HDFS-12177. NameNode exits due to setting BlockPlacementPolicy loglevel to Debug. Contributed by Jiandan Yang.

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

@@ -391,6 +391,9 @@ Release 2.7.4 - UNRELEASED
     HDFS-11472. Fix inconsistent replica size after a data pipeline failure.
     (Erik Krogen and Wei-Chiu Chuang via shv)
 
+    HDFS-12177. NameNode exits due to setting BlockPlacementPolicy loglevel to Debug.
+    (Jiandan Yang via Brahma Reddy Battula)
+
 Release 2.7.3 - 2016-08-25
 
   INCOMPATIBLE CHANGES

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

@@ -637,7 +637,7 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
     while(numOfReplicas > 0 && numOfAvailableNodes > 0) {
       DatanodeDescriptor chosenNode = chooseDataNode(scope);
       if (excludedNodes.add(chosenNode)) { //was not in the excluded list
-        if (LOG.isDebugEnabled()) {
+        if (LOG.isDebugEnabled() && builder != null) {
           builder.append("\nNode ").append(NodeBase.getPath(chosenNode)).append(" [");
         }
         numOfAvailableNodes--;
@@ -671,7 +671,7 @@ public class BlockPlacementPolicyDefault extends BlockPlacementPolicy {
             }
           }
         }
-        if (LOG.isDebugEnabled()) {
+        if (LOG.isDebugEnabled() && builder != null) {
           builder.append("\n]");
         }