HBASE-25793 Move BaseLoadBalancer.Cluster to a separated file (#3185) (#3190)

Signed-off-by: Yulin Niu <niuyulin@apache.org>

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/AssignRegionAction.java

@@ -0,0 +1,54 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.balancer;
+
+import org.apache.hadoop.hbase.HConstants;
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+class AssignRegionAction extends BalanceAction {
+  private final int region;
+  private final int server;
+
+  public AssignRegionAction(int region, int server) {
+    super(Type.ASSIGN_REGION);
+    this.region = region;
+    this.server = server;
+  }
+
+  public int getRegion() {
+    return region;
+  }
+
+  public int getServer() {
+    return server;
+  }
+
+  @Override
+  public BalanceAction undoAction() {
+    // TODO implement this. This action is not being used by the StochasticLB for now
+    // in case it uses it, we should implement this function.
+    throw new UnsupportedOperationException(HConstants.NOT_IMPLEMENTED);
+  }
+
+  @Override
+  public String toString() {
+    return getType() + ": " + region + ":" + server;
+  }
+
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BalanceAction.java

@@ -0,0 +1,55 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.balancer;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+/**
+ * An action to move or swap a region
+ */
+@InterfaceAudience.Private
+abstract class BalanceAction {
+  enum Type {
+    ASSIGN_REGION, MOVE_REGION, SWAP_REGIONS, NULL,
+  }
+
+  static final BalanceAction NULL_ACTION = new BalanceAction(Type.NULL) {
+  };
+
+  private final Type type;
+
+  BalanceAction(Type type) {
+    this.type = type;
+  }
+
+  /**
+   * Returns an Action which would undo this action
+   */
+  BalanceAction undoAction() {
+    return this;
+  }
+
+  Type getType() {
+    return type;
+  }
+
+  @Override
+  public String toString() {
+    return type + ":";
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/BalancerClusterState.java

@@ -0,0 +1,865 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.balancer;
+
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.Collection;
+import java.util.Collections;
+import java.util.Comparator;
+import java.util.Deque;
+import java.util.HashMap;
+import java.util.List;
+import java.util.Map;
+import org.apache.hadoop.hbase.HDFSBlocksDistribution;
+import org.apache.hadoop.hbase.ServerName;
+import org.apache.hadoop.hbase.client.RegionInfo;
+import org.apache.hadoop.hbase.client.RegionReplicaUtil;
+import org.apache.hadoop.hbase.master.RackManager;
+import org.apache.hadoop.hbase.net.Address;
+import org.apache.yetus.audience.InterfaceAudience;
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * An efficient array based implementation similar to ClusterState for keeping the status of the
+ * cluster in terms of region assignment and distribution. LoadBalancers, such as
+ * StochasticLoadBalancer uses this Cluster object because of hundreds of thousands of hashmap
+ * manipulations are very costly, which is why this class uses mostly indexes and arrays.
+ * <p/>
+ * BalancerClusterState tracks a list of unassigned regions, region assignments, and the server
+ * topology in terms of server names, hostnames and racks.
+ */
+@InterfaceAudience.Private
+class BalancerClusterState {
+
+  private static final Logger LOG = LoggerFactory.getLogger(BalancerClusterState.class);
+
+  ServerName[] servers;
+  // ServerName uniquely identifies a region server. multiple RS can run on the same host
+  String[] hosts;
+  String[] racks;
+  boolean multiServersPerHost = false; // whether or not any host has more than one server
+
+  ArrayList<String> tables;
+  RegionInfo[] regions;
+  Deque<BalancerRegionLoad>[] regionLoads;
+  private RegionLocationFinder regionFinder;
+
+  int[][] regionLocations; // regionIndex -> list of serverIndex sorted by locality
+
+  int[] serverIndexToHostIndex; // serverIndex -> host index
+  int[] serverIndexToRackIndex; // serverIndex -> rack index
+
+  int[][] regionsPerServer; // serverIndex -> region list
+  int[] serverIndexToRegionsOffset; // serverIndex -> offset of region list
+  int[][] regionsPerHost; // hostIndex -> list of regions
+  int[][] regionsPerRack; // rackIndex -> region list
+  int[][] primariesOfRegionsPerServer; // serverIndex -> sorted list of regions by primary region
+                                       // index
+  int[][] primariesOfRegionsPerHost; // hostIndex -> sorted list of regions by primary region index
+  int[][] primariesOfRegionsPerRack; // rackIndex -> sorted list of regions by primary region index
+
+  int[][] serversPerHost; // hostIndex -> list of server indexes
+  int[][] serversPerRack; // rackIndex -> list of server indexes
+  int[] regionIndexToServerIndex; // regionIndex -> serverIndex
+  int[] initialRegionIndexToServerIndex; // regionIndex -> serverIndex (initial cluster state)
+  int[] regionIndexToTableIndex; // regionIndex -> tableIndex
+  int[][] numRegionsPerServerPerTable; // serverIndex -> tableIndex -> # regions
+  int[] numMaxRegionsPerTable; // tableIndex -> max number of regions in a single RS
+  int[] regionIndexToPrimaryIndex; // regionIndex -> regionIndex of the primary
+  boolean hasRegionReplicas = false; // whether there is regions with replicas
+
+  Integer[] serverIndicesSortedByRegionCount;
+  Integer[] serverIndicesSortedByLocality;
+
+  Map<Address, Integer> serversToIndex;
+  Map<String, Integer> hostsToIndex;
+  Map<String, Integer> racksToIndex;
+  Map<String, Integer> tablesToIndex;
+  Map<RegionInfo, Integer> regionsToIndex;
+  float[] localityPerServer;
+
+  int numServers;
+  int numHosts;
+  int numRacks;
+  int numTables;
+  int numRegions;
+
+  int numMovedRegions = 0; // num moved regions from the initial configuration
+  Map<ServerName, List<RegionInfo>> clusterState;
+
+  private final RackManager rackManager;
+  // Maps region -> rackIndex -> locality of region on rack
+  private float[][] rackLocalities;
+  // Maps localityType -> region -> [server|rack]Index with highest locality
+  private int[][] regionsToMostLocalEntities;
+
+  static class DefaultRackManager extends RackManager {
+    @Override
+    public String getRack(ServerName server) {
+      return UNKNOWN_RACK;
+    }
+  }
+
+  BalancerClusterState(Map<ServerName, List<RegionInfo>> clusterState,
+    Map<String, Deque<BalancerRegionLoad>> loads, RegionLocationFinder regionFinder,
+    RackManager rackManager) {
+    this(null, clusterState, loads, regionFinder, rackManager);
+  }
+
+  @SuppressWarnings("unchecked")
+  BalancerClusterState(Collection<RegionInfo> unassignedRegions,
+    Map<ServerName, List<RegionInfo>> clusterState, Map<String, Deque<BalancerRegionLoad>> loads,
+    RegionLocationFinder regionFinder, RackManager rackManager) {
+    if (unassignedRegions == null) {
+      unassignedRegions = Collections.emptyList();
+    }
+
+    serversToIndex = new HashMap<>();
+    hostsToIndex = new HashMap<>();
+    racksToIndex = new HashMap<>();
+    tablesToIndex = new HashMap<>();
+
+    // TODO: We should get the list of tables from master
+    tables = new ArrayList<>();
+    this.rackManager = rackManager != null ? rackManager : new DefaultRackManager();
+
+    numRegions = 0;
+
+    List<List<Integer>> serversPerHostList = new ArrayList<>();
+    List<List<Integer>> serversPerRackList = new ArrayList<>();
+    this.clusterState = clusterState;
+    this.regionFinder = regionFinder;
+
+    // Use servername and port as there can be dead servers in this list. We want everything with
+    // a matching hostname and port to have the same index.
+    for (ServerName sn : clusterState.keySet()) {
+      if (sn == null) {
+        LOG.warn("TODO: Enable TRACE on BaseLoadBalancer. Empty servername); " +
+          "skipping; unassigned regions?");
+        if (LOG.isTraceEnabled()) {
+          LOG.trace("EMPTY SERVERNAME " + clusterState.toString());
+        }
+        continue;
+      }
+      if (serversToIndex.get(sn.getAddress()) == null) {
+        serversToIndex.put(sn.getAddress(), numServers++);
+      }
+      if (!hostsToIndex.containsKey(sn.getHostname())) {
+        hostsToIndex.put(sn.getHostname(), numHosts++);
+        serversPerHostList.add(new ArrayList<>(1));
+      }
+
+      int serverIndex = serversToIndex.get(sn.getAddress());
+      int hostIndex = hostsToIndex.get(sn.getHostname());
+      serversPerHostList.get(hostIndex).add(serverIndex);
+
+      String rack = this.rackManager.getRack(sn);
+      if (!racksToIndex.containsKey(rack)) {
+        racksToIndex.put(rack, numRacks++);
+        serversPerRackList.add(new ArrayList<>());
+      }
+      int rackIndex = racksToIndex.get(rack);
+      serversPerRackList.get(rackIndex).add(serverIndex);
+    }
+
+    // Count how many regions there are.
+    for (Map.Entry<ServerName, List<RegionInfo>> entry : clusterState.entrySet()) {
+      numRegions += entry.getValue().size();
+    }
+    numRegions += unassignedRegions.size();
+
+    regionsToIndex = new HashMap<>(numRegions);
+    servers = new ServerName[numServers];
+    serversPerHost = new int[numHosts][];
+    serversPerRack = new int[numRacks][];
+    regions = new RegionInfo[numRegions];
+    regionIndexToServerIndex = new int[numRegions];
+    initialRegionIndexToServerIndex = new int[numRegions];
+    regionIndexToTableIndex = new int[numRegions];
+    regionIndexToPrimaryIndex = new int[numRegions];
+    regionLoads = new Deque[numRegions];
+
+    regionLocations = new int[numRegions][];
+    serverIndicesSortedByRegionCount = new Integer[numServers];
+    serverIndicesSortedByLocality = new Integer[numServers];
+    localityPerServer = new float[numServers];
+
+    serverIndexToHostIndex = new int[numServers];
+    serverIndexToRackIndex = new int[numServers];
+    regionsPerServer = new int[numServers][];
+    serverIndexToRegionsOffset = new int[numServers];
+    regionsPerHost = new int[numHosts][];
+    regionsPerRack = new int[numRacks][];
+    primariesOfRegionsPerServer = new int[numServers][];
+    primariesOfRegionsPerHost = new int[numHosts][];
+    primariesOfRegionsPerRack = new int[numRacks][];
+
+    int tableIndex = 0, regionIndex = 0, regionPerServerIndex = 0;
+
+    for (Map.Entry<ServerName, List<RegionInfo>> entry : clusterState.entrySet()) {
+      if (entry.getKey() == null) {
+        LOG.warn("SERVERNAME IS NULL, skipping " + entry.getValue());
+        continue;
+      }
+      int serverIndex = serversToIndex.get(entry.getKey().getAddress());
+
+      // keep the servername if this is the first server name for this hostname
+      // or this servername has the newest startcode.
+      if (servers[serverIndex] == null ||
+        servers[serverIndex].getStartcode() < entry.getKey().getStartcode()) {
+        servers[serverIndex] = entry.getKey();
+      }
+
+      if (regionsPerServer[serverIndex] != null) {
+        // there is another server with the same hostAndPort in ClusterState.
+        // allocate the array for the total size
+        regionsPerServer[serverIndex] =
+          new int[entry.getValue().size() + regionsPerServer[serverIndex].length];
+      } else {
+        regionsPerServer[serverIndex] = new int[entry.getValue().size()];
+      }
+      primariesOfRegionsPerServer[serverIndex] = new int[regionsPerServer[serverIndex].length];
+      serverIndicesSortedByRegionCount[serverIndex] = serverIndex;
+      serverIndicesSortedByLocality[serverIndex] = serverIndex;
+    }
+
+    hosts = new String[numHosts];
+    for (Map.Entry<String, Integer> entry : hostsToIndex.entrySet()) {
+      hosts[entry.getValue()] = entry.getKey();
+    }
+    racks = new String[numRacks];
+    for (Map.Entry<String, Integer> entry : racksToIndex.entrySet()) {
+      racks[entry.getValue()] = entry.getKey();
+    }
+
+    for (Map.Entry<ServerName, List<RegionInfo>> entry : clusterState.entrySet()) {
+      int serverIndex = serversToIndex.get(entry.getKey().getAddress());
+      regionPerServerIndex = serverIndexToRegionsOffset[serverIndex];
+
+      int hostIndex = hostsToIndex.get(entry.getKey().getHostname());
+      serverIndexToHostIndex[serverIndex] = hostIndex;
+
+      int rackIndex = racksToIndex.get(this.rackManager.getRack(entry.getKey()));
+      serverIndexToRackIndex[serverIndex] = rackIndex;
+
+      for (RegionInfo region : entry.getValue()) {
+        registerRegion(region, regionIndex, serverIndex, loads, regionFinder);
+        regionsPerServer[serverIndex][regionPerServerIndex++] = regionIndex;
+        regionIndex++;
+      }
+      serverIndexToRegionsOffset[serverIndex] = regionPerServerIndex;
+    }
+
+    for (RegionInfo region : unassignedRegions) {
+      registerRegion(region, regionIndex, -1, loads, regionFinder);
+      regionIndex++;
+    }
+
+    for (int i = 0; i < serversPerHostList.size(); i++) {
+      serversPerHost[i] = new int[serversPerHostList.get(i).size()];
+      for (int j = 0; j < serversPerHost[i].length; j++) {
+        serversPerHost[i][j] = serversPerHostList.get(i).get(j);
+      }
+      if (serversPerHost[i].length > 1) {
+        multiServersPerHost = true;
+      }
+    }
+
+    for (int i = 0; i < serversPerRackList.size(); i++) {
+      serversPerRack[i] = new int[serversPerRackList.get(i).size()];
+      for (int j = 0; j < serversPerRack[i].length; j++) {
+        serversPerRack[i][j] = serversPerRackList.get(i).get(j);
+      }
+    }
+
+    numTables = tables.size();
+    numRegionsPerServerPerTable = new int[numServers][numTables];
+
+    for (int i = 0; i < numServers; i++) {
+      for (int j = 0; j < numTables; j++) {
+        numRegionsPerServerPerTable[i][j] = 0;
+      }
+    }
+
+    for (int i = 0; i < regionIndexToServerIndex.length; i++) {
+      if (regionIndexToServerIndex[i] >= 0) {
+        numRegionsPerServerPerTable[regionIndexToServerIndex[i]][regionIndexToTableIndex[i]]++;
+      }
+    }
+
+    numMaxRegionsPerTable = new int[numTables];
+    for (int[] aNumRegionsPerServerPerTable : numRegionsPerServerPerTable) {
+      for (tableIndex = 0; tableIndex < aNumRegionsPerServerPerTable.length; tableIndex++) {
+        if (aNumRegionsPerServerPerTable[tableIndex] > numMaxRegionsPerTable[tableIndex]) {
+          numMaxRegionsPerTable[tableIndex] = aNumRegionsPerServerPerTable[tableIndex];
+        }
+      }
+    }
+
+    for (int i = 0; i < regions.length; i++) {
+      RegionInfo info = regions[i];
+      if (RegionReplicaUtil.isDefaultReplica(info)) {
+        regionIndexToPrimaryIndex[i] = i;
+      } else {
+        hasRegionReplicas = true;
+        RegionInfo primaryInfo = RegionReplicaUtil.getRegionInfoForDefaultReplica(info);
+        regionIndexToPrimaryIndex[i] = regionsToIndex.getOrDefault(primaryInfo, -1);
+      }
+    }
+
+    for (int i = 0; i < regionsPerServer.length; i++) {
+      primariesOfRegionsPerServer[i] = new int[regionsPerServer[i].length];
+      for (int j = 0; j < regionsPerServer[i].length; j++) {
+        int primaryIndex = regionIndexToPrimaryIndex[regionsPerServer[i][j]];
+        primariesOfRegionsPerServer[i][j] = primaryIndex;
+      }
+      // sort the regions by primaries.
+      Arrays.sort(primariesOfRegionsPerServer[i]);
+    }
+
+    // compute regionsPerHost
+    if (multiServersPerHost) {
+      for (int i = 0; i < serversPerHost.length; i++) {
+        int numRegionsPerHost = 0;
+        for (int j = 0; j < serversPerHost[i].length; j++) {
+          numRegionsPerHost += regionsPerServer[serversPerHost[i][j]].length;
+        }
+        regionsPerHost[i] = new int[numRegionsPerHost];
+        primariesOfRegionsPerHost[i] = new int[numRegionsPerHost];
+      }
+      for (int i = 0; i < serversPerHost.length; i++) {
+        int numRegionPerHostIndex = 0;
+        for (int j = 0; j < serversPerHost[i].length; j++) {
+          for (int k = 0; k < regionsPerServer[serversPerHost[i][j]].length; k++) {
+            int region = regionsPerServer[serversPerHost[i][j]][k];
+            regionsPerHost[i][numRegionPerHostIndex] = region;
+            int primaryIndex = regionIndexToPrimaryIndex[region];
+            primariesOfRegionsPerHost[i][numRegionPerHostIndex] = primaryIndex;
+            numRegionPerHostIndex++;
+          }
+        }
+        // sort the regions by primaries.
+        Arrays.sort(primariesOfRegionsPerHost[i]);
+      }
+    }
+
+    // compute regionsPerRack
+    if (numRacks > 1) {
+      for (int i = 0; i < serversPerRack.length; i++) {
+        int numRegionsPerRack = 0;
+        for (int j = 0; j < serversPerRack[i].length; j++) {
+          numRegionsPerRack += regionsPerServer[serversPerRack[i][j]].length;
+        }
+        regionsPerRack[i] = new int[numRegionsPerRack];
+        primariesOfRegionsPerRack[i] = new int[numRegionsPerRack];
+      }
+
+      for (int i = 0; i < serversPerRack.length; i++) {
+        int numRegionPerRackIndex = 0;
+        for (int j = 0; j < serversPerRack[i].length; j++) {
+          for (int k = 0; k < regionsPerServer[serversPerRack[i][j]].length; k++) {
+            int region = regionsPerServer[serversPerRack[i][j]][k];
+            regionsPerRack[i][numRegionPerRackIndex] = region;
+            int primaryIndex = regionIndexToPrimaryIndex[region];
+            primariesOfRegionsPerRack[i][numRegionPerRackIndex] = primaryIndex;
+            numRegionPerRackIndex++;
+          }
+        }
+        // sort the regions by primaries.
+        Arrays.sort(primariesOfRegionsPerRack[i]);
+      }
+    }
+  }
+
+  /** Helper for Cluster constructor to handle a region */
+  private void registerRegion(RegionInfo region, int regionIndex, int serverIndex,
+    Map<String, Deque<BalancerRegionLoad>> loads, RegionLocationFinder regionFinder) {
+    String tableName = region.getTable().getNameAsString();
+    if (!tablesToIndex.containsKey(tableName)) {
+      tables.add(tableName);
+      tablesToIndex.put(tableName, tablesToIndex.size());
+    }
+    int tableIndex = tablesToIndex.get(tableName);
+
+    regionsToIndex.put(region, regionIndex);
+    regions[regionIndex] = region;
+    regionIndexToServerIndex[regionIndex] = serverIndex;
+    initialRegionIndexToServerIndex[regionIndex] = serverIndex;
+    regionIndexToTableIndex[regionIndex] = tableIndex;
+
+    // region load
+    if (loads != null) {
+      Deque<BalancerRegionLoad> rl = loads.get(region.getRegionNameAsString());
+      // That could have failed if the RegionLoad is using the other regionName
+      if (rl == null) {
+        // Try getting the region load using encoded name.
+        rl = loads.get(region.getEncodedName());
+      }
+      regionLoads[regionIndex] = rl;
+    }
+
+    if (regionFinder != null) {
+      // region location
+      List<ServerName> loc = regionFinder.getTopBlockLocations(region);
+      regionLocations[regionIndex] = new int[loc.size()];
+      for (int i = 0; i < loc.size(); i++) {
+        regionLocations[regionIndex][i] = loc.get(i) == null ? -1 :
+          (serversToIndex.get(loc.get(i).getAddress()) == null ? -1 :
+            serversToIndex.get(loc.get(i).getAddress()));
+      }
+    }
+  }
+
+  /**
+   * Returns true iff a given server has less regions than the balanced amount
+   */
+  public boolean serverHasTooFewRegions(int server) {
+    int minLoad = this.numRegions / numServers;
+    int numRegions = getNumRegions(server);
+    return numRegions < minLoad;
+  }
+
+  /**
+   * Retrieves and lazily initializes a field storing the locality of every region/server
+   * combination
+   */
+  public float[][] getOrComputeRackLocalities() {
+    if (rackLocalities == null || regionsToMostLocalEntities == null) {
+      computeCachedLocalities();
+    }
+    return rackLocalities;
+  }
+
+  /**
+   * Lazily initializes and retrieves a mapping of region -> server for which region has the highest
+   * the locality
+   */
+  public int[] getOrComputeRegionsToMostLocalEntities(BalancerClusterState.LocalityType type) {
+    if (rackLocalities == null || regionsToMostLocalEntities == null) {
+      computeCachedLocalities();
+    }
+    return regionsToMostLocalEntities[type.ordinal()];
+  }
+
+  /**
+   * Looks up locality from cache of localities. Will create cache if it does not already exist.
+   */
+  public float getOrComputeLocality(int region, int entity,
+    BalancerClusterState.LocalityType type) {
+    switch (type) {
+      case SERVER:
+        return getLocalityOfRegion(region, entity);
+      case RACK:
+        return getOrComputeRackLocalities()[region][entity];
+      default:
+        throw new IllegalArgumentException("Unsupported LocalityType: " + type);
+    }
+  }
+
+  /**
+   * Returns locality weighted by region size in MB. Will create locality cache if it does not
+   * already exist.
+   */
+  public double getOrComputeWeightedLocality(int region, int server,
+    BalancerClusterState.LocalityType type) {
+    return getRegionSizeMB(region) * getOrComputeLocality(region, server, type);
+  }
+
+  /**
+   * Returns the size in MB from the most recent RegionLoad for region
+   */
+  public int getRegionSizeMB(int region) {
+    Deque<BalancerRegionLoad> load = regionLoads[region];
+    // This means regions have no actual data on disk
+    if (load == null) {
+      return 0;
+    }
+    return regionLoads[region].getLast().getStorefileSizeMB();
+  }
+
+  /**
+   * Computes and caches the locality for each region/rack combinations, as well as storing a
+   * mapping of region -> server and region -> rack such that server and rack have the highest
+   * locality for region
+   */
+  private void computeCachedLocalities() {
+    rackLocalities = new float[numRegions][numRacks];
+    regionsToMostLocalEntities = new int[LocalityType.values().length][numRegions];
+
+    // Compute localities and find most local server per region
+    for (int region = 0; region < numRegions; region++) {
+      int serverWithBestLocality = 0;
+      float bestLocalityForRegion = 0;
+      for (int server = 0; server < numServers; server++) {
+        // Aggregate per-rack locality
+        float locality = getLocalityOfRegion(region, server);
+        int rack = serverIndexToRackIndex[server];
+        int numServersInRack = serversPerRack[rack].length;
+        rackLocalities[region][rack] += locality / numServersInRack;
+
+        if (locality > bestLocalityForRegion) {
+          serverWithBestLocality = server;
+          bestLocalityForRegion = locality;
+        }
+      }
+      regionsToMostLocalEntities[LocalityType.SERVER.ordinal()][region] = serverWithBestLocality;
+
+      // Find most local rack per region
+      int rackWithBestLocality = 0;
+      float bestRackLocalityForRegion = 0.0f;
+      for (int rack = 0; rack < numRacks; rack++) {
+        float rackLocality = rackLocalities[region][rack];
+        if (rackLocality > bestRackLocalityForRegion) {
+          bestRackLocalityForRegion = rackLocality;
+          rackWithBestLocality = rack;
+        }
+      }
+      regionsToMostLocalEntities[LocalityType.RACK.ordinal()][region] = rackWithBestLocality;
+    }
+
+  }
+
+  /**
+   * Maps region index to rack index
+   */
+  public int getRackForRegion(int region) {
+    return serverIndexToRackIndex[regionIndexToServerIndex[region]];
+  }
+
+  enum LocalityType {
+    SERVER, RACK
+  }
+
+  public void doAction(BalanceAction action) {
+    switch (action.getType()) {
+      case NULL:
+        break;
+      case ASSIGN_REGION:
+        // FindBugs: Having the assert quietens FB BC_UNCONFIRMED_CAST warnings
+        assert action instanceof AssignRegionAction : action.getClass();
+        AssignRegionAction ar = (AssignRegionAction) action;
+        regionsPerServer[ar.getServer()] =
+          addRegion(regionsPerServer[ar.getServer()], ar.getRegion());
+        regionMoved(ar.getRegion(), -1, ar.getServer());
+        break;
+      case MOVE_REGION:
+        assert action instanceof MoveRegionAction : action.getClass();
+        MoveRegionAction mra = (MoveRegionAction) action;
+        regionsPerServer[mra.getFromServer()] =
+          removeRegion(regionsPerServer[mra.getFromServer()], mra.getRegion());
+        regionsPerServer[mra.getToServer()] =
+          addRegion(regionsPerServer[mra.getToServer()], mra.getRegion());
+        regionMoved(mra.getRegion(), mra.getFromServer(), mra.getToServer());
+        break;
+      case SWAP_REGIONS:
+        assert action instanceof SwapRegionsAction : action.getClass();
+        SwapRegionsAction a = (SwapRegionsAction) action;
+        regionsPerServer[a.getFromServer()] =
+          replaceRegion(regionsPerServer[a.getFromServer()], a.getFromRegion(), a.getToRegion());
+        regionsPerServer[a.getToServer()] =
+          replaceRegion(regionsPerServer[a.getToServer()], a.getToRegion(), a.getFromRegion());
+        regionMoved(a.getFromRegion(), a.getFromServer(), a.getToServer());
+        regionMoved(a.getToRegion(), a.getToServer(), a.getFromServer());
+        break;
+      default:
+        throw new RuntimeException("Uknown action:" + action.getType());
+    }
+  }
+
+  /**
+   * Return true if the placement of region on server would lower the availability of the region in
+   * question
+   * @return true or false
+   */
+  boolean wouldLowerAvailability(RegionInfo regionInfo, ServerName serverName) {
+    if (!serversToIndex.containsKey(serverName.getAddress())) {
+      return false; // safeguard against race between cluster.servers and servers from LB method
+                    // args
+    }
+    int server = serversToIndex.get(serverName.getAddress());
+    int region = regionsToIndex.get(regionInfo);
+
+    // Region replicas for same region should better assign to different servers
+    for (int i : regionsPerServer[server]) {
+      RegionInfo otherRegionInfo = regions[i];
+      if (RegionReplicaUtil.isReplicasForSameRegion(regionInfo, otherRegionInfo)) {
+        return true;
+      }
+    }
+
+    int primary = regionIndexToPrimaryIndex[region];
+    if (primary == -1) {
+      return false;
+    }
+    // there is a subset relation for server < host < rack
+    // check server first
+    if (contains(primariesOfRegionsPerServer[server], primary)) {
+      // check for whether there are other servers that we can place this region
+      for (int i = 0; i < primariesOfRegionsPerServer.length; i++) {
+        if (i != server && !contains(primariesOfRegionsPerServer[i], primary)) {
+          return true; // meaning there is a better server
+        }
+      }
+      return false; // there is not a better server to place this
+    }
+
+    // check host
+    if (multiServersPerHost) {
+      // these arrays would only be allocated if we have more than one server per host
+      int host = serverIndexToHostIndex[server];
+      if (contains(primariesOfRegionsPerHost[host], primary)) {
+        // check for whether there are other hosts that we can place this region
+        for (int i = 0; i < primariesOfRegionsPerHost.length; i++) {
+          if (i != host && !contains(primariesOfRegionsPerHost[i], primary)) {
+            return true; // meaning there is a better host
+          }
+        }
+        return false; // there is not a better host to place this
+      }
+    }
+
+    // check rack
+    if (numRacks > 1) {
+      int rack = serverIndexToRackIndex[server];
+      if (contains(primariesOfRegionsPerRack[rack], primary)) {
+        // check for whether there are other racks that we can place this region
+        for (int i = 0; i < primariesOfRegionsPerRack.length; i++) {
+          if (i != rack && !contains(primariesOfRegionsPerRack[i], primary)) {
+            return true; // meaning there is a better rack
+          }
+        }
+        return false; // there is not a better rack to place this
+      }
+    }
+
+    return false;
+  }
+
+  void doAssignRegion(RegionInfo regionInfo, ServerName serverName) {
+    if (!serversToIndex.containsKey(serverName.getAddress())) {
+      return;
+    }
+    int server = serversToIndex.get(serverName.getAddress());
+    int region = regionsToIndex.get(regionInfo);
+    doAction(new AssignRegionAction(region, server));
+  }
+
+  void regionMoved(int region, int oldServer, int newServer) {
+    regionIndexToServerIndex[region] = newServer;
+    if (initialRegionIndexToServerIndex[region] == newServer) {
+      numMovedRegions--; // region moved back to original location
+    } else if (oldServer >= 0 && initialRegionIndexToServerIndex[region] == oldServer) {
+      numMovedRegions++; // region moved from original location
+    }
+    int tableIndex = regionIndexToTableIndex[region];
+    if (oldServer >= 0) {
+      numRegionsPerServerPerTable[oldServer][tableIndex]--;
+    }
+    numRegionsPerServerPerTable[newServer][tableIndex]++;
+
+    // check whether this caused maxRegionsPerTable in the new Server to be updated
+    if (numRegionsPerServerPerTable[newServer][tableIndex] > numMaxRegionsPerTable[tableIndex]) {
+      numMaxRegionsPerTable[tableIndex] = numRegionsPerServerPerTable[newServer][tableIndex];
+    } else if (oldServer >= 0 && (numRegionsPerServerPerTable[oldServer][tableIndex]
+        + 1) == numMaxRegionsPerTable[tableIndex]) {
+      // recompute maxRegionsPerTable since the previous value was coming from the old server
+      numMaxRegionsPerTable[tableIndex] = 0;
+      for (int[] aNumRegionsPerServerPerTable : numRegionsPerServerPerTable) {
+        if (aNumRegionsPerServerPerTable[tableIndex] > numMaxRegionsPerTable[tableIndex]) {
+          numMaxRegionsPerTable[tableIndex] = aNumRegionsPerServerPerTable[tableIndex];
+        }
+      }
+    }
+
+    // update for servers
+    int primary = regionIndexToPrimaryIndex[region];
+    if (oldServer >= 0) {
+      primariesOfRegionsPerServer[oldServer] =
+        removeRegion(primariesOfRegionsPerServer[oldServer], primary);
+    }
+    primariesOfRegionsPerServer[newServer] =
+      addRegionSorted(primariesOfRegionsPerServer[newServer], primary);
+
+    // update for hosts
+    if (multiServersPerHost) {
+      int oldHost = oldServer >= 0 ? serverIndexToHostIndex[oldServer] : -1;
+      int newHost = serverIndexToHostIndex[newServer];
+      if (newHost != oldHost) {
+        regionsPerHost[newHost] = addRegion(regionsPerHost[newHost], region);
+        primariesOfRegionsPerHost[newHost] =
+          addRegionSorted(primariesOfRegionsPerHost[newHost], primary);
+        if (oldHost >= 0) {
+          regionsPerHost[oldHost] = removeRegion(regionsPerHost[oldHost], region);
+          primariesOfRegionsPerHost[oldHost] =
+            removeRegion(primariesOfRegionsPerHost[oldHost], primary); // will still be sorted
+        }
+      }
+    }
+
+    // update for racks
+    if (numRacks > 1) {
+      int oldRack = oldServer >= 0 ? serverIndexToRackIndex[oldServer] : -1;
+      int newRack = serverIndexToRackIndex[newServer];
+      if (newRack != oldRack) {
+        regionsPerRack[newRack] = addRegion(regionsPerRack[newRack], region);
+        primariesOfRegionsPerRack[newRack] =
+          addRegionSorted(primariesOfRegionsPerRack[newRack], primary);
+        if (oldRack >= 0) {
+          regionsPerRack[oldRack] = removeRegion(regionsPerRack[oldRack], region);
+          primariesOfRegionsPerRack[oldRack] =
+            removeRegion(primariesOfRegionsPerRack[oldRack], primary); // will still be sorted
+        }
+      }
+    }
+  }
+
+  int[] removeRegion(int[] regions, int regionIndex) {
+    // TODO: this maybe costly. Consider using linked lists
+    int[] newRegions = new int[regions.length - 1];
+    int i = 0;
+    for (i = 0; i < regions.length; i++) {
+      if (regions[i] == regionIndex) {
+        break;
+      }
+      newRegions[i] = regions[i];
+    }
+    System.arraycopy(regions, i + 1, newRegions, i, newRegions.length - i);
+    return newRegions;
+  }
+
+  int[] addRegion(int[] regions, int regionIndex) {
+    int[] newRegions = new int[regions.length + 1];
+    System.arraycopy(regions, 0, newRegions, 0, regions.length);
+    newRegions[newRegions.length - 1] = regionIndex;
+    return newRegions;
+  }
+
+  int[] addRegionSorted(int[] regions, int regionIndex) {
+    int[] newRegions = new int[regions.length + 1];
+    int i = 0;
+    for (i = 0; i < regions.length; i++) { // find the index to insert
+      if (regions[i] > regionIndex) {
+        break;
+      }
+    }
+    System.arraycopy(regions, 0, newRegions, 0, i); // copy first half
+    System.arraycopy(regions, i, newRegions, i + 1, regions.length - i); // copy second half
+    newRegions[i] = regionIndex;
+
+    return newRegions;
+  }
+
+  int[] replaceRegion(int[] regions, int regionIndex, int newRegionIndex) {
+    int i = 0;
+    for (i = 0; i < regions.length; i++) {
+      if (regions[i] == regionIndex) {
+        regions[i] = newRegionIndex;
+        break;
+      }
+    }
+    return regions;
+  }
+
+  void sortServersByRegionCount() {
+    Arrays.sort(serverIndicesSortedByRegionCount, numRegionsComparator);
+  }
+
+  int getNumRegions(int server) {
+    return regionsPerServer[server].length;
+  }
+
+  boolean contains(int[] arr, int val) {
+    return Arrays.binarySearch(arr, val) >= 0;
+  }
+
+  private Comparator<Integer> numRegionsComparator = Comparator.comparingInt(this::getNumRegions);
+
+  int getLowestLocalityRegionOnServer(int serverIndex) {
+    if (regionFinder != null) {
+      float lowestLocality = 1.0f;
+      int lowestLocalityRegionIndex = -1;
+      if (regionsPerServer[serverIndex].length == 0) {
+        // No regions on that region server
+        return -1;
+      }
+      for (int j = 0; j < regionsPerServer[serverIndex].length; j++) {
+        int regionIndex = regionsPerServer[serverIndex][j];
+        HDFSBlocksDistribution distribution =
+          regionFinder.getBlockDistribution(regions[regionIndex]);
+        float locality = distribution.getBlockLocalityIndex(servers[serverIndex].getHostname());
+        // skip empty region
+        if (distribution.getUniqueBlocksTotalWeight() == 0) {
+          continue;
+        }
+        if (locality < lowestLocality) {
+          lowestLocality = locality;
+          lowestLocalityRegionIndex = j;
+        }
+      }
+      if (lowestLocalityRegionIndex == -1) {
+        return -1;
+      }
+      if (LOG.isTraceEnabled()) {
+        LOG.trace("Lowest locality region is " +
+          regions[regionsPerServer[serverIndex][lowestLocalityRegionIndex]]
+            .getRegionNameAsString() +
+          " with locality " + lowestLocality + " and its region server contains " +
+          regionsPerServer[serverIndex].length + " regions");
+      }
+      return regionsPerServer[serverIndex][lowestLocalityRegionIndex];
+    } else {
+      return -1;
+    }
+  }
+
+  float getLocalityOfRegion(int region, int server) {
+    if (regionFinder != null) {
+      HDFSBlocksDistribution distribution = regionFinder.getBlockDistribution(regions[region]);
+      return distribution.getBlockLocalityIndex(servers[server].getHostname());
+    } else {
+      return 0f;
+    }
+  }
+
+  void setNumRegions(int numRegions) {
+    this.numRegions = numRegions;
+  }
+
+  void setNumMovedRegions(int numMovedRegions) {
+    this.numMovedRegions = numMovedRegions;
+  }
+
+  @Override
+  public String toString() {
+    StringBuilder desc = new StringBuilder("Cluster={servers=[");
+    for (ServerName sn : servers) {
+      desc.append(sn.getAddress().toString()).append(", ");
+    }
+    desc.append("], serverIndicesSortedByRegionCount=")
+      .append(Arrays.toString(serverIndicesSortedByRegionCount)).append(", regionsPerServer=")
+      .append(Arrays.deepToString(regionsPerServer));
+
+    desc.append(", numMaxRegionsPerTable=").append(Arrays.toString(numMaxRegionsPerTable))
+      .append(", numRegions=").append(numRegions).append(", numServers=").append(numServers)
+      .append(", numTables=").append(numTables).append(", numMovedRegions=").append(numMovedRegions)
+      .append('}');
+    return desc.toString();
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/CandidateGenerator.java

@@ -28,7 +28,7 @@ import org.apache.yetus.audience.InterfaceAudience;
 @InterfaceAudience.Private
 abstract class CandidateGenerator {
 
-  abstract BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster);
+  abstract BalanceAction generate(BalancerClusterState cluster);
 
   /**
    * From a list of regions pick a random one. Null can be returned which
@@ -42,7 +42,7 @@ abstract class CandidateGenerator {
    * @return a random {@link RegionInfo} or null if an asymmetrical move is
    *   suggested.
    */
-  int pickRandomRegion(BaseLoadBalancer.Cluster cluster, int server,
+  int pickRandomRegion(BalancerClusterState cluster, int server,
     double chanceOfNoSwap) {
     // Check to see if this is just a move.
     if (cluster.regionsPerServer[server].length == 0
@@ -54,7 +54,7 @@ abstract class CandidateGenerator {
     return cluster.regionsPerServer[server][rand];
   }
 
-  int pickRandomServer(BaseLoadBalancer.Cluster cluster) {
+  int pickRandomServer(BalancerClusterState cluster) {
     if (cluster.numServers < 1) {
       return -1;
     }
@@ -62,7 +62,7 @@ abstract class CandidateGenerator {
     return StochasticLoadBalancer.RANDOM.nextInt(cluster.numServers);
   }
 
-  int pickRandomRack(BaseLoadBalancer.Cluster cluster) {
+  int pickRandomRack(BalancerClusterState cluster) {
     if (cluster.numRacks < 1) {
       return -1;
     }
@@ -70,7 +70,7 @@ abstract class CandidateGenerator {
     return StochasticLoadBalancer.RANDOM.nextInt(cluster.numRacks);
   }
 
-  int pickOtherRandomServer(BaseLoadBalancer.Cluster cluster, int serverIndex) {
+  int pickOtherRandomServer(BalancerClusterState cluster, int serverIndex) {
     if (cluster.numServers < 2) {
       return -1;
     }
@@ -82,7 +82,7 @@ abstract class CandidateGenerator {
     }
   }
 
-  int pickOtherRandomRack(BaseLoadBalancer.Cluster cluster, int rackIndex) {
+  int pickOtherRandomRack(BalancerClusterState cluster, int rackIndex) {
     if (cluster.numRacks < 2) {
       return -1;
     }
@@ -94,10 +94,10 @@ abstract class CandidateGenerator {
     }
   }
 
-  BaseLoadBalancer.Cluster.Action pickRandomRegions(BaseLoadBalancer.Cluster cluster,
+  BalanceAction pickRandomRegions(BalancerClusterState cluster,
     int thisServer, int otherServer) {
     if (thisServer < 0 || otherServer < 0) {
-      return BaseLoadBalancer.Cluster.NullAction;
+      return BalanceAction.NULL_ACTION;
     }
 
     // Decide who is most likely to need another region
@@ -114,20 +114,20 @@ abstract class CandidateGenerator {
     return getAction(thisServer, thisRegion, otherServer, otherRegion);
   }
 
-  protected BaseLoadBalancer.Cluster.Action getAction(int fromServer, int fromRegion,
+  protected BalanceAction getAction(int fromServer, int fromRegion,
       int toServer, int toRegion) {
     if (fromServer < 0 || toServer < 0) {
-      return BaseLoadBalancer.Cluster.NullAction;
+      return BalanceAction.NULL_ACTION;
     }
     if (fromRegion >= 0 && toRegion >= 0) {
-      return new BaseLoadBalancer.Cluster.SwapRegionsAction(fromServer, fromRegion,
+      return new SwapRegionsAction(fromServer, fromRegion,
         toServer, toRegion);
     } else if (fromRegion >= 0) {
-      return new BaseLoadBalancer.Cluster.MoveRegionAction(fromRegion, fromServer, toServer);
+      return new MoveRegionAction(fromRegion, fromServer, toServer);
     } else if (toRegion >= 0) {
-      return new BaseLoadBalancer.Cluster.MoveRegionAction(toRegion, toServer, fromServer);
+      return new MoveRegionAction(toRegion, toServer, fromServer);
     } else {
-      return BaseLoadBalancer.Cluster.NullAction;
+      return BalanceAction.NULL_ACTION;
     }
   }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/FavoredStochasticBalancer.java

@@ -559,13 +559,13 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
   private class FavoredNodeLocalityPicker extends CandidateGenerator {
 
     @Override
-    protected Cluster.Action generate(Cluster cluster) {
+    protected BalanceAction generate(BalancerClusterState cluster) {
 
       int thisServer = pickRandomServer(cluster);
       int thisRegion;
       if (thisServer == -1) {
         LOG.trace("Could not pick lowest local region server");
-        return Cluster.NullAction;
+        return BalanceAction.NULL_ACTION;
       } else {
         // Pick lowest local region on this server
         thisRegion = pickLowestLocalRegionOnServer(cluster, thisServer);
@@ -575,7 +575,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
           LOG.trace("Could not pick lowest local region even when region server held "
             + cluster.regionsPerServer[thisServer].length + " regions");
         }
-        return Cluster.NullAction;
+        return BalanceAction.NULL_ACTION;
       }
 
       RegionInfo hri = cluster.regions[thisRegion];
@@ -587,7 +587,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
         } else {
           // No FN, ignore
           LOG.trace("Ignoring, no favored nodes for region: " + hri);
-          return Cluster.NullAction;
+          return BalanceAction.NULL_ACTION;
         }
       } else {
         // Pick other favored node with the highest locality
@@ -596,7 +596,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
       return getAction(thisServer, thisRegion, otherServer, -1);
     }
 
-    private int getDifferentFavoredNode(Cluster cluster, List<ServerName> favoredNodes,
+    private int getDifferentFavoredNode(BalancerClusterState cluster, List<ServerName> favoredNodes,
         int currentServer) {
       List<Integer> fnIndex = new ArrayList<>();
       for (ServerName sn : favoredNodes) {
@@ -618,7 +618,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
       return highestLocalRSIndex;
     }
 
-    private int pickLowestLocalRegionOnServer(Cluster cluster, int server) {
+    private int pickLowestLocalRegionOnServer(BalancerClusterState cluster, int server) {
       return cluster.getLowestLocalityRegionOnServer(server);
     }
   }
@@ -630,7 +630,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
   class FavoredNodeLoadPicker extends CandidateGenerator {
 
     @Override
-    Cluster.Action generate(Cluster cluster) {
+    BalanceAction generate(BalancerClusterState cluster) {
       cluster.sortServersByRegionCount();
       int thisServer = pickMostLoadedServer(cluster);
       int thisRegion = pickRandomRegion(cluster, thisServer, 0);
@@ -641,7 +641,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
         if (!FavoredNodesManager.isFavoredNodeApplicable(hri)) {
           otherServer = pickLeastLoadedServer(cluster, thisServer);
         } else {
-          return Cluster.NullAction;
+          return BalanceAction.NULL_ACTION;
         }
       } else {
         otherServer = pickLeastLoadedFNServer(cluster, favoredNodes, thisServer);
@@ -649,7 +649,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
       return getAction(thisServer, thisRegion, otherServer, -1);
     }
 
-    private int pickLeastLoadedServer(final Cluster cluster, int thisServer) {
+    private int pickLeastLoadedServer(final BalancerClusterState cluster, int thisServer) {
       Integer[] servers = cluster.serverIndicesSortedByRegionCount;
       int index;
       for (index = 0; index < servers.length ; index++) {
@@ -660,8 +660,8 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
       return servers[index];
     }
 
-    private int pickLeastLoadedFNServer(final Cluster cluster, List<ServerName> favoredNodes,
+    private int pickLeastLoadedFNServer(final BalancerClusterState cluster,
-        int currentServerIndex) {
+      List<ServerName> favoredNodes, int currentServerIndex) {
       List<Integer> fnIndex = new ArrayList<>();
       for (ServerName sn : favoredNodes) {
         if (cluster.serversToIndex.containsKey(sn.getAddress())) {
@@ -682,7 +682,7 @@ public class FavoredStochasticBalancer extends StochasticLoadBalancer implements
       return leastLoadedFN;
     }
 
-    private int pickMostLoadedServer(final Cluster cluster) {
+    private int pickMostLoadedServer(final BalancerClusterState cluster) {
       Integer[] servers = cluster.serverIndicesSortedByRegionCount;
       int index;
       for (index = servers.length - 1; index > 0 ; index--) {

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/HeterogeneousRegionCountCostFunction.java

@@ -120,7 +120,7 @@ public class HeterogeneousRegionCountCostFunction extends StochasticLoadBalancer
    * any costly calculation.
    */
   @Override
-  void init(final BaseLoadBalancer.Cluster cluster) {
+  void init(final BalancerClusterState cluster) {
     this.cluster = cluster;
     this.loadRules();
   }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/LoadCandidateGenerator.java

@@ -24,14 +24,14 @@ import org.apache.yetus.audience.InterfaceAudience;
 class LoadCandidateGenerator extends CandidateGenerator {
 
   @Override
-  BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
+  BalanceAction generate(BalancerClusterState cluster) {
     cluster.sortServersByRegionCount();
     int thisServer = pickMostLoadedServer(cluster, -1);
     int otherServer = pickLeastLoadedServer(cluster, thisServer);
     return pickRandomRegions(cluster, thisServer, otherServer);
   }
 
-  private int pickLeastLoadedServer(final BaseLoadBalancer.Cluster cluster, int thisServer) {
+  private int pickLeastLoadedServer(final BalancerClusterState cluster, int thisServer) {
     Integer[] servers = cluster.serverIndicesSortedByRegionCount;
 
     int index = 0;
@@ -44,7 +44,7 @@ class LoadCandidateGenerator extends CandidateGenerator {
     return servers[index];
   }
 
-  private int pickMostLoadedServer(final BaseLoadBalancer.Cluster cluster, int thisServer) {
+  private int pickMostLoadedServer(final BalancerClusterState cluster, int thisServer) {
     Integer[] servers = cluster.serverIndicesSortedByRegionCount;
 
     int index = servers.length - 1;

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/LocalityBasedCandidateGenerator.java

@@ -26,7 +26,7 @@ import org.apache.yetus.audience.InterfaceAudience;
 class LocalityBasedCandidateGenerator extends CandidateGenerator {
 
   @Override
-  BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
+  BalanceAction generate(BalancerClusterState cluster) {
     // iterate through regions until you find one that is not on ideal host
     // start from a random point to avoid always balance the regions in front
     if (cluster.numRegions > 0) {
@@ -35,20 +35,20 @@ class LocalityBasedCandidateGenerator extends CandidateGenerator {
         int region = (startIndex + i) % cluster.numRegions;
         int currentServer = cluster.regionIndexToServerIndex[region];
         if (currentServer != cluster.getOrComputeRegionsToMostLocalEntities(
-          BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]) {
+          BalancerClusterState.LocalityType.SERVER)[region]) {
-          Optional<BaseLoadBalancer.Cluster.Action> potential = tryMoveOrSwap(cluster,
+          Optional<BalanceAction> potential = tryMoveOrSwap(cluster,
             currentServer, region, cluster.getOrComputeRegionsToMostLocalEntities(
-              BaseLoadBalancer.Cluster.LocalityType.SERVER)[region]);
+              BalancerClusterState.LocalityType.SERVER)[region]);
           if (potential.isPresent()) {
             return potential.get();
           }
         }
       }
     }
-    return BaseLoadBalancer.Cluster.NullAction;
+    return BalanceAction.NULL_ACTION;
   }
 
-  private Optional<BaseLoadBalancer.Cluster.Action> tryMoveOrSwap(BaseLoadBalancer.Cluster cluster,
+  private Optional<BalanceAction> tryMoveOrSwap(BalancerClusterState cluster,
       int fromServer, int fromRegion, int toServer) {
     // Try move first. We know apriori fromRegion has the highest locality on toServer
     if (cluster.serverHasTooFewRegions(toServer)) {
@@ -74,8 +74,8 @@ class LocalityBasedCandidateGenerator extends CandidateGenerator {
     return Optional.empty();
   }
 
-  private double getWeightedLocality(BaseLoadBalancer.Cluster cluster, int region, int server) {
+  private double getWeightedLocality(BalancerClusterState cluster, int region, int server) {
     return cluster.getOrComputeWeightedLocality(region, server,
-      BaseLoadBalancer.Cluster.LocalityType.SERVER);
+      BalancerClusterState.LocalityType.SERVER);
   }
 }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/MoveRegionAction.java

@@ -0,0 +1,57 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+package org.apache.hadoop.hbase.master.balancer;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+class MoveRegionAction extends BalanceAction {
+  private final int region;
+  private final int fromServer;
+  private final int toServer;
+
+  public MoveRegionAction(int region, int fromServer, int toServer) {
+    super(Type.MOVE_REGION);
+    this.fromServer = fromServer;
+    this.region = region;
+    this.toServer = toServer;
+  }
+
+  public int getRegion() {
+    return region;
+  }
+
+  public int getFromServer() {
+    return fromServer;
+  }
+
+  public int getToServer() {
+    return toServer;
+  }
+
+  @Override
+  public BalanceAction undoAction() {
+    return new MoveRegionAction(region, toServer, fromServer);
+  }
+
+  @Override
+  public String toString() {
+    return getType() + ": " + region + ":" + fromServer + " -> " + toServer;
+  }
+}

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/RegionReplicaCandidateGenerator.java

@@ -83,10 +83,10 @@ class RegionReplicaCandidateGenerator extends CandidateGenerator {
   }
 
   @Override
-  BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
+  BalanceAction generate(BalancerClusterState cluster) {
     int serverIndex = pickRandomServer(cluster);
     if (cluster.numServers <= 1 || serverIndex == -1) {
-      return BaseLoadBalancer.Cluster.NullAction;
+      return BalanceAction.NULL_ACTION;
     }
 
     int regionIndex = selectCoHostedRegionPerGroup(

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/SimpleLoadBalancer.java

@@ -271,7 +271,8 @@ public class SimpleLoadBalancer extends BaseLoadBalancer {
 
     // construct a Cluster object with clusterMap and rest of the
     // argument as defaults
-    Cluster c = new Cluster(loadOfOneTable, null, this.regionFinder, this.rackManager);
+    BalancerClusterState c =
+      new BalancerClusterState(loadOfOneTable, null, this.regionFinder, this.rackManager);
     if (!this.needsBalance(tableName, c) && !this.overallNeedsBalance()) {
       return null;
     }

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java

@@ -39,12 +39,7 @@ import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.client.BalancerDecision;
 import org.apache.hadoop.hbase.client.RegionInfo;
 import org.apache.hadoop.hbase.master.RegionPlan;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.Action;
+import org.apache.hadoop.hbase.master.balancer.BalancerClusterState.LocalityType;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.Action.Type;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.AssignRegionAction;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.LocalityType;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.MoveRegionAction;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.SwapRegionsAction;
 import org.apache.hadoop.hbase.namequeues.BalancerDecisionDetails;
 import org.apache.hadoop.hbase.namequeues.NamedQueueRecorder;
 import org.apache.hadoop.hbase.regionserver.compactions.OffPeakHours;
@@ -307,7 +302,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   }
 
   @Override
-  protected synchronized boolean areSomeRegionReplicasColocated(Cluster c) {
+  protected synchronized boolean areSomeRegionReplicasColocated(BalancerClusterState c) {
     regionReplicaHostCostFunction.init(c);
     if (regionReplicaHostCostFunction.cost() > 0) {
       return true;
@@ -320,7 +315,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   }
 
   @Override
-  protected boolean needsBalance(TableName tableName, Cluster cluster) {
+  protected boolean needsBalance(TableName tableName, BalancerClusterState cluster) {
     ClusterLoadState cs = new ClusterLoadState(cluster.clusterState);
     if (cs.getNumServers() < MIN_SERVER_BALANCE) {
       if (LOG.isDebugEnabled()) {
@@ -367,8 +362,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     return !balanced;
   }
 
-  @InterfaceAudience.Private
+  BalanceAction nextAction(BalancerClusterState cluster) {
-  Cluster.Action nextAction(Cluster cluster) {
     return candidateGenerators.get(RANDOM.nextInt(candidateGenerators.size()))
             .generate(cluster);
   }
@@ -406,7 +400,8 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     //The clusterState that is given to this method contains the state
     //of all the regions in the table(s) (that's true today)
     // Keep track of servers to iterate through them.
-    Cluster cluster = new Cluster(loadOfOneTable, loads, finder, rackManager);
+    BalancerClusterState cluster =
+      new BalancerClusterState(loadOfOneTable, loads, finder, rackManager);
 
     long startTime = EnvironmentEdgeManager.currentTime();
 
@@ -446,9 +441,9 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     long step;
 
     for (step = 0; step < computedMaxSteps; step++) {
-      Cluster.Action action = nextAction(cluster);
+      BalanceAction action = nextAction(cluster);
 
-      if (action.type == Type.NULL) {
+      if (action.getType() == BalanceAction.Type.NULL) {
         continue;
       }
 
@@ -467,7 +462,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
       } else {
         // Put things back the way they were before.
         // TODO: undo by remembering old values
-        Action undoAction = action.undoAction();
+        BalanceAction undoAction = action.undoAction();
         cluster.doAction(undoAction);
         updateCostsWithAction(cluster, undoAction);
       }
@@ -588,7 +583,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
    * @param cluster The state of the cluster
    * @return List of RegionPlan's that represent the moves needed to get to desired final state.
    */
-  private List<RegionPlan> createRegionPlans(Cluster cluster) {
+  private List<RegionPlan> createRegionPlans(BalancerClusterState cluster) {
     List<RegionPlan> plans = new LinkedList<>();
     for (int regionIndex = 0;
          regionIndex < cluster.regionIndexToServerIndex.length; regionIndex++) {
@@ -639,13 +634,13 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     }
   }
 
-  protected void initCosts(Cluster cluster) {
+  protected void initCosts(BalancerClusterState cluster) {
     for (CostFunction c:costFunctions) {
       c.init(cluster);
     }
   }
 
-  protected void updateCostsWithAction(Cluster cluster, Action action) {
+  protected void updateCostsWithAction(BalancerClusterState cluster, BalanceAction action) {
     for (CostFunction c : costFunctions) {
       c.postAction(action);
     }
@@ -674,7 +669,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
    * @return a double of a cost associated with the proposed cluster state.  This cost is an
    *         aggregate of all individual cost functions.
    */
-  protected double computeCost(Cluster cluster, double previousCost) {
+  protected double computeCost(BalancerClusterState cluster, double previousCost) {
     double total = 0;
 
     for (int i = 0; i < costFunctions.size(); i++) {
@@ -702,7 +697,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   static class RandomCandidateGenerator extends CandidateGenerator {
 
     @Override
-    Cluster.Action generate(Cluster cluster) {
+    BalanceAction generate(BalancerClusterState cluster) {
 
       int thisServer = pickRandomServer(cluster);
 
@@ -719,7 +714,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
    */
   static class RegionReplicaRackCandidateGenerator extends RegionReplicaCandidateGenerator {
     @Override
-    Cluster.Action generate(Cluster cluster) {
+    BalanceAction generate(BalancerClusterState cluster) {
       int rackIndex = pickRandomRack(cluster);
       if (cluster.numRacks <= 1 || rackIndex == -1) {
         return super.generate(cluster);
@@ -753,7 +748,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
 
     private float multiplier = 0;
 
-    protected Cluster cluster;
+    protected BalancerClusterState cluster;
 
     public CostFunction(Configuration c) {
     }
@@ -772,7 +767,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     /** Called once per LB invocation to give the cost function
      * to initialize it's state, and perform any costly calculation.
      */
-    void init(Cluster cluster) {
+    void init(BalancerClusterState cluster) {
       this.cluster = cluster;
     }
 
@@ -780,24 +775,25 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
      * an opportunity to update it's state. postAction() is always
      * called at least once before cost() is called with the cluster
      * that this action is performed on. */
-    void postAction(Action action) {
+    void postAction(BalanceAction action) {
-      switch (action.type) {
+      switch (action.getType()) {
-      case NULL: break;
+        case NULL:
-      case ASSIGN_REGION:
+          break;
-        AssignRegionAction ar = (AssignRegionAction) action;
+        case ASSIGN_REGION:
-        regionMoved(ar.region, -1, ar.server);
+          AssignRegionAction ar = (AssignRegionAction) action;
-        break;
+          regionMoved(ar.getRegion(), -1, ar.getServer());
-      case MOVE_REGION:
+          break;
-        MoveRegionAction mra = (MoveRegionAction) action;
+        case MOVE_REGION:
-        regionMoved(mra.region, mra.fromServer, mra.toServer);
+          MoveRegionAction mra = (MoveRegionAction) action;
-        break;
+          regionMoved(mra.getRegion(), mra.getFromServer(), mra.getToServer());
-      case SWAP_REGIONS:
+          break;
-        SwapRegionsAction a = (SwapRegionsAction) action;
+        case SWAP_REGIONS:
-        regionMoved(a.fromRegion, a.fromServer, a.toServer);
+          SwapRegionsAction a = (SwapRegionsAction) action;
-        regionMoved(a.toRegion, a.toServer, a.fromServer);
+          regionMoved(a.getFromRegion(), a.getFromServer(), a.getToServer());
-        break;
+          regionMoved(a.getToRegion(), a.getToServer(), a.getFromServer());
-      default:
+          break;
-        throw new RuntimeException("Uknown action:" + action.type);
+        default:
+          throw new RuntimeException("Uknown action:" + action.getType());
       }
     }
 
@@ -948,7 +944,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     }
 
     @Override
-    void init(Cluster cluster) {
+    void init(BalancerClusterState cluster) {
       super.init(cluster);
       LOG.debug("{} sees a total of {} servers and {} regions.", getClass().getSimpleName(),
           cluster.numServers, cluster.numRegions);
@@ -1072,7 +1068,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     abstract int regionIndexToEntityIndex(int region);
 
     @Override
-    void init(Cluster cluster) {
+    void init(BalancerClusterState cluster) {
       super.init(cluster);
       locality = 0.0;
       bestLocality = 0.0;
@@ -1300,7 +1296,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     }
 
     @Override
-    void init(Cluster cluster) {
+    void init(BalancerClusterState cluster) {
       super.init(cluster);
       // max cost is the case where every region replica is hosted together regardless of host
       maxCost = cluster.numHosts > 1 ? getMaxCost(cluster) : 0;
@@ -1313,7 +1309,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
       }
     }
 
-    long getMaxCost(Cluster cluster) {
+    long getMaxCost(BalancerClusterState cluster) {
       if (!cluster.hasRegionReplicas) {
         return 0; // short circuit
       }
@@ -1412,7 +1408,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     }
 
     @Override
-    void init(Cluster cluster) {
+    void init(BalancerClusterState cluster) {
       this.cluster = cluster;
       if (cluster.numRacks <= 1) {
         maxCost = 0;

hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/SwapRegionsAction.java

@@ -0,0 +1,62 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.apache.hadoop.hbase.master.balancer;
+
+import org.apache.yetus.audience.InterfaceAudience;
+
+@InterfaceAudience.Private
+public class SwapRegionsAction extends BalanceAction {
+  private final int fromServer;
+  private final int fromRegion;
+  private final int toServer;
+  private final int toRegion;
+
+  SwapRegionsAction(int fromServer, int fromRegion, int toServer, int toRegion) {
+    super(Type.SWAP_REGIONS);
+    this.fromServer = fromServer;
+    this.fromRegion = fromRegion;
+    this.toServer = toServer;
+    this.toRegion = toRegion;
+  }
+
+  public int getFromServer() {
+    return fromServer;
+  }
+
+  public int getFromRegion() {
+    return fromRegion;
+  }
+
+  public int getToServer() {
+    return toServer;
+  }
+
+  public int getToRegion() {
+    return toRegion;
+  }
+
+  @Override
+  public BalanceAction undoAction() {
+    return new SwapRegionsAction(fromServer, toRegion, toServer, fromRegion);
+  }
+
+  @Override
+  public String toString() {
+    return getType() + ": " + fromRegion + ":" + fromServer + " <-> " + toRegion + ":" + toServer;
+  }
+}

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/BalancerTestBase.java

@@ -376,8 +376,8 @@ public class BalancerTestBase {
     return mockClusterServers(mockCluster, -1);
   }
 
-  protected BaseLoadBalancer.Cluster mockCluster(int[] mockCluster) {
+  protected BalancerClusterState mockCluster(int[] mockCluster) {
-    return new BaseLoadBalancer.Cluster(
+    return new BalancerClusterState(
       mockClusterServers(mockCluster, -1), null, null, null);
   }
 

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestBaseLoadBalancer.java

@@ -47,8 +47,6 @@ import org.apache.hadoop.hbase.master.MasterServices;
 import org.apache.hadoop.hbase.master.RackManager;
 import org.apache.hadoop.hbase.master.RegionPlan;
 import org.apache.hadoop.hbase.master.ServerManager;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster.MoveRegionAction;
 import org.apache.hadoop.hbase.testclassification.MasterTests;
 import org.apache.hadoop.hbase.testclassification.MediumTests;
 import org.apache.hadoop.net.DNSToSwitchMapping;
@@ -309,7 +307,7 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     // cluster is created (constructor code) would make sure the indices of
     // the servers are in the order in which it is inserted in the clusterState
     // map (linkedhashmap is important). A similar thing applies to the region lists
-    Cluster cluster = new Cluster(clusterState, null, null, rackManager);
+    BalancerClusterState cluster = new BalancerClusterState(clusterState, null, null, rackManager);
     // check whether a move of region1 from servers[0] to servers[1] would lower
     // the availability of region1
     assertTrue(cluster.wouldLowerAvailability(hri1, servers[1]));
@@ -326,7 +324,7 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     // now lets have servers[1] host replica_of_region2
     list1.add(RegionReplicaUtil.getRegionInfoForReplica(hri3, 1));
     // create a new clusterState with the above change
-    cluster = new Cluster(clusterState, null, null, rackManager);
+    cluster = new BalancerClusterState(clusterState, null, null, rackManager);
     // now check whether a move of a replica from servers[0] to servers[1] would lower
     // the availability of region2
     assertTrue(cluster.wouldLowerAvailability(hri3, servers[1]));
@@ -338,14 +336,14 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     clusterState.put(servers[6], list2); //servers[6], rack2 hosts region2
     clusterState.put(servers[10], new ArrayList<>()); //servers[10], rack3 hosts no region
     // create a cluster with the above clusterState
-    cluster = new Cluster(clusterState, null, null, rackManager);
+    cluster = new BalancerClusterState(clusterState, null, null, rackManager);
     // check whether a move of region1 from servers[0],rack1 to servers[6],rack2 would
     // lower the availability
 
     assertTrue(cluster.wouldLowerAvailability(hri1, servers[0]));
 
     // now create a cluster without the rack manager
-    cluster = new Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     // now repeat check whether a move of region1 from servers[0] to servers[6] would
     // lower the availability
     assertTrue(!cluster.wouldLowerAvailability(hri1, servers[6]));
@@ -383,7 +381,7 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     // cluster is created (constructor code) would make sure the indices of
     // the servers are in the order in which it is inserted in the clusterState
     // map (linkedhashmap is important).
-    Cluster cluster = new Cluster(clusterState, null, null, rackManager);
+    BalancerClusterState cluster = new BalancerClusterState(clusterState, null, null, rackManager);
     // check whether moving region1 from servers[1] to servers[2] would lower availability
     assertTrue(!cluster.wouldLowerAvailability(hri1, servers[2]));
 
@@ -405,7 +403,7 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     clusterState.put(servers[6], list2); //servers[6], rack2 hosts region2
     clusterState.put(servers[12], list3); //servers[12], rack3 hosts replica_of_region2
     // create a cluster with the above clusterState
-    cluster = new Cluster(clusterState, null, null, rackManager);
+    cluster = new BalancerClusterState(clusterState, null, null, rackManager);
     // check whether a move of replica_of_region2 from servers[12],rack3 to servers[0],rack1 would
     // lower the availability
     assertTrue(!cluster.wouldLowerAvailability(hri4, servers[0]));
@@ -487,7 +485,7 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
     assignRegions(regions, oldServers, clusterState);
 
     // should not throw exception:
-    BaseLoadBalancer.Cluster cluster = new Cluster(clusterState, null, null, null);
+    BalancerClusterState cluster = new BalancerClusterState(clusterState, null, null, null);
     assertEquals(101 + 9, cluster.numRegions);
     assertEquals(10, cluster.numServers); // only 10 servers because they share the same host + port
 
@@ -533,12 +531,15 @@ public class TestBaseLoadBalancer extends BalancerTestBase {
         Lists.newArrayList(servers.get(0), servers.get(1)));
     when(locationFinder.getTopBlockLocations(regions.get(42))).thenReturn(
         Lists.newArrayList(servers.get(4), servers.get(9), servers.get(5)));
-    when(locationFinder.getTopBlockLocations(regions.get(43))).thenReturn(
+    // this server does not exists in clusterStatus
-        Lists.newArrayList(ServerName.valueOf("foo", 0, 0))); // this server does not exists in clusterStatus
+    when(locationFinder.getTopBlockLocations(regions.get(43)))
+      .thenReturn(Lists.newArrayList(ServerName.valueOf("foo", 0, 0)));
 
-    BaseLoadBalancer.Cluster cluster = new Cluster(clusterState, null, locationFinder, null);
+    BalancerClusterState cluster =
+      new BalancerClusterState(clusterState, null, locationFinder, null);
 
-    int r0 = ArrayUtils.indexOf(cluster.regions, regions.get(0)); // this is ok, it is just a test
+    // this is ok, it is just a test
+    int r0 = ArrayUtils.indexOf(cluster.regions, regions.get(0));
     int r1 = ArrayUtils.indexOf(cluster.regions, regions.get(1));
     int r10 = ArrayUtils.indexOf(cluster.regions, regions.get(10));
     int r42 = ArrayUtils.indexOf(cluster.regions, regions.get(42));

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestFavoredStochasticBalancerPickers.java

@@ -48,7 +48,6 @@ import org.apache.hadoop.hbase.master.HMaster;
 import org.apache.hadoop.hbase.master.LoadBalancer;
 import org.apache.hadoop.hbase.master.RackManager;
 import org.apache.hadoop.hbase.master.assignment.RegionStates;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster;
 import org.apache.hadoop.hbase.regionserver.HRegion;
 import org.apache.hadoop.hbase.regionserver.HRegionServer;
 import org.apache.hadoop.hbase.regionserver.Region;
@@ -184,9 +183,10 @@ public class TestFavoredStochasticBalancerPickers extends BalancerTestBase {
     regionFinder.setClusterMetrics(admin.getClusterMetrics(EnumSet.of(Option.LIVE_SERVERS)));
     regionFinder.setConf(conf);
     regionFinder.setServices(TEST_UTIL.getMiniHBaseCluster().getMaster());
-    Cluster cluster = new Cluster(serverAssignments, null, regionFinder, new RackManager(conf));
+    BalancerClusterState cluster =
+      new BalancerClusterState(serverAssignments, null, regionFinder, new RackManager(conf));
     LoadOnlyFavoredStochasticBalancer balancer = (LoadOnlyFavoredStochasticBalancer) TEST_UTIL
-        .getMiniHBaseCluster().getMaster().getLoadBalancer();
+      .getMiniHBaseCluster().getMaster().getLoadBalancer();
 
     cluster.sortServersByRegionCount();
     Integer[] servers = cluster.serverIndicesSortedByRegionCount;
@@ -203,13 +203,13 @@ public class TestFavoredStochasticBalancerPickers extends BalancerTestBase {
       if (userRegionPicked) {
         break;
       } else {
-        Cluster.Action action = loadPicker.generate(cluster);
+        BalanceAction action = loadPicker.generate(cluster);
-        if (action.type == Cluster.Action.Type.MOVE_REGION) {
+        if (action.getType() == BalanceAction.Type.MOVE_REGION) {
-          Cluster.MoveRegionAction moveRegionAction = (Cluster.MoveRegionAction) action;
+          MoveRegionAction moveRegionAction = (MoveRegionAction) action;
-          RegionInfo region = cluster.regions[moveRegionAction.region];
+          RegionInfo region = cluster.regions[moveRegionAction.getRegion()];
-          assertNotEquals(-1, moveRegionAction.toServer);
+          assertNotEquals(-1, moveRegionAction.getToServer());
-          ServerName destinationServer = cluster.servers[moveRegionAction.toServer];
+          ServerName destinationServer = cluster.servers[moveRegionAction.getToServer()];
-          assertEquals(cluster.servers[moveRegionAction.fromServer], mostLoadedServer);
+          assertEquals(cluster.servers[moveRegionAction.getFromServer()], mostLoadedServer);
           if (!region.getTable().isSystemTable()) {
             List<ServerName> favNodes = fnm.getFavoredNodes(region);
             assertTrue(favNodes.contains(

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java

@@ -44,7 +44,6 @@ import org.apache.hadoop.hbase.TableName;
 import org.apache.hadoop.hbase.client.RegionInfo;
 import org.apache.hadoop.hbase.master.MockNoopMasterServices;
 import org.apache.hadoop.hbase.master.RegionPlan;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster;
 import org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer.ServerLocalityCostFunction;
 import org.apache.hadoop.hbase.testclassification.MasterTests;
 import org.apache.hadoop.hbase.testclassification.MediumTests;
@@ -214,7 +213,7 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
     Configuration conf = HBaseConfiguration.create();
     StochasticLoadBalancer.CostFunction
       costFunction = new StochasticLoadBalancer.MoveCostFunction(conf);
-    BaseLoadBalancer.Cluster cluster = mockCluster(clusterStateMocks[0]);
+    BalancerClusterState cluster = mockCluster(clusterStateMocks[0]);
     costFunction.init(cluster);
     costFunction.cost();
     assertEquals(StochasticLoadBalancer.MoveCostFunction.DEFAULT_MOVE_COST,
@@ -241,7 +240,7 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
     StochasticLoadBalancer.CostFunction
         costFunction = new StochasticLoadBalancer.MoveCostFunction(conf);
     for (int[] mockCluster : clusterStateMocks) {
-      BaseLoadBalancer.Cluster cluster = mockCluster(mockCluster);
+      BalancerClusterState cluster = mockCluster(mockCluster);
       costFunction.init(cluster);
       double cost = costFunction.cost();
       assertEquals(0.0f, cost, 0.001);
@@ -304,14 +303,14 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
     final int runs = 10;
     loadBalancer.setConf(conf);
     for (int[] mockCluster : clusterStateMocks) {
-      BaseLoadBalancer.Cluster cluster = mockCluster(mockCluster);
+      BalancerClusterState cluster = mockCluster(mockCluster);
       loadBalancer.initCosts(cluster);
       for (int i = 0; i != runs; ++i) {
         final double expectedCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
-        Cluster.Action action = loadBalancer.nextAction(cluster);
+        BalanceAction action = loadBalancer.nextAction(cluster);
         cluster.doAction(action);
         loadBalancer.updateCostsWithAction(cluster, action);
-        Cluster.Action undoAction = action.undoAction();
+        BalanceAction undoAction = action.undoAction();
         cluster.doAction(undoAction);
         loadBalancer.updateCostsWithAction(cluster, undoAction);
         final double actualCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
@@ -326,7 +325,7 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
     StochasticLoadBalancer.CostFunction
         costFunction = new StochasticLoadBalancer.TableSkewCostFunction(conf);
     for (int[] mockCluster : clusterStateMocks) {
-      BaseLoadBalancer.Cluster cluster = mockCluster(mockCluster);
+      BalancerClusterState cluster = mockCluster(mockCluster);
       costFunction.init(cluster);
       double cost = costFunction.cost();
       assertTrue(cost >= 0);
@@ -459,7 +458,7 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
   }
 
   // This mock allows us to test the LocalityCostFunction
-  private class MockCluster extends BaseLoadBalancer.Cluster {
+  private class MockCluster extends BalancerClusterState {
 
     private int[][] localities = null;   // [region][server] = percent of blocks
 

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancerHeterogeneousCost.java

@@ -197,8 +197,8 @@ public class TestStochasticLoadBalancerHeterogeneousCost extends BalancerTestBas
         final HeterogeneousRegionCountCostFunction cf =
             new HeterogeneousRegionCountCostFunction(conf);
         assertNotNull(cf);
-        BaseLoadBalancer.Cluster cluster =
+        BalancerClusterState cluster =
-            new BaseLoadBalancer.Cluster(serverMap, null, null, null);
+            new BalancerClusterState(serverMap, null, null, null);
         cf.init(cluster);
 
         // checking that we all hosts have a number of regions below their limit
@@ -285,10 +285,10 @@ public class TestStochasticLoadBalancerHeterogeneousCost extends BalancerTestBas
     StochasticLoadBalancer.RandomCandidateGenerator {
 
     @Override
-    public BaseLoadBalancer.Cluster.Action pickRandomRegions(BaseLoadBalancer.Cluster cluster,
+    public BalanceAction pickRandomRegions(BalancerClusterState cluster,
       int thisServer, int otherServer) {
       if (thisServer < 0 || otherServer < 0) {
-        return BaseLoadBalancer.Cluster.NullAction;
+        return BalanceAction.NULL_ACTION;
       }
 
       int thisRegion = pickRandomRegion(cluster, thisServer, 0.5);
@@ -298,7 +298,7 @@ public class TestStochasticLoadBalancerHeterogeneousCost extends BalancerTestBas
     }
 
     @Override
-    BaseLoadBalancer.Cluster.Action generate(BaseLoadBalancer.Cluster cluster) {
+    BalanceAction generate(BalancerClusterState cluster) {
       return super.generate(cluster);
     }
   }

hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancerRegionReplica.java

@@ -35,7 +35,6 @@ import org.apache.hadoop.hbase.ServerName;
 import org.apache.hadoop.hbase.client.RegionInfo;
 import org.apache.hadoop.hbase.client.RegionReplicaUtil;
 import org.apache.hadoop.hbase.master.RackManager;
-import org.apache.hadoop.hbase.master.balancer.BaseLoadBalancer.Cluster;
 import org.apache.hadoop.hbase.testclassification.LargeTests;
 import org.apache.hadoop.hbase.testclassification.MasterTests;
 import org.junit.ClassRule;
@@ -55,7 +54,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     StochasticLoadBalancer.CostFunction costFunction =
         new StochasticLoadBalancer.RegionReplicaHostCostFunction(conf);
     for (int[] mockCluster : clusterStateMocks) {
-      BaseLoadBalancer.Cluster cluster = mockCluster(mockCluster);
+      BalancerClusterState cluster = mockCluster(mockCluster);
       costFunction.init(cluster);
       double cost = costFunction.cost();
       assertTrue(cost >= 0);
@@ -72,9 +71,9 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     int[] servers = new int[] { 3, 3, 3, 3, 3 };
     TreeMap<ServerName, List<RegionInfo>> clusterState = mockClusterServers(servers);
 
-    BaseLoadBalancer.Cluster cluster;
+    BalancerClusterState cluster;
 
-    cluster = new BaseLoadBalancer.Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     costFunction.init(cluster);
     double costWithoutReplicas = costFunction.cost();
     assertEquals(0, costWithoutReplicas, 0);
@@ -84,7 +83,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
         RegionReplicaUtil.getRegionInfoForReplica(clusterState.firstEntry().getValue().get(0), 1);
     clusterState.lastEntry().getValue().add(replica1);
 
-    cluster = new BaseLoadBalancer.Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     costFunction.init(cluster);
     double costWith1ReplicaDifferentServer = costFunction.cost();
 
@@ -94,7 +93,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     RegionInfo replica2 = RegionReplicaUtil.getRegionInfoForReplica(replica1, 2);
     clusterState.lastEntry().getValue().add(replica2);
 
-    cluster = new BaseLoadBalancer.Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     costFunction.init(cluster);
     double costWith1ReplicaSameServer = costFunction.cost();
 
@@ -117,7 +116,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     entry.getValue().add(replica2);
     it.next().getValue().add(replica3); // 2nd server
 
-    cluster = new BaseLoadBalancer.Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     costFunction.init(cluster);
     double costWith3ReplicasSameServer = costFunction.cost();
 
@@ -131,7 +130,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     clusterState.lastEntry().getValue().add(replica2);
     clusterState.lastEntry().getValue().add(replica3);
 
-    cluster = new BaseLoadBalancer.Cluster(clusterState, null, null, null);
+    cluster = new BalancerClusterState(clusterState, null, null, null);
     costFunction.init(cluster);
     double costWith2ReplicasOnTwoServers = costFunction.cost();
 
@@ -152,7 +151,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     regions = randomRegions(1);
     map.put(s2, regions);
     assertTrue(loadBalancer.needsBalance(HConstants.ENSEMBLE_TABLE_NAME,
-      new Cluster(map, null, null, null)));
+      new BalancerClusterState(map, null, null, null)));
     // check for the case where there are two hosts on the same rack and there are two racks
     // and both the replicas are on the same rack
     map.clear();
@@ -165,7 +164,7 @@ public class TestStochasticLoadBalancerRegionReplica extends BalancerTestBase {
     map.put(ServerName.valueOf("host2", 1000, 11111), randomRegions(1));
     assertTrue(
       loadBalancer.needsBalance(HConstants.ENSEMBLE_TABLE_NAME,
-        new Cluster(map, null, null, new ForTestRackManagerOne())));
+        new BalancerClusterState(map, null, null, new ForTestRackManagerOne())));
   }
 
   @Test