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From "Arpit Agarwal (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11395) RequestHedgingProxyProvider#RequestHedgingInvocationHandler hides the Exception thrown from NameNode
Date Wed, 22 Feb 2017 18:53:44 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15878972#comment-15878972
] 

Arpit Agarwal commented on HDFS-11395:
--------------------------------------

Hi [~nandakumar131], RetryInvocationHandler has some logic for unwrapping MultiException ([code
here|https://github.com/apache/hadoop/blob/trunk/hadoop-common-project/hadoop-common/src/main/java/org/apache/hadoop/io/retry/RetryInvocationHandler.java#L267]).
I haven't looked at it carefully so don't know if it does the right thing. Deciding what to
do when we get a MultiException should probably be handled in the RetryInvocationHandler.

The reason the short-circuit failure path looks incorrect is because it can cause spurious
request failures if the standby thinks it is active and throws something other than StandbyException.

> 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
>
>
> 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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