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https://issues.apache.org/jira/browse/HDFS-14116?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=16723752#comment-16723752
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Chao Sun commented on HDFS-14116:
---------------------------------
OK. I was just concerned that in some edge cases people may be caught by
surprise. For instance, they _may_ get ClassCastException if running
{{HAServiceProtocol}} or {{RouterProtocol}} on a host where it is set to use
ORPP.
> Fix class cast error in NNThroughputBenchmark with 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
> Assignee: Chao Sun
> Priority: Major
> Fix For: HDFS-12943
>
> Attachments: HDFS-14116-HDFS-12943.000.patch,
> HDFS-14116-HDFS-12943.001.patch, HDFS-14116-HDFS-12943.002.patch,
> HDFS-14116-HDFS-12943.003.patch, HDFS-14116-HDFS-12943.004.patch,
> HDFS-14116-HDFS-12943.005.patch
>
>
> 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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