HADOOP-5595. NameNode does not need to run a replicator to choose a random DataNode. Contributed by Hairong Kuang.

git-svn-id: https://svn.apache.org/repos/asf/hadoop/core/trunk@761447 13f79535-47bb-0310-9956-ffa450edef68

CHANGES.txt

@@ -202,6 +202,9 @@ Trunk (unreleased changes)
 
   OPTIMIZATIONS
 
+    HADOOP-5595. NameNode does not need to run a replicator to choose a
+    random DataNode. (hairong)
+
   BUG FIXES
     
     HADOOP-5379. CBZip2InputStream to throw IOException on data crc error.

src/hdfs/org/apache/hadoop/hdfs/server/namenode/FSNamesystem.java

@@ -37,6 +37,7 @@ import org.apache.hadoop.metrics.util.MBeanUtil;
 import org.apache.hadoop.net.CachedDNSToSwitchMapping;
 import org.apache.hadoop.net.DNSToSwitchMapping;
 import org.apache.hadoop.net.NetworkTopology;
+import org.apache.hadoop.net.NodeBase;
 import org.apache.hadoop.net.ScriptBasedMapping;
 import org.apache.hadoop.hdfs.server.namenode.LeaseManager.Lease;
 import org.apache.hadoop.hdfs.server.protocol.BlocksWithLocations;
@@ -3910,8 +3911,12 @@ public class FSNamesystem implements FSConstants, FSNamesystemMBean {
     return null;
   }
 
+  /** Choose a random datanode
+   * 
+   * @return a randomly chosen datanode
+   */
   public DatanodeDescriptor getRandomDatanode() {
-    return replicator.chooseTarget(1, null, null, 0)[0];
+    return (DatanodeDescriptor)clusterMap.chooseRandom(NodeBase.ROOT);
   }
 
   /**