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 java.util.Map;
021import java.util.concurrent.ThreadLocalRandom;
022import org.apache.hadoop.hbase.client.RegionInfo;
023import org.apache.yetus.audience.InterfaceAudience;
024
025/**
026 * Generates a candidate action to be applied to the cluster for cost function search
027 */
028@InterfaceAudience.Private
029abstract class CandidateGenerator {
030
031  abstract BalanceAction generate(BalancerClusterState cluster);
032
033  /**
034   * From a list of regions pick a random one. Null can be returned which
035   * {@link StochasticLoadBalancer#balanceCluster(Map)} recognize as signal to try a region move
036   * rather than swap.
037   * @param cluster        The state of the cluster
038   * @param server         index of the server
039   * @param chanceOfNoSwap Chance that this will decide to try a move rather than a swap.
040   * @return a random {@link RegionInfo} or null if an asymmetrical move is suggested.
041   */
042  int pickRandomRegion(BalancerClusterState cluster, int server, double chanceOfNoSwap) {
043    // Check to see if this is just a move.
044    if (
045      cluster.regionsPerServer[server].length == 0
046        || ThreadLocalRandom.current().nextFloat() < chanceOfNoSwap
047    ) {
048      // signal a move only.
049      return -1;
050    }
051    int rand = ThreadLocalRandom.current().nextInt(cluster.regionsPerServer[server].length);
052    return cluster.regionsPerServer[server][rand];
053  }
054
055  int pickRandomServer(BalancerClusterState cluster) {
056    if (cluster.numServers < 1) {
057      return -1;
058    }
059
060    return ThreadLocalRandom.current().nextInt(cluster.numServers);
061  }
062
063  int pickRandomRack(BalancerClusterState cluster) {
064    if (cluster.numRacks < 1) {
065      return -1;
066    }
067
068    return ThreadLocalRandom.current().nextInt(cluster.numRacks);
069  }
070
071  int pickOtherRandomServer(BalancerClusterState cluster, int serverIndex) {
072    if (cluster.numServers < 2) {
073      return -1;
074    }
075    while (true) {
076      int otherServerIndex = pickRandomServer(cluster);
077      if (otherServerIndex != serverIndex) {
078        return otherServerIndex;
079      }
080    }
081  }
082
083  int pickOtherRandomRack(BalancerClusterState cluster, int rackIndex) {
084    if (cluster.numRacks < 2) {
085      return -1;
086    }
087    while (true) {
088      int otherRackIndex = pickRandomRack(cluster);
089      if (otherRackIndex != rackIndex) {
090        return otherRackIndex;
091      }
092    }
093  }
094
095  BalanceAction pickRandomRegions(BalancerClusterState cluster, int thisServer, int otherServer) {
096    if (thisServer < 0 || otherServer < 0) {
097      return BalanceAction.NULL_ACTION;
098    }
099
100    // Decide who is most likely to need another region
101    int thisRegionCount = cluster.getNumRegions(thisServer);
102    int otherRegionCount = cluster.getNumRegions(otherServer);
103
104    // Assign the chance based upon the above
105    double thisChance = (thisRegionCount > otherRegionCount) ? 0 : 0.5;
106    double otherChance = (thisRegionCount <= otherRegionCount) ? 0 : 0.5;
107
108    int thisRegion = pickRandomRegion(cluster, thisServer, thisChance);
109    int otherRegion = pickRandomRegion(cluster, otherServer, otherChance);
110
111    return getAction(thisServer, thisRegion, otherServer, otherRegion);
112  }
113
114  protected BalanceAction getAction(int fromServer, int fromRegion, int toServer, int toRegion) {
115    if (fromServer < 0 || toServer < 0) {
116      return BalanceAction.NULL_ACTION;
117    }
118    if (fromRegion >= 0 && toRegion >= 0) {
119      return new SwapRegionsAction(fromServer, fromRegion, toServer, toRegion);
120    } else if (fromRegion >= 0) {
121      return new MoveRegionAction(fromRegion, fromServer, toServer);
122    } else if (toRegion >= 0) {
123      return new MoveRegionAction(toRegion, toServer, fromServer);
124    } else {
125      return BalanceAction.NULL_ACTION;
126    }
127  }
128}