HDFS-6840. Clients are always sent to the same datanode when read is off rack. (wang)

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopology.java

@@ -26,6 +26,7 @@ import java.util.TreeMap;
 import java.util.concurrent.locks.ReadWriteLock;
 import java.util.concurrent.locks.ReentrantReadWriteLock;
 
+import com.google.common.annotations.VisibleForTesting;
 import org.apache.commons.logging.Log;
 import org.apache.commons.logging.LogFactory;
 import org.apache.hadoop.classification.InterfaceAudience;
@@ -689,6 +690,12 @@ public class NetworkTopology {
     return rand;
   }
 
+  @VisibleForTesting
+  void setRandomSeed(long seed) {
+    Random rand = getRandom();
+    rand.setSeed(seed);
+  }
+
   /** randomly choose one node from <i>scope</i>
    * if scope starts with ~, choose one from the all nodes except for the
    * ones in <i>scope</i>; otherwise, choose one from <i>scope</i>
@@ -870,21 +877,19 @@ public class NetworkTopology {
   /**
    * Sort nodes array by network distance to <i>reader</i>.
    * <p/>
-   * In a three-level topology, a node can be either local, on the same rack, or
-   * on a different rack from the reader. Sorting the nodes based on network
-   * distance from the reader reduces network traffic and improves performance.
+   * In a three-level topology, a node can be either local, on the same rack,
+   * or on a different rack from the reader. Sorting the nodes based on network
+   * distance from the reader reduces network traffic and improves
+   * performance.
    * <p/>
    * As an additional twist, we also randomize the nodes at each network
-   * distance using the provided random seed. This helps with load balancing
-   * when there is data skew.
-   * 
-   * @param reader Node where data will be read
-   * @param nodes Available replicas with the requested data
-   * @param seed Used to seed the pseudo-random generator that randomizes the
-   *          set of nodes at each network distance.
+   * distance. This helps with load balancing when there is data skew.
+   *
+   * @param reader    Node where data will be read
+   * @param nodes     Available replicas with the requested data
+   * @param activeLen Number of active nodes at the front of the array
    */
-  public void sortByDistance(Node reader, Node[] nodes, int activeLen,
-      long seed, boolean randomizeBlockLocationsPerBlock) {
+  public void sortByDistance(Node reader, Node[] nodes, int activeLen) {
     /** Sort weights for the nodes array */
     int[] weights = new int[activeLen];
     for (int i=0; i<activeLen; i++) {
@@ -903,14 +908,7 @@ public class NetworkTopology {
       list.add(node);
     }
 
-    // Seed is normally the block id
-    // This means we use the same pseudo-random order for each block, for
-    // potentially better page cache usage.
-    // Seed is not used if we want to randomize block location for every block
     Random rand = getRandom();
-    if (!randomizeBlockLocationsPerBlock) {
-      rand.setSeed(seed);
-    }
     int idx = 0;
     for (List<Node> list: tree.values()) {
       if (list != null) {

hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/net/NetworkTopologyWithNodeGroup.java

@@ -268,19 +268,17 @@ public class NetworkTopologyWithNodeGroup extends NetworkTopology {
   /**
    * Sort nodes array by their distances to <i>reader</i>.
    * <p/>
-   * This is the same as
-   * {@link NetworkTopology#sortByDistance(Node, Node[], long)} except with a
-   * four-level network topology which contains the additional network distance
-   * of a "node group" which is between local and same rack.
-   * 
-   * @param reader Node where data will be read
-   * @param nodes Available replicas with the requested data
-   * @param seed Used to seed the pseudo-random generator that randomizes the
-   *          set of nodes at each network distance.
+   * This is the same as {@link NetworkTopology#sortByDistance(Node, Node[],
+   * int)} except with a four-level network topology which contains the
+   * additional network distance of a "node group" which is between local and
+   * same rack.
+   *
+   * @param reader    Node where data will be read
+   * @param nodes     Available replicas with the requested data
+   * @param activeLen Number of active nodes at the front of the array
    */
   @Override
-  public void sortByDistance(Node reader, Node[] nodes, int activeLen,
-      long seed, boolean randomizeBlockLocationsPerBlock) {
+  public void sortByDistance(Node reader, Node[] nodes, int activeLen) {
     // If reader is not a datanode (not in NetworkTopology tree), we need to
     // replace this reader with a sibling leaf node in tree.
     if (reader != null && !this.contains(reader)) {
@@ -293,8 +291,7 @@ public class NetworkTopologyWithNodeGroup extends NetworkTopology {
         return;
       }
     }
-    super.sortByDistance(reader, nodes, activeLen, seed,
-        randomizeBlockLocationsPerBlock);
+    super.sortByDistance(reader, nodes, activeLen);
   }
 
   /** InnerNodeWithNodeGroup represents a switch/router of a data center, rack

hadoop-common-project/hadoop-common/src/test/java/org/apache/hadoop/net/TestNetworkTopologyWithNodeGroup.java

@@ -104,8 +104,7 @@ public class TestNetworkTopologyWithNodeGroup {
     testNodes[1] = dataNodes[2];
     testNodes[2] = dataNodes[3];
     testNodes[3] = dataNodes[0];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[1]);
     assertTrue(testNodes[2] == dataNodes[2]);
@@ -116,8 +115,7 @@ public class TestNetworkTopologyWithNodeGroup {
     testNodes[1] = dataNodes[4];
     testNodes[2] = dataNodes[1];
     testNodes[3] = dataNodes[0];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[1]);
 
@@ -126,8 +124,7 @@ public class TestNetworkTopologyWithNodeGroup {
     testNodes[1] = dataNodes[3];
     testNodes[2] = dataNodes[2];
     testNodes[3] = dataNodes[0];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[2]);
 
@@ -136,8 +133,7 @@ public class TestNetworkTopologyWithNodeGroup {
     testNodes[1] = dataNodes[7];
     testNodes[2] = dataNodes[2];
     testNodes[3] = dataNodes[0];
-    cluster.sortByDistance(computeNode, testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.sortByDistance(computeNode, testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[2]);
   }

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

@@ -771,6 +771,9 @@ Release 2.6.0 - UNRELEASED
 
     HDFS-7078. Fix listEZs to work correctly with snapshots. (wang)
 
+    HDFS-6840. Clients are always sent to the same datanode when read
+    is off rack. (wang)
+
     BREAKDOWN OF HDFS-6134 AND HADOOP-10150 SUBTASKS AND RELATED JIRAS
   
       HDFS-6387. HDFS CLI admin tool for creating & deleting an

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

@@ -221,9 +221,6 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final String  DFS_NAMENODE_MIN_SUPPORTED_DATANODE_VERSION_KEY = "dfs.namenode.min.supported.datanode.version";
   public static final String  DFS_NAMENODE_MIN_SUPPORTED_DATANODE_VERSION_DEFAULT = "3.0.0-SNAPSHOT";
 
-  public static final String DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK = "dfs.namenode.randomize-block-locations-per-block";
-  public static final boolean DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK_DEFAULT = false;
-
   public static final String  DFS_NAMENODE_EDITS_DIR_MINIMUM_KEY = "dfs.namenode.edits.dir.minimum";
   public static final int     DFS_NAMENODE_EDITS_DIR_MINIMUM_DEFAULT = 1;
 

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

@@ -348,8 +348,7 @@ public class DatanodeManager {
   
   /** Sort the located blocks by the distance to the target host. */
   public void sortLocatedBlocks(final String targethost,
-      final List<LocatedBlock> locatedblocks,
-      boolean randomizeBlockLocationsPerBlock) {
+      final List<LocatedBlock> locatedblocks) {
     //sort the blocks
     // As it is possible for the separation of node manager and datanode, 
     // here we should get node but not datanode only .
@@ -376,8 +375,7 @@ public class DatanodeManager {
           --lastActiveIndex;
       }
       int activeLen = lastActiveIndex + 1;      
-      networktopology.sortByDistance(client, b.getLocations(), activeLen, b
-          .getBlock().getBlockId(), randomizeBlockLocationsPerBlock);
+      networktopology.sortByDistance(client, b.getLocations(), activeLen);
     }
   }
   

hadoop-hdfs-project/hadoop-hdfs/src/main/java/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -65,8 +65,6 @@ import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_ENABLE_RETRY_CAC
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_MAX_OBJECTS_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_MAX_OBJECTS_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_NAME_DIR_KEY;
-import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK;
-import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_REPLICATION_MIN_DEFAULT;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_REPLICATION_MIN_KEY;
 import static org.apache.hadoop.hdfs.DFSConfigKeys.DFS_NAMENODE_REPL_QUEUE_THRESHOLD_PCT_KEY;
@@ -547,8 +545,6 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
 
   private final FSImage fsImage;
 
-  private boolean randomizeBlockLocationsPerBlock;
-
   /**
    * Notify that loading of this FSDirectory is complete, and
    * it is imageLoaded for use
@@ -865,10 +861,6 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
           DFS_NAMENODE_DELEGATION_TOKEN_ALWAYS_USE_KEY,
           DFS_NAMENODE_DELEGATION_TOKEN_ALWAYS_USE_DEFAULT);
       
-      this.randomizeBlockLocationsPerBlock = conf.getBoolean(
-          DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK,
-          DFS_NAMENODE_RANDOMIZE_BLOCK_LOCATIONS_PER_BLOCK_DEFAULT);
-
       this.dtSecretManager = createDelegationTokenSecretManager(conf);
       this.dir = new FSDirectory(this, conf);
       this.snapshotManager = new SnapshotManager(dir);
@@ -1739,7 +1731,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
         true);
     if (blocks != null) {
       blockManager.getDatanodeManager().sortLocatedBlocks(clientMachine,
-          blocks.getLocatedBlocks(), randomizeBlockLocationsPerBlock);
+          blocks.getLocatedBlocks());
 
       // lastBlock is not part of getLocatedBlocks(), might need to sort it too
       LocatedBlock lastBlock = blocks.getLastLocatedBlock();
@@ -1748,7 +1740,7 @@ public class FSNamesystem implements Namesystem, FSClusterStats,
             Lists.newArrayListWithCapacity(1);
         lastBlockList.add(lastBlock);
         blockManager.getDatanodeManager().sortLocatedBlocks(clientMachine,
-            lastBlockList, randomizeBlockLocationsPerBlock);
+            lastBlockList);
       }
     }
     return blocks;

hadoop-hdfs-project/hadoop-hdfs/src/main/resources/hdfs-default.xml

@@ -2069,19 +2069,6 @@
   </description>
 </property>
 
-<property>
-  <name>dfs.namenode.randomize-block-locations-per-block</name>
-  <value>false</value>
-  <description>When fetching replica locations of a block, the replicas
-   are sorted based on network distance. This configuration parameter
-   determines whether the replicas at the same network distance are randomly
-   shuffled. By default, this is false, such that repeated requests for a block's
-   replicas always result in the same order. This potentially improves page cache
-   behavior. However, for some network topologies, it is desirable to shuffle this
-   order for better load balancing.
-  </description>
-</property>
-
 <property>
   <name>dfs.datanode.block.id.layout.upgrade.threads</name>
   <value>12</value>

hadoop-hdfs-project/hadoop-hdfs/src/test/java/org/apache/hadoop/net/TestNetworkTopology.java

@@ -139,8 +139,8 @@ public class TestNetworkTopology {
     testNodes[0] = dataNodes[1];
     testNodes[1] = dataNodes[2];
     testNodes[2] = dataNodes[0];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.setRandomSeed(0xDEADBEEF);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[1]);
     assertTrue(testNodes[2] == dataNodes[2]);
@@ -152,8 +152,8 @@ public class TestNetworkTopology {
     dtestNodes[2] = dataNodes[11];
     dtestNodes[3] = dataNodes[9];
     dtestNodes[4] = dataNodes[10];
-    cluster.sortByDistance(dataNodes[8], dtestNodes,
-        dtestNodes.length - 2, 0xDEADBEEF, false);
+    cluster.setRandomSeed(0xDEADBEEF);
+    cluster.sortByDistance(dataNodes[8], dtestNodes, dtestNodes.length - 2);
     assertTrue(dtestNodes[0] == dataNodes[8]);
     assertTrue(dtestNodes[1] == dataNodes[11]);
     assertTrue(dtestNodes[2] == dataNodes[12]);
@@ -164,8 +164,8 @@ public class TestNetworkTopology {
     testNodes[0] = dataNodes[1];
     testNodes[1] = dataNodes[3];
     testNodes[2] = dataNodes[0];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.setRandomSeed(0xDEADBEEF);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[0]);
     assertTrue(testNodes[1] == dataNodes[1]);
     assertTrue(testNodes[2] == dataNodes[3]);
@@ -174,8 +174,8 @@ public class TestNetworkTopology {
     testNodes[0] = dataNodes[5];
     testNodes[1] = dataNodes[3];
     testNodes[2] = dataNodes[1];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.setRandomSeed(0xDEADBEEF);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[1]);
     assertTrue(testNodes[1] == dataNodes[3]);
     assertTrue(testNodes[2] == dataNodes[5]);
@@ -184,8 +184,8 @@ public class TestNetworkTopology {
     testNodes[0] = dataNodes[1];
     testNodes[1] = dataNodes[5];
     testNodes[2] = dataNodes[3];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEADBEEF, false);
+    cluster.setRandomSeed(0xDEADBEEF);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     assertTrue(testNodes[0] == dataNodes[1]);
     assertTrue(testNodes[1] == dataNodes[3]);
     assertTrue(testNodes[2] == dataNodes[5]);
@@ -194,24 +194,23 @@ public class TestNetworkTopology {
     testNodes[0] = dataNodes[1];
     testNodes[1] = dataNodes[5];
     testNodes[2] = dataNodes[3];
-    cluster.sortByDistance(dataNodes[0], testNodes,
-        testNodes.length, 0xDEAD, false);
+    cluster.setRandomSeed(0xDEAD);
+    cluster.sortByDistance(dataNodes[0], testNodes, testNodes.length);
     // sortByDistance does not take the "data center" layer into consideration
     // and it doesn't sort by getDistance, so 1, 5, 3 is also valid here
     assertTrue(testNodes[0] == dataNodes[1]);
     assertTrue(testNodes[1] == dataNodes[5]);
     assertTrue(testNodes[2] == dataNodes[3]);
 
-    // Array is just local rack nodes
-    // Expect a random first node depending on the seed (normally the block ID).
+    // Array of just rack-local nodes
+    // Expect a random first node
     DatanodeDescriptor first = null;
     boolean foundRandom = false;
     for (int i=5; i<=7; i++) {
       testNodes[0] = dataNodes[5];
       testNodes[1] = dataNodes[6];
       testNodes[2] = dataNodes[7];
-      cluster.sortByDistance(dataNodes[i], testNodes,
-          testNodes.length, 0xBEADED+i, false);
+      cluster.sortByDistance(dataNodes[i], testNodes, testNodes.length);
       if (first == null) {
         first = testNodes[0];
       } else {
@@ -222,16 +221,15 @@ public class TestNetworkTopology {
       }
     }
     assertTrue("Expected to find a different first location", foundRandom);
-    // Array of rack local nodes with randomizeBlockLocationsPerBlock set to
-    // true
-    // Expect random order of block locations for same block
+
+    // Array of just remote nodes
+    // Expect random first node
     first = null;
     for (int i = 1; i <= 4; i++) {
       testNodes[0] = dataNodes[13];
       testNodes[1] = dataNodes[14];
       testNodes[2] = dataNodes[15];
-      cluster.sortByDistance(dataNodes[15 + i], testNodes, testNodes.length,
-          0xBEADED, true);
+      cluster.sortByDistance(dataNodes[i], testNodes, testNodes.length);
       if (first == null) {
         first = testNodes[0];
       } else {