/*
 * 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 static org.junit.Assert.assertEquals;
import static org.junit.Assert.assertFalse;
import static org.junit.Assert.assertNotNull;
import static org.junit.Assert.assertNull;
import static org.junit.Assert.assertTrue;
import static org.mockito.Mockito.mock;
import static org.mockito.Mockito.when;

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.Map;
import java.util.Queue;
import java.util.TimeZone;
import java.util.TreeMap;
import org.apache.hadoop.conf.Configuration;
import org.apache.hadoop.hbase.ClusterMetrics;
import org.apache.hadoop.hbase.HBaseClassTestRule;
import org.apache.hadoop.hbase.HBaseConfiguration;
import org.apache.hadoop.hbase.HConstants;
import org.apache.hadoop.hbase.RegionMetrics;
import org.apache.hadoop.hbase.ServerMetrics;
import org.apache.hadoop.hbase.ServerName;
import org.apache.hadoop.hbase.Size;
import org.apache.hadoop.hbase.TableName;
import org.apache.hadoop.hbase.client.RegionInfo;
import org.apache.hadoop.hbase.master.RegionPlan;
import org.apache.hadoop.hbase.testclassification.MasterTests;
import org.apache.hadoop.hbase.testclassification.MediumTests;
import org.apache.hadoop.hbase.util.Bytes;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import org.junit.Before;
import org.junit.BeforeClass;
import org.junit.ClassRule;
import org.junit.Test;
import org.junit.experimental.categories.Category;

import org.apache.hbase.thirdparty.org.apache.commons.collections4.CollectionUtils;

@Category({ MasterTests.class, MediumTests.class })
public class TestStochasticLoadBalancer extends BalancerTestBase {

  @ClassRule
  public static final HBaseClassTestRule CLASS_RULE =
    HBaseClassTestRule.forClass(TestStochasticLoadBalancer.class);

  private static final String REGION_KEY = "testRegion";

  // Mapping of locality test -> expected locality
  private float[] expectedLocalities = { 1.0f, 0.0f, 0.50f, 0.25f, 1.0f };
  private static Configuration storedConfiguration;

  @BeforeClass
  public static void saveInitialConfiguration() {
    storedConfiguration = new Configuration(conf);
  }

  @Before
  public void beforeEachTest() {
    conf = new Configuration(storedConfiguration);
    loadBalancer.onConfigurationChange(conf);
  }

  /**
   * Data set for testLocalityCost: [test][0][0] = mapping of server to number of regions it hosts
   * [test][region + 1][0] = server that region is hosted on [test][region + 1][server + 1] =
   * locality for region on server
   */
  private int[][][] clusterRegionLocationMocks = new int[][][] {
    // Test 1: each region is entirely on server that hosts it
    new int[][] { new int[] { 2, 1, 1 }, new int[] { 2, 0, 0, 100 }, // region 0 is hosted and
                                                                     // entirely local on server 2
      new int[] { 0, 100, 0, 0 }, // region 1 is hosted and entirely on server 0
      new int[] { 0, 100, 0, 0 }, // region 2 is hosted and entirely on server 0
      new int[] { 1, 0, 100, 0 }, // region 3 is hosted and entirely on server 1
    },

    // Test 2: each region is 0% local on the server that hosts it
    new int[][] { new int[] { 1, 2, 1 }, new int[] { 0, 0, 0, 100 }, // region 0 is hosted and
                                                                     // entirely local on server 2
      new int[] { 1, 100, 0, 0 }, // region 1 is hosted and entirely on server 0
      new int[] { 1, 100, 0, 0 }, // region 2 is hosted and entirely on server 0
      new int[] { 2, 0, 100, 0 }, // region 3 is hosted and entirely on server 1
    },

    // Test 3: each region is 25% local on the server that hosts it (and 50% locality is possible)
    new int[][] { new int[] { 1, 2, 1 }, new int[] { 0, 25, 0, 50 }, // region 0 is hosted and
                                                                     // entirely local on server 2
      new int[] { 1, 50, 25, 0 }, // region 1 is hosted and entirely on server 0
      new int[] { 1, 50, 25, 0 }, // region 2 is hosted and entirely on server 0
      new int[] { 2, 0, 50, 25 }, // region 3 is hosted and entirely on server 1
    },

    // Test 4: each region is 25% local on the server that hosts it (and 100% locality is possible)
    new int[][] { new int[] { 1, 2, 1 }, new int[] { 0, 25, 0, 100 }, // region 0 is hosted and
                                                                      // entirely local on server 2
      new int[] { 1, 100, 25, 0 }, // region 1 is hosted and entirely on server 0
      new int[] { 1, 100, 25, 0 }, // region 2 is hosted and entirely on server 0
      new int[] { 2, 0, 100, 25 }, // region 3 is hosted and entirely on server 1
    },

    // Test 5: each region is 75% local on the server that hosts it (and 75% locality is possible
    // everywhere)
    new int[][] { new int[] { 1, 2, 1 }, new int[] { 0, 75, 75, 75 }, // region 0 is hosted and
                                                                      // entirely local on server 2
      new int[] { 1, 75, 75, 75 }, // region 1 is hosted and entirely on server 0
      new int[] { 1, 75, 75, 75 }, // region 2 is hosted and entirely on server 0
      new int[] { 2, 75, 75, 75 }, // region 3 is hosted and entirely on server 1
    }, };

  @Test
  public void testKeepRegionLoad() throws Exception {
    ServerName sn = ServerName.valueOf("test:8080", 100);
    int numClusterStatusToAdd = 20000;
    for (int i = 0; i < numClusterStatusToAdd; i++) {
      ServerMetrics sl = mock(ServerMetrics.class);

      RegionMetrics rl = mock(RegionMetrics.class);
      when(rl.getReadRequestCount()).thenReturn(0L);
      when(rl.getWriteRequestCount()).thenReturn(0L);
      when(rl.getMemStoreSize()).thenReturn(Size.ZERO);
      when(rl.getStoreFileSize()).thenReturn(new Size(i, Size.Unit.MEGABYTE));
      when(rl.getRegionSizeMB()).thenReturn(Size.ZERO);
      when(rl.getCurrentRegionCachedRatio()).thenReturn(0.0f);

      Map<byte[], RegionMetrics> regionLoadMap = new TreeMap<>(Bytes.BYTES_COMPARATOR);
      regionLoadMap.put(Bytes.toBytes(REGION_KEY), rl);
      when(sl.getRegionMetrics()).thenReturn(regionLoadMap);

      ClusterMetrics clusterStatus = mock(ClusterMetrics.class);
      Map<ServerName, ServerMetrics> serverMetricsMap = new TreeMap<>();
      serverMetricsMap.put(sn, sl);
      when(clusterStatus.getLiveServerMetrics()).thenReturn(serverMetricsMap);
      // when(clusterStatus.getLoad(sn)).thenReturn(sl);

      loadBalancer.updateClusterMetrics(clusterStatus);
    }

    String regionNameAsString = RegionInfo.getRegionNameAsString(Bytes.toBytes(REGION_KEY));
    assertTrue(loadBalancer.loads.get(regionNameAsString) != null);
    assertTrue(loadBalancer.loads.get(regionNameAsString).size() == 15);
    assertNull(loadBalancer.namedQueueRecorder);

    Queue<BalancerRegionLoad> loads = loadBalancer.loads.get(regionNameAsString);
    int i = 0;
    while (loads.size() > 0) {
      BalancerRegionLoad rl = loads.remove();
      assertEquals(i + (numClusterStatusToAdd - 15), rl.getStorefileSizeMB());
      i++;
    }
  }

  @Test
  public void testUpdateBalancerLoadInfo() {
    int[] cluster = new int[] { 10, 0 };
    Map<ServerName, List<RegionInfo>> servers = mockClusterServers(cluster);
    BalancerClusterState clusterState = mockCluster(cluster);
    Map<TableName, Map<ServerName, List<RegionInfo>>> LoadOfAllTable =
      (Map) mockClusterServersWithTables(servers);
    boolean[] perTableBalancerConfigs = { true, false };
    for (boolean isByTable : perTableBalancerConfigs) {
      conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, isByTable);
      loadBalancer.onConfigurationChange(conf);
      dummyMetricsStochasticBalancer.clearDummyMetrics();
      loadBalancer.updateBalancerLoadInfo(LoadOfAllTable);
      assertTrue("Metrics should be recorded!",
        dummyMetricsStochasticBalancer.getDummyCostsMap() != null
          && !dummyMetricsStochasticBalancer.getDummyCostsMap().isEmpty());

      String metricRecordKey;
      if (isByTable) {
        metricRecordKey = "table1#" + StochasticLoadBalancer.OVERALL_COST_FUNCTION_NAME;
      } else {
        metricRecordKey =
          HConstants.ENSEMBLE_TABLE_NAME + "#" + StochasticLoadBalancer.OVERALL_COST_FUNCTION_NAME;
      }
      double curOverallCost = loadBalancer.computeCost(clusterState, Double.MAX_VALUE);
      double curOverallCostInMetrics =
        dummyMetricsStochasticBalancer.getDummyCostsMap().get(metricRecordKey);
      assertEquals(curOverallCost, curOverallCostInMetrics, 0.001);
    }
  }

  @Test
  public void testUpdateStochasticCosts() {
    int[] cluster = new int[] { 10, 0 };
    Map<ServerName, List<RegionInfo>> servers = mockClusterServers(cluster);
    BalancerClusterState clusterState = mockCluster(cluster);
    conf.setFloat("hbase.master.balancer.stochastic.minCostNeedBalance", 1.0f);
    conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, false);
    loadBalancer.onConfigurationChange(conf);
    dummyMetricsStochasticBalancer.clearDummyMetrics();
    List<RegionPlan> plans =
      loadBalancer.balanceCluster((Map) mockClusterServersWithTables(servers));

    assertTrue("Balance plan should not be empty!", plans != null && !plans.isEmpty());
    assertTrue("There should be metrics record in MetricsStochasticBalancer",
      !dummyMetricsStochasticBalancer.getDummyCostsMap().isEmpty());

    double overallCostOfCluster = loadBalancer.computeCost(clusterState, Double.MAX_VALUE);
    double overallCostInMetrics = dummyMetricsStochasticBalancer.getDummyCostsMap().get(
      HConstants.ENSEMBLE_TABLE_NAME + "#" + StochasticLoadBalancer.OVERALL_COST_FUNCTION_NAME);
    assertEquals(overallCostOfCluster, overallCostInMetrics, 0.001);
  }

  @Test
  public void testUpdateStochasticCostsIfBalanceNotRan() {
    int[] cluster = new int[] { 10, 10 };
    Map<ServerName, List<RegionInfo>> servers = mockClusterServers(cluster);
    BalancerClusterState clusterState = mockCluster(cluster);
    conf.setFloat("hbase.master.balancer.stochastic.minCostNeedBalance", Float.MAX_VALUE);
    conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, false);
    loadBalancer.onConfigurationChange(conf);
    dummyMetricsStochasticBalancer.clearDummyMetrics();
    List<RegionPlan> plans =
      loadBalancer.balanceCluster((Map) mockClusterServersWithTables(servers));

    assertTrue("Balance plan should be empty!", plans == null || plans.isEmpty());
    assertTrue("There should be metrics record in MetricsStochasticBalancer!",
      !dummyMetricsStochasticBalancer.getDummyCostsMap().isEmpty());

    double overallCostOfCluster = loadBalancer.computeCost(clusterState, Double.MAX_VALUE);
    double overallCostInMetrics = dummyMetricsStochasticBalancer.getDummyCostsMap().get(
      HConstants.ENSEMBLE_TABLE_NAME + "#" + StochasticLoadBalancer.OVERALL_COST_FUNCTION_NAME);
    assertEquals(overallCostOfCluster, overallCostInMetrics, 0.001);
  }

  @Test
  public void testNeedBalance() {
    conf.setFloat("hbase.master.balancer.stochastic.minCostNeedBalance", 1.0f);
    conf.setFloat(HConstants.LOAD_BALANCER_SLOP_KEY, -1f);
    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", false);
    conf.setLong("hbase.master.balancer.stochastic.maxSteps", 5000L);
    // Test with/without per table balancer.
    boolean[] perTableBalancerConfigs = { true, false };
    for (boolean isByTable : perTableBalancerConfigs) {
      conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, isByTable);
      loadBalancer.onConfigurationChange(conf);
      for (int[] mockCluster : clusterStateMocks) {
        assertTrue(hasEmptyBalancerPlans(mockCluster) || needsBalanceIdleRegion(mockCluster));
      }
    }
  }

  @Test
  public void testBalanceOfSloppyServers() {
    // We are testing slop checks, so don't "accidentally" balance due to a minCost calculation.
    // During development, imbalance of a 100 server cluster, with one node having 10 regions
    // and the rest having 5, is 0.0048. With minCostNeedBalance default of 0.025, test should
    // validate slop checks without this override. We override just to ensure we will always
    // validate slop check here, and for small clusters as well.
    conf.setFloat("hbase.master.balancer.stochastic.minCostNeedBalance", 1.0f);
    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", false);
    conf.setLong("hbase.master.balancer.stochastic.maxSteps", 5000L);
    loadBalancer.onConfigurationChange(conf);
    for (int[] mockCluster : clusterStateMocksWithNoSlop) {
      assertTrue(hasEmptyBalancerPlans(mockCluster));
    }
    for (int[] mockCluster : clusterStateMocksWithSlop) {
      assertFalse(hasEmptyBalancerPlans(mockCluster));
    }
  }

  @Test
  public void testSloppyTablesLoadBalanceByTable() {
    int[][] regionsPerServerPerTable = new int[][] {
      new int[] { 8, 2, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
        5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 },
      new int[] { 2, 8, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5,
        5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5, 5 }, };
    conf.setFloat("hbase.master.balancer.stochastic.minCostNeedBalance", 1.0f);
    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", false);
    conf.setLong("hbase.master.balancer.stochastic.maxSteps", 5000L);
    conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, true);
    loadBalancer.onConfigurationChange(conf);
    assertFalse(hasEmptyBalancerPlans(regionsPerServerPerTable));
  }

  private boolean hasEmptyBalancerPlans(int[] mockCluster) {
    Map<ServerName, List<RegionInfo>> servers = mockClusterServers(mockCluster);
    return hasEmptyBalancerPlans(servers);
  }

  private boolean hasEmptyBalancerPlans(int[][] mockCluster) {
    Map<ServerName, List<RegionInfo>> servers = mockClusterServers(mockCluster);
    return hasEmptyBalancerPlans(servers);
  }

  private boolean hasEmptyBalancerPlans(Map<ServerName, List<RegionInfo>> servers) {
    Map<TableName, Map<ServerName, List<RegionInfo>>> loadOfAllTable =
      (Map) mockClusterServersWithTables(servers);
    List<RegionPlan> plans = loadBalancer.balanceCluster(loadOfAllTable);
    return plans == null || plans.isEmpty();
  }

  @Test
  public void testLocalityCost() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    CostFunction costFunction = new ServerLocalityCostFunction(conf);

    for (int test = 0; test < clusterRegionLocationMocks.length; test++) {
      int[][] clusterRegionLocations = clusterRegionLocationMocks[test];
      MockCluster cluster = new MockCluster(clusterRegionLocations);
      costFunction.prepare(cluster);
      double cost = costFunction.cost();
      double expected = 1 - expectedLocalities[test];
      assertEquals(expected, cost, 0.001);
    }
    assertNull(loadBalancer.namedQueueRecorder);
  }

  @Test
  public void testMoveCostMultiplier() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    CostFunction costFunction = new MoveCostFunction(conf);
    BalancerClusterState cluster = mockCluster(clusterStateMocks[0]);
    costFunction.prepare(cluster);
    costFunction.cost();
    assertEquals(MoveCostFunction.DEFAULT_MOVE_COST, costFunction.getMultiplier(), 0.01);

    // In offpeak hours, the multiplier of move cost should be lower
    conf.setInt("hbase.offpeak.start.hour", 0);
    conf.setInt("hbase.offpeak.end.hour", 23);
    // Set a fixed time which hour is 15, so it will always in offpeak
    // See HBASE-24898 for more info of the calculation here
    long deltaFor15 = TimeZone.getDefault().getRawOffset() - 28800000;
    long timeFor15 = 1597907081000L - deltaFor15;
    EnvironmentEdgeManager.injectEdge(() -> timeFor15);
    costFunction = new MoveCostFunction(conf);
    costFunction.prepare(cluster);
    costFunction.cost();
    assertEquals(MoveCostFunction.DEFAULT_MOVE_COST_OFFPEAK, costFunction.getMultiplier(), 0.01);
  }

  @Test
  public void testMoveCost() throws Exception {
    Configuration conf = HBaseConfiguration.create();
    CostFunction costFunction = new MoveCostFunction(conf);
    for (int[] mockCluster : clusterStateMocks) {
      BalancerClusterState cluster = mockCluster(mockCluster);
      costFunction.prepare(cluster);
      double cost = costFunction.cost();
      assertEquals(0.0f, cost, 0.001);

      // cluster region number is smaller than maxMoves=600
      cluster.setNumRegions(200);
      cluster.setNumMovedRegions(10);
      cost = costFunction.cost();
      assertEquals(0.05f, cost, 0.001);
      cluster.setNumMovedRegions(100);
      cost = costFunction.cost();
      assertEquals(0.5f, cost, 0.001);
      cluster.setNumMovedRegions(200);
      cost = costFunction.cost();
      assertEquals(1.0f, cost, 0.001);

      // cluster region number is bigger than maxMoves=2500
      cluster.setNumRegions(10000);
      cluster.setNumMovedRegions(250);
      cost = costFunction.cost();
      assertEquals(0.025f, cost, 0.001);
      cluster.setNumMovedRegions(1250);
      cost = costFunction.cost();
      assertEquals(0.125f, cost, 0.001);
      cluster.setNumMovedRegions(2500);
      cost = costFunction.cost();
      assertEquals(0.25f, cost, 0.01);
    }
  }

  @Test
  public void testSkewCost() {
    Configuration conf = HBaseConfiguration.create();
    CostFunction costFunction = new RegionCountSkewCostFunction(conf);
    for (int[] mockCluster : clusterStateMocks) {
      costFunction.prepare(mockCluster(mockCluster));
      double cost = costFunction.cost();
      assertTrue(cost >= 0);
      assertTrue(cost <= 1.01);
    }

    costFunction.prepare(mockCluster(new int[] { 0, 0, 0, 0, 1 }));
    assertEquals(0, costFunction.cost(), 0.01);
    costFunction.prepare(mockCluster(new int[] { 0, 0, 0, 1, 1 }));
    assertEquals(0, costFunction.cost(), 0.01);
    costFunction.prepare(mockCluster(new int[] { 0, 0, 1, 1, 1 }));
    assertEquals(0, costFunction.cost(), 0.01);
    costFunction.prepare(mockCluster(new int[] { 0, 1, 1, 1, 1 }));
    assertEquals(0, costFunction.cost(), 0.01);
    costFunction.prepare(mockCluster(new int[] { 1, 1, 1, 1, 1 }));
    assertEquals(0, costFunction.cost(), 0.01);
    costFunction.prepare(mockCluster(new int[] { 10000, 0, 0, 0, 0 }));
    assertEquals(1, costFunction.cost(), 0.01);
  }

  @Test
  public void testCostAfterUndoAction() {
    final int runs = 10;
    for (int[] mockCluster : clusterStateMocks) {
      BalancerClusterState cluster = mockCluster(mockCluster);
      loadBalancer.initCosts(cluster);
      for (int i = 0; i != runs; ++i) {
        final double expectedCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
        BalanceAction action = loadBalancer.nextAction(cluster);
        cluster.doAction(action);
        loadBalancer.updateCostsAndWeightsWithAction(cluster, action);
        BalanceAction undoAction = action.undoAction();
        cluster.doAction(undoAction);
        loadBalancer.updateCostsAndWeightsWithAction(cluster, undoAction);
        final double actualCost = loadBalancer.computeCost(cluster, Double.MAX_VALUE);
        assertEquals(expectedCost, actualCost, 0);
      }
    }
  }

  @Test
  public void testTableSkewCost() {
    Configuration conf = HBaseConfiguration.create();
    CostFunction costFunction = new TableSkewCostFunction(conf);
    for (int[] mockCluster : clusterStateMocks) {
      BalancerClusterState cluster = mockCluster(mockCluster);
      costFunction.prepare(cluster);
      double cost = costFunction.cost();
      assertTrue(cost >= 0);
      assertTrue(cost <= 1.01);
    }
  }

  @Test
  public void testRegionLoadCost() {
    List<BalancerRegionLoad> regionLoads = new ArrayList<>();
    for (int i = 1; i < 5; i++) {
      BalancerRegionLoad regionLoad = mock(BalancerRegionLoad.class);
      when(regionLoad.getReadRequestsCount()).thenReturn(new Long(i));
      when(regionLoad.getStorefileSizeMB()).thenReturn(i);
      regionLoads.add(regionLoad);
    }

    Configuration conf = HBaseConfiguration.create();
    ReadRequestCostFunction readCostFunction = new ReadRequestCostFunction(conf);
    double rateResult = readCostFunction.getRegionLoadCost(regionLoads);
    // read requests are treated as a rate so the average rate here is simply 1
    assertEquals(1, rateResult, 0.01);

    StoreFileCostFunction storeFileCostFunction = new StoreFileCostFunction(conf);
    double result = storeFileCostFunction.getRegionLoadCost(regionLoads);
    // storefile size cost is simply an average of it's value over time
    assertEquals(2.5, result, 0.01);
  }

  @Test
  public void testRegionLoadCostWhenDecrease() {
    List<BalancerRegionLoad> regionLoads = new ArrayList<>();
    // test region loads of [1,2,1,4]
    for (int i = 1; i < 5; i++) {
      int load = i == 3 ? 1 : i;
      BalancerRegionLoad regionLoad = mock(BalancerRegionLoad.class);
      when(regionLoad.getReadRequestsCount()).thenReturn((long) load);
      regionLoads.add(regionLoad);
    }

    Configuration conf = HBaseConfiguration.create();
    ReadRequestCostFunction readCostFunction = new ReadRequestCostFunction(conf);
    double rateResult = readCostFunction.getRegionLoadCost(regionLoads);
    // read requests are treated as a rate so the average rate here is simply 1
    assertEquals(1.67, rateResult, 0.01);
  }

  @Test
  public void testLosingRs() throws Exception {
    int numNodes = 3;
    int numRegions = 20;
    int numRegionsPerServer = 3; // all servers except one
    int replication = 1;
    int numTables = 2;

    Map<ServerName, List<RegionInfo>> serverMap =
      createServerMap(numNodes, numRegions, numRegionsPerServer, replication, numTables);
    List<ServerAndLoad> list = convertToList(serverMap);

    List<RegionPlan> plans = loadBalancer.balanceTable(HConstants.ENSEMBLE_TABLE_NAME, serverMap);
    assertNotNull(plans);

    // Apply the plan to the mock cluster.
    List<ServerAndLoad> balancedCluster = reconcile(list, plans, serverMap);

    assertClusterAsBalanced(balancedCluster);

    ServerName sn = serverMap.keySet().toArray(new ServerName[serverMap.size()])[0];

    ServerName deadSn = ServerName.valueOf(sn.getHostname(), sn.getPort(), sn.getStartcode() - 100);

    serverMap.put(deadSn, new ArrayList<>(0));

    plans = loadBalancer.balanceTable(HConstants.ENSEMBLE_TABLE_NAME, serverMap);
    assertNull(plans);
  }

  @Test
  public void testAdditionalCostFunction() {
    conf.set(StochasticLoadBalancer.COST_FUNCTIONS_COST_FUNCTIONS_KEY,
      DummyCostFunction.class.getName());

    loadBalancer.onConfigurationChange(conf);
    assertTrue(Arrays.asList(loadBalancer.getCostFunctionNames())
      .contains(DummyCostFunction.class.getSimpleName()));
  }

  @Test
  public void testDefaultCostFunctionList() {
    List<String> expected = Arrays.asList(RegionCountSkewCostFunction.class.getSimpleName(),
      PrimaryRegionCountSkewCostFunction.class.getSimpleName(),
      MoveCostFunction.class.getSimpleName(), RackLocalityCostFunction.class.getSimpleName(),
      TableSkewCostFunction.class.getSimpleName(),
      RegionReplicaHostCostFunction.class.getSimpleName(),
      RegionReplicaRackCostFunction.class.getSimpleName(),
      ReadRequestCostFunction.class.getSimpleName(), WriteRequestCostFunction.class.getSimpleName(),
      MemStoreSizeCostFunction.class.getSimpleName(), StoreFileCostFunction.class.getSimpleName());

    List<String> actual = Arrays.asList(loadBalancer.getCostFunctionNames());
    assertTrue("ExpectedCostFunctions: " + expected + " ActualCostFunctions: " + actual,
      CollectionUtils.isEqualCollection(expected, actual));
  }

  private boolean needsBalanceIdleRegion(int[] cluster) {
    return Arrays.stream(cluster).anyMatch(x -> x > 1)
      && Arrays.stream(cluster).anyMatch(x -> x < 1);
  }

  // This mock allows us to test the LocalityCostFunction
  private class MockCluster extends BalancerClusterState {

    private int[][] localities = null; // [region][server] = percent of blocks

    public MockCluster(int[][] regions) {

      // regions[0] is an array where index = serverIndex an value = number of regions
      super(mockClusterServers(regions[0], 1), null, null, null);

      localities = new int[regions.length - 1][];
      for (int i = 1; i < regions.length; i++) {
        int regionIndex = i - 1;
        localities[regionIndex] = new int[regions[i].length - 1];
        regionIndexToServerIndex[regionIndex] = regions[i][0];
        for (int j = 1; j < regions[i].length; j++) {
          int serverIndex = j - 1;
          localities[regionIndex][serverIndex] =
            regions[i][j] > 100 ? regions[i][j] % 100 : regions[i][j];
        }
      }
    }

    @Override
    float getLocalityOfRegion(int region, int server) {
      // convert the locality percentage to a fraction
      return localities[region][server] / 100.0f;
    }

    @Override
    public int getRegionSizeMB(int region) {
      return 1;
    }
  }
}