[jira] [Commented] (HDFS-11395) RequestHedgingProxyProvider#RequestHedgingInvocationHandler hides the Exception thrown from NameNode

["Jing Zhao (JIRA)" <ji...@apache.org>]

    [ https://issues.apache.org/jira/browse/HDFS-11395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15890867#comment-15890867 ] 

Jing Zhao commented on HDFS-11395:
----------------------------------

Thanks for working on this, [~nandakumar131]. I agree we should not directly throw a MultiException. But I have similar concern as Arpit, i.e., we should not simply throw the first exception. I think we should
# Not mix detailed exception handling logic into {{RequestHedgingProxyProvider}}. In {{RequestHedgingProxyProvider}}, we only need to get the RemoteException from {{ExecutionException}}, and put all the exceptions into {{badResults}}. No need for special handling for StandbyException etc there. These should be handled by {{RetryInvocationHandler#newRetryInfo}}.
# Then in {{RetryInvocationHandler#newRetryInfo}}, we should let this method return both the RetryInfo and the exception to throw from the MultiException. These two information should comes from the same internal exception inside of the MultiException.

> RequestHedgingProxyProvider#RequestHedgingInvocationHandler hides the Exception thrown from NameNode
> ----------------------------------------------------------------------------------------------------
>
>                 Key: HDFS-11395
>                 URL: https://issues.apache.org/jira/browse/HDFS-11395
>             Project: Hadoop HDFS
>          Issue Type: Bug
>          Components: ha
>            Reporter: Nandakumar
>            Assignee: Nandakumar
>         Attachments: HDFS-11395.000.patch, HDFS-11395.001.patch
>
>
> When using RequestHedgingProxyProvider, in case of Exception (like FileNotFoundException) from ActiveNameNode, {{RequestHedgingProxyProvider#RequestHedgingInvocationHandler.invoke}} receives {{ExecutionException}} since we use {{CompletionService}} for the call. The ExecutionException is put into a map and wrapped with {{MultiException}}.
> So for a FileNotFoundException the client receives {{MultiException(Map(ExecutionException(InvocationTargetException(RemoteException(FileNotFoundException)))))}}
> It will cause problem in clients which are handling RemoteExceptions.



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