HBASE-26311 Balancer gets stuck in cohosted replica distribution (#3724)

Signed-off-by: Huaxiang Sun <[email protected]>

Author: clarax

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

@@ -84,12 +84,9 @@ class BalancerClusterState {
   int[] regionIndexToServerIndex; // regionIndex -> serverIndex
   int[] initialRegionIndexToServerIndex; // regionIndex -> serverIndex (initial cluster state)
   int[] regionIndexToTableIndex; // regionIndex -> tableIndex
-  int[][] numRegionsPerServerPerTable; // serverIndex -> tableIndex -> # regions
+  int[][] numRegionsPerServerPerTable; // tableIndex -> serverIndex -> tableIndex -> # regions
   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
 
@@ -283,6 +280,11 @@ public String getRack(ServerName server) {
       regionIndex++;
     }
 
+    if (LOG.isDebugEnabled()) {
+      for (int i = 0; i < numServers; i++) {
+        LOG.debug("server {} has {} regions", i, regionsPerServer[i].length);
+      }
+    }
     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++) {
@@ -303,40 +305,29 @@ public String getRack(ServerName server) {
     }
 
     numTables = tables.size();
-    LOG.debug("Number of tables={}", numTables);
-    numRegionsPerServerPerTable = new int[numServers][numTables];
+    LOG.debug("Number of tables={}, number of hosts={}, number of racks={}", numTables,
+      numHosts, numRacks);
+    numRegionsPerServerPerTable = new int[numTables][numServers];
     numRegionsPerTable = new int[numTables];
 
-    for (int i = 0; i < numServers; i++) {
-      for (int j = 0; j < numTables; j++) {
+    for (int i = 0; i < numTables; i++) {
+      for (int j = 0; j < numServers; j++) {
         numRegionsPerServerPerTable[i][j] = 0;
       }
     }
 
     for (int i = 0; i < regionIndexToServerIndex.length; i++) {
       if (regionIndexToServerIndex[i] >= 0) {
-        numRegionsPerServerPerTable[regionIndexToServerIndex[i]][regionIndexToTableIndex[i]]++;
+        numRegionsPerServerPerTable[regionIndexToTableIndex[i]][regionIndexToServerIndex[i]]++;
         numRegionsPerTable[regionIndexToTableIndex[i]]++;
       }
     }
 
     // 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 (int tableIdx = 0; tableIdx < aNumRegionsPerServerPerTable.length; tableIdx++) {
-        regionSkewByTable[tableIdx] += Math.abs(aNumRegionsPerServerPerTable[tableIdx] -
-          meanRegionsPerTable[tableIdx]);
-      }
     }
 
     for (int i = 0; i < regions.length; i++) {
@@ -684,14 +675,9 @@ 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[tableIndex][oldServer]--;
     }
-    numRegionsPerServerPerTable[newServer][tableIndex]++;
-
-    // update regionSkewPerTable for the move to new server
-    regionSkewByTable[tableIndex] += getSkewChangeFor(newServer, tableIndex, 1);
+    numRegionsPerServerPerTable[tableIndex][newServer]++;
 
     // update for servers
     int primary = regionIndexToPrimaryIndex[region];
@@ -865,18 +851,9 @@ public String toString() {
       .append(Arrays.toString(serverIndicesSortedByRegionCount)).append(", regionsPerServer=")
       .append(Arrays.deepToString(regionsPerServer));
 
-    desc.append(", regionSkewByTable=").append(Arrays.toString(regionSkewByTable))
-      .append(", numRegions=").append(numRegions).append(", numServers=").append(numServers)
+    desc.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/DoubleArrayCost.java

@@ -66,17 +66,21 @@ void applyCostsChange(Consumer<double[]> consumer) {
   }
 
   private static double computeCost(double[] stats) {
+    if (stats == null || stats.length == 0) {
+      return 0;
+    }
     double totalCost = 0;
     double total = getSum(stats);
 
     double count = stats.length;
     double mean = total / count;
-
     for (int i = 0; i < stats.length; i++) {
       double n = stats[i];
-      double diff = Math.abs(mean - n);
+      double diff = (mean - n) * (mean - n);
       totalCost += diff;
     }
+    // No need to compute standard deviation with division by cluster size when scaling.
+    totalCost = Math.sqrt(totalCost);
     return CostFunction.scale(getMinSkew(total, count),
       getMaxSkew(total, count), totalCost);
   }
@@ -94,18 +98,22 @@ private static double getSum(double[] stats) {
    * @param total is total number of regions
    */
   public static double getMinSkew(double total, double numServers) {
+    if (numServers == 0) {
+      return 0;
+    }
     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) ;
+      min = ((numServers - total) * mean * mean + (1 - 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));
+      min = numHigh * (Math.ceil(mean) - mean) * (Math.ceil(mean) - mean) +
+        numLow * (mean - Math.floor(mean)) * (mean - Math.floor(mean));
     }
-    return min;
+    return Math.sqrt(min);
   }
 
   /**
@@ -114,7 +122,10 @@ public static double getMinSkew(double total, double numServers) {
    * a zero sum cost for this to make sense.
    */
   public static double getMaxSkew(double total, double numServers) {
+    if (numServers == 0) {
+      return 0;
+    }
     double mean = total / numServers;
-    return (total - mean) + (numServers - 1) * mean;
+    return Math.sqrt((total - mean) * (total - mean) + (numServers - 1) * mean * mean);
   }
 }

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

@@ -34,7 +34,7 @@ class MoveCostFunction extends CostFunction {
   static final float DEFAULT_MOVE_COST = 7;
   static final float DEFAULT_MOVE_COST_OFFPEAK = 3;
   private static final int DEFAULT_MAX_MOVES = 600;
-  private static final float DEFAULT_MAX_MOVE_PERCENT = 0.25f;
+  private static final float DEFAULT_MAX_MOVE_PERCENT = 1.0f;
 
   private final float maxMovesPercent;
   private final ClusterInfoProvider provider;
@@ -79,4 +79,4 @@ protected double cost() {
 
     return scale(0, Math.min(cluster.numRegions, maxMoves), moveCost);
   }
-}
+}

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

@@ -19,17 +19,12 @@
 
 import org.apache.hadoop.conf.Configuration;
 import org.apache.yetus.audience.InterfaceAudience;
-import org.slf4j.Logger;
-import org.slf4j.LoggerFactory;
 
 /**
  * Compute the cost of a potential cluster state from skew in number of regions on a cluster.
  */
 @InterfaceAudience.Private
 class RegionCountSkewCostFunction extends CostFunction {
-
-  private static final Logger LOG = LoggerFactory.getLogger(RegionCountSkewCostFunction.class);
-
   static final String REGION_COUNT_SKEW_COST_KEY =
     "hbase.master.balancer.stochastic.regionCountCost";
   static final float DEFAULT_REGION_COUNT_SKEW_COST = 500;
@@ -50,14 +45,6 @@ void prepare(BalancerClusterState cluster) {
         costs[i] = cluster.regionsPerServer[i].length;
       }
     });
-    LOG.debug("{} sees a total of {} servers and {} regions.", getClass().getSimpleName(),
-      cluster.numServers, cluster.numRegions);
-    if (LOG.isTraceEnabled()) {
-      for (int i = 0; i < cluster.numServers; i++) {
-        LOG.trace("{} sees server '{}' has {} regions", getClass().getSimpleName(),
-          cluster.servers[i], cluster.regionsPerServer[i].length);
-      }
-    }
   }
 
   @Override
@@ -72,4 +59,4 @@ protected void regionMoved(int region, int oldServer, int newServer) {
       costs[newServer] = cluster.regionsPerServer[newServer].length;
     });
   }
-}
+}

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

@@ -29,17 +29,43 @@ 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;
+  DoubleArrayCost[] costsPerTable;
 
   TableSkewCostFunction(Configuration conf) {
     this.setMultiplier(conf.getFloat(TABLE_SKEW_COST_KEY, DEFAULT_TABLE_SKEW_COST));
   }
 
+  @Override
+  void prepare(BalancerClusterState cluster) {
+    super.prepare(cluster);
+    costsPerTable = new DoubleArrayCost[cluster.numTables];
+    for (int tableIdx = 0; tableIdx < cluster.numTables; tableIdx++) {
+      costsPerTable[tableIdx] = new DoubleArrayCost();
+      costsPerTable[tableIdx].prepare(cluster.numServers);
+      final int tableIndex = tableIdx;
+      costsPerTable[tableIdx].applyCostsChange(costs -> {
+        // Keep a cached deep copy for change-only recomputation
+        for (int i = 0; i < cluster.numServers; i++) {
+          costs[i] = cluster.numRegionsPerServerPerTable[tableIndex][i];
+        }
+      });
+    }
+  }
+
+  @Override
+  protected void regionMoved(int region, int oldServer, int newServer) {
+    int tableIdx = cluster.regionIndexToTableIndex[region];
+    costsPerTable[tableIdx].applyCostsChange(costs -> {
+      costs[oldServer] = cluster.numRegionsPerServerPerTable[tableIdx][oldServer];
+      costs[newServer] = cluster.numRegionsPerServerPerTable[tableIdx][newServer];
+    });
+  }
+
   @Override
   protected double cost() {
     double cost = 0;
     for (int tableIdx = 0; tableIdx < cluster.numTables; tableIdx++) {
-      cost += scale(cluster.minRegionSkewByTable[tableIdx],
-        cluster.maxRegionSkewByTable[tableIdx], cluster.regionSkewByTable[tableIdx]);
+      cost += costsPerTable[tableIdx].cost();
     }
     return cost;
   }

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

@@ -45,7 +45,6 @@ public class StochasticBalancerTestBase extends BalancerTestBase {
   public static void beforeAllTests() throws Exception {
     conf = HBaseConfiguration.create();
     conf.setClass("hbase.util.ip.to.rack.determiner", MockMapping.class, DNSToSwitchMapping.class);
-    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);

hbase-balancer/src/test/java/org/apache/hadoop/hbase/master/balancer/StochasticBalancerTestBase2.java

@@ -24,7 +24,6 @@ public class StochasticBalancerTestBase2 extends StochasticBalancerTestBase {
 
   @Before
   public void before() {
-    conf.setFloat("hbase.master.balancer.stochastic.maxMovePercent", 1.0f);
     conf.setLong(StochasticLoadBalancer.MAX_STEPS_KEY, 2000000L);
     conf.setFloat("hbase.master.balancer.stochastic.localityCost", 0);
     conf.setLong("hbase.master.balancer.stochastic.maxRunningTime", 3 * 60 * 1000L);

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

@@ -355,8 +355,6 @@ public void testRegionAvailabilityWithRegionMoves() throws Exception {
 
     // now move region1 from servers[0] to servers[2]
     cluster.doAction(new MoveRegionAction(0, 0, 2));
-    // 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/TestDoubleArrayCost.java

@@ -62,6 +62,6 @@ public void testComputeCost() {
       }
       costs[100] = 100;
     });
-    assertEquals(0.5, cost.cost(), 0.01);
+    assertEquals(0.0708, cost.cost(), 0.01);
   }
 }

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

@@ -417,13 +417,13 @@ public void testMoveCost() throws Exception {
       cluster.setNumRegions(10000);
       cluster.setNumMovedRegions(250);
       cost = costFunction.cost();
-      assertEquals(0.1f, cost, 0.001);
+      assertEquals(0.025f, cost, 0.001);
       cluster.setNumMovedRegions(1250);
       cost = costFunction.cost();
-      assertEquals(0.5f, cost, 0.001);
+      assertEquals(0.125f, cost, 0.001);
       cluster.setNumMovedRegions(2500);
       cost = costFunction.cost();
-      assertEquals(1.0f, cost, 0.01);
+      assertEquals(0.25f, cost, 0.01);
     }
   }