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 */
018
019package org.apache.hadoop.hbase.master.balancer;
020
021import org.apache.hadoop.hbase.master.MasterServices;
022
023import org.apache.hbase.thirdparty.com.google.common.base.Optional;
024
025import org.apache.yetus.audience.InterfaceAudience;
026
027@InterfaceAudience.Private
028class LocalityBasedCandidateGenerator extends CandidateGenerator {
029
030  private MasterServices masterServices;
031
032  LocalityBasedCandidateGenerator(MasterServices masterServices) {
033    this.masterServices = masterServices;
034  }
035
036  @Override
037  BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
038    if (this.masterServices == null) {
039      int thisServer = pickRandomServer(cluster);
040      // Pick the other server
041      int otherServer = pickOtherRandomServer(cluster, thisServer);
042      return pickRandomRegions(cluster, thisServer, otherServer);
043    }
044
045    // Randomly iterate through regions until you find one that is not on ideal host
046    for (int region : getRandomIterationOrder(cluster.numRegions)) {
047      int currentServer = cluster.regionIndexToServerIndex[region];
048      if (currentServer != cluster.getOrComputeRegionsToMostLocalEntities(
049        BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]) {
050        Optional<BaseLoadBalancer.Cluster.Action> potential = tryMoveOrSwap(cluster,
051          currentServer, region,
052          cluster.getOrComputeRegionsToMostLocalEntities(
053            BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]
054        );
055        if (potential.isPresent()) {
056          return potential.get();
057        }
058      }
059    }
060    return BaseLoadBalancer.Cluster.NullAction;
061  }
062
063  private Optional<BaseLoadBalancer.Cluster.Action> tryMoveOrSwap(BaseLoadBalancer.Cluster cluster,
064      int fromServer, int fromRegion, int toServer) {
065    // Try move first. We know apriori fromRegion has the highest locality on toServer
066    if (cluster.serverHasTooFewRegions(toServer)) {
067      return Optional.of(getAction(fromServer, fromRegion, toServer, -1));
068    }
069    // Compare locality gain/loss from swapping fromRegion with regions on toServer
070    double fromRegionLocalityDelta = getWeightedLocality(cluster, fromRegion, toServer)
071      - getWeightedLocality(cluster, fromRegion, fromServer);
072    for (int toRegionIndex : getRandomIterationOrder(cluster.regionsPerServer[toServer].length)) {
073      int toRegion = cluster.regionsPerServer[toServer][toRegionIndex];
074      double toRegionLocalityDelta = getWeightedLocality(cluster, toRegion, fromServer)
075        - getWeightedLocality(cluster, toRegion, toServer);
076      // If locality would remain neutral or improve, attempt the swap
077      if (fromRegionLocalityDelta + toRegionLocalityDelta >= 0) {
078        return Optional.of(getAction(fromServer, fromRegion, toServer, toRegion));
079      }
080    }
081    return Optional.absent();
082  }
083
084  private double getWeightedLocality(BaseLoadBalancer.Cluster cluster, int region, int server) {
085    return cluster.getOrComputeWeightedLocality(region, server,
086      BaseLoadBalancer.Cluster.LocalityType.SERVER);
087  }
088
089  void setServices(MasterServices services) {
090    this.masterServices = services;
091  }
092
093}