
066        break;
067      case MOVE_REGION:
068        MoveRegionAction mra = (MoveRegionAction) action;
069        regionMoved(mra.getRegion(), mra.getFromServer(), mra.getToServer());
070        break;
071      case SWAP_REGIONS:
072        SwapRegionsAction a = (SwapRegionsAction) action;
073        regionMoved(a.getFromRegion(), a.getFromServer(), a.getToServer());
074        regionMoved(a.getToRegion(), a.getToServer(), a.getFromServer());
075        break;
076      default:
077        throw new RuntimeException("Uknown action:" + action.getType());
078    }
079  }
080
081  protected void regionMoved(int region, int oldServer, int newServer) {
082  }
083
084  protected abstract double cost();
085
086  /**
087   * Scale the value between 0 and 1.
088   * @param min   Min value
089   * @param max   The Max value
090   * @param value The value to be scaled.
091   * @return The scaled value.
092   */
093  protected static double scale(double min, double max, double value) {
094    if (
095      max <= min || value <= min || Math.abs(max - min) <= COST_EPSILON
096        || Math.abs(value - min) <= COST_EPSILON
097    ) {
098      return 0;
099    }
100    if (max <= min || Math.abs(max - min) <= COST_EPSILON) {
101      return 0;
102    }
103
104    return Math.max(0d, Math.min(1d, (value - min) / (max - min)));
105  }
106
107  /**
108   * Add the cost of this cost function to the weight of the candidate generator that is optimized
109   * for this cost function. By default it is the RandomCandiateGenerator for a cost function.
110   * Called once per init or after postAction.
111   * @param weights the weights for every generator.
112   */
113  public void updateWeight(double[] weights) {
114    weights[StochasticLoadBalancer.GeneratorType.RANDOM.ordinal()] += cost();
115  }
116}