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  1. Hadoop HDFS
  2. HDFS-7009

Active NN and standby NN have different live nodes

    Details

    • Target Version/s:
    • Hadoop Flags:
      Reviewed

      Description

      To follow up on https://issues.apache.org/jira/browse/HDFS-6478, in most cases, given DN sends HB and BR to NN regularly, if a specific RPC call fails, it isn't a big deal.

      However, there are cases where DN fails to register with NN during initial handshake due to exceptions not covered by RPC client's connection retry. When this happens, the DN won't talk to that NN until the DN restarts.

      BPServiceActor
      
        public void run() {
          LOG.info(this + " starting to offer service");
      
          try {
            // init stuff
            try {
              // setup storage
              connectToNNAndHandshake();
            } catch (IOException ioe) {
              // Initial handshake, storage recovery or registration failed
              // End BPOfferService thread
              LOG.fatal("Initialization failed for block pool " + this, ioe);
              return;
            }
      
            initialized = true; // bp is initialized;
            
            while (shouldRun()) {
              try {
                offerService();
              } catch (Exception ex) {
                LOG.error("Exception in BPOfferService for " + this, ex);
                sleepAndLogInterrupts(5000, "offering service");
              }
            }
      ...
      

      Here is an example of the call stack.

      java.io.IOException: Failed on local exception: java.io.IOException: Response is null.; Host Details : local host is: "xxx"; destination host is: "yyy":8030;
              at org.apache.hadoop.net.NetUtils.wrapException(NetUtils.java:761)
              at org.apache.hadoop.ipc.Client.call(Client.java:1239)
              at org.apache.hadoop.ipc.ProtobufRpcEngine$Invoker.invoke(ProtobufRpcEngine.java:202)
              at com.sun.proxy.$Proxy9.registerDatanode(Unknown Source)
              at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
              at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
              at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
              at java.lang.reflect.Method.invoke(Method.java:606)
              at org.apache.hadoop.io.retry.RetryInvocationHandler.invokeMethod(RetryInvocationHandler.java:164)
              at org.apache.hadoop.io.retry.RetryInvocationHandler.invoke(RetryInvocationHandler.java:83)
              at com.sun.proxy.$Proxy9.registerDatanode(Unknown Source)
              at org.apache.hadoop.hdfs.protocolPB.DatanodeProtocolClientSideTranslatorPB.registerDatanode(DatanodeProtocolClientSideTranslatorPB.java:146)
              at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.register(BPServiceActor.java:623)
              at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.connectToNNAndHandshake(BPServiceActor.java:225)
              at org.apache.hadoop.hdfs.server.datanode.BPServiceActor.run(BPServiceActor.java:664)
              at java.lang.Thread.run(Thread.java:745)
      Caused by: java.io.IOException: Response is null.
              at org.apache.hadoop.ipc.Client$Connection.receiveResponse(Client.java:949)
              at org.apache.hadoop.ipc.Client$Connection.run(Client.java:844)
      

      This will create discrepancy between active NN and standby NN in terms of live nodes.

      Here is a possible scenario of missing blocks after failover.

      1. DN A, B set up handshakes with active NN, but not with standby NN.
      2. A block is replicated to DN A, B and C.
      3. From standby NN's point of view, given A and B are dead nodes, the block is under replicated.
      4. DN C is down.
      5. Before active NN detects DN C is down, it fails over.
      6. The new active NN considers the block is missing. Even though there are two replicas on DN A and B.

        Attachments

        1. HDFS-7009.patch
          10 kB
          Ming Ma
        2. HDFS-7009-2.patch
          10 kB
          Ming Ma
        3. HDFS-7009-3.patch
          10 kB
          Ming Ma
        4. HDFS-7009-4.patch
          10 kB
          Ming Ma

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              • Assignee:
                mingma Ming Ma
                Reporter:
                mingma Ming Ma
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                • Created:
                  Updated:
                  Resolved: