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From "Jing Zhao (JIRA)" <j...@apache.org>
Subject [jira] [Commented] (HDFS-11395) RequestHedgingProxyProvider#RequestHedgingInvocationHandler hides the Exception thrown from NameNode
Date Fri, 03 Mar 2017 19:46:45 GMT

    [ https://issues.apache.org/jira/browse/HDFS-11395?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15894925#comment-15894925

Jing Zhao commented on HDFS-11395:

Thanks for updating the patch, [~nandakumar131]. Some further comments on the latest patch:
# In RetryAction, the usage of the new member field {{exception}} is for FAIL case. Thus maybe
we can:
#* rename "exception" to failException
#* assign a value to this field only when the action is FAIL:
+      Exception ex = null;
# Looks like we should not only get {{RemoteException}} out of {{ex}}, but more generally
get the cause of other types of exceptions. Note exceptions like ConnectException and EOFException
should also be exposed to retry policies.
            RemoteException rEx = getRemoteException(ex);
            if(rEx != null) {
              badResults.put(tProxyInfo.proxyInfo, rEx);
            } else {
              badResults.put(tProxyInfo.proxyInfo, ex);
# It will be helpful if we can also have a unit test for the above ConnectException/EOFException
# Need to fix indentation, line length etc. for {{testHedgingWhenFileNotFoundException}}.

> 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, HDFS-11395.002.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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