HBASE-25973 Balancer should explain progress in a better way in log -… (#3483)

Signed-off-by: Andrew Purtell <apurtell@apache.org>

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

@@ -1877,6 +1877,8 @@ public class HMaster extends HRegionServer implements MasterServices {
         }
       }
     }
+    LOG.info("Balancer is going into sleep until next period in {}ms", getConfiguration()
+      .getInt(HConstants.HBASE_BALANCER_PERIOD, HConstants.DEFAULT_HBASE_BALANCER_PERIOD));
     return successRegionPlans;
   }
 

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

@@ -133,7 +133,8 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
 
   private List<CandidateGenerator> candidateGenerators;
   private List<CostFunction> costFunctions; // FindBugs: Wants this protected; IS2_INCONSISTENT_SYNC
-
+  // To save currently configed sum of multiplier. Defaulted at 1 for cases that carry high cost
+  private float sumMultiplier = 1.0f;
   // to save and report costs to JMX
   private double curOverallCost = 0d;
   private double[] tempFunctionCosts;
@@ -229,7 +230,6 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
 
     regionReplicaHostCostFunction = new RegionReplicaHostCostFunction(conf);
     regionReplicaRackCostFunction = new RegionReplicaRackCostFunction(conf);
-
     costFunctions = new ArrayList<>();
     addCostFunction(new RegionCountSkewCostFunction(conf));
     addCostFunction(new PrimaryRegionCountSkewCostFunction(conf));
@@ -310,63 +310,66 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   boolean needsBalance(TableName tableName, BalancerClusterState cluster) {
     ClusterLoadState cs = new ClusterLoadState(cluster.clusterState);
     if (cs.getNumServers() < MIN_SERVER_BALANCE) {
-      if (LOG.isDebugEnabled()) {
+      LOG.info("Not running balancer because only " + cs.getNumServers() +
-        LOG.debug("Not running balancer because only " + cs.getNumServers()
+        " active regionserver(s)");
-            + " active regionserver(s)");
+      sendRejectionReasonToRingBuffer(
-      }
+        "The number of RegionServers " + cs.getNumServers() + " < MIN_SERVER_BALANCE(" +
-      if (this.isBalancerRejectionRecording) {
+          MIN_SERVER_BALANCE + ")", null);
-        sendRejectionReasonToRingBuffer("The number of RegionServers " +
-          cs.getNumServers() + " < MIN_SERVER_BALANCE(" + MIN_SERVER_BALANCE + ")", null);
-      }
       return false;
     }
     if (areSomeRegionReplicasColocated(cluster)) {
+      LOG.info("Running balancer because at least one server hosts replicas of the same region.");
       return true;
     }
 
     if (idleRegionServerExist(cluster)){
+      LOG.info("Running balancer because cluster has idle server(s).");
       return true;
     }
 
+    sumMultiplier = 0.0f;
     double total = 0.0;
-    float sumMultiplier = 0.0f;
     for (CostFunction c : costFunctions) {
       float multiplier = c.getMultiplier();
-      if (multiplier <= 0) {
+      double cost = c.cost();
-        LOG.trace("{} not needed because multiplier is <= 0", c.getClass().getSimpleName());
-        continue;
-      }
       if (!c.isNeeded()) {
         LOG.trace("{} not needed", c.getClass().getSimpleName());
         continue;
       }
+      total += cost * multiplier;
       sumMultiplier += multiplier;
-      total += c.cost() * multiplier;
+    }
+    if (sumMultiplier <= 0) {
+      LOG.error("At least one cost function needs a multiplier > 0. For example, set "
+        + "hbase.master.balancer.stochastic.regionCountCost to a positive value or default");
+      return false;
     }
 
-    boolean balanced = total <= 0 || sumMultiplier <= 0 ||
+    boolean balanced = (total / sumMultiplier < minCostNeedBalance);
-        (sumMultiplier > 0 && (total / sumMultiplier) < minCostNeedBalance);
+    if (balanced) {
-    if(balanced && isBalancerRejectionRecording){
+      if (isBalancerRejectionRecording) {
         String reason = "";
         if (total <= 0) {
-        reason = "(cost1*multiplier1)+(cost2*multiplier2)+...+(costn*multipliern) = " + total + " <= 0";
+          reason = "(cost1*multiplier1)+(cost2*multiplier2)+...+(costn*multipliern) = " +
+            total + " <= 0";
         } else if (sumMultiplier <= 0) {
           reason = "sumMultiplier = " + sumMultiplier + " <= 0";
         } else if ((total / sumMultiplier) < minCostNeedBalance) {
           reason =
-          "[(cost1*multiplier1)+(cost2*multiplier2)+...+(costn*multipliern)]/sumMultiplier = " + (total
+            "[(cost1*multiplier1)+(cost2*multiplier2)+...+(costn*multipliern)]/sumMultiplier = " +
-            / sumMultiplier) + " <= minCostNeedBalance(" + minCostNeedBalance + ")";
+              (total / sumMultiplier) + " <= minCostNeedBalance(" + minCostNeedBalance + ")";
         }
         sendRejectionReasonToRingBuffer(reason, costFunctions);
       }
-    if (LOG.isDebugEnabled()) {
+      LOG.info("{} - skipping load balancing because weighted average imbalance={} <= "
-      LOG.debug("{} {}; total cost={}, sum multiplier={}; cost/multiplier to need a balance is {}",
+        + "threshold({}). If you want more aggressive balancing, either lower "
-          balanced ? "Skipping load balancing because balanced" : "We need to load balance",
+        + "hbase.master.balancer.stochastic.minCostNeedBalance from {} or increase the relative "
-          isByTable ? String.format("table (%s)", tableName) : "cluster",
+        + "multiplier(s) of the specific cost function(s). functionCost={}",
-          total, sumMultiplier, minCostNeedBalance);
+        isByTable ? "Table specific ("+tableName+")" : "Cluster wide", total / sumMultiplier,
-      if (LOG.isTraceEnabled()) {
+        minCostNeedBalance, minCostNeedBalance, functionCost());
-        LOG.trace("Balance decision detailed function costs={}", functionCost());
+    } else {
-      }
+      LOG.info("{} - Calculating plan. may take up to {}ms to complete.",
+        isByTable ? "Table specific ("+tableName+")" : "Cluster wide", maxRunningTime);
     }
     return !balanced;
   }
@@ -452,8 +455,9 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
             maxSteps);
       }
     }
-    LOG.info("start StochasticLoadBalancer.balancer, initCost=" + currentCost + ", functionCost="
+    LOG.info("Start StochasticLoadBalancer.balancer, initial weighted average imbalance={}, "
-        + functionCost() + " computedMaxSteps: " + computedMaxSteps);
+      + "functionCost={} computedMaxSteps={}",
+      currentCost / sumMultiplier, functionCost(), computedMaxSteps);
 
     final String initFunctionTotalCosts = totalCostsPerFunc();
     // Perform a stochastic walk to see if we can get a good fit.
@@ -499,17 +503,19 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     updateStochasticCosts(tableName, curOverallCost, curFunctionCosts);
     if (initCost > currentCost) {
       plans = createRegionPlans(cluster);
-      LOG.info("Finished computing new load balance plan. Computation took {}" +
+      LOG.info("Finished computing new moving plan. Computation took {} ms" +
           " to try {} different iterations.  Found a solution that moves " +
-        "{} regions; Going from a computed cost of {}" +
+          "{} regions; Going from a computed imbalance of {}" +
-        " to a new cost of {}", java.time.Duration.ofMillis(endTime - startTime),
+          " to a new imbalance of {}. ",
-        step, plans.size(), initCost, currentCost);
+        endTime - startTime, step, plans.size(),
+        initCost / sumMultiplier, currentCost / sumMultiplier);
+
       sendRegionPlansToRingBuffer(plans, currentCost, initCost, initFunctionTotalCosts, step);
       return plans;
     }
-    LOG.info("Could not find a better load balance plan.  Tried {} different configurations in " +
+    LOG.info("Could not find a better moving plan.  Tried {} different configurations in " +
-      "{}, and did not find anything with a computed cost less than {}", step,
+        "{} ms, and did not find anything with an imbalance score less than {}", step,
-      java.time.Duration.ofMillis(endTime - startTime), initCost);
+      endTime - startTime, initCost / sumMultiplier);
     return null;
   }
 
@@ -520,8 +526,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
         .setReason(reason);
       if (costFunctions != null) {
         for (CostFunction c : costFunctions) {
-          float multiplier = c.getMultiplier();
+          if (!c.isNeeded()) {
-          if (multiplier <= 0 || !c.isNeeded()) {
             continue;
           }
           builder.addCostFuncInfo(c.getClass().getName(), c.cost(), c.getMultiplier());
@@ -580,7 +585,8 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   }
 
   private void addCostFunction(CostFunction costFunction) {
-    if (costFunction.getMultiplier() > 0) {
+    float multiplier = costFunction.getMultiplier();
+    if (multiplier > 0) {
       costFunctions.add(costFunction);
     }
   }
@@ -591,9 +597,13 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
       builder.append(c.getClass().getSimpleName());
       builder.append(" : (");
       if (c.isNeeded()) {
-        builder.append(c.getMultiplier());
+        builder.append("multiplier=" + c.getMultiplier());
         builder.append(", ");
-        builder.append(c.cost());
+        double cost = c.cost();
+        builder.append("imbalance=" + cost);
+        if (cost < minCostNeedBalance) {
+          builder.append(", balanced");
+        }
       } else {
         builder.append("not needed");
       }
@@ -605,7 +615,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   private String totalCostsPerFunc() {
     StringBuilder builder = new StringBuilder();
     for (CostFunction c : costFunctions) {
-      if (c.getMultiplier() <= 0 || !c.isNeeded()) {
+      if (!c.isNeeded()) {
         continue;
       }
       double cost = c.getMultiplier() * c.cost();
@@ -689,7 +699,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
     allowedOnPath = ".*(/src/test/.*|StochasticLoadBalancer).java")
   void updateCostsWithAction(BalancerClusterState cluster, BalanceAction action) {
     for (CostFunction c : costFunctions) {
-      if (c.getMultiplier() > 0 && c.isNeeded()) {
+      if (c.isNeeded()) {
         c.postAction(action);
       }
     }
@@ -728,7 +738,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
       CostFunction c = costFunctions.get(i);
       this.tempFunctionCosts[i] = 0.0;
 
-      if (c.getMultiplier() <= 0 || !c.isNeeded()) {
+      if (!c.isNeeded()) {
         continue;
       }
 

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

@@ -75,7 +75,6 @@ public class BalancerTestBase {
     conf.setFloat("hbase.master.balancer.stochastic.maxMovePercent", 0.75f);
     conf.setFloat("hbase.regions.slop", 0.0f);
     conf.setFloat("hbase.master.balancer.stochastic.localityCost", 0);
-    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", true);
     loadBalancer = new StochasticLoadBalancer();
     MasterServices services = mock(MasterServices.class);
     when(services.getConfiguration()).thenReturn(conf);

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

@@ -169,6 +169,7 @@ public class TestStochasticLoadBalancer extends BalancerTestBase {
       for (boolean isByTable : perTableBalancerConfigs) {
         conf.setBoolean(HConstants.HBASE_MASTER_LOADBALANCE_BYTABLE, isByTable);
         loadBalancer.onConfigurationChange(conf);
+
         for (int[] mockCluster : clusterStateMocks) {
           Map<ServerName, List<RegionInfo>> servers = mockClusterServers(mockCluster);
           Map<TableName, Map<ServerName, List<RegionInfo>>> LoadOfAllTable =

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

@@ -53,12 +53,13 @@ public class TestStochasticLoadBalancerBalanceCluster extends BalancerTestBase {
   public void testBalanceCluster() throws Exception {
     conf.setLong("hbase.master.balancer.stochastic.maxRunningTime", 3 * 60 * 1000); // 3 min
     conf.setFloat("hbase.master.balancer.stochastic.maxMovePercent", 1.0f);
+    conf.setLong(StochasticLoadBalancer.MAX_STEPS_KEY, 20000000L);
     loadBalancer.onConfigurationChange(conf);
+
     for (int[] mockCluster : clusterStateMocks) {
       Map<ServerName, List<RegionInfo>> servers = mockClusterServers(mockCluster);
       List<ServerAndLoad> list = convertToList(servers);
       LOG.info("Mock Cluster : " + printMock(list) + " " + printStats(list));
-
       Map<TableName, Map<ServerName, List<RegionInfo>>> LoadOfAllTable =
           (Map) mockClusterServersWithTables(servers);
       List<RegionPlan> plans = loadBalancer.balanceCluster(LoadOfAllTable);

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

@@ -39,7 +39,7 @@ public class TestStochasticLoadBalancerLargeCluster extends BalancerTestBase {
     int numTables = 100;
     int replication = 1;
     conf.setLong("hbase.master.balancer.stochastic.maxRunningTime", 6 * 60 * 1000);
-    conf.setFloat("hbase.master.balancer.stochastic.maxMovePercent", 1.0f);
+    conf.setLong(StochasticLoadBalancer.MAX_STEPS_KEY, 20000000L);
     loadBalancer.onConfigurationChange(conf);
     testWithCluster(numNodes, numRegions, numRegionsPerServer, replication, numTables, true, true);
   }

patch

@@ -0,0 +1,838 @@
+From debf8555c2fb0f309e3389aa196a788d8c4a5bb5 Mon Sep 17 00:00:00 2001
+From: Duo Zhang <zhangduo@apache.org>
+Date: Sat, 29 May 2021 10:54:44 +0800
+Subject: [PATCH] HBASE-25947 Backport 'HBASE-25894 Improve the performance for
+ region load and region count related cost functions' to branch-2.4 and
+ branch-2.3
+
+---
+ .../master/balancer/DoubleArrayCost.java      | 100 ++++++
+ .../balancer/StochasticLoadBalancer.java      | 337 +++++++++---------
+ .../master/balancer/TestDoubleArrayCost.java  |  67 ++++
+ .../TestStochasticBalancerJmxMetrics.java     |  19 +-
+ .../balancer/TestStochasticLoadBalancer.java  |  28 --
+ 5 files changed, 342 insertions(+), 209 deletions(-)
+ create mode 100644 hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java
+ create mode 100644 hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestDoubleArrayCost.java
+ rename hbase-server/src/test/java/org/apache/hadoop/hbase/{ => master/balancer}/TestStochasticBalancerJmxMetrics.java (95%)
+
+diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java
+new file mode 100644
+index 000000000000..f370b8077d1b
+--- /dev/null
++++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/DoubleArrayCost.java
+@@ -0,0 +1,100 @@
++/**
++ * 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.function.Consumer;
++import org.apache.yetus.audience.InterfaceAudience;
++
++/**
++ * A helper class to compute a scaled cost using
++ * {@link org.apache.commons.math3.stat.descriptive.DescriptiveStatistics#DescriptiveStatistics()}.
++ * It assumes that this is a zero sum set of costs. It assumes that the worst case possible is all
++ * of the elements in one region server and the rest having 0.
++ */
++@InterfaceAudience.Private
++final class DoubleArrayCost {
++
++  private double[] costs;
++
++  // computeCost call is expensive so we use this flag to indicate whether we need to recalculate
++  // the cost by calling computeCost
++  private boolean costsChanged;
++
++  private double cost;
++
++  void prepare(int length) {
++    if (costs == null || costs.length != length) {
++      costs = new double[length];
++    }
++  }
++
++  void setCosts(Consumer<double[]> consumer) {
++    consumer.accept(costs);
++    costsChanged = true;
++  }
++
++  double cost() {
++    if (costsChanged) {
++      cost = computeCost(costs);
++      costsChanged = false;
++    }
++    return cost;
++  }
++
++  private static double computeCost(double[] stats) {
++    double totalCost = 0;
++    double total = getSum(stats);
++
++    double count = stats.length;
++    double mean = total / count;
++
++    // Compute max as if all region servers had 0 and one had the sum of all costs. This must be
++    // a zero sum cost for this to make sense.
++    double max = ((count - 1) * mean) + (total - mean);
++
++    // It's possible that there aren't enough regions to go around
++    double min;
++    if (count > total) {
++      min = ((count - total) * mean) + ((1 - mean) * total);
++    } else {
++      // Some will have 1 more than everything else.
++      int numHigh = (int) (total - (Math.floor(mean) * count));
++      int numLow = (int) (count - numHigh);
++
++      min = (numHigh * (Math.ceil(mean) - mean)) + (numLow * (mean - Math.floor(mean)));
++
++    }
++    min = Math.max(0, min);
++    for (int i = 0; i < stats.length; i++) {
++      double n = stats[i];
++      double diff = Math.abs(mean - n);
++      totalCost += diff;
++    }
++
++    double scaled = StochasticLoadBalancer.scale(min, max, totalCost);
++    return scaled;
++  }
++
++  private static double getSum(double[] stats) {
++    double total = 0;
++    for (double s : stats) {
++      total += s;
++    }
++    return total;
++  }
++}
+\ No newline at end of file
+diff --git a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java
+index 3e341d0f7718..26d8d43f5bef 100644
+--- a/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java
++++ b/hbase-server/src/main/java/org/apache/hadoop/hbase/master/balancer/StochasticLoadBalancer.java
+@@ -17,12 +17,14 @@
+  */
+ package org.apache.hadoop.hbase.master.balancer;
+ 
++import com.google.errorprone.annotations.RestrictedApi;
+ import java.util.ArrayDeque;
+ import java.util.ArrayList;
+ import java.util.Arrays;
+ import java.util.Collection;
+ import java.util.Deque;
+ import java.util.HashMap;
++import java.util.Iterator;
+ import java.util.LinkedList;
+ import java.util.List;
+ import java.util.Map;
+@@ -145,7 +147,6 @@
+   private boolean isBalancerRejectionRecording = false;
+ 
+   private List<CandidateGenerator> candidateGenerators;
+-  private CostFromRegionLoadFunction[] regionLoadFunctions;
+   private List<CostFunction> costFunctions; // FindBugs: Wants this protected; IS2_INCONSISTENT_SYNC
+ 
+   // to save and report costs to JMX
+@@ -202,12 +203,6 @@ public synchronized void setConf(Configuration conf) {
+       candidateGenerators.add(localityCandidateGenerator);
+       candidateGenerators.add(new RegionReplicaRackCandidateGenerator());
+     }
+-    regionLoadFunctions = new CostFromRegionLoadFunction[] {
+-      new ReadRequestCostFunction(conf),
+-      new WriteRequestCostFunction(conf),
+-      new MemStoreSizeCostFunction(conf),
+-      new StoreFileCostFunction(conf)
+-    };
+     regionReplicaHostCostFunction = new RegionReplicaHostCostFunction(conf);
+     regionReplicaRackCostFunction = new RegionReplicaRackCostFunction(conf);
+ 
+@@ -220,10 +215,10 @@ public synchronized void setConf(Configuration conf) {
+     addCostFunction(new TableSkewCostFunction(conf));
+     addCostFunction(regionReplicaHostCostFunction);
+     addCostFunction(regionReplicaRackCostFunction);
+-    addCostFunction(regionLoadFunctions[0]);
+-    addCostFunction(regionLoadFunctions[1]);
+-    addCostFunction(regionLoadFunctions[2]);
+-    addCostFunction(regionLoadFunctions[3]);
++    addCostFunction(new ReadRequestCostFunction(conf));
++    addCostFunction(new WriteRequestCostFunction(conf));
++    addCostFunction(new MemStoreSizeCostFunction(conf));
++    addCostFunction(new StoreFileCostFunction(conf));
+     loadCustomCostFunctions(conf);
+ 
+     curFunctionCosts = new double[costFunctions.size()];
+@@ -290,9 +285,6 @@ protected void setSlop(Configuration conf) {
+   public synchronized void setClusterMetrics(ClusterMetrics st) {
+     super.setClusterMetrics(st);
+     updateRegionLoad();
+-    for(CostFromRegionLoadFunction cost : regionLoadFunctions) {
+-      cost.setClusterMetrics(st);
+-    }
+ 
+     // update metrics size
+     try {
+@@ -599,12 +591,16 @@ private void addCostFunction(CostFunction costFunction) {
+ 
+   private String functionCost() {
+     StringBuilder builder = new StringBuilder();
+-    for (CostFunction c:costFunctions) {
++    for (CostFunction c : costFunctions) {
+       builder.append(c.getClass().getSimpleName());
+       builder.append(" : (");
+-      builder.append(c.getMultiplier());
+-      builder.append(", ");
+-      builder.append(c.cost());
++      if (c.isNeeded()) {
++        builder.append(c.getMultiplier());
++        builder.append(", ");
++        builder.append(c.cost());
++      } else {
++        builder.append("not needed");
++      }
+       builder.append("); ");
+     }
+     return builder.toString();
+@@ -613,11 +609,15 @@ private String functionCost() {
+   private String totalCostsPerFunc() {
+     StringBuilder builder = new StringBuilder();
+     for (CostFunction c : costFunctions) {
+-      if (c.getMultiplier() * c.cost() > 0.0) {
++      if (c.getMultiplier() <= 0 || !c.isNeeded()) {
++        continue;
++      }
++      double cost = c.getMultiplier() * c.cost();
++      if (cost > 0.0) {
+         builder.append(" ");
+         builder.append(c.getClass().getSimpleName());
+         builder.append(" : ");
+-        builder.append(c.getMultiplier() * c.cost());
++        builder.append(cost);
+         builder.append(";");
+       }
+     }
+@@ -679,29 +679,32 @@ private synchronized void updateRegionLoad() {
+         loads.put(regionNameAsString, rLoads);
+       });
+     });
+-
+-    for(CostFromRegionLoadFunction cost : regionLoadFunctions) {
+-      cost.setLoads(loads);
+-    }
+   }
+ 
+-  protected void initCosts(Cluster cluster) {
++  @RestrictedApi(explanation = "Should only be called in tests", link = "",
++    allowedOnPath = ".*(/src/test/.*|StochasticLoadBalancer).java")
++  void initCosts(Cluster cluster) {
+     for (CostFunction c:costFunctions) {
+       c.init(cluster);
+     }
+   }
+ 
+-  protected void updateCostsWithAction(Cluster cluster, Action action) {
++  @RestrictedApi(explanation = "Should only be called in tests", link = "",
++    allowedOnPath = ".*(/src/test/.*|StochasticLoadBalancer).java")
++  void updateCostsWithAction(Cluster cluster, Action action) {
+     for (CostFunction c : costFunctions) {
+-      c.postAction(action);
++      if (c.getMultiplier() > 0 && c.isNeeded()) {
++        c.postAction(action);
++      }
+     }
+   }
+ 
+   /**
+    * Get the names of the cost functions
+    */
+-  public String[] getCostFunctionNames() {
+-    if (costFunctions == null) return null;
++  @RestrictedApi(explanation = "Should only be called in tests", link = "",
++    allowedOnPath = ".*(/src/test/.*|StochasticLoadBalancer).java")
++  String[] getCostFunctionNames() {
+     String[] ret = new String[costFunctions.size()];
+     for (int i = 0; i < costFunctions.size(); i++) {
+       CostFunction c = costFunctions.get(i);
+@@ -720,14 +723,16 @@ protected void updateCostsWithAction(Cluster cluster, Action action) {
+    * @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) {
++  @RestrictedApi(explanation = "Should only be called in tests", link = "",
++    allowedOnPath = ".*(/src/test/.*|StochasticLoadBalancer).java")
++  double computeCost(Cluster cluster, double previousCost) {
+     double total = 0;
+ 
+     for (int i = 0; i < costFunctions.size(); i++) {
+       CostFunction c = costFunctions.get(i);
+       this.tempFunctionCosts[i] = 0.0;
+ 
+-      if (c.getMultiplier() <= 0) {
++      if (c.getMultiplier() <= 0 || !c.isNeeded()) {
+         continue;
+       }
+ 
+@@ -851,75 +856,24 @@ protected void regionMoved(int region, int oldServer, int newServer) {
+     }
+ 
+     protected abstract double cost();
++  }
+ 
+-    @SuppressWarnings("checkstyle:linelength")
+-    /**
+-     * Function to compute a scaled cost using
+-     * {@link org.apache.commons.math3.stat.descriptive.DescriptiveStatistics#DescriptiveStatistics()}.
+-     * It assumes that this is a zero sum set of costs.  It assumes that the worst case
+-     * possible is all of the elements in one region server and the rest having 0.
+-     *
+-     * @param stats the costs
+-     * @return a scaled set of costs.
+-     */
+-    protected double costFromArray(double[] stats) {
+-      double totalCost = 0;
+-      double total = getSum(stats);
+-
+-      double count = stats.length;
+-      double mean = total/count;
+-
+-      // Compute max as if all region servers had 0 and one had the sum of all costs.  This must be
+-      // a zero sum cost for this to make sense.
+-      double max = ((count - 1) * mean) + (total - mean);
+-
+-      // It's possible that there aren't enough regions to go around
+-      double min;
+-      if (count > total) {
+-        min = ((count - total) * mean) + ((1 - mean) * total);
+-      } else {
+-        // Some will have 1 more than everything else.
+-        int numHigh = (int) (total - (Math.floor(mean) * count));
+-        int numLow = (int) (count - numHigh);
+-
+-        min = (numHigh * (Math.ceil(mean) - mean)) + (numLow * (mean - Math.floor(mean)));
+-
+-      }
+-      min = Math.max(0, min);
+-      for (int i=0; i<stats.length; i++) {
+-        double n = stats[i];
+-        double diff = Math.abs(mean - n);
+-        totalCost += diff;
+-      }
+-
+-      double scaled =  scale(min, max, totalCost);
+-      return scaled;
++  /**
++   * Scale the value between 0 and 1.
++   * @param min Min value
++   * @param max The Max value
++   * @param value The value to be scaled.
++   * @return The scaled value.
++   */
++  static double scale(double min, double max, double value) {
++    if (max <= min || value <= min) {
++      return 0;
+     }
+-
+-    private double getSum(double[] stats) {
+-      double total = 0;
+-      for(double s:stats) {
+-        total += s;
+-      }
+-      return total;
++    if ((max - min) == 0) {
++      return 0;
+     }
+ 
+-    /**
+-     * Scale the value between 0 and 1.
+-     *
+-     * @param min   Min value
+-     * @param max   The Max value
+-     * @param value The value to be scaled.
+-     * @return The scaled value.
+-     */
+-    protected double scale(double min, double max, double value) {
+-      if (max <= min || value <= min) {
+-        return 0;
+-      }
+-      if ((max - min) == 0) return 0;
+-
+-      return Math.max(0d, Math.min(1d, (value - min) / (max - min)));
+-    }
++    return Math.max(0d, Math.min(1d, (value - min) / (max - min)));
+   }
+ 
+   /**
+@@ -938,28 +892,36 @@ protected double scale(double min, double max, double value) {
+     private static final float DEFAULT_MAX_MOVE_PERCENT = 0.25f;
+ 
+     private final float maxMovesPercent;
+-    private final Configuration conf;
++    private final OffPeakHours offPeakHours;
++    private final float moveCost;
++    private final float moveCostOffPeak;
+ 
+     MoveCostFunction(Configuration conf) {
+       super(conf);
+-      this.conf = conf;
+       // What percent of the number of regions a single run of the balancer can move.
+       maxMovesPercent = conf.getFloat(MAX_MOVES_PERCENT_KEY, DEFAULT_MAX_MOVE_PERCENT);
+-
++      offPeakHours = OffPeakHours.getInstance(conf);
++      moveCost = conf.getFloat(MOVE_COST_KEY, DEFAULT_MOVE_COST);
++      moveCostOffPeak = conf.getFloat(MOVE_COST_OFFPEAK_KEY, DEFAULT_MOVE_COST_OFFPEAK);
+       // Initialize the multiplier so that addCostFunction will add this cost function.
+       // It may change during later evaluations, due to OffPeakHours.
+-      this.setMultiplier(conf.getFloat(MOVE_COST_KEY, DEFAULT_MOVE_COST));
++      this.setMultiplier(moveCost);
+     }
+ 
+     @Override
+-    protected double cost() {
++    void init(Cluster cluster) {
++      super.init(cluster);
+       // Move cost multiplier should be the same cost or higher than the rest of the costs to ensure
+       // that large benefits are need to overcome the cost of a move.
+-      if (OffPeakHours.getInstance(conf).isOffPeakHour()) {
+-        this.setMultiplier(conf.getFloat(MOVE_COST_OFFPEAK_KEY, DEFAULT_MOVE_COST_OFFPEAK));
++      if (offPeakHours.isOffPeakHour()) {
++        this.setMultiplier(moveCostOffPeak);
+       } else {
+-        this.setMultiplier(conf.getFloat(MOVE_COST_KEY, DEFAULT_MOVE_COST));
++        this.setMultiplier(moveCost);
+       }
++    }
++
++    @Override
++    protected double cost() {
+       // Try and size the max number of Moves, but always be prepared to move some.
+       int maxMoves = Math.max((int) (cluster.numRegions * maxMovesPercent),
+           DEFAULT_MAX_MOVES);
+@@ -985,7 +947,7 @@ protected double cost() {
+         "hbase.master.balancer.stochastic.regionCountCost";
+     static final float DEFAULT_REGION_COUNT_SKEW_COST = 500;
+ 
+-    private double[] stats = null;
++    private final DoubleArrayCost cost = new DoubleArrayCost();
+ 
+     RegionCountSkewCostFunction(Configuration conf) {
+       super(conf);
+@@ -996,8 +958,14 @@ protected double cost() {
+     @Override
+     void init(Cluster cluster) {
+       super.init(cluster);
++      cost.prepare(cluster.numServers);
++      cost.setCosts(costs -> {
++        for (int i = 0; i < cluster.numServers; i++) {
++          costs[i] = cluster.regionsPerServer[i].length;
++        }
++      });
+       LOG.debug("{} sees a total of {} servers and {} regions.", getClass().getSimpleName(),
+-          cluster.numServers, cluster.numRegions);
++        cluster.numServers, cluster.numRegions);
+       if (LOG.isTraceEnabled()) {
+         for (int i =0; i < cluster.numServers; i++) {
+           LOG.trace("{} sees server '{}' has {} regions", getClass().getSimpleName(),
+@@ -1008,13 +976,15 @@ void init(Cluster cluster) {
+ 
+     @Override
+     protected double cost() {
+-      if (stats == null || stats.length != cluster.numServers) {
+-        stats = new double[cluster.numServers];
+-      }
+-      for (int i =0; i < cluster.numServers; i++) {
+-        stats[i] = cluster.regionsPerServer[i].length;
+-      }
+-      return costFromArray(stats);
++      return cost.cost();
++    }
++
++    @Override
++    protected void regionMoved(int region, int oldServer, int newServer) {
++      cost.setCosts(costs -> {
++        costs[oldServer] = cluster.regionsPerServer[oldServer].length;
++        costs[newServer] = cluster.regionsPerServer[newServer].length;
++      });
+     }
+   }
+ 
+@@ -1027,7 +997,7 @@ protected double cost() {
+         "hbase.master.balancer.stochastic.primaryRegionCountCost";
+     private static final float DEFAULT_PRIMARY_REGION_COUNT_SKEW_COST = 500;
+ 
+-    private double[] stats = null;
++    private final DoubleArrayCost cost = new DoubleArrayCost();
+ 
+     PrimaryRegionCountSkewCostFunction(Configuration conf) {
+       super(conf);
+@@ -1036,30 +1006,45 @@ protected double cost() {
+         DEFAULT_PRIMARY_REGION_COUNT_SKEW_COST));
+     }
+ 
++    private double computeCostForRegionServer(int regionServerIndex) {
++      int cost = 0;
++      for (int regionIdx : cluster.regionsPerServer[regionServerIndex]) {
++        if (regionIdx == cluster.regionIndexToPrimaryIndex[regionIdx]) {
++          cost++;
++        }
++      }
++      return cost;
++    }
++
++    @Override
++    void init(Cluster cluster) {
++      super.init(cluster);
++      if (!isNeeded()) {
++        return;
++      }
++      cost.prepare(cluster.numServers);
++      cost.setCosts(costs -> {
++        for (int i = 0; i < costs.length; i++) {
++          costs[i] = computeCostForRegionServer(i);
++        }
++      });
++    }
++
+     @Override
+     boolean isNeeded() {
+       return cluster.hasRegionReplicas;
+     }
+ 
++    @Override
++    protected void regionMoved(int region, int oldServer, int newServer) {
++      cost.setCosts(costs -> {
++        costs[oldServer] = computeCostForRegionServer(oldServer);
++        costs[newServer] = computeCostForRegionServer(newServer);
++      });
++    }
+     @Override
+     protected double cost() {
+-      if (!cluster.hasRegionReplicas) {
+-        return 0;
+-      }
+-      if (stats == null || stats.length != cluster.numServers) {
+-        stats = new double[cluster.numServers];
+-      }
+-
+-      for (int i = 0; i < cluster.numServers; i++) {
+-        stats[i] = 0;
+-        for (int regionIdx : cluster.regionsPerServer[i]) {
+-          if (regionIdx == cluster.regionIndexToPrimaryIndex[regionIdx]) {
+-            stats[i]++;
+-          }
+-        }
+-      }
+-
+-      return costFromArray(stats);
++      return cost.cost();
+     }
+   }
+ 
+@@ -1194,51 +1179,51 @@ int regionIndexToEntityIndex(int region) {
+    */
+   abstract static class CostFromRegionLoadFunction extends CostFunction {
+ 
+-    private ClusterMetrics clusterStatus = null;
+-    private Map<String, Deque<BalancerRegionLoad>> loads = null;
+-    private double[] stats = null;
++    private final DoubleArrayCost cost = new DoubleArrayCost();
++
+     CostFromRegionLoadFunction(Configuration conf) {
+       super(conf);
+     }
+ 
+-    void setClusterMetrics(ClusterMetrics status) {
+-      this.clusterStatus = status;
+-    }
+-
+-    void setLoads(Map<String, Deque<BalancerRegionLoad>> l) {
+-      this.loads = l;
+-    }
++    private double computeCostForRegionServer(int regionServerIndex) {
++      // Cost this server has from RegionLoad
++      double cost = 0;
+ 
+-    @Override
+-    protected double cost() {
+-      if (clusterStatus == null || loads == null) {
+-        return 0;
+-      }
++      // for every region on this server get the rl
++      for (int regionIndex : cluster.regionsPerServer[regionServerIndex]) {
++        Collection<BalancerRegionLoad> regionLoadList = cluster.regionLoads[regionIndex];
+ 
+-      if (stats == null || stats.length != cluster.numServers) {
+-        stats = new double[cluster.numServers];
++        // Now if we found a region load get the type of cost that was requested.
++        if (regionLoadList != null) {
++          cost += getRegionLoadCost(regionLoadList);
++        }
+       }
++      return cost;
++    }
+ 
+-      for (int i =0; i < stats.length; i++) {
+-        //Cost this server has from RegionLoad
+-        long cost = 0;
+-
+-        // for every region on this server get the rl
+-        for(int regionIndex:cluster.regionsPerServer[i]) {
+-          Collection<BalancerRegionLoad> regionLoadList =  cluster.regionLoads[regionIndex];
+-
+-          // Now if we found a region load get the type of cost that was requested.
+-          if (regionLoadList != null) {
+-            cost = (long) (cost + getRegionLoadCost(regionLoadList));
+-          }
++    @Override
++    void init(Cluster cluster) {
++      super.init(cluster);
++      cost.prepare(cluster.numServers);
++      cost.setCosts(costs -> {
++        for (int i = 0; i < costs.length; i++) {
++          costs[i] = computeCostForRegionServer(i);
+         }
++      });
++    }
+ 
+-        // Add the total cost to the stats.
+-        stats[i] = cost;
+-      }
++    @Override
++    protected void regionMoved(int region, int oldServer, int newServer) {
++      // recompute the stat for the given two region servers
++      cost.setCosts(costs -> {
++        costs[oldServer] = computeCostForRegionServer(oldServer);
++        costs[newServer] = computeCostForRegionServer(newServer);
++      });
++    }
+ 
+-      // Now return the scaled cost from data held in the stats object.
+-      return costFromArray(stats);
++    @Override
++    protected final double cost() {
++      return cost.cost();
+     }
+ 
+     protected double getRegionLoadCost(Collection<BalancerRegionLoad> regionLoadList) {
+@@ -1265,18 +1250,20 @@ protected double getRegionLoadCost(Collection<BalancerRegionLoad> regionLoadList
+ 
+     @Override
+     protected double getRegionLoadCost(Collection<BalancerRegionLoad> regionLoadList) {
++      Iterator<BalancerRegionLoad> iter = regionLoadList.iterator();
++      if (!iter.hasNext()) {
++        return 0;
++      }
++      double previous = getCostFromRl(iter.next());
++      if (!iter.hasNext()) {
++        return 0;
++      }
+       double cost = 0;
+-      double previous = 0;
+-      boolean isFirst = true;
+-      for (BalancerRegionLoad rl : regionLoadList) {
+-        double current = getCostFromRl(rl);
+-        if (isFirst) {
+-          isFirst = false;
+-        } else {
+-          cost += current - previous;
+-        }
++      do {
++        double current = getCostFromRl(iter.next());
++        cost += current - previous;
+         previous = current;
+-      }
++      } while (iter.hasNext());
+       return Math.max(0, cost / (regionLoadList.size() - 1));
+     }
+   }
+diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestDoubleArrayCost.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestDoubleArrayCost.java
+new file mode 100644
+index 000000000000..8dd1e4973b68
+--- /dev/null
++++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestDoubleArrayCost.java
+@@ -0,0 +1,67 @@
++/**
++ * 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 org.apache.hadoop.hbase.HBaseClassTestRule;
++import org.apache.hadoop.hbase.testclassification.MasterTests;
++import org.apache.hadoop.hbase.testclassification.SmallTests;
++import org.junit.ClassRule;
++import org.junit.Test;
++import org.junit.experimental.categories.Category;
++
++@Category({ MasterTests.class, SmallTests.class })
++public class TestDoubleArrayCost {
++
++  @ClassRule
++  public static final HBaseClassTestRule CLASS_RULE =
++    HBaseClassTestRule.forClass(TestDoubleArrayCost.class);
++
++  @Test
++  public void testComputeCost() {
++    DoubleArrayCost cost = new DoubleArrayCost();
++
++    cost.prepare(100);
++    cost.setCosts(costs -> {
++      for (int i = 0; i < 100; i++) {
++        costs[i] = 10;
++      }
++    });
++    assertEquals(0, cost.cost(), 0.01);
++
++    cost.prepare(101);
++    cost.setCosts(costs -> {
++      for (int i = 0; i < 100; i++) {
++        costs[i] = 0;
++      }
++      costs[100] = 100;
++    });
++    assertEquals(1, cost.cost(), 0.01);
++
++    cost.prepare(200);
++    cost.setCosts(costs -> {
++      for (int i = 0; i < 100; i++) {
++        costs[i] = 0;
++        costs[i + 100] = 100;
++      }
++      costs[100] = 100;
++    });
++    assertEquals(0.5, cost.cost(), 0.01);
++  }
++}
+\ No newline at end of file
+diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/TestStochasticBalancerJmxMetrics.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticBalancerJmxMetrics.java
+similarity index 95%
+rename from hbase-server/src/test/java/org/apache/hadoop/hbase/TestStochasticBalancerJmxMetrics.java
+rename to hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticBalancerJmxMetrics.java
+index 16d2c4d7c5ba..ab1c76c2e9dd 100644
+--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/TestStochasticBalancerJmxMetrics.java
++++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticBalancerJmxMetrics.java
+@@ -15,7 +15,7 @@
+  * See the License for the specific language governing permissions and
+  * limitations under the License.
+  */
+-package org.apache.hadoop.hbase;
++package org.apache.hadoop.hbase.master.balancer;
+ 
+ import static org.junit.Assert.assertTrue;
+ 
+@@ -35,10 +35,14 @@
+ import javax.management.remote.JMXConnector;
+ import javax.management.remote.JMXConnectorFactory;
+ import org.apache.hadoop.conf.Configuration;
++import org.apache.hadoop.hbase.HBaseClassTestRule;
++import org.apache.hadoop.hbase.HBaseTestingUtility;
++import org.apache.hadoop.hbase.HConstants;
++import org.apache.hadoop.hbase.JMXListener;
++import org.apache.hadoop.hbase.ServerName;
++import org.apache.hadoop.hbase.TableName;
+ import org.apache.hadoop.hbase.client.RegionInfo;
+ import org.apache.hadoop.hbase.coprocessor.CoprocessorHost;
+-import org.apache.hadoop.hbase.master.balancer.BalancerTestBase;
+-import org.apache.hadoop.hbase.master.balancer.StochasticLoadBalancer;
+ import org.apache.hadoop.hbase.testclassification.MediumTests;
+ import org.apache.hadoop.hbase.testclassification.MiscTests;
+ import org.apache.hadoop.hbase.util.Threads;
+@@ -199,7 +203,9 @@ public void testJmxMetrics_PerTableMode() throws Exception {
+     final int count = 0;
+     for (int i = 0; i < 10; i++) {
+       Set<String> metrics = readJmxMetrics();
+-      if (metrics != null) return metrics;
++      if (metrics != null) {
++        return metrics;
++      }
+       LOG.warn("Failed to get jmxmetrics... sleeping, retrying; " + i + " of " + count + " times");
+       Threads.sleep(1000);
+     }
+@@ -208,7 +214,6 @@ public void testJmxMetrics_PerTableMode() throws Exception {
+ 
+   /**
+    * Read the attributes from Hadoop->HBase->Master->Balancer in JMX
+-   * @throws IOException
+    */
+   private Set<String> readJmxMetrics() throws IOException {
+     JMXConnector connector = null;
+@@ -273,7 +278,9 @@ public void testJmxMetrics_PerTableMode() throws Exception {
+   }
+ 
+   private static void printMetrics(Set<String> metrics, String info) {
+-    if (null != info) LOG.info("++++ ------ " + info + " ------");
++    if (null != info) {
++      LOG.info("++++ ------ " + info + " ------");
++    }
+ 
+     LOG.info("++++ metrics count = " + metrics.size());
+     for (String str : metrics) {
+diff --git a/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java
+index b97679f0470f..ea65f96eaf51 100644
+--- a/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java
++++ b/hbase-server/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancer.java
+@@ -358,34 +358,6 @@ public void testRegionLoadCost() {
+     assertEquals(2.5, result, 0.01);
+   }
+ 
+-  @Test
+-  public void testCostFromArray() {
+-    Configuration conf = HBaseConfiguration.create();
+-    StochasticLoadBalancer.CostFromRegionLoadFunction
+-        costFunction = new StochasticLoadBalancer.MemStoreSizeCostFunction(conf);
+-    costFunction.init(mockCluster(new int[]{0, 0, 0, 0, 1}));
+-
+-    double[] statOne = new double[100];
+-    for (int i =0; i < 100; i++) {
+-      statOne[i] = 10;
+-    }
+-    assertEquals(0, costFunction.costFromArray(statOne), 0.01);
+-
+-    double[] statTwo= new double[101];
+-    for (int i =0; i < 100; i++) {
+-      statTwo[i] = 0;
+-    }
+-    statTwo[100] = 100;
+-    assertEquals(1, costFunction.costFromArray(statTwo), 0.01);
+-
+-    double[] statThree = new double[200];
+-    for (int i =0; i < 100; i++) {
+-      statThree[i] = (0);
+-      statThree[i+100] = 100;
+-    }
+-    assertEquals(0.5, costFunction.costFromArray(statThree), 0.01);
+-  }
+-
+   @Test
+   public void testLosingRs() throws Exception {
+     int numNodes = 3;