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https://issues.apache.org/jira/browse/HDFS-14116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16703877#comment-16703877
 ] 

Chen Liang commented on HDFS-14116:
-----------------------------------

Thanks [~csun]! Yeah I can another look later. Posting error stack trace when 
running NNThroughput here for record:
{code}
Caused by: java.lang.ClassCastException: 
org.apache.hadoop.hdfs.server.namenode.ha.NameNodeHAProxyFactory cannot be cast 
to org.apache.hadoop.hdfs.server.namenode.ha.ClientHAProxyFactory
    at 
org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProvider.<init>(ObserverReadProxyProvider.java:118)
    at 
org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProviderWithIPFailover.<init>(ObserverReadProxyProviderWithIPFailover.java:99)
    at 
org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProviderWithIPFailover.<init>(ObserverReadProxyProviderWithIPFailover.java:86)
    ... 12 more
{code}

{code}
Exception in thread "main" java.io.IOException: Couldn't create proxy provider 
class 
org.apache.hadoop.hdfs.server.namenode.ha.ObserverReadProxyProviderWithIPFailover
        at 
org.apache.hadoop.hdfs.NameNodeProxiesClient.createFailoverProxyProvider(NameNodeProxiesClient.java:261)
        at 
org.apache.hadoop.hdfs.NameNodeProxies.createProxy(NameNodeProxies.java:115)
        at 
org.apache.hadoop.hdfs.DFSTestUtil.getRefreshUserMappingsProtocolProxy(DFSTestUtil.java:2022)
        at 
org.apache.hadoop.hdfs.server.namenode.NNThroughputBenchmark.run(NNThroughputBenchmark.java:1524)
        at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:76)
        at org.apache.hadoop.util.ToolRunner.run(ToolRunner.java:90)
        at 
org.apache.hadoop.hdfs.server.namenode.NNThroughputBenchmark.runBenchmark(NNThroughputBenchmark.java:1432)
        at 
org.apache.hadoop.hdfs.server.namenode.NNThroughputBenchmark.main(NNThroughputBenchmark.java:1552)
{code}

> Fix a potential class cast error in ObserverReadProxyProvider
> -------------------------------------------------------------
>
>                 Key: HDFS-14116
>                 URL: https://issues.apache.org/jira/browse/HDFS-14116
>             Project: Hadoop HDFS
>          Issue Type: Sub-task
>          Components: hdfs-client
>            Reporter: Chen Liang
>            Priority: Major
>
> Currently in {{ObserverReadProxyProvider}} constructor there is this line 
> {code}
> ((ClientHAProxyFactory<T>) factory).setAlignmentContext(alignmentContext);
> {code}
> This could potentially cause failure, because it is possible that factory can 
> not be casted here. Specifically,  
> {{NameNodeProxiesClient.createFailoverProxyProvider}} is where the 
> constructor will be called, and there are two paths that could call into this:
> (1).{{NameNodeProxies.createProxy}}
> (2).{{NameNodeProxiesClient.createFailoverProxyProvider}}
> (2) works fine because it always uses {{ClientHAProxyFactory}} but (1) uses 
> {{NameNodeHAProxyFactory}} which can not be casted to 
> {{ClientHAProxyFactory}}, this happens when, for example, running 
> NNThroughputBenmarck. To fix this we can at least:
> 1. introduce setAlignmentContext to HAProxyFactory which is the parent of 
> both  ClientHAProxyFactory and NameNodeHAProxyFactory OR
> 2. only setAlignmentContext when it is ClientHAProxyFactory by, say, having a 
> if check with reflection. 
> Depending on whether it make sense to have alignment context for the case (1) 
> calling code paths.



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