HDFS-8131. Implement a space balanced block placement policy. Contributed by Liu Shaohui.

hadoop-hdfs-project/hadoop-hdfs/CHANGES.txt

@@ -345,6 +345,9 @@ Release 2.8.0 - UNRELEASED
     HDFS-7891. A block placement policy with best rack failure tolerance.
     (Walter Su via szetszwo)
 
+    HDFS-8131. Implement a space balanced block placement policy (Liu Shaohui
+    via kihwal)
+
   IMPROVEMENTS
 
     HDFS-3918. EditLogTailer shouldn't log WARN when other node

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/DFSConfigKeys.java

@@ -519,7 +519,11 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_WEB_AUTHENTICATION_KERBEROS_KEYTAB_KEY = "dfs.web.authentication.kerberos.keytab";
   public static final String  DFS_NAMENODE_MAX_OP_SIZE_KEY = "dfs.namenode.max.op.size";
   public static final int     DFS_NAMENODE_MAX_OP_SIZE_DEFAULT = 50 * 1024 * 1024;
-  
+  public static final String  DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY =
+      "dfs.namenode.available-space-block-placement-policy.balanced-space-preference-fraction";
+  public static final float   DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT =
+      0.6f;
+
   public static final String DFS_BLOCK_LOCAL_PATH_ACCESS_USER_KEY = "dfs.block.local-path-access.user";
   public static final String DFS_DOMAIN_SOCKET_PATH_KEY = "dfs.domain.socket.path";
   public static final String DFS_DOMAIN_SOCKET_PATH_DEFAULT = "";

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/AvailableSpaceBlockPlacementPolicy.java

@@ -0,0 +1,95 @@
+/**
+ * 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.hdfs.server.blockmanagement;
+
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY;
+import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT;
+
+import java.util.Random;
+
+import org.apache.commons.logging.Log;
+import org.apache.commons.logging.LogFactory;
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.net.NetworkTopology;
+
+/**
+ * Space balanced block placement policy.
+ */
+public class AvailableSpaceBlockPlacementPolicy extends
+    BlockPlacementPolicyDefault {
+  private static final Log LOG = LogFactory
+      .getLog(AvailableSpaceBlockPlacementPolicy.class);
+  private static final Random RAND = new Random();
+  private int balancedPreference =
+      (int) (100 * DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT);
+
+  @Override
+  public void initialize(Configuration conf, FSClusterStats stats,
+      NetworkTopology clusterMap, Host2NodesMap host2datanodeMap) {
+    super.initialize(conf, stats, clusterMap, host2datanodeMap);
+    float balancedPreferencePercent =
+        conf.getFloat(
+          DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY,
+          DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_DEFAULT);
+
+    LOG.info("Available space block placement policy initialized: "
+        + DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
+        + " = " + balancedPreferencePercent);
+
+    if (balancedPreferencePercent > 1.0) {
+      LOG.warn("The value of "
+          + DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
+          + " is greater than 1.0 but should be in the range 0.0 - 1.0");
+    }
+    if (balancedPreferencePercent < 0.5) {
+      LOG.warn("The value of "
+          + DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY
+          + " is less than 0.5 so datanodes with more used percent will"
+          + " receive  more block allocations.");
+    }
+    balancedPreference = (int) (100 * balancedPreferencePercent);
+  }
+
+  @Override
+  protected DatanodeDescriptor chooseDataNode(String scope) {
+    DatanodeDescriptor a = (DatanodeDescriptor) clusterMap.chooseRandom(scope);
+    DatanodeDescriptor b = (DatanodeDescriptor) clusterMap.chooseRandom(scope);
+    int ret = compareDataNode(a, b);
+    if (ret == 0) {
+      return a;
+    } else if (ret < 0) {
+      return (RAND.nextInt(100) < balancedPreference) ? a : b;
+    } else {
+      return (RAND.nextInt(100) < balancedPreference) ? b : a;
+    }
+  }
+
+  /**
+   * Compare the two data nodes.
+   */
+  protected int compareDataNode(final DatanodeDescriptor a,
+      final DatanodeDescriptor b) {
+    if (a.equals(b)
+        || Math.abs(a.getDfsUsedPercent() - b.getDfsUsedPercent()) < 5) {
+      return 0;
+    }
+    return a.getDfsUsedPercent() < b.getDfsUsedPercent() ? -1 : 1;
+  }
+}

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/blockmanagement/BlockPlacementPolicyDefault.java

@@ -646,8 +646,7 @@ protected DatanodeStorageInfo chooseRandom(int numOfReplicas,
     boolean badTarget = false;
     DatanodeStorageInfo firstChosen = null;
     while(numOfReplicas > 0 && numOfAvailableNodes > 0) {
-      DatanodeDescriptor chosenNode = 
-          (DatanodeDescriptor)clusterMap.chooseRandom(scope);
+      DatanodeDescriptor chosenNode = chooseDataNode(scope);
       if (excludedNodes.add(chosenNode)) { //was not in the excluded list
         if (LOG.isDebugEnabled()) {
           builder.append("\nNode ").append(NodeBase.getPath(chosenNode)).append(" [");
@@ -708,6 +707,14 @@ protected DatanodeStorageInfo chooseRandom(int numOfReplicas,
     return firstChosen;
   }
 
+  /**
+   * Choose a datanode from the given <i>scope</i>.
+   * @return the chosen node, if there is any.
+   */
+  protected DatanodeDescriptor chooseDataNode(final String scope) {
+    return (DatanodeDescriptor) clusterMap.chooseRandom(scope);
+  }
+
   /**
    * If the given storage is a good target, add it to the result list and
    * update the set of excluded nodes.

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/hdfs/server/blockmanagement/TestAvailableSpaceBlockPlacementPolicy.java

@@ -0,0 +1,167 @@
+/**
+ * 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.hdfs.server.blockmanagement;
+
+import java.io.File;
+import java.util.ArrayList;
+
+import org.apache.hadoop.conf.Configuration;
+import org.apache.hadoop.fs.FileSystem;
+import org.apache.hadoop.hdfs.DFSConfigKeys;
+import org.apache.hadoop.hdfs.DFSTestUtil;
+import org.apache.hadoop.hdfs.HdfsConfiguration;
+import org.apache.hadoop.hdfs.TestBlockStoragePolicy;
+import org.apache.hadoop.hdfs.server.common.HdfsServerConstants;
+import org.apache.hadoop.hdfs.server.namenode.NameNode;
+import org.apache.hadoop.net.NetworkTopology;
+import org.apache.hadoop.test.PathUtils;
+import org.junit.AfterClass;
+import org.junit.Assert;
+import org.junit.BeforeClass;
+import org.junit.Test;
+
+public class TestAvailableSpaceBlockPlacementPolicy {
+  private final static int numRacks = 4;
+  private final static int nodesPerRack = 5;
+  private final static int blockSize = 1024;
+  private final static int chooseTimes = 10000;
+  private final static String file = "/tobers/test";
+  private final static int replica = 3;
+
+  private static DatanodeStorageInfo[] storages;
+  private static DatanodeDescriptor[] dataNodes;
+  private static Configuration conf;
+  private static NameNode namenode;
+  private static BlockPlacementPolicy placementPolicy;
+  private static NetworkTopology cluster;
+
+  @BeforeClass
+  public static void setupCluster() throws Exception {
+    conf = new HdfsConfiguration();
+    conf.setFloat(
+      DFSConfigKeys.DFS_NAMENODE_AVAILABLE_SPACE_BLOCK_PLACEMENT_POLICY_BALANCED_SPACE_PREFERENCE_FRACTION_KEY,
+      0.6f);
+    String[] racks = new String[numRacks];
+    for (int i = 0; i < numRacks; i++) {
+      racks[i] = "/rack" + i;
+    }
+
+    String[] owerRackOfNodes = new String[numRacks * nodesPerRack];
+    for (int i = 0; i < nodesPerRack; i++) {
+      for (int j = 0; j < numRacks; j++) {
+        owerRackOfNodes[i * numRacks + j] = racks[j];
+      }
+    }
+
+    storages = DFSTestUtil.createDatanodeStorageInfos(owerRackOfNodes);
+    dataNodes = DFSTestUtil.toDatanodeDescriptor(storages);
+
+    FileSystem.setDefaultUri(conf, "hdfs://localhost:0");
+    conf.set(DFSConfigKeys.DFS_NAMENODE_HTTP_ADDRESS_KEY, "0.0.0.0:0");
+    File baseDir = PathUtils.getTestDir(AvailableSpaceBlockPlacementPolicy.class);
+    conf.set(DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY, new File(baseDir, "name").getPath());
+    conf.set(DFSConfigKeys.DFS_BLOCK_REPLICATOR_CLASSNAME_KEY,
+      AvailableSpaceBlockPlacementPolicy.class.getName());
+
+    DFSTestUtil.formatNameNode(conf);
+    namenode = new NameNode(conf);
+
+    final BlockManager bm = namenode.getNamesystem().getBlockManager();
+    placementPolicy = bm.getBlockPlacementPolicy();
+    cluster = bm.getDatanodeManager().getNetworkTopology();
+    for (int i = 0; i < nodesPerRack * numRacks; i++) {
+      cluster.add(dataNodes[i]);
+    }
+
+    setupDataNodeCapacity();
+  }
+
+  private static void updateHeartbeatWithUsage(DatanodeDescriptor dn,
+      long capacity, long dfsUsed, long remaining, long blockPoolUsed,
+      long dnCacheCapacity, long dnCacheUsed, int xceiverCount,
+      int volFailures) {
+    dn.getStorageInfos()[0].setUtilizationForTesting(
+        capacity, dfsUsed, remaining, blockPoolUsed);
+    dn.updateHeartbeat(
+        BlockManagerTestUtil.getStorageReportsForDatanode(dn),
+        dnCacheCapacity, dnCacheUsed, xceiverCount, volFailures, null);
+  }
+
+  private static void setupDataNodeCapacity() {
+    for (int i = 0; i < nodesPerRack * numRacks; i++) {
+      if ((i % 2) == 0) {
+        // remaining 100%
+        updateHeartbeatWithUsage(dataNodes[i], 2 * HdfsServerConstants.MIN_BLOCKS_FOR_WRITE * blockSize,
+          0L, 2 * HdfsServerConstants.MIN_BLOCKS_FOR_WRITE * blockSize, 0L, 0L, 0L, 0, 0);
+      } else {
+        // remaining 50%
+        updateHeartbeatWithUsage(dataNodes[i], 2 * HdfsServerConstants.MIN_BLOCKS_FOR_WRITE * blockSize,
+          HdfsServerConstants.MIN_BLOCKS_FOR_WRITE * blockSize, HdfsServerConstants.MIN_BLOCKS_FOR_WRITE
+              * blockSize, 0L, 0L, 0L, 0, 0);
+      }
+    }
+  }
+
+  /*
+   * To verify that the BlockPlacementPolicy can be replaced by AvailableSpaceBlockPlacementPolicy via
+   * changing the configuration.
+   */
+  @Test
+  public void testPolicyReplacement() {
+    Assert.assertTrue((placementPolicy instanceof AvailableSpaceBlockPlacementPolicy));
+  }
+
+  /*
+   * Call choose target many times and verify that nodes with more remaining percent will be chosen
+   * with high possibility.
+   */
+  @Test
+  public void testChooseTarget() {
+    int total = 0;
+    int moreRemainingNode = 0;
+    for (int i = 0; i < chooseTimes; i++) {
+      DatanodeStorageInfo[] targets =
+          namenode
+              .getNamesystem()
+              .getBlockManager()
+              .getBlockPlacementPolicy()
+              .chooseTarget(file, replica, null, new ArrayList<DatanodeStorageInfo>(), false, null,
+                blockSize, TestBlockStoragePolicy.DEFAULT_STORAGE_POLICY);
+
+      Assert.assertTrue(targets.length == replica);
+      for (int j = 0; j < replica; j++) {
+        total++;
+        if (targets[j].getDatanodeDescriptor().getRemainingPercent() > 60) {
+          moreRemainingNode++;
+        }
+      }
+    }
+    Assert.assertTrue(total == replica * chooseTimes);
+    double possibility = 1.0 * moreRemainingNode / total;
+    Assert.assertTrue(possibility > 0.52);
+    Assert.assertTrue(possibility < 0.55);
+  }
+
+  @AfterClass
+  public static void teardownCluster() {
+    if (namenode != null) {
+      namenode.stop();
+    }
+  }
+}