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From "Ming Ma (JIRA)" <j...@apache.org>
Subject [jira] [Updated] (HDFS-7009) Active NN and standby NN have different live nodes
Date Sat, 14 Feb 2015 06:01:12 GMT

     [ https://issues.apache.org/jira/browse/HDFS-7009?page=com.atlassian.jira.plugin.system.issuetabpanels:all-tabpanel
]

Ming Ma updated HDFS-7009:
--------------------------
    Attachment: HDFS-7009-3.patch

Thanks, Arpit. Yes, I meant reRegister.

Thanks, Chris. I agree with both of your points. Here is the updated patch. The fix is to
return specific exception from RPC client; it appears EOFException is good choice for this
specific scenario.

> Active NN and standby NN have different live nodes
> --------------------------------------------------
>
>                 Key: HDFS-7009
>                 URL: https://issues.apache.org/jira/browse/HDFS-7009
>             Project: Hadoop HDFS
>          Issue Type: Bug
>            Reporter: Ming Ma
>            Assignee: Ming Ma
>         Attachments: HDFS-7009-2.patch, HDFS-7009-3.patch, HDFS-7009.patch
>
>
> 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.
> {noformat}
> 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");
>         }
>       }
> ...
> {noformat}
> Here is an example of the call stack.
> {noformat}
> 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)
> {noformat}
> 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.



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