HBASE-25739 TableSkewCostFunction need to use aggregated deviation

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

@@ -81,7 +81,11 @@ class BalancerClusterState {
   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[] numRegionsPerTable; // tableIndex -> region count
+  double[] meanRegionsPerTable; // mean region count per table
+  double[] regionSkewByTable;       // skew on RS per by table
+  double[] minRegionSkewByTable;       // min skew on RS per by table
+  double[] maxRegionSkewByTable;       // max skew on RS per by table
   int[] regionIndexToPrimaryIndex; // regionIndex -> regionIndex of the primary
   boolean hasRegionReplicas = false; // whether there is regions with replicas
 
@@ -290,7 +294,9 @@ public String getRack(ServerName server) {
     }
 
     numTables = tables.size();
+    LOG.debug("Number of tables={}", numTables);
     numRegionsPerServerPerTable = new int[numServers][numTables];
+    numRegionsPerTable = new int[numTables];
 
     for (int i = 0; i < numServers; i++) {
       for (int j = 0; j < numTables; j++) {
@@ -301,15 +307,26 @@ public String getRack(ServerName server) {
     for (int i = 0; i < regionIndexToServerIndex.length; i++) {
       if (regionIndexToServerIndex[i] >= 0) {
         numRegionsPerServerPerTable[regionIndexToServerIndex[i]][regionIndexToTableIndex[i]]++;
+        numRegionsPerTable[regionIndexToTableIndex[i]]++;
       }
     }
 
-    numMaxRegionsPerTable = new int[numTables];
+    // Avoid repeated computation for planning
+    meanRegionsPerTable = new double[numTables];
+    regionSkewByTable = new double[numTables];
+    maxRegionSkewByTable  = new double[numTables];
+    minRegionSkewByTable = new double[numTables];
+
+    for (int i = 0; i < numTables; i++) {
+      meanRegionsPerTable[i] = Double.valueOf(numRegionsPerTable[i]) / numServers;
+      minRegionSkewByTable[i] += DoubleArrayCost.getMinSkew(numRegionsPerTable[i], numServers);
+      maxRegionSkewByTable[i] += DoubleArrayCost.getMaxSkew(numRegionsPerTable[i], numServers);
+    }
+
     for (int[] aNumRegionsPerServerPerTable : numRegionsPerServerPerTable) {
-      for (tableIndex = 0; tableIndex < aNumRegionsPerServerPerTable.length; tableIndex++) {
-        if (aNumRegionsPerServerPerTable[tableIndex] > numMaxRegionsPerTable[tableIndex]) {
-          numMaxRegionsPerTable[tableIndex] = aNumRegionsPerServerPerTable[tableIndex];
-        }
+      for (int tableIdx = 0; tableIdx < aNumRegionsPerServerPerTable.length; tableIdx++) {
+        regionSkewByTable[tableIdx] += Math.abs(aNumRegionsPerServerPerTable[tableIdx] -
+          meanRegionsPerTable[tableIdx]);
       }
     }
 
@@ -671,22 +688,13 @@ void regionMoved(int region, int oldServer, int newServer) {
     int tableIndex = regionIndexToTableIndex[region];
     if (oldServer >= 0) {
       numRegionsPerServerPerTable[oldServer][tableIndex]--;
+      // update regionSkewPerTable for the move from old server
+      regionSkewByTable[tableIndex] += getSkewChangeFor(oldServer, tableIndex, -1);
     }
     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 regionSkewPerTable for the move to new server
+    regionSkewByTable[tableIndex] += getSkewChangeFor(newServer, tableIndex, 1);
 
     // update for servers
     int primary = regionIndexToPrimaryIndex[region];
@@ -856,10 +864,18 @@ public String toString() {
       .append(Arrays.toString(serverIndicesSortedByRegionCount)).append(", regionsPerServer=")
       .append(Arrays.deepToString(regionsPerServer));
 
-    desc.append(", numMaxRegionsPerTable=").append(Arrays.toString(numMaxRegionsPerTable))
+    desc.append(", regionSkewByTable=").append(Arrays.toString(regionSkewByTable))
       .append(", numRegions=").append(numRegions).append(", numServers=").append(numServers)
       .append(", numTables=").append(numTables).append(", numMovedRegions=").append(numMovedRegions)
       .append('}');
     return desc.toString();
   }
-}
+
+  private double getSkewChangeFor(int serverIndex, int tableIndex, int regionCountChange) {
+    double curSkew = Math.abs(numRegionsPerServerPerTable[serverIndex][tableIndex] -
+      meanRegionsPerTable[tableIndex]);
+    double oldSkew = Math.abs(numRegionsPerServerPerTable[serverIndex][tableIndex] -
+      regionCountChange - meanRegionsPerTable[tableIndex]);
+    return curSkew - oldSkew;
+  }
+}

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

@@ -25,6 +25,8 @@
 @InterfaceAudience.Private
 abstract class CostFunction {
 
+  public static final double COST_EPSILON = 0.0001;
+
   private float multiplier = 0;
 
   protected BalancerClusterState cluster;
@@ -89,13 +91,14 @@ protected void regionMoved(int region, int oldServer, int newServer) {
    * @return The scaled value.
    */
   protected static double scale(double min, double max, double value) {
-    if (max <= min || value <= min) {
+    if (max <= min || value <= min
+      || Math.abs(max - min) <= COST_EPSILON || Math.abs(value - min) <= COST_EPSILON) {
       return 0;
     }
-    if ((max - min) == 0) {
+    if (max <= min || Math.abs(max - min) <= COST_EPSILON) {
       return 0;
     }
 
     return Math.max(0d, Math.min(1d, (value - min) / (max - min)));
   }
-}
+}

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

@@ -72,31 +72,13 @@ private static double computeCost(double[] 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 = CostFunction.scale(min, max, totalCost);
-    return scaled;
+    return CostFunction.scale(getMinSkew(total, count),
+      getMaxSkew(total, count), totalCost);
   }
 
   private static double getSum(double[] stats) {
@@ -106,4 +88,33 @@ private static double getSum(double[] stats) {
     }
     return total;
   }
+
+  /**
+   * Return the min skew of distribution
+   * @param total is total number of regions
+   */
+  public static double getMinSkew(double total, double numServers) {
+    double mean = total / numServers;
+    // It's possible that there aren't enough regions to go around
+    double min;
+    if (numServers > total) {
+      min = ((numServers - total) * mean + (1 - mean) * total) ;
+    } else {
+      // Some will have 1 more than everything else.
+      int numHigh = (int) (total - (Math.floor(mean) * numServers));
+      int numLow = (int) (numServers - numHigh);
+      min = numHigh * (Math.ceil(mean) - mean) + numLow * (mean - Math.floor(mean));
+    }
+    return min;
+  }
+
+  /**
+   * Return the max deviation of distribution
+   * 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.
+   */
+  public static double getMaxSkew(double total, double numServers) {
+    double mean = total / numServers;
+    return (total - mean) + (numServers - 1) * mean;
+  }
 }

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

@@ -125,7 +125,7 @@ public class StochasticLoadBalancer extends BaseLoadBalancer {
   private int stepsPerRegion = 800;
   private long maxRunningTime = 30 * 1000 * 1; // 30 seconds.
   private int numRegionLoadsToRemember = 15;
-  private float minCostNeedBalance = 0.05f;
+  private float minCostNeedBalance = 0.025f;
 
   private List<CandidateGenerator> candidateGenerators;
   private List<CostFunction> costFunctions; // FindBugs: Wants this protected; IS2_INCONSISTENT_SYNC
@@ -240,7 +240,8 @@ protected void loadConf(Configuration conf) {
     curFunctionCosts = new double[costFunctions.size()];
     tempFunctionCosts = new double[costFunctions.size()];
 
-    LOG.info("Loaded config; maxSteps=" + maxSteps + ", stepsPerRegion=" + stepsPerRegion +
+    LOG.info("Loaded config; maxSteps=" + maxSteps + ", runMaxSteps=" + runMaxSteps,
+      ", stepsPerRegion=" + stepsPerRegion +
       ", maxRunningTime=" + maxRunningTime + ", isByTable=" + isByTable + ", CostFunctions=" +
       Arrays.toString(getCostFunctionNames()) + " etc.");
   }

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

@@ -26,7 +26,6 @@
  */
 @InterfaceAudience.Private
 class TableSkewCostFunction extends CostFunction {
-
   private static final String TABLE_SKEW_COST_KEY =
     "hbase.master.balancer.stochastic.tableSkewCost";
   private static final float DEFAULT_TABLE_SKEW_COST = 35;
@@ -37,14 +36,11 @@ class TableSkewCostFunction extends CostFunction {
 
   @Override
   protected double cost() {
-    double max = cluster.numRegions;
-    double min = ((double) cluster.numRegions) / cluster.numServers;
-    double value = 0;
-
-    for (int i = 0; i < cluster.numMaxRegionsPerTable.length; i++) {
-      value += cluster.numMaxRegionsPerTable[i];
+    double cost = 0;
+    for (int tableIdx = 0; tableIdx < cluster.numTables; tableIdx++) {
+      cost += scale(cluster.minRegionSkewByTable[tableIdx],
+        cluster.maxRegionSkewByTable[tableIdx], cluster.regionSkewByTable[tableIdx]);
     }
-
-    return scale(min, max, value);
+    return cost;
   }
-}
+}

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

@@ -46,7 +46,7 @@ public static void beforeAllTests() throws Exception {
     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.setLong(StochasticLoadBalancer.MAX_RUNNING_TIME_KEY, 3 * 60 * 1000L);
+    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", true);
     loadBalancer = new StochasticLoadBalancer();
     loadBalancer.setClusterInfoProvider(new DummyClusterInfoProvider(conf));
     loadBalancer.initialize();

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

@@ -355,8 +355,8 @@ public void testRegionAvailabilityWithRegionMoves() throws Exception {
 
     // now move region1 from servers[0] to servers[2]
     cluster.doAction(new MoveRegionAction(0, 0, 2));
-    // check that the numMaxRegionsPerTable for "table" has increased to 2
-    assertEquals(2, cluster.numMaxRegionsPerTable[0]);
+    // check that the regionSkewByTable for "table" has increased to 2
+    assertEquals(2, cluster.regionSkewByTable[0], 0.01);
     // now repeat check whether moving region1 from servers[1] to servers[2]
     // would lower availability
     assertTrue(cluster.wouldLowerAvailability(hri1, servers[2]));

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

@@ -51,15 +51,12 @@ public class TestStochasticLoadBalancerBalanceCluster extends StochasticBalancer
    */
   @Test
   public void testBalanceCluster() throws Exception {
-    conf.setLong(StochasticLoadBalancer.MAX_STEPS_KEY, 2000000L);
-    conf.setLong("hbase.master.balancer.stochastic.maxRunningTime", 90 * 1000); // 90 sec
     conf.setFloat("hbase.master.balancer.stochastic.maxMovePercent", 1.0f);
     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-balancer/src/test/java/org/apache/hadoop/hbase/master/balancer/TestStochasticLoadBalancerHeterogeneousCost.java

@@ -70,7 +70,6 @@ public static void beforeAllTests() throws IOException {
     conf.setFloat("hbase.master.balancer.stochastic.regionCountCost", 0);
     conf.setFloat("hbase.master.balancer.stochastic.primaryRegionCountCost", 0);
     conf.setFloat("hbase.master.balancer.stochastic.tableSkewCost", 0);
-    conf.setBoolean("hbase.master.balancer.stochastic.runMaxSteps", true);
     conf.set(StochasticLoadBalancer.COST_FUNCTIONS_COST_FUNCTIONS_KEY,
       HeterogeneousRegionCountCostFunction.class.getName());
     // Need to ensure test dir has been created.
@@ -303,4 +302,4 @@ BalanceAction generate(BalancerClusterState cluster) {
       return super.generate(cluster);
     }
   }
-}
+}

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

@@ -38,6 +38,9 @@ public void testLargeCluster() {
     int numRegionsPerServer = 80; // all servers except one
     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);
+    loadBalancer.onConfigurationChange(conf);
     testWithCluster(numNodes, numRegions, numRegionsPerServer, replication, numTables, true, true);
   }
 }