Zhu Guangbin created HDFS-10715:
-----------------------------------

             Summary: NPE 
                 Key: HDFS-10715
                 URL: https://issues.apache.org/jira/browse/HDFS-10715
             Project: Hadoop HDFS
          Issue Type: Bug
          Components: namenode
    Affects Versions: 2.8.0
         Environment: cdh5.8.0
            Reporter: Zhu Guangbin


As HDFS-8131 introduced an AvailableSpaceBlockPlacementPolicy, but In some 
cases, it caused NPE. 

Here are my namenode daemon logs : 

2016-08-02 13:05:03,271 WARN org.apache.hadoop.ipc.Server: IPC Server handler 
13 on 8020, call org.apache.hadoop.hdfs.protocol.ClientProtocol.addBlock from 
10.132.89.79:14001 Call#56 Retry#0
java.lang.NullPointerException
        at 
org.apache.hadoop.hdfs.server.blockmanagement.AvailableSpaceBlockPlacementPolicy.compareDataNode(AvailableSpaceBlockPlacementPolicy.java:95)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.AvailableSpaceBlockPlacementPolicy.chooseDataNode(AvailableSpaceBlockPlacementPolicy.java:80)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRandom(BlockPlacementPolicyDefault.java:691)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseRandom(BlockPlacementPolicyDefault.java:665)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseLocalRack(BlockPlacementPolicyDefault.java:572)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTargetInOrder(BlockPlacementPolicyDefault.java:457)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:367)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:242)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:114)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockPlacementPolicyDefault.chooseTarget(BlockPlacementPolicyDefault.java:130)
        at 
org.apache.hadoop.hdfs.server.blockmanagement.BlockManager.chooseTarget4NewBlock(BlockManager.java:1606)
        at 
org.apache.hadoop.hdfs.server.namenode.FSNamesystem.getAdditionalBlock(FSNamesystem.java:3315)
        at 
org.apache.hadoop.hdfs.server.namenode.NameNodeRpcServer.addBlock(NameNodeRpcServer.java:679)
        at 
org.apache.hadoop.hdfs.server.namenode.AuthorizationProviderProxyClientProtocol.addBlock(AuthorizationProviderProxyClientProtocol.java:214)
        at 
org.apache.hadoop.hdfs.protocolPB.ClientNamenodeProtocolServerSideTranslatorPB.addBlock(ClientNamenodeProtocolServerSideTranslatorPB.java:489)
        at 
org.apache.hadoop.hdfs.protocol.proto.ClientNamenodeProtocolProtos$ClientNamenodeProtocol$2.callBlockingMethod(ClientNamenodeProtocolProtos.java)
        at 
org.apache.hadoop.ipc.ProtobufRpcEngine$Server$ProtoBufRpcInvoker.call(ProtobufRpcEngine.java:617)
        at org.apache.hadoop.ipc.RPC$Server.call(RPC.java:1073)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2086)
        at org.apache.hadoop.ipc.Server$Handler$1.run(Server.java:2082)
        at java.security.AccessController.doPrivileged(Native Method)
        at javax.security.auth.Subject.doAs(Subject.java:422)
        at 
org.apache.hadoop.security.UserGroupInformation.doAs(UserGroupInformation.java:1693)
        at org.apache.hadoop.ipc.Server$Handler.run(Server.java:2080)

I reviewed the source code, and found the bug in method chooseDataNode. 
clusterMap.chooseRandom may return null, which cannot compare using equals 
a.equals(b) method.  

Though this exception can be caught, and then retry another call. I think this 
bug should be fixed.



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