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From "Yongjun Zhang (JIRA)" <j...@apache.org>
Subject [jira] [Created] (HDFS-11656) RetryInvocationHandler may report ANN as SNN in messages.
Date Fri, 14 Apr 2017 19:23:42 GMT
Yongjun Zhang created HDFS-11656:
------------------------------------

             Summary: RetryInvocationHandler  may report ANN as SNN in messages.
                 Key: HDFS-11656
                 URL: https://issues.apache.org/jira/browse/HDFS-11656
             Project: Hadoop HDFS
          Issue Type: Bug
            Reporter: Yongjun Zhang


When multiple threads use the same DFSClient to make RPC calls, they may report incorrect
NN host name in messages like

 INFO [pool-3-thread-13] retry.RetryInvocationHandler (RetryInvocationHandler.java:invoke(148))
- Exception while invoking delete of class ClientNamenodeProtocolTranslatorPB over hdpb-nn0001.prn.parsec.apple.com/*a.b.c.d*:8020.
Trying to fail over immediately.
org.apache.hadoop.ipc.RemoteException(org.apache.hadoop.ipc.StandbyException): Operation category
WRITE is not supported in state standby. Visit https://s.apache.org/sbnn-error

where *a.b.c.d* is the active NN, which confuses user to think failover is not behaving correctly.

The reason is that the ProxyDescriptor data field of RetryInvocationHandler may be shared
by multiple threads that do the RPC calls, the failover done by one thread may be visible
to other threads when reporting the above kind of message. 

As an example, 
# multiple threads start with the same SNN to to the call, 
# all threads discover that a failover is needed, 
# thread X failover first, and changed the ProxyDescriptor's proxyInfo to ANN
# other threads reports the above message with the proxyInfo changed by thread X, and reported
ANN instead of SNN in the message.

Some details:

RetryInvocationHandler does the following when failing over:
{code}
  synchronized void failover(long expectedFailoverCount, Method method,
                               int callId) {
      // Make sure that concurrent failed invocations only cause a single
      // actual failover.
      if (failoverCount == expectedFailoverCount) {
        fpp.performFailover(proxyInfo.proxy);
        failoverCount++;
      } else {
        LOG.warn("A failover has occurred since the start of call #" + callId
            + " " + proxyInfo.getString(method.getName()));
      }
      proxyInfo = fpp.getProxy();
    }
{code}
and changed the proxyInfo in the ProxyDescriptor.

While the log method below report message with ProxyDescriotor's proxyinfo:
{code}
private void log(final Method method, final boolean isFailover,
      final int failovers, final long delay, final Exception ex) {
......
   final StringBuilder b = new StringBuilder()
        .append(ex + ", while invoking ")
        .append(proxyDescriptor.getProxyInfo().getString(method.getName()));
    if (failovers > 0) {
      b.append(" after ").append(failovers).append(" failover attempts");
    }
    b.append(isFailover? ". Trying to failover ": ". Retrying ");
    b.append(delay > 0? "after sleeping for " + delay + "ms.": "immediately.");
{code}
and so does  {{handleException}} method do
{code}
        if (LOG.isDebugEnabled()) {
          LOG.debug("Exception while invoking call #" + callId + " "
              + proxyDescriptor.getProxyInfo().getString(method.getName())
              + ". Not retrying because " + retryInfo.action.reason, e);
        }
{code}

FailoverProxyProvider
{code}
   public String getString(String methodName) {
      return proxy.getClass().getSimpleName() + "." + methodName
          + " over " + proxyInfo;
    }

    @Override
    public String toString() {
      return proxy.getClass().getSimpleName() + " over " + proxyInfo;
    }
{code}
 




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