HDFS-4270. Replications of the highest priority should be allowed to choose a source datanode that has reached its max replication limit (Derek Dagit via tgraves)

git-svn-id: https://svn.apache.org/repos/asf/hadoop/common/branches/branch-0.23@1428883 13f79535-47bb-0310-9956-ffa450edef68

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

@@ -29,6 +29,10 @@ Release 0.23.6 - UNRELEASED
     HDFS-4315. DNs with multiple BPs can have BPOfferServices fail to start
     due to unsynchronized map access. (atm via tgraves)
 
+    HDFS-4270. Replications of the highest priority should be allowed to 
+    choose a source datanode that has reached its max replication limit 
+    (Derek Dagit via tgraves)
+
 Release 0.23.5 - UNRELEASED
 
   INCOMPATIBLE CHANGES

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

@@ -118,6 +118,8 @@ public class DFSConfigKeys extends CommonConfigurationKeys {
   public static final int     DFS_NAMENODE_REPLICATION_PENDING_TIMEOUT_SEC_DEFAULT = -1;
   public static final String  DFS_NAMENODE_REPLICATION_MAX_STREAMS_KEY = "dfs.namenode.replication.max-streams";
   public static final int     DFS_NAMENODE_REPLICATION_MAX_STREAMS_DEFAULT = 2;
+  public static final String  DFS_NAMENODE_REPLICATION_STREAMS_HARD_LIMIT_KEY = "dfs.namenode.replication.max-streams-hard-limit";
+  public static final int     DFS_NAMENODE_REPLICATION_STREAMS_HARD_LIMIT_DEFAULT = 4;
   public static final String  DFS_WEBHDFS_ENABLED_KEY = "dfs.webhdfs.enabled";
   public static final boolean DFS_WEBHDFS_ENABLED_DEFAULT = false;
   public static final String  DFS_PERMISSIONS_ENABLED_KEY = "dfs.permissions.enabled";

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

@@ -156,10 +156,16 @@ public class BlockManager {
 
   /** The maximum number of replicas allowed for a block */
   public final short maxReplication;
-  /** The maximum number of outgoing replication streams
-   *  a given node should have at one time 
+  /**
+   * The maximum number of outgoing replication streams a given node should have
+   * at one time considering all but the highest priority replications needed.
    */
   int maxReplicationStreams;
+  /**
+   * The maximum number of outgoing replication streams a given node should have
+   * at one time.
+   */
+  int replicationStreamsHardLimit;
   /** Minimum copies needed or else write is disallowed */
   public final short minReplication;
   /** Default number of replicas */
@@ -219,10 +225,16 @@ public class BlockManager {
     this.minReplication = (short)minR;
     this.maxReplication = (short)maxR;
 
-    this.maxReplicationStreams = conf.getInt(DFSConfigKeys.DFS_NAMENODE_REPLICATION_MAX_STREAMS_KEY,
-                                             DFSConfigKeys.DFS_NAMENODE_REPLICATION_MAX_STREAMS_DEFAULT);
-    this.shouldCheckForEnoughRacks = conf.get(DFSConfigKeys.NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY) == null ? false
-                                                                             : true;
+    this.maxReplicationStreams =
+        conf.getInt(DFSConfigKeys.DFS_NAMENODE_REPLICATION_MAX_STREAMS_KEY,
+            DFSConfigKeys.DFS_NAMENODE_REPLICATION_MAX_STREAMS_DEFAULT);
+    this.replicationStreamsHardLimit =
+        conf.getInt(
+            DFSConfigKeys.DFS_NAMENODE_REPLICATION_STREAMS_HARD_LIMIT_KEY,
+            DFSConfigKeys.DFS_NAMENODE_REPLICATION_STREAMS_HARD_LIMIT_DEFAULT);
+    this.shouldCheckForEnoughRacks =
+        conf.get(DFSConfigKeys.NET_TOPOLOGY_SCRIPT_FILE_NAME_KEY) == null
+            ? false : true;
     
     this.replicationRecheckInterval = 
       conf.getInt(DFSConfigKeys.DFS_NAMENODE_REPLICATION_INTERVAL_KEY, 
@@ -329,7 +341,8 @@ public class BlockManager {
         NumberReplicas numReplicas = new NumberReplicas();
         // source node returned is not used
         chooseSourceDatanode(block, containingNodes,
-            containingLiveReplicasNodes, numReplicas);
+            containingLiveReplicasNodes, numReplicas,
+            UnderReplicatedBlocks.LEVEL);
         assert containingLiveReplicasNodes.size() == numReplicas.liveReplicas();
         int usableReplicas = numReplicas.liveReplicas() +
                              numReplicas.decommissionedReplicas();
@@ -1047,9 +1060,11 @@ public class BlockManager {
         liveReplicaNodes = new ArrayList<DatanodeDescriptor>();
         NumberReplicas numReplicas = new NumberReplicas();
         srcNode = chooseSourceDatanode(
-            block, containingNodes, liveReplicaNodes, numReplicas);
+            block, containingNodes, liveReplicaNodes, numReplicas, priority);
         if(srcNode == null) // block can not be replicated from any node
+        {
           return false;
+        }
 
         assert liveReplicaNodes.size() == numReplicas.liveReplicas();
         // do not schedule more if enough replicas is already pending
@@ -1212,16 +1227,34 @@ public class BlockManager {
    * since the former do not have write traffic and hence are less busy.
    * We do not use already decommissioned nodes as a source.
    * Otherwise we choose a random node among those that did not reach their
-   * replication limit.
+   * replication limits.  However, if the replication is of the highest priority
+   * and all nodes have reached their replication limits, we will choose a
+   * random node despite the replication limit.
    *
    * In addition form a list of all nodes containing the block
    * and calculate its replication numbers.
+   *
+   * @param block Block for which a replication source is needed
+   * @param containingNodes List to be populated with nodes found to contain the
+   *                        given block
+   * @param nodesContainingLiveReplicas List to be populated with nodes found to
+   *                                    contain live replicas of the given block
+   * @param numReplicas NumberReplicas instance to be initialized with the
+   *                                   counts of live, corrupt, excess, and
+   *                                   decommissioned replicas of the given
+   *                                   block.
+   * @param priority integer representing replication priority of the given
+   *                 block
+   * @return the DatanodeDescriptor of the chosen node from which to replicate
+   *         the given block
    */
-  private DatanodeDescriptor chooseSourceDatanode(
+  @VisibleForTesting
+  DatanodeDescriptor chooseSourceDatanode(
                                     Block block,
                                     List<DatanodeDescriptor> containingNodes,
                                     List<DatanodeDescriptor> nodesContainingLiveReplicas,
-                                    NumberReplicas numReplicas) {
+                                    NumberReplicas numReplicas,
+                                    int priority) {
     containingNodes.clear();
     nodesContainingLiveReplicas.clear();
     DatanodeDescriptor srcNode = null;
@@ -1250,8 +1283,15 @@ public class BlockManager {
       // If so, do not select the node as src node
       if ((nodesCorrupt != null) && nodesCorrupt.contains(node))
         continue;
-      if(node.getNumberOfBlocksToBeReplicated() >= maxReplicationStreams)
+      if(priority != UnderReplicatedBlocks.QUEUE_HIGHEST_PRIORITY
+          && node.getNumberOfBlocksToBeReplicated() >= maxReplicationStreams)
+      {
         continue; // already reached replication limit
+      }
+      if (node.getNumberOfBlocksToBeReplicated() >= replicationStreamsHardLimit)
+      {
+        continue;
+      }
       // the block must not be scheduled for removal on srcNode
       if(excessBlocks != null && excessBlocks.contains(block))
         continue;

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

@@ -20,6 +20,7 @@ package org.apache.hadoop.hdfs.server.blockmanagement;
 import static org.junit.Assert.*;
 
 import java.io.IOException;
+import java.util.LinkedList;
 import java.util.List;
 import java.util.Map.Entry;
 
@@ -388,4 +389,57 @@ public class TestBlockManager {
     }
     return repls;
   }
+
+  /**
+   * Test that a source node for a highest-priority replication is chosen even if all available
+   * source nodes have reached their replication limits.
+   */
+  @Test
+  public void testHighestPriReplSrcChosenDespiteMaxReplLimit() throws Exception {
+    bm.maxReplicationStreams = 0;
+    bm.replicationStreamsHardLimit = 1;
+
+    long blockId = 42;         // arbitrary
+    Block aBlock = new Block(blockId, 0, 0);
+
+    List<DatanodeDescriptor> origNodes = nodes(0, 1);
+    // Add the block to the first node.
+    addBlockOnNodes(blockId,origNodes.subList(0,1));
+
+    List<DatanodeDescriptor> cntNodes = new LinkedList<DatanodeDescriptor>();
+    List<DatanodeDescriptor> liveNodes = new LinkedList<DatanodeDescriptor>();
+
+    assertNotNull("Chooses source node for a highest-priority replication"
+        + " even if all available source nodes have reached their replication"
+        + " limits below the hard limit.",
+        bm.chooseSourceDatanode(
+            aBlock,
+            cntNodes,
+            liveNodes,
+            new NumberReplicas(),
+            UnderReplicatedBlocks.QUEUE_HIGHEST_PRIORITY));
+
+    assertNull("Does not choose a source node for a less-than-highest-priority"
+        + " replication since all available source nodes have reached"
+        + " their replication limits.",
+        bm.chooseSourceDatanode(
+            aBlock,
+            cntNodes,
+            liveNodes,
+            new NumberReplicas(),
+            UnderReplicatedBlocks.QUEUE_VERY_UNDER_REPLICATED));
+
+    // Increase the replication count to test replication count > hard limit
+    DatanodeDescriptor targets[] = { origNodes.get(1) };
+    origNodes.get(0).addBlockToBeReplicated(aBlock, targets);
+
+    assertNull("Does not choose a source node for a highest-priority"
+        + " replication when all available nodes exceed the hard limit.",
+        bm.chooseSourceDatanode(
+            aBlock,
+            cntNodes,
+            liveNodes,
+            new NumberReplicas(),
+            UnderReplicatedBlocks.QUEUE_HIGHEST_PRIORITY));
+  }
 }